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01 silverado 5.3 265k miles. I am unsure if the engine is original. Truck is in excellent condition, zero sludge under valve covers. Wouldn’t surprise me if it was original or if it had been replaced. I’ve owned the truck since around 190k.
•engine has had what I am confident is a lifter tick for at least 2 years.
•about 1.5 years ago, engine developed a slight occasional “bump” at idle and p0300 CEL
•fast forward to very recently, idle misfire is a little worse but nothing crazy. Still just random, but more consistent “bumps”. While towing a small car recently the truck seemed to lose power in the 1900-2300 rpm range, but no noticeable misfire.
I believe my scan tool is really limiting me here as I can’t view individual cylinder misfire counts. So far I’ve changed plugs and wires(no change)Sprayed starting fluid/carb cleaner all over to check for vacuum leaks. Checked fuel pressure. Swapped coils from my other 5.3 equipped vehicle (no change). Performed compression test, all cylinders were around 180 psi.
Stft always +/- 10 when I’m looking
Ltft was +20 on bank 1 last I checked. Bank 2 was in normal range.
I took a chance today and changed the intake manifold gasket because the design of the intake makes it hard to spray to the inside of the runners, no change in idle issue.
I really wish I could get more as far as a code goes. I’m not sure where I should be looking now except maybe injectors
Almost forgot, I did a vacuum test to check for exhaust restriction. Also pulled 02 sensors and let engine idle, misfire still present.
Last notes: truck seem to idle fine while cold but once it reaches operated temp and rpms lower the “bump”/misfire starts. Truck runs great while driving, no misfire at all. The only drivability issue has been the power loss while towing.
What does your o2 sensor voltage look like? Does it cycle or is it stuck lean on one bank? I would think it would throw a code if it was, but never know.
Exhaust leaks?
MAF sensor clean, seem to rise in voltage proportional to expected air flow. Maybe fail the MAF to keep it closed loop (you mentioned it runs good cold, open loop mode)
I checked everything except the MAF suggestion. The transmission in the truck took a dump a few days ago and I refuse to put another one in it. I’m moving on from this truck. Thanks anyway.
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