Rough idle

[oldenginejim]

Hello. My 1991 Park Avenue has a cylinder (back middle, not sure what #?) that will not work! The spark plug is very wet indicating not firing. I put new plugs and wires on with no change. A mechanic friend cleaned and checked the injectors so I know their working ok. It is getting a good spark and compression is good. He's thinking a cam lobe may be wiped out or bent push rod. Any ideas on what else to check for??
Like I said, I have spark and am getting fuel. How could you figure out if it was a cam problem? Any help would be graetly appreciated. Thanks..
P.S. When I snap the throttle hard , it seems like it backfires through the throttle body.

[maxwedge]

Maybe pull the valve cover and look for proper valve train operation, if you have good compression it could still be cam or valve related problem.

[HotZ28]

How did you check the spark to know it is good? Is the new plug wet? The motor has a roller cam and they very seldom wear out! Do you have any nosie in the engine?
You may have a weak coil on that cylinder. Change the coil with another one and see if the problem moves to another cylinder.

[oldenginejim]

Thanks hotz28, I will try that tomorrow and let you know what happens. There is a knock at idle though and this worries me. It seemed to come on really fast so I'm sure it couldn't be the cam. This seemed to start almost imediately after my water pump went out and broke the serpentine belt in half! I did not over heat the engine though. I'll let you know what happens. Thanks again..........

[oldenginejim]

Oh, and also, we checked the spark through a spark tester not through the plug. Don't know if thats the right test or not?

[oldenginejim]

Well, I pulled the valve cover off and found my problem. Broken rocker arm bolt. The darn rocker arm was just layin there and the push rod still in it's hole where it ought to be!! Can't believe this didn't cause more damage! Now I have to try and get the broken bolt out. It is broken off flush. Any idea's on how to go about this?? I tried just spining it out with a punch but it didn't move. I don't think it will be too tight as the bolt bottoms on the plate that is in there. Left handed drill maybe?? I never have good luck with east-outs, but may resort to trying this. Thanks all..................