DAVECS1

iTrader: (2)

I would like this to become a long thread! I hope others can learn from my trials tribulations. I have inherited my father's 77 vette. 2 years ago we put a Beck's racing engine in it. Unfortuneatly my senile old man lost the paper work. Before the conversion I luckily thought ahead and took down some base data. Here is what I know.

1. At idle it has approx 50 kpa of vac @ 700 rpm
2. timing initial is 12 BTDC and 38 all in by 2500
3. Has ported Edelbrock performer RPM straight plug heads
4. compression ratio is 10.5-1 (best guess using a compression gauge and degree wheel.
5.ran good but rich with a unmodified edelbrock 750 carb and airgap manifold.

I am on my 50th chip revision using a 7730 ECM and starting with the AUJP 1350 from a wrecked 92 Camaro. The current intake system is the following.

1. 92 TPI
2. Edelbrock large tube runners. (try making these fit in a day! Ha)
3. Ford 30lb injectors
4. Masters E2000 inline pump
5. Accel AFPR ( fine craftsmanship.... for a five year old!)

The fuel pressure is set to 48 psi. any lower and all my BLMS go to the lean limit 108 and after about 20 mins of driving it throughs a code and goes into limp mode.

My injector constant was at 30, but that also created a lean condition it is at 28 right now.

I modified the VE tables little by little so the idle parmeters are at the 50 KPA mark. The engine seams to be coming around the more i modify each RPM band from 50-100KPA usually giving it more fuel.

i am using a heated O2 sensor from a ZR1 due to the long tube headers. The heating element is hooked into the ignition.

Knock adjustments are many and are playing havac I think with the timing I have tried to FF everything for know, but must be missing something. I am thinking maybe FF in the recovery and attack rates may be a bad thing. What all is there to adjust? Any ideas on this would be great.

On other fuel controlers (electromtive for example) you can adjust the stoic mix. I usually bring it to about thirteen or twelve when emissions are not a concern. I tried to change this but I do not think I accomplished anything. Maybe I have the wrong address.

Well I will quit here and see if anyone out there can give some creative input to this giant mess. I LURK NO LONGER :-) I hope there are still some people around that are here to bat around ideas and not just ask for a starter chip to get the nitrous fed 454 out of there parent driveway tonite because it is of the upmost inportance and I need to go to work in the morning in this car.

Sorry for the sarcasm and the long post!

Grumpy

Hidden answers

DAVECS1

iTrader: (2)

Thanks for the response. Hey I give slack to old men. What my old man doesn't know is once I get this thing to drive like a grocery getter on steroids I am going to give it back to him. He initially gave it to me so he would have room for a milder vette he wouldn't have to mess with all the time (91 C4). I wanted to play with one of these ecms so this became the perfect project. IF I get this right the old man can have c4 driveability with C3 style and mega power.

Thanks for the fuel pressure tips. I will try these. Will lower or raising the fuel pressure constant effectively lean or richen the whole curve or am I effecting alot more such as the throttle enrichment.

I have got it driveable but I am way down on power. I am going to attack the timing tables today. Right now I am running 12 degrees advance. You suggested 25-30 BTDC. Is that initial?? That seams like alot, but with a carb this engine ran 22 BTDC. I have always been able to retard the timing with fuel injection. Is that not the case with the 7730. It seems I always end up advancing the timing when I start it to get to run smoothly?

The comment on world peace gives me great hope Oh well maybe something will come of this. I have read the internet classes you guys have narated in the past years. Maybe this can be the hands on lab to show others that chip burning is NOT that hard it just takes PATIENCE and the ability to listen, read, and learn.

Grumpy

DAVECS1

iTrader: (2)

I guess retard the timing was thwrong choice of words. What I meant to say is during a retrofit I have been able to reduce the amount of advance in the timing and get the same power. Every time I start this vette it seems I need to manually advance the distributor to get it to run smooth. 8D!!!!! that is like 50 degrees advance. Is that just start up or is that you initial advance setting. I am going to start by trynig to mimc the original setup with 18 initial and 40 all in by 2800 rpm. will the 7730 cooperate or am I barking up the wrong tree. I looked at your bin that you posted. That was helpful. I use a scanner, but sometimes I like to just try and listen to the engine and give it what it sounds like it wants. If it has trouble I then usually start to analyse the numbers. I hope you do not take offense, but it seems you too like to tune the engine by giving it what it sounds like it wants. Ive tuned numerous 350s with numerous setups, but I don;t think any of them ever respnded the same.

goneracin

2x a year I have a EFI POWWOW at my place, just outside Dayton OH. Lots of cool info., and parts to stare at..


