Possessed 944

[alphaspeed]

I have a 1984 N/A 944 that has a intermittent misfire on start-up. I have isolated it to the # 4 cylinder. I have done a full tune up on it and have tried 3 different types of plugs and nothing has worked. The only other thing I have done to it is a compression check. It also s a hesitation problem when I floor it and it has an idle stumble when I left off the gas and at idle where it will also sometimes rev up and stay for a little bit. Any help on any of these will be much appreciated.

[SoCal Driver]

Spark plug wires.

Injector.

Debrise in the fuel rail.

Low or high fuel pressure/delivery rate.

Broken wire in the injector harness.

Broken connector at the injector.

Air leak at the intake manifold to head.

Air leak at the injector to the head.

What procedure did you use to isolate the problem to #4?

[alphaspeed]

I first pulled the plug wire and then I grounded out the wire and both times there were no drops in RPM's.

The wires are brand new Jacobs and work on all othe cylinder (I swapped the wires around to make sure).

[SoCal Driver]

Check the compression.

Check the injector connector for voltage with the key on. One side will have battery voltage the other a bit less as it comes through the other three injectors. Note that all four injectors fire at the same time -- twice per combustion cycle.

While the Beru/Bosh wire set is pricey I prefer them. You can just replace the wires should the four resistance ends be ok.

Also pull and check the dist cap. May be cracked -- even if it's new.