Tracking down a miss in my 4.5

[Litton]

I have had a miss in the engine ever since I bought the car and today it was time to track it down. The miss occurs all the time hot or cold.

Pulled the spark plugs (Bosch Platimum) and 7 are nice an clean near the tip but black lower down the insulator. I have leaned the MAP back a bit. One plug (#5 cyl) is completly black with just a smidgen of white right at the electrode. To me this says it is trying to fire but can't quite do it. I checked the spark plug wire and all have 1,280 ohms resitance. The cap is new and the pertronix ignition and high voltage coil are also new.

I also had all the injectors cleaned and tested to factory specs by a Bosch service center.

Any thoughts would be greatly appreciated.

[Tomguy]

The platinum plugs are resistor plugs - I think I measured them at 5K ohms at one point. The ones that should be in there - copper core - have ~0 ohms of resistance (nothing has absolutely 0 but you get the idea).

Wires themselves are supposed to be non-resistor. Mine measure at about 0.5 ohms each.

The plug boots are 5K ohms, the cap connectors are 1K.

Typical setup should have ~6K ohms of resistance from cap to plug electrode. Yours has about 12K ohms of resistance. I can't say this is definetly the cause but it's possible.

Have you checked valve clearances? It's also possible that one of the valves (or more) don't close all the way, thereby reducing compression in that cyl to a signifigant degree.

[psfred]

Leaking injector on #5.

Also check compression, you may have a bad valve.

Peter