I am at a loss. I have been battling poor fuel mileage and performance for a few months now. All of this seemed to have started after a clutch/header install. First off I have changed the o2 sensors and to no avail. I then had a diagnostics check done on it at the dealership and it didn't show anything out of the ordinary. The dealer did tell me that since the shop I used put RTV on the header gasket to hold it on that it could be eating the o2's. Anyone heard of this? Also, some of my spark plug wires are a little burned but I have had failing wires before and the car acts nothing like it did then (the car doesn' t missfire at all it just runs poorly). Could the wires acutally be giving me these symptoms without causing any misfires? Am I overlooking anything? Any replies are greatly appreciated.

 

If you have any doubts about the wires, replace them.

Rich Krause

 

Actually there are several things that could be contributing to your poor mileage problems. What the dealer said about the O2s is correct. A lot of chemicals can lead to early failure of the O2s however, I do not personally know if RTV is one of them.

Another possible cause is you may be running on less than 8 cylinders. If that is the case, you do NOT want to drive it long like that. A bad wire may cause that problem. If you have been driving long with that problem, you may have a hint of gas smell to the oil. This could be detected by pulling one plug wire off at a time to see which one does not change the idle when removed. But the wires are almost impossible to get to at either end and particularly when the engine is running.

2 other causes for poor mileage that come to mind are, a ruptured fuel pressure regulator diaphragm or leaky injectors.

The regulator diaphragm can be checked by pulling the vac line off and see if its wet. I also like to apply a vacuum with a hand pump to see if it holds. If the diaphragm is ruptured it allows fuel to enter the vac line and is sucked back into the intake.

If the injectors are clogged, they could be leaking but this problem usually gives the engine a hard starting (longer cranking) problem. Both regulator and injector problems could be detected by using a fuel pressure gage to monitor fuel pressure after the engine is shut down.

The list could go on and on for possible causes. A clogged cat. converter. Bad sensors like TPS or MAF.

Depending on your mileage, consider doing a tune up and having the injectors professionally cleaned through the fuel rail so they don't have to be taken off. Don't forget all the filters too.

 

Thanks for your replies. I know that I am running on all 8 cylinders and I will be replacing them shortly. I just find it odd that they would the culprit. I am also getting ready to get a fuel pressure gauge to check the fuel system out.

 

im pretty sure all the RTV gasket sealants say "Safe for O2 sensors" right on the tube.