Newbie tuner with 3800 V6 having lean LTFTs at idle, please help.

I have an 2000 F-body with the series II 3800, and just to check up on the car I scanned it for a while and found the LTFTs to be a bit leaner than I'd like to see at idle, and under some throttle they'd run a little richer than they had previously. I hadn't changed anything in the tune between the two times I logged it, and I can't think of why the fuel trims would suddenly go a little off like that, I am new to tuning though and have a lot too lean. Any suggestions, thoughts, or any input would be greatly appreciated.

Sorry if this problem has been discussed somewhere else on the forum, I've looked for the last few days but couldn't find anything so I figured I'd finally ask.

Here's the scan files, trial 6 is the first log, free ride trial is when I noticed the fuel trims

Attachment 45145Attachment 45146

I couldnt really tell ya, try cleaning the MAF or something. Different fuel maybe. To me along as it's not over +10 at idle and just midly bouncing around while driving, I don't even care what it says as it really doesnt matter and rarely hurts fuel mileage. If it locks in within 2-3 of zero at WOT you are good.

One thing though, you are running a thermostat thats far far too cold, the 3800's would rather run at 180-190 all day long. Only time I'd ever think about running a 160 is if you where going to hot lap the car, but even then it will heatsoak.

Thank you for the feedback, After work today I logged the car again as is just for the heck of it, and the fuel trims seemed to be even a little more off than before, and at WOT the LTFTs went to between +4% and +6%. I forgot to save that file so unfortunately I can't upload that one to be looked at, but I am uploading a log I did after cleaning the MAF, and I did look over my tune and tried a few little things but none of them seemed to do anything, my LTFTs at WOT are a lot closer to 0% afterwards but that is it. A couple things I noticed that kind of have me puzzled is how at the beginning of the log the LTFTs at idle went leaner towards as much as -14% and then crept back towards -6%, and also how under deceleration the injectors and O2 sensors go to zero yet the fuel trim is still -7%ish. I know the injectors and O2s should go to 0 ( or at least I'm fairly sure they're supposed to) but the LTFTs use to always go to 0.0% as well, any ideas what is going on there? Or is there something I'm missing and should know with those?

I don't know if there is a problem with the car or what, cause the tune I have had in it was fine with the LTFTs up until the last week or two. Do you (or anyone) know of any sensors, electrical, or mechanical problems that might cause the fuel trims to go like this? Please let me know, even if it is a wild guess, cause I'm stumped on this one. If not, I was wondering if any VE and MAF tuning would be a good or bad idea, all the airflow tables in the tune right now are stock because the fuel trims have always been good, and because I haven't been able to dedicate the time to do so, also I don't have a wideband sensor yet so nothing about my tunes can be perfectly ideal.

And about the thermostat, thanks for taking note and advising me on that, I'd always been taught-up that 160 was kind of a go-to for trying to get the most from an engine (aside from emmisions obviously). But I'll look into getting a 180 thermostat. Do you think you could tell me why 180 is better in a 3800, and what is wrong with a 160? Also does the preferred thermostat temp differ from engine to engine, and what about an engine helps decide what the ideal thermostat is?

Again thanks a lot for the help,

Attachment 45162

On the thermostat deal, I'm sure some "experts" would have different opinions than me but I've been around the 3800's for a couple years and with everything I see, running anything cooler than a 180 is always pointless. There was never any gains from it, and most lost a mpg or 2. You want the motor to be as hot as it can but to an extent or for what you feel is right. On a stock tune the knock sensor don't even turn on till the coolant temp hits 160º, and the motors are more effiecent when warmer. I run the stock tstat myself and never see an issue with temps around 195-200 as it never affected my car when modded.

I can't really say much else on the lfts, stft etc at this time as it's something small throwing it off and I can't really tell what it is. Posting the actual tune aswell might help with suggestion from things to do.

Alright, thanks. I think I'm gonna dig into the thermostat deal and see what I come up with. My last question with the thermostat would be if running a 160 will harm the engine at all? I'm not too worried about fuel mileage because I barely ever get to drive the car anyway, and beings I live at an altitude of almost 5,000ft above sea level, nothing up here gets good mileage. That and I still get 26.7mpg on a tank where I spend most of the fuel under heavier throttle and mid to higher revs.

