Quote:
Originally Posted by djtc
I'm thinking to change the Idle air control valve and the coolant temp sensor next.
Let me know if you guys have any ideas please!!!
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I have a few observations to make here...
First, in this picture, notice the Long Term Fuel Trim on Bank 1!! WHOA...
The ECU is cutting fuel 39.8% on Bank 1 (which is the side that the MIL is referring to as well). The short term fuel trim (SHRTFT1) refers to immediate changes in fuel occurring several times per second. The long term fuel trims (LONGFT1) are driven by the short term fuel trims. LTFT refers to changes in STFT but averaged over a longer period of time.
If your ECU is cutting fuel by that much, there's only one culprit in my mind and that is a
leaking fuel injector.
The reading on your Engine Coolant Temp looks fine, so I doubt your coolant temp sensor is causing the problem. If the ECTS ws the problem, it would be giving a low reading, causing the ECU to run the engine in "warm up" mode, adding additional fuel @ all times, rather than only immediately after a cold start. This would cause the engine to run rich, but not so rich that the fuel trims would reach -39.8%... Again, WHOA!!!
Second, in this picture. Notice the Hydrocarbon #'s (HC ppm) both @ idle and @ 2500 RPM. Hydrocarbon's are essentially soot, aka black smoke, aka... running rich. The idle number is pretty high, and getting close the limit for passing your smog test. To me, this again indicates that the ECU is having to work very hard to control the amount of fuel entering one (or more) of the cylinders on Bank 1. It takes a much finer degree of control to keep the truck idling than it does to keep it running @ 2500 RPM. This is probably the reason it is stalling... Too much fuel and the ECU can't trim enough to keep it running @ low RPM's.
Every sign here points to a leaky fuel injector that is introducing too much fuel into one of the cylinders on Bank 1, which should be the Driver's side.
The fact that you have replaced both 02 sensors eliminates the possiblity of a faulty AFR reading causing the ECU to trim fuel.
If it was your ISC motor, you'd be experiencing issues @ idle... either too much air (high revs) or not enough air (stalling)... in any case, unless you spend hours with the truck idling, there's no way a problem w/the ISC motor would result in fuel trim #'s that high.
Finally, a clogged fuel injector (as suggested by harleydoc), would result in POSITIVE fuel trim #'s as the ECU would try to increase fuel delivery to compensate for the reduction in fuel on the clogged injector, and the resulting LEAN running condition.
Good luck!