Hey guys, just got a 1988 mustang convertible. I know its off topic, but i ran in to a problem i can't solve. I replaced the engine, and its missing. cylinder number 4 is missing. I replaced the spark plugs, wires, cap, rotor. When i pull the wire off when its running, i can see the spark grounding to the engine. I replaced the fuel injector, and still missing. I tried to adjust the ignition timing, but it still misses. I know i have the correct firing order. Would any of you know what the problem could be? I would appreciate any help.

Did you check compression in that cylinder ? You may have a burned valve. If your compession is good look for a vacuum leak.


Kurt

The cylinder has good compression. I can't find a vacuum leak. I see a spark when i pull the wire off, could there be bad voltage to the plug?

Is it running points or electronic ignition?

check the wiring to the fuel injector , you can get a noid light that will plug into that injector harness, if it flashes with the motor cranking or running the harness is good.
Check mechanicals,......bent push rod, broken valve spring, ect....

The engine is single overhead cam. Would the cylinder get compression with a bad valve spring or bent valve? I checked the injectors by pulling the rail out and cranking the engine, they are all spitting fuel. I replaced the ignition module and ignition coil, but no luck yet. I don't get why the cylinder can't be firing. It's got compression, fuel and a spark? Any more suggestions? Thanks.

I have had a similar problem with the same engine. It turned out to be a leaky intake gasket on the intake runner of the problem cylinder. If you have access to a small propane or butane bottle, turn it on and hold it around the intake gasket area. If the idle picks up and the cylinder no longer misses (b/c that cylinder will now have fuel), you have found your problem.

Are you talking about the intake manifold gasket, the one that connects the intake with the head? Thanks.

Yup, that is the one. If you go all around the intake manifold gasket area with propane, you will find out right away if there is a leak. This area of the intake manifold is always under vacuum, and combustable gasses will be sucked in the intake plenum (through the leaky gasket) and be ignited.