5.0 Missing Under Load When Hot

[Bigeasy08]

I'm a little stumped with this one. I have a 1990 foxbody with a 306 H/C/I. The car ran fine until i swapped the T5 out for a TKO 600. Now it is missing pretty bad at low RPM (<3500) under a load but only when it is hot. I assume it has to do with the way the car determines the air/fuel ratio in closed loop, but when I unplug the MAF it idles like crap and runs a little rough, but the miss mostly goes away when I accelerate under a load.

I have done the following:
- Replaced O2 sensors
- Replaced Plugs
- Replaced Plug wires
- Cleaned the MAF (with actual MAF cleaner)

It has an almost new cap/rotor, coil, MSD box, fuel pump, and the injectors/MAF sensor are not too old either. I am just trying to figure out what could have happened during the tranny swap. I looked at the vacuum lines along the intake and did not see/hear anything obvious. It will buck/skip/sputter pretty bad under acceleration in any gear less than 3000RPM..if I give it gas past 3000RPM, the miss/sputter will go away and the car will pull and run great. I've done web searches and can't seem to pin point a common problem. Any help is greatly appreciated. Thanks guys

 

[clement]

that's a common TFI module issue. the trans swap could just be a coincidence.

 

[jrichker]

The TFI module mounted on the distributor is usually the culprit for a high speed miss on a warm engine. If the problem does not occur when the engine is cold, the TFI module is definitely suspect. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

View attachment 126346

See Automotive Tools Specialty | Auto Mechanic & Technician Diagnostic, Testing Equipment | Thexton

diagram courtesy of Tmoss & Stang&2Birds

 

[Bigeasy08]

I suspect it could be the TFI module. I have been down that road before when using an old unit off a parts car. But I had always remembered TFI modules as either working or not working. And this is a low speed/low RPM miss. The diagrams are awesome though, I will definitely run an Ohm meter on it when I get home and see what it says.

 

[clement]

a while back I was looking through my storage building and found a half dozen stock tfi distributors I have collected over the years and forgot about. I hit the junkyard lotto.

 

[Wldstang88]

Clement do you still have the stock distributors you would be willing to sell. I suspect I have a bad pip in my stocker. Ill be driving down the road and the car will sputter then die, it will not start up it will crank but not start untill it cools off. I replaced the tfi but I suspect it's garbage also as it is an cheap aftermarket. I just put in a 331 stroker

 

[84Ttop]

Clement do you still have the stock distributors you would be willing to sell. I suspect I have a bad pip in my stocker. Ill be driving down the road and the car will sputter then die, it will not start up it will crank but not start untill it cools off. I replaced the tfi but I suspect it's garbage also as it is an cheap aftermarket. I just put in a 331 stroker

Dear grasshopper,

This should be a new thread, or kindly pm him
High jacking threads is never cool

 

[Wldstang88]

Dear grasshopper,

This should be a new thread, or kindly pm him
High jacking threads is never cool

Wow really I'm not high jacking threads I was just simply asking a question and I stated why that's all. That grasshopper s**t is not needed. And all you had to do was come at me a different way about this.