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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 09-02-2014, 09:40 PM   #1
mechguy

 
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Vehicle: 1991 ford mustang GT 5.0 with sunroof
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Question in gear engine stops running, no roughness, no noise, no warning.

Have been fixing my 1991 5.0 mustang myself for 14 years to over 3,000,000 miles. But I still need help..

I can start the engine just fine and it runs smooth. But after I drive around the block about 6 times still in gear engine stops running, no roughness, no noise, no warning. I pull over. Turn the key engine stars fine then runs smooth for about 3 seconds then shuts off. Turn the key engine stars and immediately shuts off. and so on. Wait 4 hours and repeat. I can also repeat this buy just running the car in my driveway for a while.

So far I have checked:
engine light is off
fuel pressure is 33 psi running and when failing. (seams to be within spec of 30 to 40psi)
timing is between -1 and -2 depending on rpm.
slightly warm engine the ECT sensor reads 17k ohm and the leads read 21k ohm. (i don't know if thats normal)

Please advise.
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Old 09-02-2014, 11:41 PM   #2
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wait to hear from some smarter guys here, but it sounds alot like a problem i have with my 95gt. i havent fixed it yet because the engine is apart, but seems most people say it is the TFI module or whatever its called for the distributor. it seems mine is on the fender, while for your car it may be on the distributor itself. apparently they go bad and when they got hot, the engine shuts down (no more spark).

now, this is slightly more than a guess, but its where im putting my money
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Old 09-03-2014, 08:00 AM   #3
88 orangepeel notch
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+1 ^^^

That's a good place to start. Pull off the TFI and have your local parts store test it 3 times in a row, so it gets good and hot.

One other thing that has cured a similar problem for me is check all your grounds, they need to be clean and tight.

After that, pull codes to see what's stored. Just because there's no light, doesn't mean all is OK.

Let us know what you find.
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Old 09-03-2014, 08:23 AM   #4
dawson1112
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3 million miles ?? holy bat smoke lol

It could well be the TFI, but generally they will start to give warning in the way of bucking and kicking until they get so hot that the car just shuts off. And then they usually wont start right back up smoothly.

What your describing almost sounds fuel pump related, but if your sure that your at 33 psi even when the failure occurs I guess it rules that out. I wonder is there a way for you to install a fuel pressure gauge that you can read while your driving so you can monitor fuel pressure in real time?
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Old 09-03-2014, 09:46 AM   #5
mechguy

 
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Lol 300,000 miles. I guess I a little "0" happy.
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Old 09-03-2014, 10:02 AM   #6
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Quote:
Originally Posted by dawson1112 View Post
3 million miles ?? holy bat smoke lol

It could well be the TFI, but generally they will start to give warning in the way of bucking and kicking until they get so hot that the car just shuts off. And then they usually wont start right back up smoothly.

What your describing almost sounds fuel pump related, but if your sure that your at 33 psi even when the failure occurs I guess it rules that out. I wonder is there a way for you to install a fuel pressure gauge that you can read while your driving so you can monitor fuel pressure in real time?
Yes my fuel pressure gauge can be read from the drivers seat. but the hood must be open so no real driving. But i was able to run the car for a few seconds after it was warm until failure with the gauge installed. And it stayed at 33psi when running and during failure. it also jumps to 45 psi when ignition is first turned on which is also normal.

About 3 years ago I replace the entire distributor assembly after the magnet fell of of the camshaft position sensor. And I cant remember if i Also replaced the TFI at the same time. But I guess is stll could be bad.
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Old 09-03-2014, 10:06 AM   #7
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Do you recommend a specific manufacturer for a replacement TFI?

And i replaced the fuel pump about 5 years ago.
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Old 09-03-2014, 10:15 AM   #8
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Ya know its been a while since I replaced a TFI but I want to say motercraft if I recall that was the OEM brand.

But MSD makes them as well. I would stick with OEM though.
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Old 09-04-2014, 11:40 AM   #9
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Thanks guys I replaced the TFI module and it runs like a champ! I got the special removal tool but didn't need it. I guess when I replaced the distributor assembly I had the forethought to use standard screws instead of the frustrating ones.

Another question. After 300k I have never replaced the timing chain. how do I know if I need to? and how big of a job is that?
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Old 09-04-2014, 11:52 AM   #10
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Generally timing chains will last longer than the life of the car, But not always they do stretch out over time,

IF you put a timing light on it and watch the mark, a bad timing chain will not be able to hold the timing in place , it will bounce up and down and be very inconsistent and almost impossible to get in time. How ever at 300k I would probly just change it lol .
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Old 09-04-2014, 11:52 AM
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