Starting to think this may be black magic
 

I have a 7747 ecm and the motor specs are on the left in my description. Why is it I can never get anywhere while reading all this stuff when you guys got it friggin memorized... I can't find any 7747 idle tuning tips... I have had a truck that has lived in a storage unit for 1 year now...(about 900 bucks just on storage) and I'm wondering if I should just cut my losses.

I just don't know where to start a year into this stuff... I still don't know what does what or even what questions to ask to get the answers I'm looking for. I have read alot of the articles over and over but I still don't understand alot of this stuff.

Is there a specific place where I can get some 7747 tips on how to get a stable idle and lean the desired o2 mv because of my cam? (272 dur, .447 lift.)

You just have to keep reading. I don't know if you started tuning yet, but you kind of have to jump in with both feet for any of it to make any sense. Read and re-read the stickies in the DIY Prom board and the TBI board. There is a ton of information in there and I've probably read it all about 4 or 5 times. I've been tuning for about 4 months now and I know what you're talking about. Start slow, changing small things like flags and switches. Then work into the more complicated stuff. All of the tables are kind of intimidating, but remember that there are some that you won't even touch.

What idle problems are you having?

RBob has many good papers on diy-efi.org http://www.diy-efi.org/gmecm/papers/

As far as the idle goes, the 7747 doesnt actually have much control at all over the idle, and the action isnt linear. The later computers have sophisticated PID routines that actually linearize the action of the IAC and also use the SA and fuel to help control the idle.

From my experience with the earlier computers, the best thing to do was to not let it really control the idle at all. Set the dead band (area that the ECM wont adjust the idle) so something like 75 RPM and open up the throttle blades to get close to the desired idle speed that you want (also set this in the prom). There are also some delay parameters that you can adjust. Increasing these will make the ECM adjust the idle only when its been out of range for a certain ammount of time. IIRC, thats a fairly aggressive cam, and the idle routine cant keep up with the variations anyhow, so you might as well use the min air to get the desired idle speed. Also, the fueling will have a large effect on how the engine idles. If its running lean or the fueling/SA varies alot, the idle will surge wildly. Dialing in the fueling and spark will help a great deal with the idle.

What is min air? The thing is I don't know what to change in order to stop it from controlling Idle... I really don't know what will control it.

i think min air is setting of the iac steps at idle? first off my cam is 224/230 @ .05. i have 0 steps at idle for IAC counts. i idle at 800-850 rpms(manual trans). The idle is forced open loop(not closed loop) and is about 14.0/1 per WB as commanded. i would suggest you idle in open loop due to the size of your cam. also i forced "synch" as i saw it falling into asynch causing fuel cut off (0% DC) and erratic idle. Forcing synch has seemed to help most with idle. my issue there was high fuel pressure and large injectors. that should be resolved for me with VAFPR this spring.

How do can I force an open loop idle on a 7747? Also how can I force sync?

by the way I am really, really "green"(as you can tell:idiot: ) with this so please bear with me...

So closed loop means the computer is trying to "help" the motor run better but open loop just lets it do what its doing?



Also, what is sync and async?

I really appreciate the expertise... sounds like you might have hit the nail on the head with fuel cutting off. Even thought I don't know what async is, the symtoms you described are a match for what its doing.

Well, enabling open loop idle in a 7747 is not all that difficult. It involves changing a couple of enable/disable parameters and changing a time delay. Look at this BIN. It is the leaded fuel option bin without closed loop of any form.

ftp://ftp.diy-efi.org/pub/gmecm/bins...7/akaj1147.bin

Sync simply means an injector fires every distributer reference pulse or every 90 crankshaft degrees.

Async means that the injectors are firing every 12.5 milliseconds.

You force sync by setting the maximum async pulsewidth setting in the calibration to Zero.

I've always wondered when you want sync over async. I see the technical difference but what does it mean for fueling?

my experience with large injectors at 23 lbs FP was that at idle it would start synch and after CL sets in a few minutes later it would then cycle to asynch and then start dropping DC% from say 4% to zero in a rhymthic pattern. engine would surge and stall saver eventully came to rescue(bugles sounded) as RPMs dropped and more surge. back and forth. the worse part was the car next to me thought i was doing it. forcing synch at idle makes for a rich idle but i am ok with that. also i idle OL(13.5-14.0/1). the VAFPR will allow me to reduce the FP and help idle further(i hope). have not driven car since 11/2006. looking forward to tune 04/2007.

