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Discussion Starter · #1 ·
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?
 

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Right around 2001 or 02 I had a similar issue. Car would start running very poorly until I pulled over, shut it down, then restarted it.
It seemed random and there were no codes, but I finally realized it was water temp related.
Swapped in an ECT and it went away.
 

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Discussion Starter · #3 ·
Right around 2001 or 02 I had a similar issue. Car would start running very poorly until I pulled over, shut it down, then restarted it.
It seemed random and there were no codes, but I finally realized it was water temp related.
Swapped in an ECT and it went away.
I don’t think my car has one lol it’s a 5 speed
 

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87 Gt 400hp Holley Terminator, Systemax 2, TW 170cc, N41, 6psi Powerdyne, 3:73
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Just replaced the tfi module in my 87 Gt. Fired up great cold and then went to a hot no start. Changed the tfi module and have not had an issue since.
 

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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!


Sent from my iPhone using Tapatalk
 
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you can keep it running by keeping the AIR pedal open, correct?

kinda rules out spark or fuel or compression,,,,,,dont you think?????

by keeping the AIR pedal open, what do you think the engine is missing?
 

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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.


Sent from my iPhone using Tapatalk
 

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Discussion Starter · #11 ·
you can keep it running by keeping the AIR pedal open, correct?

kinda rules out spark or fuel or compression,,,,,,dont you think?????

by keeping the AIR pedal open, what do you think the engine is missing?
I don’t know if it’s “missing” anything per se, but I’m guessing from the way you worded it that it’s an air intake/idle set issue? So does this point to the IAC?
So what do you think is happening and how do I fix it lol
 

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if it doesn’t run

ITS missing something, that is not up for debate

AND NO, i am not going to spoon feed you, you are going to put your diagnostic hat on.

so, again, if it requires you to ADD AIR to keep it running

what is it missing?
 

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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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there is no gas pedal

i seem to think, the OP is mixing it up with a carb
 

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Discussion Starter · #14 ·
if it doesn’t run

ITS missing something, that is not up for debate

AND NO, i am not going to spoon feed you, you are going to put your diagnostic hat on.

so, again, if it requires you to ADD AIR to keep it running

what is it missing?
Come on man I’m just trying to learn. This isn’t a class at university lol I’m just asking for help fixing an issue. My other car is also undriveable because the alternator died and I’m also working on fixing that. So I am in a tough spot and if I can get this fixed it would make my life a lot easier, and the lives of those who depend on me.

Based on the fact that it only exhibits symptoms at idle, I THINK it’s not getting enough air at idle, which leads me to believe it’s the idle air control valve. Based on the similarity in how it cuts out is much like the way it cuts out when the AC is on and I’m coming to a stop, it would make sense that this is the issue. So I’m guessing I need to clean or replace the IAC. Beyond that, based on the fact that it only does this once the car has some temperature in it, my guess would be bad feedback from a sensor once it goes into closed loop.

I am still unsure because it doesn’t idle low, idles perfectly (for a cammed engine) until it just dies. If it was just not getting enough air at idle, I’d expect it to stumble and sputter before dying. Maybe with the cam it doesn’t even have enough vacuum to do that?

Am I close?
 

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you will learn, dont worry!

no amount of begging or sob story, is gonna get ya spoon fed.

so dont waste valuable time on that.

if the IAC was the issue, how could it start and run cold? it needs more air and fuel cold.

what test can we do do prove it, when cold?
 

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Discussion Starter · #16 ·
you will learn, dont worry!

no amount of begging or sob story, is gonna get ya spoon fed.

so dont waste valuable time on that.

if the IAC was the issue, how could it start and run cold? it needs more air and fuel cold.

what test can we do do prove it, when cold?
It would start and run cold because of the fuel trims in the open loop cycle. Either that, or it’s on the verge of failing completely, and somewhere in the system there’s a part that expands just enough to exacerbate the issue to where it starts stalling.

I plan on starting it up when cold and unplugging the IAC to see if the car dies. If it keeps running and potentially doesn’t stall (despite probably exhibiting some surging) I’ll know it’s the IAC
 

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good test, but does NOT mean bad IAC
 

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do the test, i said it was good, why are you even thinking maf or tps?

STAY THE COURSE! ONE THING at ONE TIME!

report what you find.

and stop!! with the excuses
 
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