anyways, i have a 99 GMC with a 5.3L. well its been running like **** lately, so installed new plug wires and NGK TR55's 2 days ago. before it would miss under WOT and a load. well now sometimes it runs fine, then other times i'll go to drive it and it'll miss really bad and act like its only firing on 7 cylinders. Usually, the check engine light will come on when this happens (like its supposed to) and then i'll go drive it again later and the check engine light will be off and it runs fine. its really starting to **** me off. the motor has 176K on it, so i've been debating just buying another 5.3 from a salvage yard and being done with this ordeal. i also cleaned the MAF with electronics cleaner right after i installed plugs and wires. any help would be greatly appreciated.

 

how much did you gap the plugs?

 

You may have one or more of the 8 coils total you have, starting to fail.
That can really be the only other answer as long as you gapped your plugs correctly and all your plug wires are secured onto the coils and plugs propperly.
I'm going to have to lean toward one of the coils due to the check eng light code being thrown at you when it acts up. If you go to Autozone or somewhere you can have your truck placed on a scanner, then that particular problem should still be saved in your PCM's computer memory.
Then you will know exactly which coil or what to replace.
Other than that, I think it is a pretty simple fix.

Jim

 

I had the same problem. It was actually one of the new plug wires that was bad. One more set, and been fine since.

 

But......it was already acting up before he changed his plugs and wires.
I think it's a coil.

Jim

 

Mine was acting up, changed plugs and wires, still had the same problem, one of the new wires was bad. Im not by any means suggesting that a coil is NOT bad, just letting him know that I had the exact same problem, and it was a bad wire.


You could always OHM the wires and double check them, the one wire I had that was bad would only show bad when twisted though.

 

i've got a buddy that works at a dealership here in MO, so i'll have him bring home his scanner one night and i'll try to get this bitch buttoned up. you guys don't think the the MAF could possibly be taking a **** and sending all kinds of effed up signals to the computer do you?

 

Your scanner should tell you.

Jim

 

lol...
before I scan the computer to see the problem, should I just go ahead and replace the motor?
sorry...i thought it was funny

Id lean towards the coils too...thats the first thought that jumped into my head when reading your complaint.

The scanner should tell you which cylinder is misfiring, then you will know which coil to replace.

You should also be able to double check to make sure its your coil with a multi-meter... but I dont know what the OHMs are suposed to be. I am sure someone knows.

 

the only reason that i've considered replacing the motor is due to the fact that it has 176K on it. It's not that many miles for an LSx motor, but the piece of mind helps, plus i'd kinda like to put a small cam in my truck to give me a bit more torque for towing. as well as headers, K&N setup and a mail order tune.