I didn't know that was MY theory of tuning. Why would you tune an idle AFR of say 14 when it idles best at 15? Why would you tune for an PE AFR of 13 when it runs stronger at 12.5? Simply... give the engine what it wants, not what you think it wants.
Tuning the idle VE's to get a stable strong idle isn't rocket science and you can tell when you're too lean. You know you're too lean when it either backfires through the intake with even the slightest increase in throttle opening, it stalls when put into gear, or the engine surges high and low.
Tuning a stable idle is hardest with TBI because the computers have terrible AE code, it basically uses no RPM, only 2 TPS values, a MAP value, and compensates with IAT fuel trim tables @$$ backwards to keep it from backfiring in the intake. That and they run REALLY rich factory open loop, so AE can hide a lean idle AFR, you can tell if you need a lot of AE to keep it from backfiring at low engine speeds but around town the AE is so much that it brings the PE AFRs WAY rich and takes a while to clean out.

 

What whas your method to tune the car more rich than lean in closed loop and not having the ecm compensate for your changes?

 

Good question. I'm curious as well.

Reason being is that I "can" richen up part throttle cruise ( VE ), however it's never a stable WB A/F ratio result do to the computer making constant changes via INT and BLM (from how I understand it, I could be wrong). However, it will richen up the range it fluctuates to show a more rich result on the WB.

Generic example.... 19:1 - 18:1 to a better 15:1 - 14:1 constant fluctuation.

This is what I'm currently experiencing.

The motor doesn't back-fire or stall when I had it 19:1 at 2,500 rpms (part throttle cruise), but the plugs were on the white side. Motor also ran a little warmer.

Also, I've noticed that the WB results (when making a WOT pass) are more stable (not fluctuating as much) and start gradually making it's way to 11.8:1 where I currently have it. PE WB a/f ratios seems to not fluctuate near as much as part throttle cruise. I still have more PE tweaking to do. But, the more and more I lean it out in PE (as the WB A/f ratios are leaning out), the more power it feels I'm picking up. When I finally get it to ~ 12.8 - 13.0 I should notice even more power. I'm still not getting barely ANY knock retard. So I feel I'm still on the safe side. Plugs are looking better and better too.

 

If you put all this "new" knowledge practical. How do you tune part time throttel and idle, please anyone enlight me?
For me I own datamaster a diy wb.
I tuned my idle and part time throttel using the blms. And PE using my WB, car seems to like it, i dunno???I guess if I tweak it 1000h more I can get it better, when does it stops?..
Now with this im not sure anymore. Sometimes it feels like all this tuning takes away the fun with the car. Nowdays I just keep stare on the WB, datamaster and thirdgen.org, forget to have fun driving
Perhaps its time to get a stand-alone efi system with WB auto logging

 

Ahh I thought of that to Keep us noted how it works out for you.

 

I'm thinking that too much thought is being put into this. . .

RBob.

 

:hail:


mmmm think the same, I guess if GM used the nb and blms to get the closed loop working, it should be ok for us to use it to. Perhaps its not the ultimate thing to use. And perhaps the afr of 14.7:1 is not ultimate for any engine, BUT its a tool that has been giving to us.

I will tune my car in closed loop using the BLMS. And use the my WB to get the "windows" rich instead of lean.
ANd then PE using the WB. THen drive the car, watch the plugs, and have fun.

good night...

 

just a reflection. I heard "give the engine what it whants" time to time on this board. But thats not really going to happens as long the stock ecm in closed loop struggel to get 14.7:1 is there?

Regards

 

Yes & no. The calibration tables for the O2 sensor define the real AFR the engine runs at while in closed loop. These tables can be changed to have closed loop be an AFR other then 14.7:1.

If running a cat-con closed loop is important. The whole GM calibration thing is about keeping the cat-con operational, alive, and healthy.

Once there is no cat-con, there is no reason to operate in closed loop.

RBob.

