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Always use this site for information but this is my first post so sorry if I don't so certain things properly. Hope I can get some useful opinions though or just to pick the brains of someone who knows these cars better.
So I've been dealing with some pretty annoying issues trying to get my car running back in tip top shape. For starters she has 240k miles on her. So for a long time I've struggled with trying to get my fuel trims to act somewhat normal but nothing I do seems to help it. It all started when I was getting lean codes, usually only happened during the winter and I wasn't super concerned about it because after I cleared the codes it wouldn't come back on for around a month only during winter. I also had plans to do the timing belt, valve adjustment and spark plugs soon so I thought that would probably help the issue. Ended up getting around to doing the 4 service at 220k but even after that, it was better but it was still running lean, about 12% on short fuel trim so not too bad but not great. I ended up checking compression, fuel pressure and cleaning my egr ports. All readings came up normal/within spec and the CEL wasn't coming on for lean codes anymore so I wasn't too worried about it and just kept driving it as normal. Never really had any performance issues so wasn't super concerned.
But about 10k miles after all that I noticed that it randomly started running really rich like -15 to -25% short term and after awhile of driving it would get up to -18% long term, was the highest it got. I once again didn't worry about it too much because there were zero codes, no drivability issues and wasn't practically in the mood to try and figure it out. About 7k miles later it started having stalling issues, so it was definitely the time to start fixing her all up back to normal since she's my only car. So after weeks of diagnosing, replacing and cleaning misc parts, finally figure out it was the main relay had some messed up solder points. But during all that time I replaced the fuel pump, fuel injectors, both 02 sensors, map sensor, reinstalled the IMRC but someone took it off for some reason and negative battery cable due to high resistance. I also cleaned the IACV and the egr/ports and reset the ecm each time I did something new.
But after all that my fuel trims were still very rich and high in the negative, the same -15% to -25% short term and -18% long term. Also I should say that both banks on the short term have been practically equal so it's something that is causes both banks to act that way. Which my last two suspicions would be the fuel pressure regulator or the ecm but I already dropped enough money on all the other stuff so I was taking a break from it. 2k miles later I noticed when I started her cold as soon as I would try to take off from parked she would bog down a hair/hesitate then after a second she was completely fine for the rest of the drive. So check fuel trims again recently and noticed now it's back to running really lean 15%-20% short term and up to 10% long term (haven't checked it on a long drive but I bet the long term would keep going up).
Now before I start dropping money on a fuel pressure regulator I wanted to get some other opinions on this. Because I've never seen a fuel pressure regulator or an ecm switch back and forth so drastically on fuel trims before but those are also the only other things I could think of that would cause this. I really just want to get her back to running as good as she can and back to at least having fuel trims below -10% or below 10% because this has been such a struggle. Thanks for your time!
When you replaced the fuel pump, where did you buy it from? I know of at least one person on here that bought oem and received a defective unit; I think twice.
best tool to confirm is the fuel pressure gauge; but the adaptor to fit it to your fuel system is not cheap and thus, a pain.
Whitetiger5, if you are talking about me it was the canister, the fuel filter, that the fuel pump gets mounted into, and yes it was defective twice.
Jax_666, Whitetiger5 is correct about the fuel pressure gauge. I went through several modifications to trace it down. here is the link to the thread https://acurazine.com/forums/2g-tl-p...-ideas-991328/
For the negative fuel trim issues, have you looked at your fuel injectors? I know you said that your OBDII reader can read both banks separately but you could have problems with an individual injector on each bank. There are some cheap cleaning kits on ebay, probably amazon too that you hold the fuel injector within a plastic housing, apply 12v, and a can of carburetor cleaner and you can then check the spray pattern.
I also think in my old thread that I put in the PSI that the regulator should put out. I think it was ~48-53 PSI.
Whitetiger5, if you are talking about me it was the canister, the fuel filter, that the fuel pump gets mounted into, and yes it was defective twice.
Jax_666, Whitetiger5 is correct about the fuel pressure gauge. I went through several modifications to trace it down. here is the link to the thread https://acurazine.com/forums/2g-tl-p...-ideas-991328/
For the negative fuel trim issues, have you looked at your fuel injectors? I know you said that your OBDII reader can read both banks separately but you could have problems with an individual injector on each bank. There are some cheap cleaning kits on ebay, probably amazon too that you hold the fuel injector within a plastic housing, apply 12v, and a can of carburetor cleaner and you can then check the spray pattern.
I also think in my old thread that I put in the PSI that the regulator should put out. I think it was ~48-53 PSI.
Yes I remember reading that thread when I was hunting down my stalling issues. But the stalling issues are fixed, so that's not my concern and this issue was happening before I replaced the fuel pump. Also the injectors were already replaced as well.
As of right now it's running lean not rich anymore. My concern is that over the past 20k it's randomly switching from running really rich to really lean without any rhyme or reason. Nothing I've done/replaced has just caused it to switch it will just do it randomly. Why I say that is because I checked the fuel trims quite often when I'm making these repairs and monitor it for a few days. For a year or so it was running lean, then switched to running rich one day and stayed that way, now it's back to lean as of a week ago and I've haven't changed or done anything in the last month or 2. I'm not sure why it's doing that, and can't really figure out why it would. My concern is the fuel trims being so high in positive or negative, when I'm trying to get it to run within spec but it seems to just refuse to do so. Also last time I checked fuel pressure it was reading 50 or 51 psi.
Did you replace the gaskets after doing all that work? there are three: throttle body to the intake manifold, upper intake manifold cover and lower intake.
Agree with Whitetiger5 also check for a vacuum leak at the front and rear motor mounts. The other item I can think of would be the front O2 sensor. Give it a few taps (don't break the connector) and see if there are any differences. I personally had one not working then when I was taking it out I had tapped it a few times and the STFTRIM changed. I did replace it as I didn't trust it.
Did you replace the gaskets after doing all that work? there are three: throttle body to the intake manifold, upper intake manifold cover and lower intake.
Well I say without rhyme or reason but these are still year long gaps of switching between heavily rich to heavily lean. No vacuum leaks though, that's usually the first thing I check. I didn't replace them because they were all fairly new when I did the 4 service 20k ago.
Agree with Whitetiger5 also check for a vacuum leak at the front and rear motor mounts. The other item I can think of would be the front O2 sensor. Give it a few taps (don't break the connector) and see if there are any differences. I personally had one not working then when I was taking it out I had tapped it a few times and the STFTRIM changed. I did replace it as I didn't trust it.
Do you know how much pressure to put them at? Isn't it like between 20-28hg, though it'll be easy to tell if it's leaking by just putting some in and waiting but I don't want to over pressurize it either.
The O2 sensors are both new. Though I know I could easily get a faulty one but they are both reading properly and within spec.
Pull about 5-10 Hg of vacuum should hold for at least 20 seconds. You can find it on page 4-48 of the repair manual. Did you download a copy? Motor mount Vacuum test. Pg 4-48 of the manual.
Can always just cap everything off at the manifold with the exception of fpr and brake booster and see if that changes anything. Be good to try a smoke check on the intake too.
09-14-2022, 03:35 AM