:hail: Grumpy
When do you usually have these gatherings. I'd love to be able to attend. I get to travel alot with my job, so maybe I'd get lucky.
Thanks
Bob

DAVECS1

iTrader: (2)

Well I am a little confused.
Grumpy: I tried your suggestions with the fuel pressure and injector setting. I had no luck. I set the fuel pressure to 43 and the injectors at 30. It read lean and it would not increase idle when the throttle blades were tipped open. The accelerator pump worked but if you held it,, it would either pop out the exhaust or intake.

My new iteration of chip failed miserably. I brought all the timing tables up to 50 kpa then interpolated to condense the 12 settings into 6.

I made one chip were only the fuel tables were raised to 50 kpa and the timing was left stock. The injectors read 28. And initial advance was 12 degrees BTDC.

This chip ran very well with the fuel pressure set at 52psi. the only problem I ran into was a high idle 1000 rpm and top end power were lacking. I also encounter no punch when I tried to accelerate from cruising speed, but no back fires or stumbles.

I am thinking of richening the midrange pump shot also fatting up the 80-100 kpa range from 2800-3600 rpm. To get the idle down I am going to play with the minimum air setting, because turning the timing back causes it to loose power.

Suggestions anyone??????

DAVECS1

iTrader: (2)

Well it looks as if everyone could care less, but I will document my progress in hopes of helping future hotrodders.

Well I made the proposed changes and I am glad to say things are coming along. The BLMs hovered between 120-130 most of the time. Spots that seem to still need attention are tip in from 1500-2500 and also the maps in there. Twice I got a code for to lean when I left the RPMs in this range for to long and the BLMs were in the low limit.

I got the idle down, but as I drove it it seem to want more timing so I would stop and bump it up a couple degrees every so often untill the throttle response and decell begin to come in, but when I got home the idle was back up to 1000-1500. I am at a loss here suggestions would be very appreciated.

Another thing that baffles me is everytime I start it up hot or cold for about ten-20 secs the engine idles at about 1500-2000 grand and then drops down to were it is suppose to be. I am also a little stumped on this problem.

Last but not least I am some what concerned with the injector setting. The chips that seem to be working best are those set for 25lb injectors. I supposedly have 30lb ford racing injectors. While driving tonight I once again tried Grumpy's suggestion and tried chips at 28, 30, and 32. Each time I adjusted the fuel pressure down as I turned the injector constant up. All of these chips ran lean. Pressures ranged from 40-43. When I set the pressure 52 and the injector constant at 25 everthing comes right back to life.

How high is to high of a setting for an injector in the VE table? I have about 6 cells that have numbers over 90. If these numbers represent duty cycle I have heard eighty is about the max you want to run.

Come on someone throw me a bone. You guys have to be somewhat interested in 77 vette with TPI.

drive it

iTrader: (1)

Yes interested, but please slow down! Again take it one thing at a time-remember most folk here have burned at least a 100 or so proms while getting things dialed in.....

Grumpy

Wow, your way of track here.
You change injector constants and F/P ever two minutes it seems.

You also backtracking.
Are you taking good notes on what you're doing?.

With 1/2 of what you done, you should be able to draw some conclusions on where you need to go, and yet you're repeating yourself.

You have 300 table switchs and settings, some tables have 200 entries, so this is going to take some dialing in to get right.

You need to use a scan tool or some way to measure Duty Cycle, looking at the VE table is just part of the equation.

DAVECS1

iTrader: (2)

Sorry! I will slow down. My mind races when I get to working on a project.

First things first. It seems the car just runs a lot better with the injector setting at 25 and the fuel presure at 52. Is this OK?

Timing is all over the place the only thing I have deduced is that it likes to be advanced..

I keep a detailed notebook, that is how I knew to go back to 25 on the injector constant and 52lbs of fuel pressure.

91L98Z28

I'm by no means an expert, but I'll try to help out and contribute here. Grumpy & the other experts, please correct me if I'm wrong, because this is the tuning process I plan to use on my 406!

