Steezy_baugh

I have a 1999 f body with the 3.8l v6 3800 series engine and I just recently started having those pesky misfire problems. Well I drove on it about another 200 miles and now it sounds like there is a grinding noise coming from the passenger side of the motor I'm thinking it could be connecting rod bearings and my stepdad is thinking push rods anybody else have this problem? If so what was the solution?

Injuneer

Your description of the noisy is extremely vague - in the topic you call it a "knock", then you describe it as a "grinding noise". Two completely different sounds. Have you used a stethoscope or a long metal rod to try and pin down the exact location of the noise? Does the frequency of the noise change with engine RPM? Does it get louder with the engine under load?

Describe the nature of the misfire. Under what operating conditions does it occur? Does the misfire cause the SES light to flash? Did you have the PCM scanned for codes? With a scanner capable of "GM Enhanced Parameters" you can determine the misfire count by individual cylinder, which may point to the cause. How long did you drive it knowing it was misfiring? Have you checked the spark plugs for condition?

Have you checked the condition of the oil? Is there any sign of dilution due to presence of gasoline?

Steezy_baugh

It's definitely a knock but when I accelerate it does speed up. It does get louder when the engine is under load. I had it scanned with an obdII the misfire was in the number 4 cylinder. But these engines are famous for the coils going out I haven't much checked for anything in my ignition system because I've been more worried about the knock. The ses light does flash but it's only occasionally while it is always misfiring when I pull up to a light. I drove it an extra 200-300 knowing it was misfiring and only drove about 2 miles after it started knocking. The car also overheats while I'm driving it I'm not sure if that has anything to do with it. Has a very rough idle as well. The oil in it is good just a little black could used a change

Injuneer

Misfires can cause fuel buildup in the cylinder, the fuel leaks past the rings, washing the lubrication off the cylinder walls, and eventually diluting/thinning the oil to the point where it no longer provides proper lubrication. That's why it's important to check the oil for the smell of gasoline, and a very thin viscosity.

The 3.8L engine is also know to be plagued by intake manifold gasket leaks, that can dump coolant into the engine. Does the cooling system lose coolant, requiring frequent refills?