5.3 erratic idle/misfire

black77gmc · November 8, 2006

I have a 2000 gmc sierra with a 5.3 litre. A few months ago it started with an erratic idle or misfire and i have lost some power on cruise. I have tested and replaced lots of things, replaced plugs and wires (twice), changed 4 coils only one that absolutely did not fire at all, fuel pressure regulator, 2 o2 sesors, cam crank tps maf i have tested and seem to test fine, there is no mil light that comes on, however a few weeks before this started I did get a multiple random misfire code. and an egr malfunction code. I took the cats off suspecting a clog (i bought a scanner with real time sesor data) and I am still having the same problem, it seems to run better when it is cold and it is not consistant. But it happens anytime the truck is in low rpm, sometimes during hard acceleration it will slightly surge. If anyone could give me some advice on what to try i would apprieciate it, this thing is driving me crazy. Thanks!

Air Biscuit · November 8, 2006

I have a 2000 gmc sierra with a 5.3 litre. A few months ago it started with an erratic idle or misfire and i have lost some power on cruise. I have tested and replaced lots of things, replaced plugs and wires (twice), changed 4 coils only one that absolutely did not fire at all, fuel pressure regulator, 2 o2 sesors, cam crank tps maf i have tested and seem to test fine, there is no mil light that comes on, however a few weeks before this started I did get a multiple random misfire code. and an egr malfunction code. I took the cats off suspecting a clog (i bought a scanner with real time sesor data) and I am still having the same problem, it seems to run better when it is cold and it is not consistant. But it happens anytime the truck is in low rpm, sometimes during hard acceleration it will slightly surge. If anyone could give me some advice on what to try i would apprieciate it, this thing is driving me crazy. Thanks!

<{POST_SNAPBACK}>

Clogged injectors? I had misfires on 2 and 6. Cleaned out the rails and injectors and the problems disappeared. May not be the case with a random misfire but just an idea.

black77gmc · November 8, 2006

I have run several different injector and fuel system cleaners through it, however i know that it isnt as good as what the factory can clean it for, I did forget to mention that I paid a friend who has an expensive code reader and he noticed that the misfire was on #6 pretty often however the others misfired randomly on occasion which i was told is "normal". I replaced the wire, coil and plug on that cylinder and no change. Thanks for the info. The most confusing part is that it does not throw a code. I dont know what to try next.

Air Biscuit · November 9, 2006

I have run several different injector and fuel system cleaners through it, however i know that it isnt as good as what the factory can clean it for, I did forget to mention that I paid a friend who has an expensive code reader and he noticed that the misfire was on #6 pretty often however the others misfired randomly on occasion which i was told is "normal". I replaced the wire, coil and plug on that cylinder and no change. Thanks for the info. The most confusing part is that it does not throw a code. I dont know what to try next.

<{POST_SNAPBACK}>

I think # 6 is pretty far down the rail...one of the farthest from the pump. The dealer said that these engines run so lean, especially at cruise, that even a little bit of a drop in flow to or from the injectors can set a code. That's what they told me, anyway. When they cleaned the injectors, they said they had to remove each one and 'clean the screen' which makes me think there must be some kind of filter on each one (I'm shadetree so if it was snake oil, guess I got bit.) Either way, no more codes.

Anyway, hopefully someone else on here knows more. Good luck.