[TheZ06andFoxbody]

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?

 

[TheZ06andFoxbody]

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

 

[TheZ06andFoxbody]

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.

I’m on my third TFI so I’m familiar with the symptoms, this is different unfortunately

 

[TheZ06andFoxbody]

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

Nope, stock computer too

 

[TheZ06andFoxbody]

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

 

[TheZ06andFoxbody]

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?

 

[TheZ06andFoxbody]

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

 

[TheZ06andFoxbody]

good test, but does NOT mean bad IAC

Im kind of at a dead end. I could test the TPS and the MAF the same way? I don’t know man. I know the basics but I don’t have a clue as far as electrical stuff

 

[TheZ06andFoxbody]

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

Ok here’s where I’m at.

I went outside and tried to crank it. It made crunching/clicking sounds almost like a dead battery but not quite, and wouldn’t crank. I adjusted the battery cable terminal and was eventually able to get it to start. (I have video of the noise it made).

I tried disconnecting the IAC. CEL came on, but the car would idle and did the same thing it’s been doing (dying after a few minutes).

I tried disconnecting the MAF. Same exact thing.

I tried disconnecting the TPS. Same exact thing.

I tried disconnecting the other sensor that’s in the cold air intake tube between the MAF and the TB. Same exact thing.

When I first reconnected the unknown sensor and started it with everything in place, it cranked for about 4-5 seconds before it would fire.

Observing the idle closely, it seems to sputter for just one rotation before it dies. It doesn’t struggle at a low idle, it just drops extremely quickly and dies. But prior to that, it idles at a normal RPM.

I also tried a few more times to start it and let it run with everything intact. A couple times it would fire and then IMMEDIATELY die.

My theory is that the IAC is physically stuck or clogged, and needs to be replaced or cleaned.

 

[TheZ06andFoxbody]

Engine Coolant Temp sensor. You have one.

Ohhhh I was thinking the transmission control module

 

[TheZ06andFoxbody]

you started it, then unplugged IAC, and it continued to run without any rpm drop?

what do you mean, you tried to disconnect?

Correct, and I also tried restarting it with it disconnected and it acted the same.

“Tried to disconnect” meaning I disconnected the other sensors and tried the same procedure.

 

[TheZ06andFoxbody]

when it was running and you unplugged it, the idle did NOT drop or stall engine?

this is very important to be very accurate, unless you have a scope, internet diag requires you to be extremely accurate.

i am ignoring all the other stuff you are doing, i dont diag like a chicken with its head cut off.

Honestly, it doesn’t keep running for long so I had to run around and disconnect it. It eventually stalled soon thereafter (maybe a few seconds), but not immediately.
I didn’t notice much of a change in the idle at all, it’s hard to tell with the cam it has. I did also restart it with it disconnected and no difference to how it acted otherwise.

 

[TheZ06andFoxbody]

So it doesn't run cold?

you said it did????

if your information is NOT ACCURATE, this diag will get botched, much like your HCI install

What are you even talking about? Can you show me where I said it doesn’t run cold? Where are you getting this from?

I’m not the one who installed my ****ing HCI. Honestly man what is your deal? This is what happens when people treat newcomers like **** and then wonder why the hobby is dying

 

[TheZ06andFoxbody]

what does the above mean?

i get, it dont run long enough...............

if it runs cold, why is there a issue with unplugging it and seeing if rpm drops or stalls?

is this beyond your capability?

I purposefully allowed it to get to a temperature where it had the issue before i tried unplugging it. Is that concept difficult for you to understand?

 

[TheZ06andFoxbody]

then i direct to the poster's first post

runs fine, until at operating temp

does this car get to operating temp, instantly?

My post says ONCE THE MOTOR HAS A LITTLE HEAT IN IT AFTER 3-5 MINUTES. Hope this clears things up for you

 

[TheZ06andFoxbody]

can you stop whining, and just stick to the diag?

You literally have done nothing but talk **** and tell me to figure it out. You have not offered any advice beyond trying to poke holes in what I’m saying

 

[TheZ06andFoxbody]

HOLY mother of pearl

what am i dealing with here......................

I never said to get it to temp, there is a reason

ONE MORE TIME

stop trying to jump ahead, like you know something, follow the direction to a f&^&ing T

allow the engine to cool, SO IT CAN RUN FOR 3-5 MINUTES LIKE IN YOUR FREAKING FIRST POST!!

ONCE ITS RUNNING, WALK TO THE IAC, UNPLUG IT,

WHAT HAPPENS TO THE rpm?

IS THIS CLEAR?

Dont be mad that you didn’t specify. Why would it be unreasonable to test it in the condition where it actually has the issue?Aren’t base idle resets done with the engine warm?

 

[TheZ06andFoxbody]

Lol... Nobody is asking you to do an idle reset, nobody told you to warm it up before checking the iac. You're arguing with the only person actually trying to help you troubleshoot instead of just doing what is asked of you. Good luck.

Im clearly using the idle reset as an example of doing adjustments and diagnostics with the engine warmed up. I thought that was pretty obvious and I further explained why I tried it with the engine already having some heat in it.

And once again, no one told me to check it cold either. They did not specify. If you’re going to berate me for “not following instructions” then perhaps you should provide clearer instructions.

The “only person actually trying to help me” hasn’t offered a shred of any explanation whatsoever aside from “the engine isn’t getting enough air”. All they’ve done is repeat what I already posted, and hurl insults my way. I really don’t understand why you guys just can’t talk about this like adults, and I don’t understand why you’re coming here to defend them when you have nothing further to add to the discussion.

If anyone wants to offer advice and have a civilized conversation about this like adults, I’m game. I’m not interested in bickering back and forth and I’m not interested in dealing with internet tough guy edgelords.

Thanks.

 

[TheZ06andFoxbody]

To indy's defense, you did say you'd start it cold and unplug IAC.

Also, he comes off as a complete dick sometimes (OK, most of the time), but if you follow his directions and think of what and why he's suggesting certain test or asks certain questions, you'll get through it.

To indy's defense, you did say you'd start it cold and unplug IAC.

Also, he comes off as a complete dick sometimes (OK, most of the time), but if you follow his directions and think of what and why he's suggesting certain test or asks certain questions, you'll get through it.

That’s fine, I just meant that I would start it cold and wait until it died, which as I understand it meant the car had heat in it. I should have clarified.

I’m going to try it cold later this evening

 

[TheZ06andFoxbody]

honestly? i am gonna ask you to unplug the IAC when the engine doesn’t run??????????

Not when it “doesn’t run.” When it runs for 10-15 seconds before shutting off.

Ill try it cold later this evening