Leaning out at part throttle - experts opinion

[Toolman]

Okay, thought I would post this here, since my problems do not stem from the tune (in the form of the Tweecer) or my turbo system.

Here is a brief history: When I first got the car running, my 90mm MAF was wired backward. So the EEC was reding a full voltage at all times. CE lights on, MAF codes, etc, but the car ran decently enough, so that I drove it on a 140mile trip, and got 20mpg. Still, it was far from perfect, and I knew it needed some changes. Well, once I datalogged it and saw my MAF values (DOH!), I wired it up right and took it for a spin. WOT was AMAZING, car was very quick, all readings looked spot on and no CE lights, no codes.

But for some reason, I could not drive the car part throttle. Try and cruise for 5 seconds and my WB was looking like an oscilliscope (sp?), car would lean out and try to die. Well, it seemed my old fix to a HEGO was no longer working (wire had melted once, I rewired it, but it needed a new one). Well, I had a new harness, wired it in, got two new HEGO's, and went to town. Now the HEGO readings were where they should be. A full datalog showed my LAMBSE and KAMRF values were what you would expect, all other values good as well, but still the part throttle leaning out.

This is what I know, MAF read correctly, TPS is new and reads correctly, car has the air/spark/fuel to make made power, and runs awesome once in WOT, but awful in closed loop. This is what has been replaced with the last turbo swap: turbo, BOV, WG, trans, halfshafts etc. All of those of course not having an affect on my problem. BUT, I also removed the FMU, added the FPR (and yes, fp checked out great), removed CC, and rerouted a number of vacuum lines.

So, cliff notes: WOT = great, part throttle = crap - car leans out and dies within seconds. No CE lights, no codes. Idles good (though it take a while for it to drop below 17:1, is this normal?), datalogs from Tweecer give no evidence of a problem. My question to the forum, what is the problem? What would only present itself @ part throttle, but let the car run amazing @ WOT? I await your answers (and as always, a prize for the problem solver, how does driving the turbo at Memphis for a few laps sound?).

 

[Ishodu]

Do you happen to have a large fuel pump with the stock pressure regulator? If so I would think that when you come off the throttle your pressure increases a lot causing the computer to try and compensate for it by making it lean.

 

[TRSCobra]

Does it run the same in open loop as it does in closed? Or does this problem only happen when its at operating temp?

 

[Toolman]

Marcel, I have Josh's FPR. At idle, pressure is perfect, but I do not have a permanent gauge, so I can not say for sure if it is good when I am at part throttle, but I know it has plenty @ WOT.

No, when the open loop light goes off,under enough throttle, it does decent. But mainly just in open loop is when it is real bad.

 

[SeanMc]

Mine does the same thing at times. When you go in reverse and give it a little gas, and then put it in drive, it will die most of the time. I think it's due to bad O2s. No CEL, code 139 (HEGO not switching from left to right). It will do it while I'm driving sometimes as well (battery and oil lights will come on).

 

[Toolman]

new HEGOs, new TPS, new ECT, all reading in the correct and proper numbers

 

[TRSCobra]

Maybe a possible MAP/BARO sensor problem? In open loop I know the computer reads off of the MAP sensor (not sure on BARO) instead of the HEGO's for fuel mixture. But I think SHO's only have BARO's. Just brainstorming here.

 

[shomesomesho]

Have you tried disabling adaptive and/or running in open loop all the time?

 

[Toolman]

There is no way to run in open loop all the time, but I will try disabling adaptive as my next route. I swapped out computers, to no avail. Unplugged my BARO, got a CE light, no other changes. Im not sure disabling adaptive will do anything, as it is not showing lean from my HEGO's or commanded fuel. According to the datalogs all is fine and dandy. Calcon shows a nice KAMFR and LAMBSE values, but my WB is running all over the place. I would not care what my WB was showing if the car ran well, I would just chalk it up to a bad WB, but it seems to be spot on. So apparently, when the EEC is commanding a certain A/F in closed loop, the car is simply not seeing it.

If anyone has any datalogs of these 47lb injectors to send me, that would be great. Then I could see if my data matches.

