Hi everyone, my '88 300 w/5spd just developed a miss throughout the driving speed range. Although you can hardly feel it except for an occasional hiccup and some pinging under load(up a hill) what is most noticable is the tachometer swinging madly up and down even at idle which seems as smooth as it ever was. This truck has been running great. It does have 140,000 miles but I have cared for it well since new. I replaced the spark plugs, wires, cap, rotor, pcv valve, oxygen sensor, EGR valve, and Ford cleaned up the throttle body at 20,000 miles ago. Fuel filter was changed 2000 miles ago. Think this is an ignition(electrical) problem or more serious compression problems? I realize I'm probably going to have this scoped by a shop, but wondered if anyone might want to venture some ideas. Thank you.

 

Danny ,
Sounds like you have a coil / coil wire problem ? Have you run thru any deep water lately ? Start the truck in the dark , open the hood and see if you see any sparks jumping around in the area of the coil , cap or wires . Ive had a new plug die before ,spark was jumping out from under the spark plug boot to ground . Id just give it a careful inspection before you give Ford $50/ hr to diagnose something that you could fix for a lot less .
Paul

 

Besides my 2 ford trucks, I have an 89 5.0 Camaro RS. When the ignition wires, go bad, it run's like crap. I diagnosed that it needed new wires after seeing a bunch of sparking near the distributor cap. Once it had new wires (cap and rotor), it ran WAY better. But one of the wires wasn't properly loomed away from the exhaust manifold, it burnt, and just one bad wire made the motor run rough. Again I opened the hood in the dark, and it was sparking away. I tied it back (and eventually replaced) and life is good again. BTW Just try and do something as simple as changing wires and plugs on the Camaro. I love the accessibility of my old Ford trucks.

 

If the tach is an aftermarket unit, I would suspect the ignition coil first because the tach is hooked to the negative side of the coil.Try disconnecting the tach from the coil and redrive the vehicle to eliminate the possibility of the tach itself. A coil wire could be the culprit also, but the coil itself is probably damaged as well.If it is a factory tach,and is like that Escort that drove me nuts a while back, the tach is driven by the computer,and it just so happened it was the computer that was bad. Talk about feel unsure when you tell the customer you would like to try a new computer, but not sure about it, but that's the only thing you haven't tried yet ! But I still had to rule out the module and PIP(coil pick-up)and harness to the computer which is pretty basic when chasing an ignition miss. I seem to remember getting a check engine light only when the tach & engine would act up, never a continous code.

 

 

I had the same problem with my old 83 Prelude.

Take off the distributer cap and roter, One of the teeth on the little cam was broken off and stuck to the cam, I think it is magnetic. Check that out first!

jmartin60(No Email Addresses In Posts!)