I've go a '94 Z28 with 87,000 miles. When I start driving it for a couple of minutes, it will start to stumble. It used to just do it at stop lights, now it will do it while accelerating and it will do it while driving on the interstate. I checked all the wires and plugs and everything else I could think of. The GM dealer says that the water pump was leaking and the optispark was acting up. They wanted to much to fix it so I took it to a mechanic shop to get a quote from him and he said everything was fine except that the #6 cylinder had lost compression and suggested that I have both cylinder heads rebuilt. Who should I believe.

 

well that is a tough decision. I would ask to see the compression tester to see if there is none. If you have a dead cylinder then there could be a couple of problems. Either you have a bent valve or a cracke piston. if the piston is cracked then you will have blow by and that would be seen through the oil dip stick. Something would have had to cause the valve to get bent, usually it could be that the timing chain broke or something in that nature to cause the piston to come up and smack the valve. If it is the number six cylinder I would first try changing the spark plugs and plug wires to see if that causes it. If it is misfiring it should be setting off a ses message. I would then check the fuel pressure and change the fuel filter.

 

You said the water pump was leaking. If it wasn't fixed i would get that taken care of soon. The opti is right below the water pump and is an easy fix with the water pump removed. If you have any mechanical skills and tool you should be able to do it yourself. I would get a second opinion on the compression loss and what to do to fix it correctly.

 

I ckecked the spark plugs and wires, they are good. What do you mean by "blow by"? The oil looks normal. Would the engine still run with a broken timing chain? Therer are no dash lights on. The GM dealer said he was getting a code that indicated that the opti was bad. I do not see any leaks coming from the water pump. The opti has never been replaced. I'm going to get a second opinion on the compression loss.

 

No the motor would not run with a broken timing chain, that is why it does not make sense that the valve would be bent. Blow by means that the compression that the cylinder normal builds up is blowing by the piston and goes down into the crank case and would come out of the only place available, the oil dipstick. If none of this is happening then it is most likely a dead miss. This could be spark plugs, plug wires arcing off, or the opti spark. If the the water pump is not leaking out of the seep hole then the pump is still good, but it will have to come off when you go to change the opti spark, just remember to get new gaskets and seals.

 

Well, I replaced the optispark...almost done putting it all back together. I think the mechanic that said I had low compression was trying to rip me off. He gave me a quote for $2200 to rebuild the cylinder heads, and when I told him that I couldn't afford that at the time he offered to buy my camaro from me. I said no way. He just seamed kind of shady. Anyways, thanks for all the help...