Key things you need to keep in mind:

when you modify the injector constant, you are affecting the ENTIRE fuel curve. When you modify the fuel pressure, you are affecting the ENTIRE fuel curve. Basically, you want to "rough in" these values and leave them alone, so you can fine tune everything else. Every time you change then, you destroy any work you've done on the VE table.

Grumpy is spot on. Set the fuel pressure somewhere around 40-45 psi and leave it.

Now, here's what I'd do if I was you: Set the injector constant to 30#. Now start the car, let it come up to full operating temp (go for a ten minute drive). Hold the motor at 1500rpm for 10-15 seconds, and note BLM. Now hold motor at 2500rpm for 10-15 seconds and note BLM, Repeat for 3500rpm. Now go for a drive, holding the car in 1st or 2nd gear, and again note BLM's at 1500, 2500, 3500. You should have six BLM values now. Now, AVERAGE them. If they average to 128, great!! don't touch the fuel injector constant any more. But if they average to say, 105, then the car is on average rich, and you need to RAISE the injector constant. Or if they average say 140, then you need to LOWER the injector constant. Burn two or three chips and change NOTHING but the injector constant, until you can get an average of around 128 BLM at several different RPM/load values. you may end up with two or three at 115, and two or three at 140, or whatever...the key thing is "getting in the ballpark". If all six values are at 108, then you are universally rich and raising the injector constant is the quickest way to universally lean out the whole fuel curve.

Once you've gotten to this point, don't change the fuel pressure or injector constant again! leave them alone. They are fine.

Now, again go for a drive, holding various steady-state loads and RPMs for 5-10 seconds (at least) so that you can rough-in the VE tables. Keep working at this until you get all your BLM's to around 128. You won't be able to hit every cell, so you will have to interpolate a bit...

After you have the VE tables roughed in, play with the pump shots and enrichment until the car responds good.

Fine tune as necessary.

DAVECS1

iTrader: (2)

Thank you for the advice 91L98z28.

Tonite I realized I need to slow down. I have a bad habit of getting ahead of myself when a motor begins to come around.

Grumpy and you are right I need to leave the FP and injector setting alone. The injector constant I arrived at was produced by burning 5 chips with everything identical, but the injector constant. First I sat in the driveway and monitored blms and the map sensor from 1000-4000 rpms in increments of 500rpm. Each chip was tried at 40, 43, 46, 49, 52lbs. This was all done with a stock AUJP1350.bin. As far as driving at those RPMs 91L98Z28 I hope you have better luck than I did trying to hold an RPM. This large cam is giving me fits.

Right now I am planning to hold FP at 50 psi and the injector setting at 25lbs and begin to take a more detailed look at my VE tables only. The only thing I have done to the tables so far is to move all idle values up to 50 KPA and then interpolated to condense the table from 20-100 to 50-100KPA.

I went for a drive tonite for about an hour and the biggest trouble spots seem to be from 2000-3000 at part throttle. The XRAY read the O2 as rich through here about 8-1. I have ordered a cable from steve ruse and I am going to toss the scanner. I just do not think it is detailed enough for this kind of tunning.

Any tips on initial timing? Unfortuneatly I have been adjusting that like crazy also. Should I set it to what I have in the bin file or were the car runs best?

Would anyone care to see my current bin file?

91L98Z28

Keep in mind that no computer can READ the mixture. It can give a rough guess as to what it thinks it is spraying, but it can't READ how rich you are. I'm not sure how you are getting that it's spraying a 8:1 ratio but that is black-smoke belching, pig rich.

as for timing, just rough something in for right now. If i was in your shoes, I'd set the initial distributor advance to 8 degrees (with the matching 8 degree setting in the ECM), and then "rough in" a typical advance curve you might see from a mech distributor with a vacuum advance - you know, about 34 total at 3000rpm up (with the 8 initial, you only need 26 more in the timing table). make sure you unplug the advance wire when you set the distributor initial. YOu might be able to add 4-6 more for the low kPa values (just like a vacuum advance would). Or just run a stock AUJP timing tables for now, they aren't that agressive.

Why are you moving the VE Tables around? There's no point in it. either way you are still going to have to tune the values because they will all be wrong, so just don't bother, it's not helping you.