Today I didn't have a lot of time to play with the car but I tried to look it over real good, and I can't find anything wrong with any of the hardware or mechanical components (other than oil leaks, typical 3.8). Thinking back all there is that I know I did to the car was replace the upper radiator hose but that really shouldn't affect LTFTs. I also looked through my service records and other than the hose all I've done since I took the car out of hibernation was change the oil. There really aren't any engine mods to the car at this point other than the 160 stat, a K&N filter that came with the car, and a cheap and poorly fitted stock styled aftermarket exhaust and cat which also was already on the car. I know, it isn't much to brag about but it was my first car and I got it extremely cheap, that and it's a sharp looking car (I think).

I don't know if it'll do any good, but I think I'm gonna try my stock tune in the car tomorrow and see what it does. I do have the Tuning School manuals because I am a brand new tuner with no experience, and I've spent a lot of time studying them over the last couple days. After looking at my current tune I am sure I can build a bit better tune if I start from scratch and follow the manuals step by step. Problem is the OS and layout for the 3800 is fairly different from what the Tuning School manuals follow. I've never had a whole lot of time in one period to go through the car's tune and make a solid tune all at once, which may have created a few quirks in my current tune. I still don't think it is my tune though because my current tune has been in the car for a while and the fuel trims have always been fine, but I'll still rather a more perfect tune however slight it may be.

If you want I'll upload the tune that is in the car right now with the problems, I'm sure you'll find a fair amount of flaws in it.

I do have a few more questions though while I'm thinking about it. I was wondering if there was any way to change or help the PE rate of enrichment in the 3800's computer, and I was also sort of wondering about the ideal WOT afr, because I've heard it said it should be between 12.7 and 13.0, but I've also read in other sources it should be between 12.7 and 12.5? Last question would be about Acceleration Enrichment tuning, the V8's that I've dealt with don't have any AE tables and I can't find any info on tuning them. Thanks again.

For a NA, around 12.5 is good and safe. There isnt a way to change the rate of enrichment, only can change the throttle % that it will enter at. It's kinda on or off for PE.

I prefer a lower number like 35-50% throttle but I am supercharged so even then I have a few pounds of boost built. You can make it richer over time with these cars if you feel it needed more fuel up top if you got a little bit of knock. I've never done anything with AE on these pcm's, there just isnt enough in these cars to change. They are just so "stupid" compared to a V8 computer, way way less things on these 3800's.

But looking though the tune, I see nothing really wrong at all. Looks mainly stock with minor changes that I would have done. This whole LTFT is just kinda odd, not sure if a smoke test would show anything for leaks or not. Or maybe the o2 sensor is getting old and throwing things off.

I know what you mean about these PCMs, I have a 1999 GMC Sierra late model with the 4.8 V8 and it sure seems a lot more tuner friendly. This car is getting the better of me though, I can't really pin a problem. If I can find a smoke tester I would try that. I have been told though that one can use carb cleaner and give some light sprays on different possible leak areas to try and find a problem by watching the O2 sensors while spraying the carb cleaner, I've watched someone find an intake gasket leak on a 5.3 Vortec by doing this even after a smoke test didn't find any leaks. I tried this today and it didn't show any results, the O2 sensors just kept doing their thing.

Today I spent the whole day with the car trying all kinds of different things. I tried going back to square one, and the LTFTs were still real lean even with the factory tune in the car. So I tried the acclaimed 'correct' steps and got to the point of VE tuning. I tried the whole 'upload, trial, tune, retry' thing all day long without success. At one point I thought I was close but at idle the car still started off really rich, up to more than +17% LTFTs and then down towards more than -15% LTFTs. After uploading my VE calibration tune the first time I reset the fuel trims and the car logged fine, didn't even go past 1% plus or minus on the LTFTs, then things just got weird from there. I found that in the mid heat of the day with the VE calibration tune the car would consistently lean out over -10%, but as the day progressed the sun set and the temps dropped it ended up adding fuel instead of subtracting it, but it would add with the same big error, upwards of +10% LTFT consistently. After a few tweaks and attempts to get the VE table close, the car ended up adding over +20% to the LTFTs at idle. Tell me what you think but I'm guessing something is wrong with the car, and tuning isn't going to help.

Now is probably too late to state this but I do know the car has a HVAC vacuum leak because I've replaced the check valve and it still looses vacuum up hills and under load, I just haven't had the time or ambition to look for it and fix it. The car has had this problem since I bought it, but until lately the leak has never really affected the fuel trims, Tomorrow I think I'm gonna disconnect the HVAC hose and plug off the line just to see what the car does without all that vacuum garbage on it.

