1991 5.0 missing when hot

[roc-e]

My 91 5.0 runs fine at first startup and until it gets warm. Then, under, load, from light throttle to full, it'll stutter/hesitate/sputter/miss. It's not violent, just noticeabe, annoying, and power-sapping.

If I turn the car off and then restart it, it'll run okay again for a very short time before the miss rears its head again.

I have an intermittant check engine light. The only code I get is a code 94.

I've done the following to it already:
Replaced coolant temperature sensor (got rid of my code 21)
Cleaned MAF
Cleaned TB
Cleaned IAC
Checked and reset TPS
Tried driving with the EGR unplugged (no difference)
Changed both upstream oxygen sensors

So to me, the stutter seemes to be happening only in closed loop and/or when the engine is hot.

Any ideas? I'd really appreciate it.

 

[2000xp8]

Problems when hot are usually a sign that TFI module has had it.
Although first i'd check your cap and rotor.

Do not replace the cap, rotor or Tfi module with any chain store crap parts, or you will be doing this again in 6 months if it fixes the problem.
Motorcraft or ford cap and rotor, and Definetely a ford TFI module, don't be tempted by any aftermarket module upgrades, they are garbage too.

 

[nthorpe01]

What was the result? I am having the same problem on my 92 LX.

 

[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 198938

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

 

[crickifur]

Tfi could be it true, but any faulty ignition part will misfire when hot, plugs, shorted wires, cracked cap, corroded wire, bad coil... RPM goes up, dwell time is shorter. Ign circuit resistance doesn't allow the voltage to build up in the coil or transfer properly in the secondary... just my $.02

 

[347STROKER50]

replace your ignition module when things get hot they expand thats whats happening inside your module causing your miss when it cools off it retracts making good contacts again

 

[SlamminGears]

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 198453

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

What exactly do you mean by a high speed miss? Mine sputters at 4k at WOT, once at 5k its stops.

 

[jrichker]

What exactly do you mean by a high speed miss? Mine sputters at 4k at WOT, once at 5k its stops.

Start your own post and I will try to help. Hijacking someone elses post is bad manners.

 

[BlackFox93]

Mine was doing the exact same thing when I first bought it, turned out it was the distributor itself. Replaced it and havent had a problem since

 

[SlamminGears]

Start your own post and I will try to help. Hijacking someone elses post is bad manners.

well i'm pretty sure I'm having the same problem the OP is. I'm not jacking anyones thread. Why should I start ANOTHER thread for the SAME thing. I'm sorry for inquiring as another fellow mustang owner. I'm not trying to start any crap, nor do I want to recieve it. Now if anyone else has suggestions, I'm curious if a solution was found and what fixed the problem, which is the origional reason I posted to begin with.

 

[globaltefl]

My 90 5.0 craps out at about 4500rpm. It has a new Mallory ignition and new MSC coil. Could it be the wires? What else, unless the new TFI on the Mallory isn't good?

 

[2000xp8]

My 90 5.0 craps out at about 4500rpm. It has a new Mallory ignition and new MSC coil. Could it be the wires? What else, unless the new TFI on the Mallory isn't good?

Any aftermarket distributer and/or tfi is always suspect.
None of them are as good as original ford units.
I'd take a junkyard original over an aftermarket new any day.

 

[globaltefl]

Except it's the original equipment that failed.

 

[2000xp8]

Except it's the original equipment that failed.

Ya, after what 150,000 miles?

 

[globaltefl]

No, actually under 100 mi.

 

[smokin joe]

Hate to sound basic here but I had a similar problem with my 86 GT. I had platinum plugs and when I went back to copper plugs it ran much better.