 

Does the torque converter lock up in open loop? Mine doesn't seem to. That would be the only reason that I can think of why I would go back to closed loop.
John

 

I follow you so far that if you use a cat you "must" tune non PE to stock commanded A/F at around 14.7:1 to keep the cat working best.
And it whas just that i thought I did when I used the BLMS in non pe mode to tune it to 128?
But consider this new "phenomenon" you cant be sure of that a BLM of 128 really is going to keep the cat happy? Cause If a BLM of 128 really is a VERY lean AFR of 17.5 - 20.1 / 1 on a modifyed engine ( as 1bad91Z say ), you could melt your cat when you think you give it what it whants.

 

It's not a whole lot of fun tuning and tuning and tuning. BUT, it's all part of the process of getting your hot-rod to run as good at the track as it drives on highway (street manners, gas mileage, etc...).


I have a few questions for Rbob and other guys running strictly open loop.

In the next 2 months, I'm scrapping my cat, custom y, and flowmaster cat-back. I'm going back with another custom y (ovalized) and a 3 1/2 mufflex cat-back with spintech muffler (no cat).

So, what are the main tables I'm concerned with if running scrictly open loop?

Is there even a need for a narrow band o2 to bee hooked up when running all time open loop?

I also dont understand how to "lock" the BLM's in open loop.

Is there a good post or tech article on running scrictly open loop that you guys can direct me to?

 

Running open loop is easy to set up. First is to change a few calibration parameters:

a) min & max BLM to 128

b) min and max INT to 128 (not really required but nice).

c) closed loop enable temperature to 151°C (max possible)

d) disconnect power to the ECM, wait ten seconds, then reconnect (resets the BLMs).

The NB sensor is no longer required and may be tossed. A WB is required for tuning.

The ECM will no longer go into closed loop, nor will it make any corrections based on past learning.

I also like to disable PE mode by setting the PE TPS% thresholds to the maximum value.

At this point the commanded AFR will be set by the open loop AFR table(s). Some ECMs use two tables (vs Vac and vs CTS), others use one 3d table (VAC by CTS), and I believe $8D uses two tables (Vac & CTS) that change the AFR by a percentage of the stoich term.

It is now just a matter of adjusting the open loop AFR tables to command the desired AFR at that load (MAP) and CTS/MAT/IAT (whichever is used).

Then adjust the VE table vs the WB reading to provide that AFR. If the commanded AFR isn't what the engine likes, then change the commanded AFR.

In tuning open loop the commanded AFR should always be what the WB reports at the true AFR. Adjusting the VE table is the proper method of achieving a match.

As the ambient temperature changes the AFR(s) should still match. If they don't then the CTS/MAT/IAT compensation will need to be changed to suit.

RBob.

 

Doesn't VE stop at 3000RPM or so ?

I thought PE was the open loop table to adjust fuel in the upper RPM range.

 

So, what would happen if only c were done, and not a & b?

Also, what if a & b were done, and not c?

What I'm trying to ask is the importance of the combination of all 3 steps.

Thanks!

 

Steps a & b are not important as long as step d is taken. Step d being to reset the ECM. Otherwise stored BLM information can be used to make corrections while in open loop.

Steps c & d are the important ones and all that is required. I like to lock the INT & BLM's to 128 just because.

RBob.

 

I don't know of any GM ECM where the VE tables stops at 3,000 RPM. Most go up to 5,600 - 6,400 RPM.

PE is a special mode to get the ECM out of closed loop, command a different AFR and add SA until PE is no longer requested. The ECM will then re-enter closed loop immediately.

Once the ECM is forced to run in open loop there is no need for PE mode.

RBob.

 

Good info Rbob. So if you are really in open loop mode for sure, then you would use the upper load areas to set the commanded AFR for WOT tuning? In open loop the AFR goes by temp and Load, in PE mode the AFR goes by temp and RPM. So does ecm NOT use PE mode when you are in open loop? Or do you get PE fuel no matter what?

