[mcf1000x2003]

I have 95 STS with magnaflow mufflers with camaro tips and I notice every couple of days my rear bumper starts turning black right above the left tip. The guy at the muffler shop said there may be something wrong with my motor or something cuz its never suppose to get black like that.Can anyone tell what i can do to stop this? The car is still running great but i get annoyed having a black spot that makes my diamond white paint look like crap.

 

[Kev]

That of course is from running rich. Every time you start your car cold your system runs the engine rich until it gets to normal operating temp. That's the simple explanation. If it is excessive then you want to start looking for possible problems.

Has your car been running smoothly? Does it feel like it runs strong? When was it tuned last? Do you drive far enough to get the beast warmed up all the way or do you make a lot of short little trips?

These are all very basic questions that you might address first. There may be more technical causes or problems attributing once these are ruled out.

 

[mcf1000x2003]

I bought the car with 102k and it has 107k on it now im not sure if it's ever been tuned but it still runs smooth and strong.I usually go to work with it which is a 10 minute drive exept on sundays when i drive around for 2 hours dropping off papers.

 

[Kev]

How is the fuel mileage? Does it seem like it's a little low? Could be an indication of rich mixture which probably shouldn't happen if everything is working properly.

With over 100k miles on it I would first consider changing the plugs at least since you are unsure if or when that may have been done in the past.

Oh, of course, check for any error codes to see if the ECM is tracking a problem.

 

[mcf1000x2003]

No codes on the ECM exept everytime i cold start the car the it says check oil levels even tho my oil level is ok.Im getting pretty crappy gas mileage about 12-14 in the city and on a 200 mile trip i took a couple weeks ago (all highway) i only avg. 21 mpg

 

[WarrenJ]

No codes on the ECM exept everytime i cold start the car the it says check oil levels even tho my oil level is ok.Im getting pretty crappy gas mileage about 12-14 in the city and on a 200 mile trip i took a couple weeks ago (all highway) i only avg. 21 mpg

First, several of us here have suffered the CHECK OIL LEVEL nag. In every case is was due to a defective oil level sensor. It's right next to the oil filter on the oil filter adapter.

Crappy gas economy (I LOVE that technical talk! ) coupled with a rich mixture *might* account for the deposits on your bumper if a fuel injector were leaking, although I can't explain why it would appear on only one side. Of course, there are other suspects as well.

Do you have a factory service manual (FSM)? If you do, you might want to perform a "Power Balance Check." It's on page 6C-34 of Volume 1.

From the FSM:

"The Power Balance Check compares the performance of each of the cylinders by using the PCM to shut off fuel injectors. This measures the performance of each cylinder by the amount of rpm drop caused by that cylinder not producing a power stroke. If proper fuel deliver has been determined, then a cylinder that does not show good performance (RPM drop) indicates either an ignition or mechanical problem."

This will allow you to localize the problem to a specific cylinder. If you CAN localize it to a particular cylinder, then you can look at the plug/wire/injector/compression/etc. associated with that cylinder.

Regards,
Warren