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

 

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).