Ron,

The VAFPR won't necessarily allow you to drop FP. It will, however, reduce FP for you at times such as idle. If 23psi is what you need to get a reasonable DC% for the injectors at WOT, then you'll leave it there. Connecting the vacuum port of the VAFPR will reduce your FP at idle and partt throttle cruise. Mine is set for a max of 20psi but idles at 11.5.

i had it *** backwards. not surprized. thank you.

does my Aeromotive Reg then work opposite of the GM VAFPR?

Nope. Its just that we're using the VAFPR for a different reason than the PFI systems. We're using it to increase pressure and flow more fuel. The VAFPR as used in PFI maintains the same flow, as I understand it, making up for the pressure change across the injector.
















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Dom: what does PFI stand for?

I am refering to the GM VAFPR that I believe is used in BB GM TBI marine applications. dont think it had an application in trucks. the one some used in lieu of tuning the ECU. Are you possibly refering to TPI applications?

so if i understand it the EBL table for VAFPR uses a table of manifold vacuum(MAP) or if my recollection serves me it is KPA or pressure? i dont have my EBL tuning info here at office. i am confused.

PFI= Port Fuel Injection as opposed to TBI = Throttle Body Injection.

Here's a .jpg of my VAFPR table. It modifies the BPC based on Engine Vacuum.
Or the inverse of MAP. The more engine vacuum, the lower the FP since the vacuum compresses the VAFPR spring. This reduces the FP.
So idle has high vacuum and therefore lowered FP. WOT is just the opposite.
Since there is little or no vacuum, the spring can expand to its full length and increases the FP.

Sorry to hijack... but....

now i am really confused.

the aeromotive FPR i run (13301) references boost or positive manifold pressure? how can that work as a VAFPR? if i idle at 35 map that is a vacuum vs 100 MAP which is atmospheric pressure. does the Aero unit also respond to vacuum in effect decreasing fuel pressure at idle as you state?

this is posted before i read your response...

OK i read the table just now.

assuming you idle at 35 kpa would you use that BPC that was in your tuned bin before you utilized the VAPPR? IOW i would take my current BPC that my underlying tune is based upon and put that constant in the 35 kpa field so as to achieve the same A/F at idle as i had before? sort of a starting point to interpolate the others? if that is correct then when in PE and logged in WB i would set the upper kpa (90) to a corrected BPC that would achieve my desired 12.5/1 as evidenced on my WB log? i assume you need to tune that table somewhat and that you in fact did.

If you're idling at 35kPa, that means your vacuum is 65kPa or whatever your "key-on" MAP is - 35kPa. I run 20psi FP for adequate fueling at WOT.
That means that without any vacuum, my FP regulator was set for 20psi.
RBob has an .xls that will help you calculate the BPC and the corresponding FP when the VAFPR vacuum port is connected. So my motor idles at 46-48kPa. So my motor idles at a vacuum of 52-54kPa. That's where the calculated
BPC goes. I have an xls to do the calcs. I tried uploading it zipped onto this forum and it gets corrupted.

Good table, just make sure you set your injector size in the calculations, dimented has his set at 80.5 pph injectors. I have 90 punders at 24 PSi max pressure, 15 psi at idle.

Just for comparison purposes here is mine.

Attachment 134125

hold mouse over it and click expand button.

Quote: RBob has an .xls that will help you calculate the BPC and the corresponding FP when the VAFPR vacuum port is connected.

If I am OL at idle and seeing 14.0/1 before the connection of the vacuum line to FPR is there any reason why I could not use my WB to anticipate a BPC to be inserted into that table? with Prominator shouild not be difficult to achieve in a few attempts. It would seem that would be very accurrate?

same on the 80kpa part of table. that is assuming I can stay out of PE which I believe is an adder, lock OL temporarily, and run 80 kpa and observe what i see at 80 in regard to A/F? or does that table assume PE is already in the VE tables and not an adder? If so just observe my WB logs during a gradual WOT pull. is the .xls posted in the original EBL thread? I will search for it.

This is what I had, when I ran my Weiand on my 350 with the EBL.

