fuel trim failure
#1
fuel trim failure
I just wonder if anyone has an idea I haven't thought of regarding positive (lean) fuel trims.
At cold start up the trims read about +4 at idle (LTFT). As the engine warms the idle LTFT rise to about +12 to +16. At highway speeds the positive trims drop to +5 to +9. I conducted a smoke test and found a rather nasty leak at the EGR valve connection to the throttle body adapter. I removed and cleaned the EGR valve and the Throttle body, putting them back with all new gaskets. I smoke tested again and confirmed that the leak is repaired. Fuel trims still almost as bad as before though...
I replaced both upstream oxygen sensors with new Bosch units. Pretty much no change in idle fuel trims, however at highway speed the trims are better. In fact, if I accelerate while traveling at highway speeds, all four fuel trim readings settle right around zero. It is sporadic in that sometimes the LTFT will be around +4 when driving, sometimes +9, sometimes +16. I smoke tested again and could not find any leaks.
I would suspect the MAF (which has been cleaned) but it seems that bank 2 is consistently worse than bank 1, and I presume if the MAF was the culprit they would both be similar.
I also have my doubts about the coolant temperature sensor. The car seems to be at 90 to 100 degrees within just a few seconds of starting the car whereas my XJ8 works it's way up more slowly from ambient temperature. Plus the car turns a few times when the car is cold before starting, but after it's warmed up it starts on the first turn of the engine. I ordered the CTS and the part that came had the wrong size threads. I called a local auto parts store and their computer listed a CTS for my car; it too had the wrong size threads. Apparently the LRA1600AA that many sites and stores list for my car is incorrect. It is actually a LNA1600AA, which I have yet to purchase.
The only other anomaly I see that "could" be related is that the car is always showing P1111 (full readiness). Normally that's good, but I can disconnect and hard reset the system and check within a couple of minutes after re-starting the car and it already shows P1111. My XJ8 would usually take about 30 minutes of driving to show readiness.
Information overload probably, sorry. I just wanted to list anything that might be relevant for some of the more seasoned mechanics that might see something in that information that I don't.
Thanks
At cold start up the trims read about +4 at idle (LTFT). As the engine warms the idle LTFT rise to about +12 to +16. At highway speeds the positive trims drop to +5 to +9. I conducted a smoke test and found a rather nasty leak at the EGR valve connection to the throttle body adapter. I removed and cleaned the EGR valve and the Throttle body, putting them back with all new gaskets. I smoke tested again and confirmed that the leak is repaired. Fuel trims still almost as bad as before though...
I replaced both upstream oxygen sensors with new Bosch units. Pretty much no change in idle fuel trims, however at highway speed the trims are better. In fact, if I accelerate while traveling at highway speeds, all four fuel trim readings settle right around zero. It is sporadic in that sometimes the LTFT will be around +4 when driving, sometimes +9, sometimes +16. I smoke tested again and could not find any leaks.
I would suspect the MAF (which has been cleaned) but it seems that bank 2 is consistently worse than bank 1, and I presume if the MAF was the culprit they would both be similar.
I also have my doubts about the coolant temperature sensor. The car seems to be at 90 to 100 degrees within just a few seconds of starting the car whereas my XJ8 works it's way up more slowly from ambient temperature. Plus the car turns a few times when the car is cold before starting, but after it's warmed up it starts on the first turn of the engine. I ordered the CTS and the part that came had the wrong size threads. I called a local auto parts store and their computer listed a CTS for my car; it too had the wrong size threads. Apparently the LRA1600AA that many sites and stores list for my car is incorrect. It is actually a LNA1600AA, which I have yet to purchase.
The only other anomaly I see that "could" be related is that the car is always showing P1111 (full readiness). Normally that's good, but I can disconnect and hard reset the system and check within a couple of minutes after re-starting the car and it already shows P1111. My XJ8 would usually take about 30 minutes of driving to show readiness.
Information overload probably, sorry. I just wanted to list anything that might be relevant for some of the more seasoned mechanics that might see something in that information that I don't.
Thanks
#2
hmm... the P1111 is odd.
Er... not sure which of your cars you mean...
The CTS (ECT) sounds faulty. If it is then the cold start fuelling will be a bit wrong which I think fits with what you see.
Clearing the codes (I know there aren't any) should cause P1000 (but isn't going to help with trims).
The learned trims are cleared with a hard reset (or WDS / IDS can do it I believe) but it will anyway relearn new O2s with time.
If you change the ECT give it a while to relearn (a few drives) and if the trims still get to over 10 you may be looking for some leak under certain conditions (purge valve or whatever).
Er... not sure which of your cars you mean...
The CTS (ECT) sounds faulty. If it is then the cold start fuelling will be a bit wrong which I think fits with what you see.
Clearing the codes (I know there aren't any) should cause P1000 (but isn't going to help with trims).
The learned trims are cleared with a hard reset (or WDS / IDS can do it I believe) but it will anyway relearn new O2s with time.
If you change the ECT give it a while to relearn (a few drives) and if the trims still get to over 10 you may be looking for some leak under certain conditions (purge valve or whatever).
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harvest14 (04-28-2016)
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