What would make my car run lean all of a sudden??

[Rex2342]

Last night on my way home I noticed my FT02 at idle was pegged at 199% on the logger and my low fuel trim was also pegged at 118%, my mid and high where a little lean but still within the comfort range? I haven't changed anything for a few weeks and have had the tuning within +/- two clicks on the AFC depending on the weather for a little over a month now.No matter how rich I make it on the AFC the low trim will only drop for a second and then go lean again.Why would it start running lean all of a sudden?? What things should I look at to start diagnosing this beside the obvious boost leak tests. Maybe a bad MAF or ECU? I don't have a CEL and the car is still running fairly well. Any ideas??

 

[Talon-96]

What psi are you running? You might have it set to high for the amount of fuel your getting?

 

[kenamond]

What psi are you running? You might have it set to high for the amount of fuel your getting?

He's seeing a lean condition at idle, so that's under vaccuum and has nothing to do with his boost setting.

Do you see a lean condition at full throttle or just idle? If not, it might be a vaccuum leak.

You can also test to see if your O2 sensor is flaking out. I saw a description somewhere, but the basic idea was to monitor O2v for two different tests. If you add unburned propane in the intake, the O2v should go richer. If you pull a vac line (BOV line would work) and "thumb" the end, you should see the O2v go leaner when you let your thumb off the end of the hose. I'd do a search to see if you can find more about it, as that's just my vague recollection. Maybe someone else can chime in with more definitive instructions.

That's my 0.02

 

[Rex2342]

I'm seeing a lean condition all around on the FTO2 reading but haven't taken it on the highway to see if my Mid and High trims will change as drastically as my Low has. I swapped out the ECU with a known good one and still get the same thing. I triple checked the connections on the MAF, MAFT, Injectors, AFC wiring, and checked all fuses relating to fuel. I checked the fuel pump too. I didn't take out the sending unit but I can still hear the pump working from the drivers seat so as a last resort I'll pull the pump to check it. I haven't been watching the O2v on the logger but I'll check that next and look around to see how to test the O2 sensor. The vacuum on my boost gauge hasn't changed but I'm getting a bit of a high idle and it's surging a bit so the vacuum is moving around a bit now. I'm going to do a boost leak test in a bit to see if I there is one. Another thing I noticed yesterday was that my fuel pressure was a bit low? I raised it back to 38psi when I noticed this. After I swapped the ECU today the fuel pressure was to high and I had to lower it back down.I didn't notice where it was at before I swapped ECU's so I'm not sure if the ECU had anything to do with it. This was also done with the vaccum line off the regulator.

 

[Rex2342]

I just finished boost leak testing. I have to use a refillable tank so it's not the most accurate when it comes to testing. I got 20psi pumped in and it's slowly bleeding down to 10psi and holding for about a minute. I didn't find any leaks in the intercooler piping, TB, injector seals, or j-pipe. Can somebody give me or point me to a detailed procedure on testing the O2 sensor on a 1g? I guess my buddy grabbed the wrong manual last time he was here because my 1g book is gone and all I have is a 2g one. If the 2g procedure is the same as a 1g let me know and I'll just read the 2g manual.

 

[kenamond]

I just finished boost leak testing. I have to use a refillable tank so it's not the most accurate when it comes to testing. I got 20psi pumped in and it's slowly bleeding down to 10psi and holding for about a minute. I didn't find any leaks in the intercooler piping, TB, injector seals, or j-pipe. Can somebody give me or point me to a detailed procedure on testing the O2 sensor on a 1g? I guess my buddy grabbed the wrong manual last time he was here because my 1g book is gone and all I have is a 2g one. If the 2g procedure is the same as a 1g let me know and I'll just read the 2g manual.

Have you tried a search on the forum to find out about O2 testing? I forget his login name for sure, but it might have been "Old_Mitsu_Tech" who posted the O2 diagnostic test procedure.

You might also look on www.vfaq.com for something similar.

Also, for future reference, you might want to pick up the manual CDs from www.manualcd.com. It redirects you to an FP site, but they're only $38 and contain much more than a Haynes or Chilton manual. I'm sure they'd contain O2 troubleshooting.

 

[Rex2342]

I searched but only found steps for a 2g and I found one for a 1g n/t but I'm not sure if they are the same. I have the back up service manual on my computer but I couldn't find anything related to testing o2 sensors. My multimeter isn't working anyway so I'm going to just wait until my buddy gets off work. He has a good o2 sensor sitting at his house so we're gonna swap it out and see if thats the problem. I did a quick check of the o2 voltage on the logger and at idle it's at .09v - .011v. I even unplugged the sensor and started the car and still got a reading of .09v and no CEL so I think this might be my problem.

 

[speedmaster747]

A faulty fuel pump, with not enough flow. Clogged fuel filter.

 

[Rex2342]

A faulty fuel pump, with not enough flow. Clogged fuel filter.

The filter is about 3 weeks old and the fuel pump is still a suspect. It's a Walboro 255 and it's about 2 years old. I can clearly hear the pump in the tank like always but if the o2 sensor doesn't fix it thats next on the list. I hate troubleshooting!

 

[Rex2342]

I changed the o2 sensor out but found another problem that might be the cause of all my troubles today. After the o2 sensor install I tried to start the car and it wouldn't start or even kick over. I jumped it and it started took it down the street and as soon as I let off the gas it died. Jumped it again and the same thing happened. The logger is showing a battery voltage of 11.6v after the jump and dropping rapidly to 10.2v by the time it gets down the road 2 blocks and dies. It looks like my year old alternator or my 2 year old battery are toast. I'm taking them both back to Autozone as they are still under warranty. So i'm thinking my low voltage problem is causing my fuel pump to not flow enough and thus causing my sudden lean condition. I'll let you guys know tomorrow.

 

[talonproject]

get a 90 amp alternator !
mine was doin basically the same thing, and that was it,
and now with the 90 amp I don t even hear my 255 anymore

 

[Rex2342]

She's back up and running!!! New alternator + new battery = no more lean condition! I took them both to Autozone and it turned out the alternator was putting out the right voltage but no amperage, and the battery had a collapsed cell or something fom being drained so far down. Thanks to all who helped with ideas, and for those of you who suddenly go lean for no reason check your voltage!!!