Question for Mechanics????

[kevin]

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.

 

[Kurt]

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


Kurt

 

[kevin]

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?

 

[darb]

Is it running points or electronic ignition?

 

[Kurt]

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....

 

[kevin]

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.

 

[donsonn]

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.

 

[kevin]

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

 

[donsonn]

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.