Seems like in open loop the tables have a little more adjustment points.

PS what is a good open loop idle AFR? I am about 14.0, and i think that is too rich. I get a stumble when I gas it, and sometimes when I take off easy with engine warm, it bogs down. My neighbor said he saw black smoke when this happened!

 

PE can still be used in open loop. Or can just set the TPS% threshold to max and not use PE mode.

You will want to set the high load areas of the open loop AFR tables(s) to whatever AFR is required for high load operation. Basically the same as if in PE mode.

I typically set the AFR to taper down as the load increases. A 14.0:1 for idle shouldn't be too rich. There may be either too much AE and/or the MAF tables are off.

RBob.

 

Ok Rbob, good ideas to keep in mind. I think I need to lean it out a bit at idle. I thought my MAF tables were good to go, most blms range around 128, and a little lower at idle. I am still not using open loop all the time yet.

Now for another quick story, somewhat relating to this topic. I went to the track today for some TTs and bracket racing. I managed to win my first 2 eliminations, before the rains came. On the way home in a severe downpour, my SES light to came on for a few minutes, but then went out. My WB LM1 showed about 12.4-12.9 AFR. And my cheapo AM AFR idiot light guage, showed a steady light in the middle, indicated that I was NOT in closed loop. The car seemed to run ok, just a bit rich. I figured I was in some mode, and the ECM was defaulting rich due to the SES condition.

As I drove home, the ecm would go back to closed loop operation, but I did see the SES light come back on again. I was driving real easy due to the heavy rains. Eventually I drove out of the rains, and I could pick my speed up, and the car seemed to go back to closed loop. I knew that I had the code set into the ECM. When I got home and checked the code, it was 13, O2 sensor open circuit. I checked out my service manual and started thinking about it.

I beleive that water got up into the connector, and made the stock NB 1-wire sensor go wacko. I mean it was a downpour that I was driving in. I will have to reset the code and get my scan tool back on there and see how it acts. The sensor is not that old, so I don't think it died yet. I wonder if the code 13 forces the ecm to go real rich, since the LM1 was reading way richer than what I specified in my open loop tables, under normal part-throttle conditions.

My whole point to this story is, if was not using the NB sensor and closed loop, I shouldn't have gotten into this condition. IE if I was in openloop, then I would not be susceptable to getting the water up into the sensor.

All opinions appreciated to my story.

 

FWIW. first day CL WB cycled over 15/1. 15/1 appeared to be average idle. on xway cruise read approx 18/1 or so. that puzzled me till i remembered highway mode! appears to be enabled. deacceleration enleanment pushes it over 20/1 maybeup to 24/1. again one weekend with unit. my idle BLMs always showed a bit on rich side about 124-125. i left that alone as started out about 115-122 BLMS last year on first tunes.

 

I'm having just the opposite problem - my WB says I'm idling rich (12.2-12.7 readings) while the NB has the BLMs sitting pretty steady at 127-128.

Under mild acceleration I will see 13-13.5, and when decelerating I'll see 14-14.5

So what gives with this? I've even tried two separate NB sensors and get the same result.

Any ideas or recommendations?



- Vern

 

i have Bosch 02 sensor hooked to ECM. maybe GM/Delco is calibrated differently. dont think it should be. also my both 02's are at end of collector in a bung in the exhaust pipe about 2 inches behind each flange. mirror images.

 

Ronny, I'm experiencing the same exact WB readings as you are!

I'm going to try disabling highway mode and get a new WB data-log.

 

ok rbob i am finlly in open loop tuning only and love it i still use my pe tabel cuase i use a 7747 ecm and i do not have a o/l tabel besides the o/l AFR vs temp....i do not have jsut a o/l afr tabel by it self for map load conditions so am i ok to just use the pe afr tabel? aslo in the 7747 is there any thing to help in open loop tuning to?

 

For open loop AFR in the '7747 there are two tables that are added together. One for AFR vs CTS and the other is AFR vs Vacuum. You can change the AFR vs VAC table to adjust for load.