You're trying to over-engineer and over-complicate something that's pretty simple. Ya set the fuel pressure, ya set the injector constant, go for a drive with a data logger (craig moates makes some great software for free, and you can make a cable for it for a few bucks too!). you analyze the data (this is the most time consuming part!!!) and then make a few changes to the VE tables...you burn another chip, you log some more data, you analyze some more data, make a few more VE changes, burn another chip, and continue the process until you have the BLM's consistently around 128.

When you get close, you will have to push the TPS% for PE up farther so that you can hit more VE cells without getting into PE. A WB02 would also help. check out previous posts by glenn91l98gta (sorry if i got that name wrong) and grumpy and others on these subjects, they've explained it way better than I can. also check out traxion's 730 article, it really is quite good!

I know a large cam can be hard to deal with, but as you get the VE tables closer you should find that it at least smooths out somewhat.... success is not measured in time spent

good luck...i hope some of that makes sense.

DAVECS1

iTrader: (2)

well as far as moving around the VE tables goes.... Upon initial start up with the stock AUJP the engine would race and any attempt to crack the throttle resulted in pop out the intake or pipes. I checked vacuum at 800 rpm it read 50 KPA with a manual guage. So my feable attempt to calm things down was to rearrange the VE tables to work around 50kpa.

As far as reading the o2 goes I assume the Xray scanner is reading the O2 sensor output and putting on the screen, and yes you are correct from 2000-3000 the car does put out black smoke and stumbles bad.

I think I am going to walk away from the car for a couple days and just review and organize my notes. My cable will be here monday and I plan on modifing the freescan software to work with this ECM. If there is one thing I can do it is VB and C+!

Thank you for the responses! I appreciate them. I have read alot of the articles and I realize this is yesterdays news to alot of you, but I though some might be interested in the vette retrofit part of the project. I made my own harnesses using CAT surplus hardware. Those deutsch connectors are pretty sweet.

Grim Reaper

I tried to see if in all these posts whether someone pointed this out, but I couldn't see where anyone said (excuse me if they have).

Your thinking is completely backwards. You keep saying "lean" when you are really rich. Below 128 indicates running rich and above 128 indicates lean. Everytime I read your post you kept adding more fuel by either adding more fuel pressure or lowering your injector constant. All you are doing is making an overly rich car run richer.

Second, forget the 50 psi. You'll be replacing fuel pumps sooner than you have too. Also, it's a cause of your overly rich condition.

DAVECS1

iTrader: (2)

Ok I will buy that, but what concerns me is when I change the FP to 43 and the injector setting to 30 the car pops out the intake upon acceleration and out the pipes during an idle or decel. Any attempt to put a load on it in this condition causes the headers to glow red. This is usually a sign of extremely lean.

Another symptom at these settings: is the fact the accelerator pump will bosst RPMs initially but if you hold the throttle at a higher RPM it will not stay there.

Like I said I spent a couple nights trying grump's suggestion. Is it possible my pump puts out enough PSI but not enough flow?

I am using a masters E2000 From an 87 FORD F150.

Grim Reaper

Also, remember that "closed loop" doesn't necessarily mean what's happening when in WOT.

Check your plugs to see if you are running rich or lean. But the BLMs are saying overly rich (while in closed loop). The other problems show your calibration is way off. You need to work on your tip-in and AE.

hectorsn

Listen to what Glenn says. You're mixing things up too much. A pop or stumble in a transition doesn't mean that the engine is running lean or rich overall, it just means you don't have enough pump shot. I don't care how rich the tune is it won't make up for the lack of acceleration enrichment (pump shot or AE), which is what you're experiencing. Another thing, glowing headers doesn't mean lean. It means your exhaust temps are too hot or that the fuel is still burning on the way out like if it was too rich or too retarded of timing. A pop on decel is common on high compression cars and on those that are too rich, not lean. Quit playing with the inj constant and fuel pressure. Set it to what the inj is and set the FP correctly and leave it alone. Lying to the ecm about inj size to make tuning less difficult is not the right thing to do. You have a built up engine and it is very common for engines like these to have VE numbers in the 40's at low RPM. It is just the nature of things, the compromise of high rpm HP engines: they give up down below to breathe up top. Right now you are trying to "beat it into submission" but what you need to do is listen to what it's telling you and give it what it wants. Not the other way around. You need to start trying things one at a time so you can start noticing trends. At idle it will "probably" like lots of timing and low VE numbers for the 128/128 to appear. It will probably like factory settings in the mid range and the upper end will have to be bumped, especially after the factory torque and HP peak, as the factory HP peak will probably be your new torque peak. But one thing at a time, start from idle. It would be nice to see you get out of this with a sweet running ride so that this post can be a reference to those that have similar problems.

