Carbon On Plugs!

98POSCHEVY · April 3, 2011

I have a 98 chevy 5.7 vortec. It had been missing for a while. Started as very miner and got pretty bad so i changed cap,rotor,plugs and wires. Everything was going well till i got to the #5 plug and it was carbond over BAD!! So i thought that was the problem. However that did help but still had a miner miss. I changed everything a month or so back, So Friday i pulled the #5 plug again and its the same way again covered with carbon. Ive looked all over the net and some say valve job some say EGR valve. Need help with trying to figure out the problem without spending thousands of dollars and not fixing the issue! Any help you all can throw my way is GREAT!

Thanks for your time,

Lance

Wires · April 4, 2011

I have a 98 chevy 5.7 vortec. It had been missing for a while. Started as very miner and got pretty bad so i changed cap,rotor,plugs and wires. Everything was going well till i got to the #5 plug and it was carbond over BAD!! So i thought that was the problem. However that did help but still had a miner miss. I changed everything a month or so back, So Friday i pulled the #5 plug again and its the same way again covered with carbon. Ive looked all over the net and some say valve job some say EGR valve. Need help with trying to figure out the problem without spending thousands of dollars and not fixing the issue! Any help you all can throw my way is GREAT!

Thanks for your time,

Lance

I'd say if it was the EGR, you'd be having issues with the other 7 as well. If it's only 1, then you're getting oil in that cylinder. Unfortunately, you wouldn't really know until you dig into it. Could be bad rings, leaking cylinder, valve job, valve seals. Try a compression test on that cylinder and see if its in line with the rest. That would rule out some of the above.

Superperv23 · April 4, 2011

It could be a bad injector in that cyl, try a few bottles of injector cleaner and see if that helps

98POSCHEVY · April 4, 2011

It could be a bad injector in that cyl, try a few bottles of injector cleaner and see if that helps

thanks for responding! i put a bottle in the Friday after i checked the plug. I hope it helps>

98POSCHEVY · April 4, 2011

I have a 98 chevy 5.7 vortec. It had been missing for a while. Started as very miner and got pretty bad so i changed cap,rotor,plugs and wires. Everything was going well till i got to the #5 plug and it was carbond over BAD!! So i thought that was the problem. However that did help but still had a miner miss. I changed everything a month or so back, So Friday i pulled the #5 plug again and its the same way again covered with carbon. Ive looked all over the net and some say valve job some say EGR valve. Need help with trying to figure out the problem without spending thousands of dollars and not fixing the issue! Any help you all can throw my way is GREAT!

Thanks for your time,

Lance

I'd say if it was the EGR, you'd be having issues with the other 7 as well. If it's only 1, then you're getting oil in that cylinder. Unfortunately, you wouldn't really know until you dig into it. Could be bad rings, leaking cylinder, valve job, valve seals. Try a compression test on that cylinder and see if its in line with the rest. That would rule out some of the above.

That's what i didn't want to hear but its what i was thinking. i will try the compression test and post the results. Thank you for your time.

Superperv23 · April 4, 2011

I guess I could have been more clear....If it is dry caked on looking it is likely injector and that is what I figure you meant by carbon but could also be valves sticking and you can try something like amsoil engine and transmission flush than new oil, but if it is wet oily looking then that is when you have more serious problems with oil in the cyl.

98POSCHEVY · April 4, 2011

I guess I could have been more clear....If it is dry caked on looking it is likely injector and that is what I figure you meant by carbon but could also be valves sticking and you can try something like amsoil engine and transmission flush than new oil, but if it is wet oily looking then that is when you have more serious problems with oil in the cyl.

It was hard and crusty looking.. Ive read and been told it could be a injector but havnt looked into it. Should i try to clean them or just replace them?

Superperv23 · April 4, 2011

You can not really clean injectors yourself, you would have to take them somewhere to be cleaned, it likely couldn't hurt to replace them all if they never have been to be honest.

98POSCHEVY · April 4, 2011

You can not really clean injectors yourself, you would have to take them somewhere to be cleaned, it likely couldn't hurt to replace them all if they never have been to be honest.

OK. Thanks for the help.

98POSCHEVY · April 5, 2011

ok checking compression tomorrow but i talk with the guys at the parts store and they said it could be O2 sensors?? or injectors or a valve thats carboned up? Im hoping the compression test will tell more. If anybody has anymore ideas PLEASE feel free to share. Thanks.

taylorlawrance · April 6, 2011

Compression test is a decent start, however cylinder leakdown test is what you really want to do. That would pinpoint your issue to rings or valve seals. It isn't your EGR, as previously stated even if that was it pumping exhaust in your intake isnt going to carbon much up that quick. PCV valve stuck open definately, but you would see it more on all cylinders. Your truck having only 1 cylinder doing this rules out gaskets (generally). It being a 350 vortec the first thing that came to my mind is valve seals, because ive heard this issue from multiple people an 2 or 3 vortec 350's. A leaky injector could be an issue, however it is way too common for 350's to have bad valve seals on one cylinder that it would be my first place of diagnosis. Oh and about the parts store suggesting O2 sensors or carboned valve, LMFAO! Auto zone techs are hilarious!

Patrick H · April 6, 2011

Was it brown/tan in color? Oil will leave hard brown deposits, if it's burning it. Valve guides usually because there's still enough compression to burn (almost) everything...

4wd · April 6, 2011

It is always good idea to go with the simple fixes, could it be electrical? wish I can be of more help,,

98POSCHEVY · April 6, 2011

Compression test is a decent start, however cylinder leakdown test is what you really want to do. That would pinpoint your issue to rings or valve seals. It isn't your EGR, as previously stated even if that was it pumping exhaust in your intake isnt going to carbon much up that quick. PCV valve stuck open definately, but you would see it more on all cylinders. Your truck having only 1 cylinder doing this rules out gaskets (generally). It being a 350 vortec the first thing that came to my mind is valve seals, because ive heard this issue from multiple people an 2 or 3 vortec 350's. A leaky injector could be an issue, however it is way too common for 350's to have bad valve seals on one cylinder that it would be my first place of diagnosis. Oh and about the parts store suggesting O2 sensors or carboned valve, LMFAO! Auto zone techs are hilarious!

First thanks for the info! I didn't get to check the compression today but im going to saturday. Ill post results then. I have a mechanic friend and i was telling him what was happening and the first thing that came out of this mouth was injector?? I guess he's seen the problem before..i dunno. So what your saying is it could be a PCV valve? Yes, Autozone told me that when they hooked up the scanner to my truck. It came back with miss fire on #5 and my O2 sensors were bad. Again thanks for the info.

98POSCHEVY · April 6, 2011

Was it brown/tan in color? Oil will leave hard brown deposits, if it's burning it. Valve guides usually because there's still enough compression to burn (almost) everything...

It was more of a white color. So i didn't think it was oil.