The only issue with the '7747 is a lack of IAT sensor. In this case it is helpful to maintain a steady intake air temperature. That will keep the AFR in line when the ambient temperature changes.

RBob.

 

ok so like all i see in my xdf...is like afr sub chocke vac....and pe afr.....i dont see afr vs cts..do you have a xdf for 7747 i cna try...if so shoot me an e-mail with ti to curtmgulla@yahoo.com please...thanks..

 

I have not used a 7747 for quite a while. I thought there was a table for "crank" AFR. that is only on while starter cranking. the "choke on" I believe is also on for a very short duration b4 it goes to the OL table. anyway i can see my A/F on WB enlean quickly after a few seconds on cold start. Look again there has to be a open loop A/F table in that xdf ?

As RBob stated there is the "adder" table?

 

This xdf has the tables:

http://tunerpro.markmansur.com/downl.../7747-mine.ecu

Table names:

O/L AFR vs Temp
Cold AFR vs. VAC kPa (Added to AFR vs. Temp),

RBob.

 

how are to two tabels added? cause as i see...o/l afr vs temp is the actuall AFR...but the cold afr vs vac kpa.. if it is an adder tabel....all it reads is from 0-80 kpa and numbers in mine are like 3.5 at 80 kpa.. does that mean that...if my afr is set to 14.6 in the o/l afr at my temp 80C.. that my real afr is target is 17.9? and if thats true what about wot??? does it still add the 3.5 at 80kpa to it as well or do i have this wrong?

 

Need to remember that it is manifold vacuum, not manifold pressure. So if barometric is 100 KPa, then 80 KPa of vacuum is 20 KPa of pressure. Which is off the throttle.

The tables are added together as you posted. If at 80C with 14.6 and 80 KPa vacuum with 3.5, then the commanded open loop AFR will be 18.1

Once in PE mode (WOT) then the commanded AFR is from the WOT AFR table.

RBob.

 

so since i sue open loop ojnly would it not be a good idea to jsut zero out the cold afr vs vac kpa.....or what? do i need to leave it alone and adjust o/l afr tabel...or what i am now lost..

 

I have been on here a while gathering knowledge and I am looking at adding TBI to both my '78 and '81 camaros, one with a 383, and the other with a 472. They will both be driven in temperatures ranging from freezing to 90F+. I was planning on using the '7747 for both, but since it doesn't use a IAT sensor, can you recommend a better ecu to go with, or tell me if it is possible to mod the '7747 to use a IAT sensor.

 

You would need to change the firmware in the '7747 to use an IAT. The hardware for the IAT is already present. The '8746 ECM uses an IAT, although mostly for over-heat protection (it richens the AFR as the engine temperature goes up). For those engines the best bet is an EBL setup.

The reason that stock TBI ECMs don't use the IAT much is that the entire intake track is heated. From a thermostat on the air cleaner inlet to fully water jacketed intake manifolds the inlet air temperature doesn't change too much.

RBob.

 

I do like the functionality of the EBL, but since I am looking at puting TBI on 3 or more vehicles of my own and a couple for a friend, I think the Moates/Mansur combination would end up being a more cost effective route for tuning. Now if there was an option to buy the EBL Flash complete, and then later be able to just buy the daughterboard for each additional installation at a reduced price (because not buying the software again), then that would be really great. $350 per vehicle on top of the hardparts can get expensive. Oh well just dreaming again. I've got some time to think about it though.

 

A street 4-bbl carburetor costs more then an EBL Flash system. After spending thousands on an engine wouldn't it better to get an ECM that will compliment the package?

RBob.

 

What a salesman

I wanna buy another one even though I don't need it

It is indeed a great product with excellent support

 

I have already promised myself I will never buy another carb again. And if I ever buy another carbed car, the first thing I will do before I even buy gas for the thing will be to EFI it. I completely agree that the EBL is better than a carb, but so is the stock TBI. Maybe not as good as the EBL but good enough for what I need. And the AutoProm is still more affordable than 4 or 5 EBL Flash setups. That's all I am saying.