DAVECS1

iTrader: (2)

well thanks for the info guys. I appreciate the input. I listened to all of you and finally put the injector setting to 30 and FP to 44 PSI. It seems to be the general consensus.

After 62 burns I am going to start from the stock AUJP1350. My cable is to arrive today and I am going to sample with Moates software and a copy of Freescan that I modified to work with 91 SD.

Here is my question of the day! With the AUJP stock chip with FP at 44 and initial timing at 12 BTDC. The car will idle down to 800 rpm. As it warms up it will begin randomly popping out the exhuast. At 800 the vacuume gauge reads approximately 53 KPA.

My first step is to get it to idle just using the VE tables. Is this the right thing to do. I am going to let it idle with the laptop hooked up tonight, but I am thinking I need to lean it out at idle.

Thanks again guys.

Grim Reaper

Why do you have the base advance so high. At "idle" you total spark advance should be around 20*. Have you adjusted your Main Spark Tables to remove the extra 6* you've put in?

If not, set your base back to 6*. With SD the ECM adds the base to the Main Spark Table and without modifying the Main Spark Table, you have too much spark advance for idle and probably low rpm.

Also, I have a funny feeling you are probably getting a lot of knock retard @ WOT if you are running the stock spark tables.

DAVECS1

iTrader: (2)

Well I set the initial timing in the chip at 12, but I can knock it back to 6. With a carb on the engine the initial was 12 so I thought that would be a good starting point.

As far as mods to tables and arrays goes. I am starting over from a clean sheet to try and get this to work with the pressure and injector settings recommended.

I have not attempted WOT with the stock AUJP the motor will not go there. It gets real grumpy when I try and make it go there and I think the nieghbors a half mile down the road get a little excited too.

91L98Z28

the initial timing in the chip does not affect your actual, real world timing at all. The initial timing in the chip is only used to display the "actual" timing to you on a scantool. So, if the initial timing on the chip doesn't match the initial timing actually set at the distributor, the initial timing you get is whatever is at the distributor, and on top of that, whatever data the scan tool is spitting out for total timing is wrong!!! moral of the story, always match up the initial timing in the chip and the actual initial at the distributor.

if you have a distributor machine, and if you know the car ran good on the old dist, then you could go and test the distributor and chart all of the advance values, and then use the data to fill in the lower and upper advance tables in the ECM. the curve probably isn't optimum (maybe it's optimum within the limits of a distributor but an ECM can do so much more) but at least it would get you close.

DAVECS1

iTrader: (2)

I realize the chip and real world timing are seperate. To clarify I set the initial in the chip to 12 and then with the bypass unhooked set the car to 12.

I will try six, but that seems very low for this engine. It would barely idle at anything below twelve with a carb.

As far as the carbed distrubutor goes. It is good (MSD unit). It ran 12 initial with 38 all in by 2500-2800. Most of my previous chips I modified to reflect this, though I did not do much to change this curve for the different loads available 20-100KPA. It pretty much resembles 12-38 all in by 2800 across the board.

Like I said though, I am starting over agian with a clean sheet. I will even try the 6 initial, but I have a strong feeling it will not run, so I may have to do some timing mods from the start to get something to work with (which is what I was trying to do with the initial 12 BTDC).

hectorsn

Huh? You put the base timing to what it says in the prom and the factory setting is 6*. Then whatever the main spark table has at the kpa/rpm you are at it is what the timing will be. So lets say you had an idle rpm of 800 and 50 kpa the factory aujp setting is 24*. It should run pretty good with 24*.

91L98Z28

EDIT!!! Please note that this post may be inaccurate, read the rest of this topic for clarifications........

You need to step back a tiny bit and think about this.

The "initial" timing on a computer controlled distributor is NOT the same thing as the "initial" timing on a mechanical distributor.

On a mechanical distributor, the "initial" timing is defined as the advance gained by the rotation of the distributor. At idle, the springs & weights inside the distributor are not providing any further advance. So, the distributor rotation is the "initial advance".

