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Random multiple cylinder misfire

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sunfiregtp

New member
I have a stock 04 gtp 3.8SC with 90,000mi. A short while ago I noticed a sputtering/hesitation occuring with light throttle input at low speeds. It is now occcuring at all speeds with light throttle input. As soon as I give it more throttle it runs smooth as can be. The engine light came on and the code read random multiple cylinder misfire. My first instinct was plugs and wires so I installed a set of ACDelco plugs and wires. The engine light went off and for the first day it seem ok but now the engine light is on again and I am still noticing an occasional sputter but no hesitation. I am thinking it needs a new fuel filter and if so where is it located and is it difficult to install.
 


On an 04 I believe it is still located just in front of the driver's rear tire. Should be a little cylinder thing with two lines in the back, and one coming out of the front. If you don't know the service history of the car, it may not be a bad idea to start there.

But watch out, I think those are a little pricey because they are built for the "returnless" style fuel system.
 
I priced one at NAPA for $17.50 hopefully it's the right one. Also how do I relieve the pressure from the fuel line? I don't feel like getting cover in fuel.
 
find the fuel pressure test port on the rail and press the stem and it will relive the pressure, just make sure you have a rag over it. otherwise slowly loosen the nut on the filter and it will slowly relieve pressure.
 
Well it's not a fuel problem. I had a friend use his code reader to check the engine light and it came back with 3 EGR valve codes. He also looked at which cylinders were missfiring and they all are however cylinders 3 and 5 misfires were in the thousands while the others were under a hundred. Does the EGR valve have anything to do with misfires or do I need new coil packs?
 


It's also not coil packs as I just replaced them and it's still doing it. However I am noticing some very strange things going on with the cruise and traction control they turn on and off by themselves sometimes rapidly back and forth I hope my computer is not going out but I cant think of anything else that would cause it to do that.
 
It may be a separate issue, but when my fuel pump relay decided to go out, I was also getting the random misfire. I'll see if I can find the reference that fixed it, but all it took was bending one pin on the relay and putting it in "high speed" at all times. I also replaced plugs, wires, fuel pump, and coils in a vain effort to fix the problem...
 
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