 

You missed the point.

And a carb is better on a performance engine then the stock TBI setups. I know this as I've run both on the same engine/vehicle. And I've also run a '7747 for ignition only with a carb. That was the best setup with stock TBI parts ('7747 for ignition and a carb for fueling).

Which is why the EBL system was created. The most important parts of an EFI setup is the software the ECM runs and the tools provided to tune it.

RBob.

 

I'm glad I caught this post as it came to life from 4 years ago. It always bugged me how I would VE Learn my car with the WB O2 and it would be running great, then re-enable closed loop and it just didn't seem to idle or slow cruise as well. This explains a lot, also explains why I can do a Learn with BLMs and get them all set, and then run the WB and it will make huge changes after I had just setup the whole VE table hitting 128s.

Makes a lot of sense, and may explain the odd/rich? smell my car gets after long runs and then parking in the garage.

Also, for any people questioning the need for an EBL on a hopped up TBI motor, do not even think twice. EBL and WB combination is the best tuning setup by far. I spent an entire summer tuning my zz4 cammed 305 in with a stock 8746 and got it running very good. I bought the EBL and started from scratch and had it running better in a week. That is the real-world advantage of the tuneability and superior code.

 

I know you are trying to push the EBL and all, but my experience was directly opposite. The 299 ECM used in the 1992 TBI Trucks/Vans was a good platform for a performance street engine (350 HP). Not to say the EBL wasn't ALOT better, but that the stock GM ECM was still ALOT better than the best 4 bbl carb.

 

Wow very good inforamtion here. I've got a question if you all don't mind? I don't mean to change the direction of this thread but...

I'm wondering does it make sence to run only in open loop on a fairly stock TPI motor? I'm almost thinking about doing this. hoenstly it sounds like it might be a strait to the point configuration? Plus my car runs stronger in open loop. Thanks in Advance...

I plan on getting a WB02 before doing any Fuel and Spark changes in my chip right now I'm doing very basic stuff coolant temp and TCC changes. If you think so I'm going get a WB02 and being my journy

 

That is a good question, which has been debated many times before I am sure. Just do a search and you will find much discussion.
I will just give you my opinion, since my motor is also fairly stock. I had thought about going open loop, testing just for fun, but never took the time. You need a good scan tool, and WBO2 of course, and need to pay attention to the data. I would just stick with closed loop operation. Get a good NB sensor, preferably 3-wire heated, and tune your BLMs for 128. You will find it easier to do that, than using a WB. The NB is basically just a switching sensor, indicating rich or lean. If you are at 128, then the ecm thinks you are at ideal fuel mixture. For part throttle, who really cares if it is exactly 14.7. If it runs good then go for it. The WBs are much better for tuning WOT and PE modes. I have the LM1, and found my WOT was quite rich. It is good for highway mode as well.
Just my 2 cents!

Remember, when you go into PE/WOT, you are sort of in open-loop. I think you may be talking about running open-loop all the time. Might be better for a modded engine.

 

I ran open loop for a couple of months a couple years back. Here is Wisconsin the temps can be 40 in morning yesterday and 75 in afternoon. My gas mileage sucked. I like the idea of CL. I dont see any advantage to OL running. Maybe a bandaid for an underlying not so good tune. I do run stoich at 14.2/1 for ethanol blend gas. this year I will enable the deaccel enleanment and hiway cruise mode and monitor with WB02 after getting a read on gas mileage B4. 93 octane.

 

I have noticed the same thing with my 165/maf system.

When BLM's are 128'ish I'm rich. Pig rich, water your eyes, drinks gas etc. I do not have a wide band but I have started to tune to the O2 sensor instead of the BLM's. I also pay particular attention to the O2 cross counts. It idles much better and has better throttle response. Funny thing is that once I started to tune to the O2 the blm's didn't go as far out of whack as I thought they would. I took a ton of fuel out and there still only a bit too "high"- 133 at cruise and 150 at idle.