68# injectors running an Aeromotive external regulator hooked to the intake manifold under the supercharger. Vacuum decreased the pressure, Boost increased the pressure. Idle fuel pressure was 14 psi. Had 25-27 psi under 5-7 psi boost. At 7 psi, it was a BEAST, when I could keep a 700r4/4L60E in it. Broke a Richmond 3.73 gear set for a 8.5" 10-bolt as well.

Ron,

I can send you an .xls but I also think RBob will provide his to you. V8Astro has another one that makes it easy. Email me and I can send them to you.
But let me also explain how we got to the table I currently have. The BPC of 96 at 0 VAC was based on the BPC I was using WITHOUT the vacuum port connected. That's the BPC that worked for WOT at 20psi. Based on a "correct" calculation my BPC should be 86. When Bob did the calc, he first needed to find the correct engine displacement that would yield a BPC of 96 when running 20psi thru 80lb injectors. Make sense?
In other words, I was using a BPC that was correct for a 390 CID motor using 80lb injectors at 20psi FP. Now RBob may want to chime in on this because I don't know if the Injector Offset has any effect on this. I am using 732msec.
So when you start out calculating the table, you'll start with the BPC you are currently using. That will be your starting point and it will be the basis for the rest of the calculation of the table. I am now tweaking the bottom of the table because the VAFPR spring doesn't necessarily follow the calc's precisely. Seems to be working out.

On the van I took a hand vacuum pump, t'd into both the MAP and VAFPR. I then hooked the EBL up to my laptop and hooked a fuel pressure gauge up. I checked the pressure every 5KPA of vacuum, wrote down the pressure, then I hooked up to the pressure side of the hand pump, went up to 10 psi every 5KPA. Then I calculated the BPC and filled in the table with that.

The BPC spreadsheet can be found in the wavy VE table thread:

https://www.thirdgen.org/forums/diy-...es-7747-a.html

RBob.
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This is a decent method. Lots of calc's, but it corrects for any non-linearity in the fuel pressure regulator. Which is something that I've seen. When I did the original spread sheet the calc's are fudged to make up for some of what we saw.

I did not put any fudge factor into the one posted on the Wavy VE thread.

RBob.

I prefer sync fueling over async 99.9% of the time. It is very difficult to get the async fueling to be equivalent to the sync fueling. By this I mean the amount of delivered fuel. When the ECM switches from sync to async the fueling tends to go way lean.

RBob.
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Blazin4x4, can you post the ECU or XDF file that you are using? With that I can tell you what 2 parameters to set for sync fuel only.

RBob.

Is anyone else having a problem with zip files on this forum? I keep getting invalid archive message when I try to open. Bob, any chance you can email me the .xls you posted. Thanks.

FAST: as long as we are on the subject.... what port on my GM 7.4L TBI unit is the best vacuum source? or is there a source on my Holley Projection Manifold ? car in storage or I could look.

I think this should work... if not let me know. That sounds like my symptoms... it just dies after a minute or so like the ignition got cut off but if it switchted to async and the dc was zero then it would do that wouldn't it?

I used the manifold vacuum fitting where the EGR solenoid would connect for the VAFPR.

OK, here are the calibration parameters directly from the ECU file:

Minimum BPW Hyst Value: set to 0
Minimum BPW: set to 0

Max Asynch BPW: set to 11500 to 12000 u-seconds (usecs)
Min Asynch BPW: set to about 500 usecs

This will allow async AE mode while disabling regular async fueling. Try it and let us know how it works out.

RBob.

beautimus... thank you.

ok while your here, how can I idle in open loop? It seems to be the preffered idle for 7747. I tried to look at the .bin fast posted but it tried to open the prominator program and my truck is in storage.

What is async ae mode?

edit:

Another question I have is the max async values that you gave me... is there a decimal in there?

Also there is two "cells" to put values in I just put them in both, will that work?

(haven't fired it up just yet... Trying to make sure I get this right)

Attached is a corrected version of the 7747mine.ecu file. Will need to use Firefox to download it. There will now be one value each for the PW thresholds. In TP they also moved to the Constants/Scalars section. Same names as above, proper calculations now. Yes, there will be decimal points in the values.

For open loop idle, I'll need to see what needs to be changed.

RBob.