 

[shomesomesho]

So apparently, when the EEC is commanding a certain A/F in closed loop, the car is simply not seeing it.

Try changing the AFR's in the stabilized fuel table, e.g. richen the AFR's the computer commands when in closed loop / low loads / low rpms. (Turn off adaptive and clear the kam while doing this). For example, substitute the 14.6's for 12.0's or something similar. Try fiddling with them until your WB AFR is what you want them to be, although they may not be the AFR the computer commands. Basically you are titrating the stablized fuel table to get your desired WB AFR; although there may be no relation between the two, except as one goes up, the other does too, and vice versa. Crude, yes, but if it works, it works. Why you are seeing such a discrepancy between commanded AFR and WB AFR I don't know.

 

[Toolman]

Try changing the AFR's in the stabilized fuel table, e.g. richen the AFR's the computer commands when in closed loop / low loads / low rpms. Basically you are titrating the stablized fuel table to get your desired WB AFR; although there may be no relation between the two, except as one goes up, the other does too, and vice versa.

Tried 12.5 accross the board (for lower loads). Only change was that the WB will now fluctuate from 12.5 to 17 and up. If I were running a steady lean AFR that would be fine, I would just richen it up and be done. But it is far from steady. It wags like a dogs tail. Yet nothing in my datalogs would indicate a problem. Got me stumped I tell ya.

 

[shopartsnw]

I have found that if the injector slopes are too far off (or the injector is not performing correctly), the computer will stop adjusting the fuel trims and the performance goes to pieces. In my case, I had Josh's program loaded and for about 30 seconds I could watch the computer trying to hit AFR and then the KAMs and LAMBSE would "lock up" The car would give up trying to trim fuel and it would go WAY rich (could have just as easily gone WAY lean). It took me a while to get the injector slopes in range before the computer could continue to adaptive learn so I could fine tune the slopes.

Try watching your datalog to see if it is "locking up"

Just a thought.

- Mike

 

[Toolman]

what injector slopes did you end up with? I have tried a myriad of different slopes, to no avail. Something is the matter outside of the Tweecer/turbo system.

 

[shomesomesho]

. Got me stumped I tell ya.

Me too.

Quick question. When you put the old LPM in (the LPM itself, not the LPM program burned into twEECer), do you still get the same problems?

 

[Toolman]

Can not use the old LPM, it is designed for the 80mm Lincoln MAF. The curves are way to different. I am getting another 90mm to try and see if it is the problem. Once that is done, if the problem is still there, I will be really stumped.

But on a positive side note, with a real rich and safe tune, with good room to grow in my MAF and injector numbers, the EEC Analyzer showed me making 622hp and 539ft lbs. So that is cool.

 

[ShadetreeSHOguy]

But on a positive side note, with a real rich and safe tune, with good room to grow in my MAF and injector numbers, the EEC Analyzer showed me making 622hp and 539ft lbs. So that is cool.

eegad brain, dats a lot of hp

 

[Toolman]

It not accurate (it is consistent). In reality, I would guess it is about 100hp/tq high. But it is nice since the turbo keeps making power as long as I stay in it. The old unit kind of petered out before 6k. I want to see what this will do if I stay in it till 7k, with a more aggresive tune, and more than 12-13psi. Should be fun.

 

[shopartsnw]

Tim,

I am running 48lb accel injector, and the high slope is set to 47 and low slope is set at 76. Breakpoint is 2.7

I still get runability issues at very low throttle (the injector duty cycle is so low they cut out and I get surging, but the car runs very well at most other throttle positions.

- Mike

 

[Axianator]

I am running 48lb accel injector, and the high slope is set to 47 and low slope is set at 76. Breakpoint is 2.7

I still get runability issues at very low throttle (the injector duty cycle is so low they cut out and I get surging, but the car runs very well at most other throttle positions.

Out of curiosity, Mike, what do you have your base idle set to?

 

[shopartsnw]

Idle in Neutral is set to 1144. Is that the number you were looking for?

- Mike

P.S. Can't wait for the SHO specific manual.

Thanks

- Mike