Bucking Bronco Ignition

haroldj

Registered User
I have two 1990 SC's, one 35th anniversary edition with 60k miles and a silver one I have from new with 135k miles, both automatics. I purchased the 35th anniversary edition with 56k miles a few years ago. Many years ago at 62k miles, the silver one gave the Ford dealer fits and took about a week to repair the bucking ignition. I asked the mechanic what the problem was and he mumbled something about the crankshaft sensor. I changed the plug wires and plugs on the silver one at 120k miles and in a matter of months the bucking started again. The result was poor quality plug wires after having gone through the sensors and DIS again.
Now my 35th anniversary edition has started bucking at 60k miles. The engine is basically untouched as supplied from the factory. The engine starts bucking bad and the tach goes to zero after driving a few miles. It bucks so hard you cannot accelerate but only slip it into neutral and goose it until it smooths out a bit. I figured the loss of tach would be caused by the DIS since it sends a PIP signal to the computer and and camshaft sensor. I changed the DIS and it ran worse, taking three tries to get it started. I ran it for about 5 miles and the bucking came back. I cleaned the original Ford DIS, used liberal heat sink compound and reinstalled it. I also inspected all the pins in the DIS connectors for any corrosion and they looked fine. I also pulled the crankshaft sensor plug apart and inspected it for corrosion and it also looked good. I took a small pin file and scratched around each male pin and scratched the entry on the female pins to insure better contact. I assembled the plug back together and the car runs fine at least for the 15 miles I drove it so far. I'm still at the point where I don't trust this thing. I also did a scan and a code 19 is in memory which is listed as cylinder ID fault.
My question is how do we insure good connections in our sensor plugs where very low level(Current) signals are likely to have connection failures. A plastic plug heating and cooling over time can cause movement that can damage the connection over time. By just replacing sensors are we just freshening up the connections or have the sensors truly failed?
These ignition problems are a pain. I swear I've seen more dependable ignition systems in lawn mowers.
 
With this warm weather the DIS would probably act up within that 15 miles. Cam, Crank and DIS after you have the plugs and wires done. You spoke of the crank and DIS, but not the cam.

Was and dielectric grease used? That tends to help with the loose connection issue a bit.

Aftermarket DIS modules have proven to be very unreliable.
 
The cam sensor feeds the DIS, not the other way around. I solved to bucking and tach issue an my now dear departed Anni by changing the cam sensor. Not expensive and it drove like new again. You said it takes three tries to get it started. That is exactly what you do if you disconnect the cam sensor. It can take up to three tries to start because the computer has to figure out what's going on. It bucks when the cam sensor shorts out.
Alan
 
The engine starts bucking bad and the tach goes to zero after driving a few miles. It bucks so hard you cannot accelerate but only slip it into neutral and goose it until it smooths out a bit.
Replace your cam sensor. Disconnect it first if you need proof. Read up on the topic regarding how to start the engine with it disconnected.
 
Thanks for the help. I have a new Ford Cam sensor. I'll try changing that.
I didn't see any dielectric grease inside the plugs. Should I add it?
 
I would just do the cam sensor first and see how that effects it.

You should always change one thing at a time. You would never know what the culprit was without doing so. That's why I get so nervous when rebuilding an engine. Sometimes my gut tells me to replace a bunch of the sensors and such like O2's, cam sensor, crank sensor, etc. but then if the engine doesn't run well from the start it leaves you scratching your head and guessing as to what may be the cause. It's always easier to have a good baseline then begin to make your changes.
 
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