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1995 F150 Lightning
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408 Posts
1991 5.0. HCI, all kinds of bolt ons.

I need to preface this by saying I do NOT think the issue is related to a burnt TFI or anything in the distributor. The car fires up IMMEDIATELY on the first crank, every time.

The car has recently developed an issue. I have not changed anything with the car prior to this issue developing.

The issue im having is as follows:

From cold, the car will start and idle just fine for approximately 3-5 minutes, and then it will just shut off. It will NOT stumble, search or sputter. It just shuts off. Once it’s got a little heat in the motor, it won’t run for more than 10-20 seconds before it will shut off on its own. But it will fire back up immediately every time.

Fuel pressure is 35ish, 40 without the vacuum line. The car will rev up just fine and doesn’t make any noises that suggest a vacuum leak or anything. No other signs of a problem.

If I keep my foot in the gas, I can keep it running indefinitely.

I’m guessing it’s a sensor or something that once the car goes into closed loop, it triggers and tells the car to shut off. But I can’t figure out what it is.

MAF?
IAC?
TPS?
O2 Sensors?
Stock computer?
Do you have a MSD box? If so I would unhook it and try without it. Mine did the same thing and was very annoying!


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Registered
1995 F150 Lightning
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408 Posts
Nope, stock computer too
Sorry missed that you could keep it running with your foot on the gas. Mine would not run at all no matter what when the msd box went out.


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1995 F150 Lightning
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408 Posts
For what it’s worth, I just spent about 20 minutes closely checking all the vacuum lines and electrical connectors (just visually). Everything looks brand new.

I may have reached the end of my competency here. I plan on having it towed to a shop next weekend. Otherwise I’m just gonna be throwing parts at it.
Have you tried to pull and clean the IAC? I would do that first. Certainly wont hurt. You can also look to see what its doing(or not) with it taken off and plugged in by turning the key fwd but not starting.


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