On a computer controlled distributor, the "initial" timing is also defined as the advance gained by rotation of the distributor. However, the computer will be adding MORE advance to this, so the distributor setting is not the TOTAL "initial" advance. The TOTAL intial advance is distributor + computer.

Here is a FAKE advance curve I drew up in tunercat.



Now, let's think about this for a minute. Say you set the distributor to 6 degrees advanced, and the vette idles at 800rpm at 50kpa. So, we look in the chart and see that the computer would add another 8.8 degrees advance, so 6+8.8 = 14.8, so you could say that you were running "14.8 degrees total initial advance" and this is the number you'd compare to the mechanical distributor initial advance.

By the way, this curve I drew up should somewhat mimic the distributor advance you described. All in by 2800, ~12 degrees "advance" at idle. Yes, all of the values are about six degrees low...that's because you have to add the six degrees the distributor is advanced in order to get the acutal timing advance the engine sees. With that said, I would NOT just plug these values into your chip if I were you, it's quite agressive and would probably ping like heck on pump gas. Notice also that the low kPa values have a bit more timing....this is how a computer emulates "vacuum advance". low kPA = high vacuum, so you can add a few degrees in at the lower kPa values to simulate a vacuum advance.
Obviously i just faked that timing advance curve, but hopefully it proves a few points.
Also, you might cure a lot of your tuning woes if you just get the idle rpm up a bit. 700rpm is a bit low for a cammed engine, especially if it on the radical side.. I'd be thinking more like 850, or maybe even higher depending on the cam.

Hope that helps. if none of it makes sense, go take a timing light and look at the timing difference before and after plugging in the wire that you disconnect to set the "initial" timing. you'll see a jump equivalent to the advance you have set in your advance table for that rpm/kpa.

DAVECS1

iTrader: (2)

Man I feel dense!!! Thank you 91L98Z28. I have no idea why I was not grasping that concept. I am sorry for the headache I was causing you guys.

Well that explains alot about tonite. I set the timing at 6 mechanical and 6 in the chip for a total of twelve initial (now that I am grasping how this works). It idled pretty decent. I then let it warm up and achieve closed loop while idling. Then I set the minimum air adjustment and it sat there and loped away. BLMs while idling were in the 115-120 range. That is rich,,,right???

Idle was at 800-850. So I am thinking of adjusting the VE tables a little leaner from 800-1000rpm at 50-60 KPA and see what that nets me.

As far as the timing goes should I set it mechanincally at 0 and bring all the initial in with the ECM?

As far as the timing tables go. I am going to wait unitl I get the fuel some what roughed in before heavy modification. Yes that graph you made looks alot like my previous burns, but they were all way advanced now that I know what I was doing wrong.

My knock counts were 5-8 during idle with it teadering between 1-0 degrees of retard. This was gathered with Freescan. I have seen this with other DFI and dismissed it as normal. Is that also the case here.

My poor GTA! Now that I know what I know,,, that means it has been running 14 degrees initial with 7 degrees on top of the whole curve. Oh well hopefully this winter I will have enough pennies for that ZZ4.

Once again thanks guys!

91L98Z28

115-120 is a bit rich, yeah; but not out of the ballpark.

since ideal is 128, and you are at 117, here's the math

117 / 128 = 0.91

so you need to multiply whatever the value in your VE table is that the car idles in by 0.91. This will lower it by about 9% and should put you right at 128.

CustomX

hey 91l98, how did you take a scrreen shot of tunercat?

RBob

iTrader: (1)

Don't forget that the inital SA value as set in the bin gets subtracted
from the final calculated SA value.

IE: If both the distributor and the bin inital SA value are set to
6 deg (BTDC), then the values in the main SA table will be
what the engine gets at the crank.

(And keep in mind that there is startup SA and coolant comp SA that
will affect the at crank timing).

RBob.

91L98Z28

Rbob:

eh? That doesn't make sense. Everything I've ever read or seen says that the timing is additive - whatever is in the timing table, gets ADDED to the initial (distributor) advance.... and that the ONLY purpose for the "initial advance" value in the PROM is so that the calculated "total timing" value in the ALDL data stream is correct.
can you site a source or can anyone else comment????

RBob

iTrader: (1)

From the ANHT $8D hac:

RBob.