I have a theory as to why and would like some opinions,.

I think that because of re-adjusting my MAF tables (due to modded MAF meter) it skewed all my LV8's. (higher airflow = higher LV8's = more fuel) There may also be other changes I've made that are having "behind the scenes" effects. Changes add up and affect the BLM reading in my theory.

Therefore, the blm's aren't as important as what is really going on. As others have said and I'm starting to understand, tune to what makes the motor happy and let the numbers fall where they may.

It seems to work better to me than "de-tuning" to make the blm numbers "right".

 

I was thinking of tunning it to always run CL gas miles mean nothing to me I drive it maybe 5 miles a week at best.

Reason I like the idea is it sounds like much less paramitors to be changed and quicker results , or am i wrong? I'm getting ready to do a search too

My goal is to tune less. I also want to give the car what it needs not what I think it needs. you all think this is a good idea?

I live in a crappy area where it's hard to data log with all the damn traffic so it would be nice to tune and datalog less.

 

oh boy,,!!!! I was going to post a new subject as i havent been on here in a while but after reading this it sounds alot like my problems i had last summer before i put my car up.--Now my car is back out and have the issue of, off gas surge and im sure when i read my wide ban it will show lean.--last year it read any where from 14.9 ---20.0 AFR. and i had blm at 128 .And plugs were ash white. ---Still havent varified the readings tho yet[wide ban].-trying also a bin that has only the 02 lean/mean/rich, values diff,,[same] .to see how veh responds.---------Mayby ill just raise my 02 lean/mean/rich, settings very high ??--- Would 550 mv be considered to high?, for rich,, and would 500 mv ok for lean,, [just examples] ---- My tune was orig started off the asdz bin. -

 

I'm curious about something here.

I have seen no (or very little) mention of location of the WBO2 sensor or the NBO2 sensor, relative to each other, or EOM locations.

It seems that in most posts discussing the "offending" NBO2 sensor that it is most likely a single wire NBO2 sensor, and that it may be farther away from the engine than in the original location. I would think this would have an effect on the readings, since the NBO2 sensor could cool off, showing a rich condition.
I cn see how the large(r than stock) cams would add to this problem as well.

 

My NB sensor is in ext pipe just behind collector flange. Same on WB02 sensor. But the WB sensor(Bosch) failed too often. Innovate said move it back in ext stream which I did approx 16 inches as that was only possible location for clearance. Now the sensor life is proven better but not sure if NB-WB sensors are seeing same. I am commanding stoich to 14.3/1 in tune(10% ethanol) and seeing 15.0/1 at cruise(hyway disabled) 2000 rpms-67 mph but if i rev to 2400 rpms in 4th gear of five it drops to around 14.5/1. I have some reversion due to cam. so I will assume sensors are seeing same A/F.

 

The O2's (NB or WB) only read oxygen content of the exhaust gas.

With a larger over lap cam, there can be a difference between O2 positions due to the amount of fuel burning in the exhaust pipe. Scavenging from the exhaust will pull raw fuel and oxygen into the exhaust pipe.

If the exhaust gases are burning between the motor and the O2, the oxygen content will be less (at O2), the farther away from the motor you are.

The AFR reading at the O2 (NB or WB) will then be different then the combustion chamber.

This property of the exhaust gases will change from idle, cruise and WOT. Unburnt fuel and oxygen reads (lean at O2) when the mixture is really rich (at the combustion chamber). Hot burnt up cruise gases will read okay (at O2) but will have been rich at the engine.

Ever watch the flames come out of the short straight pipes. At some 2 feet from the motor and still burning (under higher loads). Not at idle.

Exactly what a pre cat does. What would your O2 read behind a pre cat?

If the engine could burn all the fuel and oxygen then why do we need a cat?