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Cylinder Missfire Please Help!!!

Cylinder Missfire Please Help!!!

Postby longtravelraptor [OP] » Feb 27 2012, 4:16am

Hello and thanks for reading and any help you can provide, I am stuck. I own a 99 silverado with the 5.3 about 160k 4x4. I have a cylinder 5 misfire. So I switched the coil spark plug wire and injector to another cylinder and I also replaced the air intake gaskets and it didn't help the misfire stayed at cyl. 5. If I drive long distance the check engine light will turn off but if I let it idle it will turn back on the freeze frame data says misfire is at idle. I have searched everywhere trying to figure this out and cant so I am hoping someone here can help thanks
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Re: Cylinder Missfire Please Help!!!

Postby ASTE25 » Feb 27 2012, 9:45pm

Well, there are only 3 things you need for it to run correctly: Fire (spark at the right time), compression and fuel. You have to be having a problem with at least one of them. Apparently you have already eliminated a spark problem by swapping the coil and wire (providing there is not a problem with getting the fire pulse to the coil from the computer and the plug itself is good). You should not have a vacuum leak, because you already changed the intake gasket. Have you done a compression test? I have heard that the 6.0 have had problems with bad valve springs, not sure about the 5.3. Maybe you have a mechanical problem on that cylinder. Let us know what you find out.
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Re: Cylinder Missfire Please Help!!!

Postby longtravelraptor [OP] » Mar 01 2012, 1:31am

I have not done a compression test I am going to buy a gauge kit this weekend as I don't own one I forgot to mention that the spark plug I pulled out was really brown which I think means its running lean. The other plugs were all still white as they don't have more than 10k miles on them when I get the gauge what should the pressure be? I was also thinking in order too eliminate any other problems I would replace the cam with an aftermarket cam from summit but they don't seem to sell one, do you know where I could purchase one and difficulty level on a swap?
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longtravelraptor
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Posts: 3
Topics: 1
Joined: Feb 27 2012, 4:03am
Years of membership: 2 years of membership2 years of membership
Location: Southern CA
Year: 1999
Make/Model: Chevrolet Silverado
Variant: VHO/Vortec Max
Extra Info: 1500 5.3 4x4
Group Membership:
Registered users

Re: Cylinder Missfire Please Help!!!

Postby ASTE25 » Mar 01 2012, 1:37am

Replacing a camshaft is a pretty in depth repair. I doubt that will be the problem anyhow (but I'm not saying it can't be). I would definatly start with a compression test and if compression is not good then I would find out where it is leaking. I'm not sure about what the compression calls for, however, I would think at least 125 psi. Since the other cylinders seem to be fine I would test them all and if the one you think is not within around 10% of their readings I would suggest a problem. Keep us updated on what you find.
Jordan
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