rough 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!

legionwagon · November 10, 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!

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I hate to say it, but maybe something mechanical? Check for a vacuum leak (maybe intake), spray starting fluid around while running (have fire extinguisher and good insurance). Maybe check compression and see if one cyl went bad (valve?). Good luck- I understand the frustration level...

desrtrat · November 10, 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}>

I hate to say it, but maybe something mechanical? Check for a vacuum leak (maybe intake), spray starting fluid around while running (have fire extinguisher and good insurance). Maybe check compression and see if one cyl went bad (valve?). Good luck- I understand the frustration level...

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first. WHAT EVER YOU DO ...DO NOT SPRAY STARTING FLUID ON OR NEER THE MOTOR!!!

if you want to ckeck for vac. leaks use carb. cleaner you will hear any rpm change very easly.

if you had to replace coils i would check your injectors also. prob. cloged a couple of them. try useing a can of seafoam and see if it clears up, it shoud then after you run it thru the tank, on your next fill up put 2 bottles of LUCAS injector cleaner in and what the seafoam missed the lucas will take care of and use 2 bottles every 2-300 mi.

good luck........

99Silver6.0 · November 11, 2006

Id seriously look at the injectors!! You can use a long handled screw driver as a stethescope. Touch it to each injector and listen for a profounf tick. Or yank your plugs and see which one is clean, dry and white!

Clavin78 · November 14, 2006

Maybe a relearn is needed. somehow the crank has gotten off.

99Silver6.0 · November 14, 2006

Maybe a relearn is needed. somehow the crank has gotten off.

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Possible the timing chain is shot. Which leads to CKP codes. Or if he swapped PCM's.

Id try the injectors first. CKP issues dont normally cause surging!!

Butch 02 Denali · November 14, 2006

If you haven't removed and cleaned the throttle body, then that is probably the problem. You will not believe the gunk in and behind the throttle body. The EGR dumps it's crap just behind the throttle body and really clogs things up. Remove and clean the EGR tube while you're in there too. Use throttle body cleaning spray rather than carb cleaner, it's safer on the sensors.