Mechanics

VIOLENT "JERK" WHEN ACCELERATING

1994 Ford Ranger

Engine Performance problem
1994 Ford Ranger 4 cyl Two Wheel Drive Manual 150000 miles

Prob: When driving usually accelerating, my truck will jerk very hard for a split second. Sometimes will stall, most of the time it won't. Also has jerked and stalled on me while on the freeway doing 65 mph. I coasted turned off all accessories and after 3 or 4 trys got it cranked up again. The jerking is very random and really scares the crapp out of you cause you never know when to expect it.

History: Prob statred with check engine light. Would idle rough when AC kicks on, voltage drops and wants to stall. When AC kicks off, idle goes up and runs fine. Took it into my mechanic. Gave 2 codes EGR bakcflow (hoses were missing, so I replaced) the EGR vacuum was tested and good. And coil pack code (replaced and the engine light still came on, made no difference. So I returned the coil packs and put back on originals) Engine light still on. Mechanic was puzzled. Then said it has to be ignition module, replaced and the engine light went off and drove fine, but occasionaly has the AC idle prob and the jerking thing. Replaced to the ignition module for another, still doing above mentioned probs. Got a 3rd ignition module this time a Motorcraft brand. Still doing the AC idle and jerking thing. He said put on the original ignition module. I did and the jerking thing goes away, but engine light comes on and the truck runs like crap. Put motorcraft module back on. He tested the fuel pressure and he said it was fine. The last thing he suggested is switching the exhaust coil pack with the intake coil pack. He is trying to save me money by not buying parts I dont need. Other than the AC idle prob and the jerking thing, the idle is smooth and the engine has great accelerating power, runs very well, best it ever has, accept the darn AC idle prob and the jerking prob. Any suggestions?
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Jgarcia281
September 8, 2010.




Hi
Is the jerk like the engine cuts off then back on again? When it dies have you been able to pull a plug wire and check for spark?
Let me know

Docfixit
Sep 8, 2010.
It is just like it cuts off for like literaly a split second. On the freeway it will be more of a gentle jerk and then wont respond to th gas pedal for a few seconds and then all the lights come on (battery, check engine, check oil)----exactly like when you turn the ignition half way on before you start.

When it dies I have not been able to check for spark. Do you mean like jump out of the truck and pull off a wire boot to see if its arcing? The stall is so random that Im usually driving in traffic and cant really check the spark. And the jerklasts just a split second.

My gut tells me its the fel pump, but the mechanic said the fuel pressure is good. Im wondering how you can test the fuel pressure while driving. The jerk doesnt occur unless you are drving. Although the AC idle prob oinly presents itself while stopped and idling. Oh I have replaced the idle air control valve to solve that, but it didnt work.

Tiny
Jgarcia281
Sep 8, 2010.
Has ignition switch been check out as possible cause? Can you wiggle key and get engine to cut off and on?

Docfixit
Sep 8, 2010.
That I have not checked, I can check it and get right back to you!

The question about wether the engine turns off during the jerk is a tricky one. The best I can describe it is that the engine bogs down. The more I think about it, its too hard to tell if the engine turns off because it happens so quickly.

I will go check the key thing you mentioned above.
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Tiny
Jgarcia281
Sep 8, 2010.
Key ignition seens to be working fine. Wiggled it up and down back and forth slightly turning and it would not cut off the engine.

Tiny
Jgarcia281
Sep 8, 2010.
Any other ideas? Any suggestions on something else I should check?

Tiny
Jgarcia281
Sep 8, 2010.
Try cleaning MAF on air cleaner box use MAF spray cleaner. Also PCM relay maybe droping out and that would shut injectors and spark off if it reset and your foot was on accelerator it would jerk

Docfixit
Sep 8, 2010.
Is the PCM the same as the ECM? I can't seem to find a " PCM" on my truck, thanks for the suggestion. I will let you know what I find out

Tiny
Jgarcia281
Sep 8, 2010.
I found an EEC relay but no PCM realy, I looked in my Chilton and I do have both EEC-IV and PCM. So to be clear should I replace the EEC Relay?

Thanks

Tiny
Jgarcia281
Sep 9, 2010.
Yes EEC is it Ford mixes its terminology
Cleaning MAF may help with AC idle

Docfixit
Sep 9, 2010.

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