Fox Help with issue after driving >1hr and high RPMS

cuhud

Member
Jan 15, 2020
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burleson Tx
I've a 91Fox - Automatic/4.10 gears with a 306 Unknown Miles / Great shape from what I can tell - Edelbrock RPM heads - E-Cam - TFI - BBK CAI - 24lb Injectors with matching MAF - Stock Ignition - Stock fuel pump - Adjustable FPR - BAMA Tune ( I Know) - Tuned for 93 octane

I've own this car for 3 years, so anything else that may help just ask, I'm sure I'm missing something. I'm leaning towards something in the ignition area but before I start replacing stuff and testing everything I wanted to see if I can get some opinions.

So I have 2 issues -
#1. This has been going on since I've had the car but has become worse. After driving for over an hour or so it gets heat soaked and I can fell the loss of power and when its at idle, it sounds like its missing. During the first hour or so it runs strong and sounds great at idle. Doesn't randomly die or cut out and will start right back up if I shut it off. I'm positive it has the original distributor.

#2. This has just recently started within the last 6 months. At highway speeds over 70mph and around 3500rpms it sounds like its breaking up with loss of power. Doesn't buck or act like its going to die just like its running out of steam.

This is what I have done so far. New plugs and Wires - New rotor & Cap - Timing set at 12 - No codes I just pulled them - No CEL - No vacuum leaks / Smoked tested. TY and go easy I'm still learning my way around foxbody's
 
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KRUISR

5 Year Member
Apr 16, 2015
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Sounds like the TFI module to me. Especially because it starts having issues after it gets hot. Any corrosion around or behind the module on the distributor?
 
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limp

wrap a little cheese around it and its a done
Oct 4, 2020
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410 gears at 70 MPH is your problem......
 
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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Most likely TFI/PIP or Ignition coil related.

Sometimes the TFI/PIP generates a code, but typically not. They cause similar symptoms to what you have. It's becoming a more and more common issue as these cars get older and the replacement parts on the market are.....crap.
 
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CAMTWO1070

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Dec 17, 2021
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Seems like your injectors are too small and maxxed out on duty cycle so the engine starts to thermally heat up at the valves overheating them.....

What are you running for a fuel pump?

Everyone says going with 1 size larger injectors than is needed is bad,, It's not...It changes the duty cycle and the linear cycling of the injectors making it easier to tune in the engine for idle quality and start up plus always have the engine covered for fuel...

Do you have a Wideband 02 controller?..

I have a QH chip and on pin #27 on my ECU I have an AEM wideband 02 controller always keeping my tune in the sweetspot or throw a code to let me know theres an issue......

Back in 92 when we first hopped up a brand new one we swapped out the timing chain,1 up injectors,and dialed in the camshaft plus put a 340lph pump in the tank plus an adjustable fuel regulator then a set of 1.7 rocker arms and a custom tune...No exhaust or intake mods either and we were spanking brand new vettes all day long....LOL