Thread: Strange engine noise

We have a 1999 grand prix with the 3.1 engine. Yesterday, my room mate was driving it. When she got home, she said it was knocking. I finally got around to looking at it today. It has a strange noise that sounds sort of like a knock, but more like a spark plug wire arcing. It is also running bad. I pulled the trouble codes and found P0306. Cylinder misfire #6. I figured out that if you pull the plug on #6 cylinder, the noise goes away. The strange thing about the noise is it is not repetative like a knock or a plug arcing.

The engine has about 200 thousand miles on it. I have a1995 camaro that the plug wires are the same on. We put in new plugs and tried the wires from the camaro to save a couple of bucks incase it didnt fix the problem, and it didnt.No gaskets have ever been changed on the engine since we have had it, which has been 5 years.We changed the wires with a new set, ( high quality autolite) about 2 years ago.

I also suspected a coil pack. I pulled one for the camaro and put on it, no help. I dont have anything to do a video. Sort of think it may be a bad injector, but not sure.

With the spark plug wire on, I used my stephoscope to try to fing the noise. It is loudest on the top of the plenum.

I cant unplug the injector without pulling the plenum.

I found the connector that leads to the injectors. I tapped into the harness to hook up my noid lite to make sure I was getting a signal to the injector, and I was. I cut the wire to the injector from the ecm and the noise went away. I think the noise is actually a backfire. I am going to replace the injector and help it fixes the proble, I will post when I get the injector replaced.

Yes compression is 160psi

Im pretty sure it is the injector too. We had to order it cause no one around here had it in stock. I think it will be in tomorrow. After I get it installed, Ill let ya know if it fixes the problem.

Ok, we got the injector today. I pulled the upper plenum and installed the new injector. Since I have never done a 3.1 before, it took me 3 hours from start to finish. I guess that isnt too bad after working a 11 hour day. The problem is, it was a waste of about a hundred bucks and three hours labor. The noise is back. I have been driving the car for the last 3 days with the #6 injector disconnected. It didnt run too bad considering it was only running on 5 cylinders.Im stumped now. It has good spark, 160 psi compression, so what am I missing??
I had my room mate take it to the local mechanic to see what they thought. They said it sounded like a valve spring had come loose and the valve was hitting the piston. They also said they could fix it for 1500 dollars.There is no way, that could be true if it has 160 psi compression. Right?

I guess my persistance paid off. I pulled the valve cover and the exhaust rocker arm had came loose and was being held on to the head by one or two threads. I guess if I had kept driving it, the rocker arm would have come loose completely and really did some damage. I dunno how it came loose. We have had the car for about 5 years and the valve cover has never been pulled. Im waiting for my room mate to go to walmart to get some threadlocker before I put it back together.I really appreciate everyones input and help. THANKS!!!