I have a dear friend with a 1997 Couger that is misfiring on plug 3 & 5 the car stumbles, car has hardly any power, cuts off at stops when warm and runs like crap. He has been fighting this for years. Four years ago he had put 8 gallon oil diesel in it by mistake (gas station had wrong fuel in tanks) It has been running poorly ever since. (gas station paid to have diesel removed at the time.

He has replaced coil packs, wires, plugs, computer (two years ago). He is not getting any sensor codes just misfire codes on plug 3 & 5. He has good flow out the exhaust so maybe not the cat. Any Help would be appreciated.

Thanks

Scott

 

Tell him to swap the coil packs around,and see if the misfire codes follow it to the alternate cylinders.
I'm betting bad coil pack,or possibly plug wires.
JL

 

They have done that and get the same results. I keep telling him to switch too Motorcraft wires but, he thinks all wires are the same.

 

What do the plugs in those two cylinders look like? Perhaps valve seals leaking are fouling the plugs. Has a compression test been done on the engine?

 

Either replace #3 and 5 injectors or get all the injectors cleaned.

It's the only thing that hasn't been changed, and I bet there's diesel oil in them.

The holes in the injector nozzle are so small that the surface tension of diesel fuel will probably keep the injector from squirting correctly. The injector might also be squirting but the atomization isn't as good.

If you're really frugal, you can move the injectors to other cylinders first and then see if the misfires move with them. Just remember to relieve the fuel pressure first

In my opinion, except for spark plugs, there's really no reason to use Motorcraft over other brand-name aftermarket parts.

The other thing I'd check is if you have the correct fuel pressure, and that the fuel pressure regulator is functioning properly.

Report back, or just ask more questions... we'll keep working with you on it