I'm just gonna upload a few of these trials to see what you think, Keep in mind the earlier logs were mid day under bad heat, and the later ones were at sunset where the temps were drastically less. Also the 'LTFTs & VE tuning log 1' is the log I first did after resetting the fuel trims.

I'd also appreciate some input on my tune I've been using to try and calibrate the VE for LTFTs if you wouldn't mind, I couldn't find a way to shut off DFCO, but hopefully I got everything else right. Thanks again, I really appreciate all the help.

If she's also a hard starter, (taking more than 3-5 cranks to start a lot) check out your fuel pressure regulator. You said this just started recently. Hopefully a cheaper repair/fix.

a small exhaust leak or vac leak could be causing some of your issues. i have experienced this as well to a minor degree. i always attributed it to weather and fuel differences. can you remember...was there a big difference in the weather from the time you tuned to the time that you did the check up scanning? how many miles are on the car and are the O2 sensors original?

Quote:

---

Originally Posted by Dr. Nopps

If she's also a hard starter, (taking more than 3-5 cranks to start a lot) check out your fuel pressure regulator. You said this just started recently. Hopefully a cheaper repair/fix.

---

I guess it does take about 3 seconds or so to start, but as long as I've had it, it always has, and the fuel trims were never as goofy as they are now. Fuel pressure regulator is a good guess though, I'm hoping to be able to run a fuel pressure test on the car this weekend so I'll see where that leads. And I've only noticed the fuel trim problem maybe two or three weeks ago, but when I got the car out of the shed in May the fuel trims were just fine. Between the last few weeks and May I haven't logged the car though, so somewhere between then the car started having these issues. I should be able to get a regulator fairly easily so I'll probably try that, thanks.

Quote:

---

Originally Posted by G_P_K

a small exhaust leak or vac leak could be causing some of your issues. i have experienced this as well to a minor degree. i always attributed it to weather and fuel differences. can you remember...was there a big difference in the weather from the time you tuned to the time that you did the check up scanning? how many miles are on the car and are the O2 sensors original?

---

The weather was about the same, I was wondering if I did something wrong in my tune so I did put the factory tune back into the car and it still has the LTFT problems. If I can get my hands on a smoke tester I would definitely do a smoke test, but I don't know if I'll be able to. With the exhaust, wouldn't an exhaust leak cause the bank with the leak to go goofy and not both, or will it affect both? I wondered about the exhaust but I couldn't hear or feel any exhaust leaks.

And the car is a higher mileage vehicle with 155,000 miles, and I would guess the O2 sensors are the originals but I don't know. I've only owned it for a little over three years and it already had 136,000 on it when I bought it.

Quote:

---

Originally Posted by '00Camaro-2tooShort

The weather was about the same, I was wondering if I did something wrong in my tune so I did put the factory tune back into the car and it still has the LTFT problems. If I can get my hands on a smoke tester I would definitely do a smoke test, but I don't know if I'll be able to. With the exhaust, wouldn't an exhaust leak cause the bank with the leak to go goofy and not both, or will it affect both? I wondered about the exhaust but I couldn't hear or feel any exhaust leaks.

And the car is a higher mileage vehicle with 155,000 miles, and I would guess the O2 sensors are the originals but I don't know. I've only owned it for a little over three years and it already had 136,000 on it when I bought it.

---

thats a tough one. if the O2's change like they are supposed too i would necessarily think its them however that is a lot of miles. im not sure on the RWD cars and how the O2's report to the computer. i mainly have only messed with the FWD cars. if each bank has a sensor just like the v8's it should only affect a specific bank.

if it sat for a while maybe some crap in the tank broke loose and clogged the fuel filter on the pump, like already mentioned worth a test anyway. good luck.

I ended up being able to borrow a fuel pressure tester today and I tested the car, KOEO the readings were at 53psi. and with the engine at idle the readings were at 46psi. If I'm not mistaken these are the kind of readings the car is supposed to have.

Just to see what would happen I ran the car with the MAF disconnected and while sitting at idle for a while the car ended up coming back towards zero on the LTFTs, they seemed to like -1%, but while cruising they never got any better than -2% to -4%, yet that's still better than it was with the MAF. Does anyone who better understands the 3800's PCM know whether or not this means the MAF is starting to go out? And yes, I tried cleaning it with MAF cleaner about a week ago. Thanks for the help.