91L98Z28

that snippet of code does appear to be subtracing the advance value from some other spark value. I didn't follow the code closely enough to find out exactly what it's doing, or where 0x00BB is getting used at, etc...

but from a gut feeling standpoint, this just doesn't make sense. The stock timing tables in an AUJP has an average timing value of 22.8 degrees from 3200-5600 for 100kPa (WOT). The PE advance in this range is about 3.9 degrees. 22.8 + 3.9 = 26.7. Now, if we subtract off the initial (26.7 - 6.0) that leaves us with only an average 20.7 degrees advance at WOT in the entire power band. That doesn't make sense!

Ok, I just went and studied a few diacom runs of my 91Z and here's what I think actually happens. The ECM calculates the timing it wants to run, based on the PE tables, advance tables, knock retard, etc. Then, the "advance" value is subtracted off fo that, and the signal is sent to the distributor. The distributor then adds back the advance value that was subtracted off (because it is mechanically advanced).

This would mean that the actual timing that occurs in the combusion chamber is:

SA (from SA table) + SA (from PE table) + dist mech SA - PROM's advance value - knock = total timing seen by combustion chamber.

Since the dist. mech. SA and prom advance value should match, they cancel out:

SA (from SA table) + SA (from PE table) - knock = total timing seen by combustion chamber

Can anyone clarify or add to this?

edit: I am ignoring the more obscure advances/retards (startup, cold temp, etc.) for the purpose of this discussion

DAVECS1

iTrader: (2)

After listening to the discussion here I looked at a breakdown of the DHC11 I have and studied the code in the snip Rob had. Using this info with what happen last night would lead me to believe that the setting in the ecm for initial timing and the initial mechanical advance if set the same will cancel each other out.

So it looks to me as if the initial ECM setting is subtracted acroos the board, but this should be compensated by the mechanical advance. My guess is GM wanted mechanical advance in the event of ECM failure. This tid bit of code accomplishes that without affecting normal operating perameters.

91L98Z28

customx:

alt-printscreen.
then paste it into your favorite image editing program.

RBob

iTrader: (1)

Yes, that is it exactly.

RBob.

RBob

iTrader: (1)

Having 6 deg of initial (or base timing) allows for additional items of help.
Cranking is now at 6 deg's, helps w/cold start. And not so much that hot start
cranking stalls. Also allows more then the distributor limit of 42 degrees
of SA at the crank. The 6 initial (base) gets added to the distributor max.
Can now have up to 48 degrees of light cruise timing.

RBob.

Grumpy

RBob has it right.

6-8 is the ideal static, or initial timing setting. I've played with everything from 0-16d in sub zero to 110dF temps.

Less then that and the engine just windmills when it's cold, and anything much over 10 can lead to hard to slow cranking when hot.

With the timing ecm controlled there is no point in trying to prove a point about intial timing.

Toooo much timing can also act like tooooo lean.

You have to carefully fade out timing from cruise to WOT, and match that with the VE and AE stuff.

Once you get that right you can play with the throttle follower.

The more you fudge on the basics you feed the ecm, the more problems you'll have down range.

The judges rate this thread as a 8.3.....

DAVECS1

iTrader: (2)

I hope it is an 8.3 out of 10

Well this last tid bit of info lines up exactly with what I did tonite. I set the initial in the chip at 8 and then st the mechanical at 8 and tightenen down the distributor for the last time.....unless something goes very bad!

I probably shouldn't have but I went into the timing tables and from 40-60kpa and 700-1000rpm I set the timing at 15. This really helped start up and idle. She purs at about 800. My only complaint now is during cold start up she jumps to 2000 for about 10 secs. Any suggestions?

So here are the settings which are never to be touched again.
FP=44
injectors=30
Mechanical advance=8

I would say these are inline and things seem to be going ok!

I idled down the road today! She pops on tip in. This sent the knock counts up to 30-40 andretard 6 degrees. The BLMs were 110-120 range.

I am thinking I need to adjust the VE tables from 700-1100RPM and 40-60 KPA or am I getting ahead of myself?

91L98Z28

At this point it's probably hard to say if the popping at tip in is AE or VE. you could be hitting a VE cell with a really bad value, or just need AE.

