'99 5.3 Has a Bad Misfire and Codes
01-04-2014, 10:48 PM
#11
I'll re-gap them to .040" then. I still need to get a fuel pressure gauge on it and see what that is reading. I don't think it's the plugs causing the problem though. The engine sometimes runs so bad the whole truck shakes like a wheel is about to fall off and other times the miss is barely noticeable unless you are accelerating hard. If it was plugs, it should more consistent. Some cylinders have a few misfires, some have none, and number 7 has thousands. Cylinder 7 has some kind of gremlin that I just can't locate. I'm contemplating pulling out the whole engine wiring harness to check it over and test resistance on each individual wire.
If thats the case can you do a cylinder balance test and drop cylinder #7 to see if there is any change?
01-05-2014, 12:43 AM
#12
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I have a similar issue, just bought the truck ran great (far from stock) took it to my tuner due to a high rpm misfire. After it was deemed untuneable, started going through gm protocall and narrowed it down to excessive crankshaft endplay due to bad thrust bearings on the crank. What is happening with my truck is, under load the crank is being pushed so far forward the reluctor wheel is out of the range of the crank sensor causing it to throw a continuous crank sensor code. So now i'm tracing the problem back to the trans and finding out exactly what caused it. Just to rule out a major problem maybe warm the truck up, obviously shut it off, and then try to move the harmonic balancer forward with a prybar. Mine was extremely bad. Hopefully its nothing serious. Good luck!
01-05-2014, 12:45 AM
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My scan tool does show misfires, live data, and freeze frame data, but it won't shut off cylinders for a balance test. I can do a balance test though by pulling the injector wires one-by-one while keeping the rpm's steady and note the changes.
01-06-2014, 03:30 PM
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01-07-2014, 06:33 PM
#20
Did you check all the ground wires?
There's two or three behind the intake, and I think two behind the p/s pump(one is batt-engine ground).
My truck had a bad relay and was throwing a MAF code because of it. I know that seems totally unrelated, but try moving the relays around in your underhood fusebox. It won't cost you anything, so it's worth a try...
There's two or three behind the intake, and I think two behind the p/s pump(one is batt-engine ground).
My truck had a bad relay and was throwing a MAF code because of it. I know that seems totally unrelated, but try moving the relays around in your underhood fusebox. It won't cost you anything, so it's worth a try...