Thread: Car running LEAN right after it was running fine for what reason?

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First image is from a 15 minute drive. 2nd is on same drive, i just stopped logging and saved log and started logging again. No engine restart. Perhaps this should have been posted in Tuning section, but I'm starting to think this is a mechanical issue. Fuel pump, injectors, regulator? Or MAF is getting screwy when car gets hot? I don't know if i would call it heat soaked, because it was moving the whole time. Tank was full.

Not the graphs, the AFR MAF error chart at top. Big difference. In the graph I wasn't locking in to a particular frame.

I'm doing an OL Maf tune right now. And I've noticed that I can have the MAF tuned withing 1 or 2 percent, then take it out the next day and it is off 5-8 percent.

Sheesh, why can't I edit posts? Anyways, I wanted to add that I set PE to zero across the table. Commanded afr is 14.7 across the table. This was from a guide on how tuners. But for some reason my car commands leaner afr until like 20% throttle, even though PE throttle table is zeroed out.

Is it possible to flash a stock gtp .hpt tune to my car and start from scratch? I'm still on my stock n/a tune, and I think I may have f'd up some time tuners tables years ago before I lost my dhp tuner.

set pe enable to 90 if you dont want it it to enter pe. at 0 your in pe all the time. in pe, afr should be 11.5 ish.

I set PE to 0 in order to command 14.7 at all times. Doing this I can tune the AFR error % for MAF. Found this here:

But the car commands leaner afr's up to about 20% throttle. No idea why. I zeroed out the adder tables.

So I can flash any 01 n/a impala tune and be fine?

Kinda sounds like the cat test causing the commanded AFR to move up to 15 or 16.

Never ran into that problem on pre 2001 vehicles.


Just a FYI, if the wideband error is setup correctly, it does not matter what the commanded air fuel ratio is. You are always getting the error based off the commanded value. So it would tell you the error at 14.7 as well as telling you the error at 11.5 commanded.

You can filter out data that you don't want or you can just take certain sections of the data you want. Like under 7,000hz and over 7,000hz.

Originally Posted by Fivefingerdeathpunch

Kinda sounds like the cat test causing the commanded AFR to move up to 15 or 16.

Never ran into that problem on pre 2001 vehicles.


Just a FYI, if the wideband error is setup correctly, it does not matter what the commanded air fuel ratio is. You are always getting the error based off the commanded value. So it would tell you the error at 14.7 as well as telling you the error at 11.5 commanded.

You can filter out data that you don't want or you can just take certain sections of the data you want. Like under 7,000hz and over 7,000hz.

Cat test is maxed out ect. I guesses the same about the different afr's. I'm on my 6th tune change. Still haven't gotten to wot tuning. I don't have any knock in either scans. I'm now wondering if it isn't a scanner bug, or an install issue. It could be as simple as the AFR error calculation being messed up, maybe because I had two scans without restarting. I'll rule that out next.

It's not a filtering difference, it's an overall AFR error % difference. At least I think.

Originally Posted by GTPpower

What happens if you put the adder tables back to stock? There might have been something there you needed.

Also, you're top swapped? What map are you running?

I'm trying to go by the guide. Lots of people have had success with this method. I'm top swapped with a gtp map.

Tried again. I get tunes dialed in. Take it for another test and the AFR error is now 6% off, where before it was 0-2%. Maybe failing MAF?

Or....just had this thought. My battery might be bad. It went dead half dozen times this winter. Voltage affects a couple tables if I remember. Guess I can have it tested.

Originally Posted by GTPpower

Not all NA pcm's work with the gtp map. I dont know if this would help your problem, but you should try switching back to the stock map and see if anything changes.

I just went by the top swap guides. If I remember right I just bought the pigtail for the 2 bar l67 map and plumbed it in like a stock gtp. So what are my options? Maybe I can just the map off vacuum instead of a boost referenced vacuum line? Or should I put the stock l36 map in place of my l67 map?

Why would this cause my issues? Is my pcm getting messed up because it's seeing boost? I'm tuning right now with maf and open loop only, 02 sensor is not activated. How does map even come into the tune? I thought VE tables wouldn't be called, unless I turned off MAF.

Or I could flash a L67 file and copy over my transmission stuff. Using hptuners, do I have to buy more credits to do this? Or could I flash like an 04 impala ss file?


But it kinda maybe sorta makes sense that it would be a map issue of some kind. I get everything dialed in one minute, then next minute everything is off by 6-8%. Really feel like I'm chasing my tail.

Oh, also, don't some boosted 3800's have 2 map sensors? One for baro?

A few setting in the PCM and the actual MAP sensor.
BUT there is an issue that noone has solved yet (AFAIK)
The L36 measures barometric pressure whenever you're at WOT. So if you have boost at WOT (and the PCM knows about it due to the 2bar MAP) your baro reading gets all messed up and your idle will suffer after going WOT (to the point of stalling in some cases).

Unless you're going to do a speed density setup just stick wtiht the 1 bar until someone figures this one out.

I found this. It does seem plausible now. May explain my super rich decel, too. Think I still have my original map.

I do have 2 Map adjustment fields. One is set to 140, and offset like 8. From memory, my laptop just died. I just picked up a new one. It's always something, eh? I did notice that some gtp files didn't have that setting available.

Anyways, gonna try my l36 map when I get home. Should I run it from just a vacuum like before blower? I read that that if it sees boost it can screw up the no boost readings.

Any idea what stock 1 bar settings are here for map?

Couldn't find my 1 bar map. Probably tossed it with upper intake. So i just ran a vacuum from TB to map for kicks. I have a boost gauge.

Went for another tune session. Tell me if i'm chasing nothing. I did a drive on a straight road, slow feed with throttle, filled as many cells as i could just over 7000hz, parked, copy pasted afr error half %, flash, go for another drive and I get what looks like a lean scan again. I don't get it.

If anyone wants to look at logs and tune I'd appreciate it.

After like two adjustments, looking better.

Make Adjustments and it goes lean.

But I keep driving and just restart log. And it looks better.

Here's my latest tune.

I'm probably wrong but what i'm currently thinking. Even though the car was up to temp in all logs, i need to drive for maybe 10 minutes before logging? Maybe the PCM is doing some weird corrections at first. But then, why does it matter because I am logging AFR % correction?