Wow, so I had the wrong ecu file... you da man. I'm heading to the storage unit tonight so I'll let you know how she runs. I changed a few things to try and force o/l idle but I didn't play with the timers just the o/l on and off rpms.

Now we're getting somewhere. It will idle now but only in park. Soon as it's in reverse or drive the rpms drop from 850 to 650 then the rpms go up a little right before it dies.

I got some flags that I'm not sure about. First off what does it mean when DRP occured?

I got that, idle/ cool flag, ready for second PE, low battery (IAC inhibited), and of course a rich flag. Could any of those affect idle in drive?

Also I got a .bin from val snyder and now the thing seems more "free"... but it's using the "bitchy" xdf. Is "bitchy" better then 7747 mine?

to me it smells and sounds like its flooding out and basically drowning but the way the rpms go up a little as it dies seems like it would be lean. On the other hand it was surging for a while so that could be why its acting like that.... but why is it surging? Could this be because of the c/l idle?

Blazin,

If you look in the Constants section of the 7747 bin, you'll find O2 Prop Gain and Prop Term parameters. Could you tell us what those values are or post the bin you are using now? Also, what are the advertised(.006" lift) duration and LSA for the cam you're using?

Ok, o2 prop gain factor at idle is 5 and o2 prop term duration at idle is 2.


The cam is the old l-79 cams that were stock in the 350 hp 327's way back when.

It's the crane cams blueprint muscle car cam: advertised lift is .447/.447 and dur. is .272/.272.

I have done alot of searching but I can't seem to find a lobe separation angle on it though. I beleive it is around 111 or 112. don't know though.

Try lowering the duration to 1 and the gain by 1. See if that helps the surging. Don't be afraid to drop the gain again by another 1. As for the cam I was looking for the amount of overlap it has. 48d of overlap if the LSA is 112.
Is this a 350 or 327?

This is a 355... specs are on the left.

Do the other prop terms have any effect? Like prop gain vs slow o2 err (Bin val to adjuist INT), prop term duration o2 err (time to allow o2 adjust to take effect), prop term duration offset vs airflow, and prop gain vs airflow?

Here is the .bin and ecu/xdf i'm using.

Just opened this file with TP. Am I correct in thinking this would take place of the $42 XDF file? Looks like this file enables much more control over the ECU?
I've been reading along as I'm having much of the same issues as Blazin4x4.:)

Well same problem different gear... Idles REALLY rich in p and sometimes dies but it will run if I give it a stab and let it settle down. I can hear it almost flood but it saves itself and it will idle till I kill it.

There is actually raw fuel in the exhaust. Once under the load of drive it floods out and dies. How should I go about leaning it out? I have leaned the ve map and it seemed to help a little but it's still pig rich. The prop gains actually seemed to make it worse. I lowered them both by 1 but I am using the bitchy.xdf with a .bin I got from val snyder. It seems to like that .bin a lot better.

Since the whole map seems very rich... should I just move the whole ve fl1 map up/leaner? I am getting rich flags all over the place. Or is there a better way then ve to lean the idle? IAC?

Also what does the "drp occurred" flag mean?

Again sorry for all the newb questions but I am starting to get excited... making a little leadway after alot of frustrating nights.

Can someone take a look at these and maybe offer a little insight?

burn 7747 is the bin and bitchy is the xdf

The rich flag is used in the PID routine, and doesnt mean actually rich. Its mainly used by the ECM to determine the heading of the O2. The DRP occured means that another pulse from the distributer has been recieved.

It sounds like it so rich that even the closed loop routine cant really compensate for it. Have you recalculated the BPC to match your current injectors? What fuel pressure are you running them at and how large are they? Depending on the holley unit and fuel pressure setting, you could have as much as 80 PPH of injector, which is more then the typical 55-65 PPH injectors the stock TBI trucks came with. Also, is this a late model TBI unit with the good delphi injectors, or one with the crappy MOPAR injectors?

Oh I see.

I was planning on making this thing firebreather so I went and got some 80 pph injectors. It is the newer delphi injectors.


I used a bpw caclulator for 80pph injectors at around 13 psi and got 90.49 for bpw. I have tinkered with bpw trying to lean it out but not since sync is off.

