Hi,

I'm not new to the forums, but It's been a Long time since I posted. I tried to revive my old account but FTE doesn't recognize my email address so I had to re-register

Anyway I have a friend with a Mazda Navaho. 1991, 5spd transmission

It jerks intermittently, and sometimes quite severely. Myself, and 4 other ASE mechanics, and 1 "old ford guru" are stumped. We know we have ruled out the clutch for sure....

We think It started when my friend put a clutch in it. He did not have the flywheel turned . When we looked at it, we were all convinced this was the issue....drive test and dumping the clutch in and out at cruising speeds could replicate the issue. However, he had just bought the truck, and it needed a clutch, however the jerking we think was happening before, but we didn't know as we couldn't drive it till we put the clutch in it.

So we re-did the clutch...had flywheel machined, and got a warrenty replacement clutch just in case, and put it back together.

Same issues. so we checked, and tested, and think we ruled out the following to make this post shorter.

1. Fuel pressure test- passed, no issues
2. Checked fuel regulator for leaks - none
3. Checked for and found no vacuum leaks-none
4. Swept, and actually replaced (3 times) the TPS -is working fine
5. Replaced the MAF - Thought we had it, as we disconnected the MAF and jerking seemed to go away instantly...however few days later jerking returned, and driving with MAF unplugged still jerking.
6. Replaced Ignition Module, checked coils, plugs etc...actually replaced plugs and wires as well
7. Disconnected Transfor case plug to make sure it wasn't the issue as well.

I really don't know what else to check. The motor runs fine, the trans shifts smoothly...the clutch is new and was done correctly. I run a small auto shop, and we have access to Mitchells, All-Data, and Identifix....all were no help. It seems you try and research jerking and hesitation all the hits come up for Auto trans and Torque converter lockout issues. This truck is a 5 spd

Gentlemen I am out of ideas...and so are the other 4 techs as well as the Ford Guru

I have owned many Aerostars back in the day (loved em, same 4.0) and I have never seen this

the jerking is random and intermittent...symptoms would be similar to a small child flicking a light switch on and off rapidly when it does it. power, no power, power, no power, and rapidly...it feels like someone herky jerking on the clutch but we have ruled that out....its definitely electrical.

Also, and naturally, even though it is Obd I we have checked and there are no pending nor stored codes....PCM thinks everything is hunky dory.

No backfiring, no smoke, no misfires....runs like new except this perplexing issue.

Help?

 

Since unplugging the MAF seemed to cause the problem to go away, I'd say you shouldn't be so certain that you don't have a vacuum leak somewhere. Carefully inspect the intake air tube between the MAF sensor and the throttle body. Check all the little accordion folds for cracks in the valleys. Make sure it's seated properly at the throttle body. If you or one of you buddies has access to a smoke machine, try that.

-Rod

 

It worked initially...We thought we finally licked it

2 days later jerking again...unplugged the MAF this time and no change, still jerking

Car runs wonderfully otherwise, which is what is so puzzling....I have acess to a smoke machine...we found no vac leaks

stumped

 

Have you looked at the live data yet?

 

It's an OBD I system (1991)

I have no way to see Live data with that...just with OBDII

 

Make sure the harness connector at the firewall is tight, and the injector harness on the engine. Look for damage on the cam and crank position sensor wires, those are really low voltage and a slight nick can cause a loss of signal.
Other than that, maybe water in the fuel?

 

I don't know if this is a common problem on Fords, but it is on Hondas and I think it would have the same effect. Honda Accords have a known problem with the ignition switch going bad. Usually, it's an intermittent problem, unless it's ignored until the switch fails completely. Have you monitored power from the ignition switch?

 

I have a scanner that reads my 1993 OBD-I Explorer.