03 gmc gremlin problems- flashing engine light, reduced power

[620nova]

not to sounds like a jerk but i feel from the beginning you should have gotten your hands on a scan tool that would show you cylinder missfires. that way you could see if it is a single cylinder that its seeing or if you have random, multiple cylinder missfire.


just to make my idea more concrete... i had an 05 silverado yesterday that came in for as SES light. had a p0420 cat low inefficiency code turning the light on. ALSO had a p0300 that had set but had yet to command the light on. you wouldnt know it was missing but it had skips on cylinders 1,3,4,5,6,8. i found out the customer had been in a other place to have some work done and that place had installed some ngk plugs and most of them were loose and plug wires loose on the plugs themselves. hell cylinder 6 i never even took the wire off, just in screwed it from the block :0. but to be honest i would never had known it was skipping if i hadnt looked that deep with a scan tool.

all im saying is if you check it with a scan tool and find out the ecm believes only one cylinder is skipping then that drastically reduces your possibliltys of what the problem could be. not only that but when you have problems like this its a lot cheaper to recheck things like ignition componants then it is to throw parts at it.

3 years ago i refused to recheck spark plugs i had recently installed in my truck when it ran like crap. went as far as putting a brand new carburetor on it and did sure as hell didnt fix my problem. ended up damaging number one plug when i dropped it on the steering shaft when i installed it. a $500 repair when a free check and $6 plug would have fixed it.

if you check missfires and find them all on one bank you could possibly be looking at plugged cats. seen it happen with my roomates truck. you could have a cylinder balance test done at a dealer or repair shop to verify the ejectors are all flowing properly. jsut some more ideas.

It was at a dealer more than once never had p0301-p0308. only ever p0300 random cyclinder misfire, which they told me the computer can not indentify a single cylinder misfire, so it puts it into the random p0300 catch all bucket. Thats when the one dealer told me it was camshaft lope wear. Also both cats are new.

trplxl2 i wasnt using my heads as a ground I was grounding my heads. I also ran a ground to the coil mounting plate thats mounting on valve covers. I give it one more trip to the dealer and then im either going to run it another 40k with a blinking light or drop of my big block race engines in it. lol

[TRPLXL2]

Has anyone checked the ECM plugs, for corrosion or backed out pins? I have a spare ECM for everyone of my vehicles for this purpose, It takes 5 minutes to swap the ECM and see if the problem replicates.

My comment with the heads is how they set them up from the factory, LS engines do have several sensors grounded to the heads. Good luck with your truck, It will all work out!!

[620nova]

Just got back from dealer service, most misfires coming from 5 and 8 but others have misfires also but majority were 5 and 8. They pressure cleaned injectors 2x, no difference. fuel pressure good, regualtor checked ok, pull plugs in 5 and 8 they looked fine, ignition tested good. told me it has something deaper, maybe injector but they are thinking lifter or valve guides ????? he also said i have exhaust manifold leaks on both sides, can this cause an issue wiht oxyg sensor ??? Im thinking i have 1 of 4 option, 1 drive it like i stole it, 2 trade it off 3, buy reman heads, 4 buy another engine form salvage yard.