It seems like there are spots in the rpm range where it's very happy and responsive but then it will go flat. My best guess is spark has alot to do with it. I dunno tho... the ve table seems pretty smooth so I don't understand why it's rich down low, good in the middle, (1200-2600 rpm), and rich up top.

as Dimented said: It sounds like it so rich that even the closed loop routine cant really compensate for it.

if so would it be reasonable to take the 02 sensor out of the equation totally and run OL as a temporary fix. the cam may be the culprit(temporarily).

that is prevent CL, leave the BPW as is, keep FP at 13, pull fuel out of VE by 20%, and see how that works. I would get idle cleaned up first! then flip back to CL check BLMs, if still rich, then pull more fuel till it swings closer to 128 at idle. once that is done, maintain CL mode, take a drive on flat terrain, easy on the gas and get some data off idle.

i bet you are overfueling bigtime. i was in same position you were day one. cept i was lean. same 80 lbs same 13 lbs FP same 350(new cam and heads)cept i had a diff manifold design that required more wetting.

Spark: It's worth trying some more idle advance once you get the fuelling right. Bigger cam means less VE at idle and so less charge which requires more advance. This should also improve your idle vacuum (reduced MAP).

VE Curve: One explanation for your fuelling issues...

• Rich low = reduced real volumetric efficiency so need for less fuel.
• Good midrange = not much difference between cams in this range.
• Rich high = better bsfc where the cam starts to function well, so needs less fuel

.

Well I took 15 percent out of the ve tables and played with r/l thresholds and it runs and smells pretty good... but not in D. It's funny I started to notice it dies in the exact same amount of time every time... 5.5 seconds on the dot 4or 5 times in a row when it goes from park to drive. My dad, not knowing much about efi, suggested that it has no spark when it dies. I said no but what the hell put a timing light on it, and somehow we ended up moving the distributor again and it dawned on me that it woun't run a couple degrees off of what it was set to. It just plain wouldn't run with the spark advance wire disconnected. But since the base timing is so finicky on where it is happy then I bet it's spark because when in d there is more kpa which means more timing. It's just a theory though... wouldn't be suprised if i'm wrong though.

More kPa generally means less timing (because this usually means more cylinder load).

John

Ah... didn't really look at it before I posted.

Does spark sound like it could be the problem?

I run(currently) about 20 deg at and around idle. I have in past run as little as 16 and as much as 24. my engine would never die. i dont think it is spark. i assume you are running a stock GM table for truck or now? if so that should get you running. i would concentrate on the fuel tables and let the spark for another day.

anyone? should he not be ruuning synch and OL to allow the car to idle?

does the car still have the idle stop screw capped from factory? i believe i could produce the same issues on my car by backing off on the idle stop screw(uncapped) since my IAC steps are zero. that would shut off air.

it seems getting a clean(reasonable decent) idle is first step?

I looked up your cam in the "How to Hot Rod a SBC" book.
They didn't measure it, but they were able to estimate it based on the factory numbers.
Using .008 for rated duration, it's 284/284 on a 114 LSA with 111 ICL & 56* of overlap. The cam was designed for a higher CR, so I hope your not trying to make it work with < 9-1. If so you might as well swap cams before you tune. The L46 came stock in 9 or 10.25 engines.
For a more common comparison of .006, add 2 degrees or so with that slow lobe it has. Figure around 222 @ .050 since the L46/48 cams were there too.

Since it doesn't die at idle like it does in gear, does it???
It's not spark related unless your dropping lots of spark from the rpm drop.
The SA table needs to be flat in the idle area. And probably around 20* minimum.

Next you need to be able to data log. Ask questions-in another post- and get some logs on it. Then post them, and even though the 747 logs real slow. I'm sure there are several people here that will be able to point you in a direction. There are several guesses that could be made but more info will narrow it down.

Re: Starting to think this may be black magic
 

Ronny: It has a holley 670 on it and I'm in sync which helped it to idle in park which it wouldn't do in async but soon as it goes into drive rpms fall, sounds like it loads up then it dies... exactly five and a half seconds after going into gear. I've been getting high map readings and high map flags... Why is this? maybe the 10:1 or the cam?


Open loop is kind of tricky to me still... it seems to run worse in o/l but this is because I don't know what to play with. Ve tables still affect o/l correct? What about o/l afr vs map. I'm just not sure what to start with in o/l.