Bad Miss And Stumble On 91

[Agent 86]

Happy holidays everyone
I'm trying to help diagnose a bad miss and stumble on my boss's son's 91. It happens around 3000 rpm under load only. It's currently sitting at a local shop where the problem has stumped them so far. No codes, they replaced the crank trigger and ignition module with no cure. Plugs and wires are good. They cannot reproduce this stumple in the shop as they have no dyno to do a load test.

Any thoughts on what to check and test before these guys just throw more parts at it in an attempt to repair.
Thanks

 

[Positive Vibes]

The only time I've had symptoms similar to yours was when my vacuum lines came off the little "vacuum tree". I guess what was happening was the modulator in the tranny was bad and I was sucking up tranny oil into the tree. The hoses got loose and would come off. Other than that, I dont know seeing how you don't have any codes. There are some easy stuff like cleaning the MAF, changing the IAC, changing the FPRC.

 

[MrShorty]

Earlier I assumed when they said "no codes" that means that they get all pass codes. I've decided not to continue with that assumption. Do you know if they are truly getting no codes at all or if they are getting all pass codes? No codes at all is a fault condition that shoudl be investigated. All pass codes suggests that the fault is in something not directly monitored by the EEC-IV computer. Check things like fuel pressure (road test might be necessary), vacuum leaks, etc.

 

[Agent 86]

Well they fixed the problem and say it was the module. They already said the new trigger and module didn't cure the problem but some how now it is the module.
Good news is they returned the trigger and module and installed a used module for $70 cad and only 2 1/2 hours for all the messing around they did. Could or could not have been as painful at the Ford dealer :mattmoon:
Thanks
Happy Holidays