A few months ago i posted about a weird stumbling issue i was having with the car. since i had gotten my VE's within 2% across the board(using LTFT's), i ruled it out as a lean condition and assumed it was an ignition problem.

well, now i know for sure that it's running lean as **** regardless of what i do with the VE's. it goes even leaner when i plug in the MAF, to the point of being barely drivable from popping and stumbling.

i figured this out by manually commanding the AFR with the scan tool. when i set it richer than 11.5:1, the problem goes away and runs exactly like it should.... strong, no stink, no popping or stammering. it took me so long to figure out, because i had only associated bad exhaust fumes with a rich condition and blamed it on my previous exhaust leaks causing it to add fuel.

so i simply added 10% across my whole VE table(which i had previously tuned within 2% trim). it ran great for a minute until the trims started cutting about 10-15%, and it started the same popping and stammering shenanigans.

being a fairly inexperienced tuner, a few possibilities come to mind:

1. my injectors are a different size than advertized, causing my IFR calculations to be WAAAY off... but wouldn't the fuel trims still correct for this?

2. my engine just likes to run rich? unlikely, being N/A at about 10.2:1 comp.
LQ4, .040 gaskets, 823 heads

3. my MAP sensor is malfunctioning..... i say this, because it started throwing a code last week.... even though it still has consistent readings.

if you're wondering why im not using a wideband, i have an LC-1 and spent 3 months trying to get it to work. despite pages of help from experts on both forums, i never got it to work with EFI live using serial or analog connections. i even tested the analog output with my multimeter, and the voltage was right where it should be.

 

The map may show consistent readings...but are those readings gettting to the pcm? Definitely start at the map sensor.

Also, are your VE and MAF charts nice and smooth? Or all jagged?

 

I mean when i record data, i see the map sensor chnaging according to throttle.

I always smooth the tables.

 

Ok, what is triggering the map code? Have u physically checked it? Maybe vac leak in the area?

 

I have to change the knock sensors soon. So I'll replace the intake seals at the same time, but all the vacuum lines are good.

 

Until i figure it out, I'm simply keeping it in SD OL and commanding it to run richer.

It wont be perfect, but at least it'll be safer for the engine and drivability should be better.

 

Maybe, post the tune and some data logs????????

 

http://forum.efilive.com/showthread....lean-condition

Check out posts 5 & 6.

 

update:

i found a tune from my old heads/cam setup that ran perfectly (pat G) and flashed it. as soon as it hit CL, the trims were going -30%. i put it in OL, and it ran perfectly fine with no other changes to the tune.

so it looks like my O2's are cooked from running so lean for so long.

there's no MAP sensor code anymore either.

 

O2 sensors don't usually fail with high voltage output.
More normal from fouling is a low output.

Do the sensors exhibit normal-ish switching behavior
under any conditions?

If so perhaps this is a problem with something like
the closed loop switchpoint voltage (like, if zeroed,
anything will appear "rich" and trim downward)?

Since open loop is roughly right and closed loop is
whacked, that's either sensors (if they source a
"stuck" >0.5V output) or the processing of their
output, in my guesstimation.

 

they're looking pretty lazy.

i thought of that, so i wiped everything and reinstalled the software and firmware to default settings. that's also why i reverted to a previous tune that was known to work well.

i'll post a log file if i have time when i get home.

 

Here's the log with the good tune in SD/OL.

Keep in mind, this tune was for 317 heads, ported f.a.s.t. 90, 9.4:1 compression, 239/247 .624.624 114 cam. (i know...)

The current setup is L76/L99 top end, 10.2:1(.040 gaskets), ~226/231 .598.601 114 cam.

 

I see what you mean the O2 are consistently over 800mV. Car could still feel pretty good though if it was actually running that rich.

 

It doesn't smell rich at all though. Maybe a tad at idle.