I would richen the AE for now (should make the tip-in popping go away), then drive for a while at various loads and rpm's so you can start roughing in the entire VE table. You may find that after the VE table is correct, you can pull some of the AE back out (or maybe not). The more accurate you can make the VE table, the easier the rest of your tuning will be. Just drive the car, log the aldl data stream, then analyze it and make corrections to the VE table as necessary, then go for another drive to verify your changes and explore a few more cells.

DAVECS1

iTrader: (2)

Well it has been a long time since the last update, but for those who remember my dilemma and helped out, the final result has turned out well. It has taken a whole car show season to straighten out the kinks but my father is pretty happy. We dynoed this last weekend at R&T performance. The results were fair. It pumped out 413 RWHP. With the carb it used to manage 470-475. It took a considerable amount of work to reach this point. Aside from 378 different chips and counting, we also ported the intake plenum and runners three times. We ended up with a ported Edlebrock base and runners with a ported stock plenum and throttle body. My father said he would gladly give up the HP for the street manners he has gained.

We still have some kinks, but will eventually figure them out.

initial start up flares to 2000 grand for a couple seconds then steps down to 1500 and then finally to 800 RPM. The old man says he doesn't mind it much because it grabs peoples attention at the car shows.

The car accelerates well, but when you let of the throttle it doesn't seem to decel very well. This kind of annoys my father. Help here would be nice.

Last but not least we have noticed higher internal engine pressures. For a while we actually were having trouble keeping oil from coming out the breathers. This weekend I installed all new gasket and a lower pressure oil pump. That has seem to fix this problem.

Once again thanks for all the help and maybe we will see you at a show or at the track some time.

Here is the close to finished product

hectorsn

Well it might be too late now but a single plane manifold converted to PFI and a big TB would have cost less than the manifold combo you have now and made more power. It looks good though and I'm sure makes plenty of torque. All the high idle problems you're having have to do with the IAC, including the lack of decel. Like Grumpy says, try and make the IAC as dumb as possible and control things with the idle screw. Try and get the counts at idle around 10-20 and play with the IAC vs Cool Temp and the IAC throttle follower tables. That might make a difference.

91L98Z28

413 *RW*HP out of a TPI is awesome!

I bet if you look at your HP curve, it flatlines at some point at 413HP when the engine reaches it's breathing limit through the TPI. What hectorsn said is right on - your power loss is basically guarnateed to be in the intake. TPI and high RPM power shall not be uttered in the same sentence!


Post pictures of the car and also of your dyno graph.

DAVECS1

iTrader: (2)

Thanks for the tip on the IAC. We tried unplugging it and capping off the feed, but the idle still comes up to 1500 at start up, which is 500 less than usual, but I think your right. I still need to fiddle with it more. I will post the dyno graph. The lines look pretty good. It does build to 5200 and then kind of flat lines from there, but that is kind what we were expecting using a TPI setup. Torque is in the 450-460 range and it comes on at about 2800 and tapers off about 4800. We would like to get HP and torque closer in the upper RPM ranges, but I think my dad and I are pretty satisfied with were we stand now. I will post the dyno numbers this weekend. Dad has the graphs so he can show them off to his buddies at work. As far as using a different intake to gain more power,, we were aware of that, but the old man liked the look of the TPI. That was most of his reason for switching over,,, silly old man I would have tried and talk him out of it, but the numbers have turned out good and driveability is pretty decent so why change it I figure.

Here is another picture I have of the car.

91L98Z28

yeah, hard to argue with TPI looks.

alternatives include the high flowing TPI base manifolds, and porting the crap out of the TPI runners.

the GM ramjet manifold isn't too bad looking either..... =) might kind of fit in with the vette, since it supposedly looks similiar to their old mechanical injection setup.

funstick

you might wanna try reseting the iac position. jump the ab pins or whatever it is with yr car to get robule codes. turn teh key forward with the key in run DO NOT START. let it sit in run for 30-60 seconds. then unplug the iac. then clear the codes and meory by unplugging the ecm for 60 seconds or the battery either one. then plus the iac back in. reconncect battery ecm then start and put in gear immeidaitely. it will relearn teh idle logic very quickly see if this fixes the flare up. the iac could be out all the time at 60 steps or more if it haesnt been reset. this would explin the flair at start up. if the iac is showing less than 10 steps at idle this is the culprit.also make sure the tps is showing less than .60 volts but more than .50 volts. check it for % opening at idle. could be driving the idle logic nuts.