Engine 1993 GT keeps stalling after 30 seconds to a minute when sitting

g23a1 · Apr 29, 2020

Hello, I recently purchased a 1993 Mustang GT. I haven't been able to register it yet due to the DMV being closed because of the quarantine. I have been letting it run in my driveway every couple of days. Yesterday it randomly stalled after 30 seconds of running. I turned it on again, same thing. Ever since then it either:

a. Runs fine and doesn't stall (only had that once)

b. Runs fine the stalls

c. RPMs go up but it can't start

d. Runs but hitting the gas takes a second for the RPMs to go up, they don't go up very high and the car sounds like it's struggling.

I've had the car for over a month now and it was fine before that. I don't think it's the battery as sometimes I can get it to run fine. I hear the fuel pump priming, and the previous owner said he replaced it, so I'm assuming that's working. Maybe fuel filter? I've also heard MAF possibly. The car does have the CEL on, but it's always been on, I'm assuming due to it having long headers and a Flowmaster exhaust. Any ideas what it could be?

Here are some videos to help me explain:

What normally happens (note: the noise at the end is my neighbor cutting his grass, not the car)

Another example where the RPMs drop low and the engine revs itself

Can't rev above 1500 no matter how much I press the gas pedal

Noobz347 · Apr 29, 2020

You need a new Thin Film Ignition module (TFI)

Fox Body TFI Module - Manual Transmission | 1986-93 Mustang

This TFI module fits your 1986-93 Ford Mustang with a Manual transmission. Shop for a Fox Body TFI module from Late Model Restoration today!

lmr.com

Have you pulled codes? Drop by Amazon and pickup an OBD1 code reader. We also have instructions on pulling codes with a paperclip if you are interested in that.

Noobz347 · Apr 29, 2020

Other possibilities include but are not limited to:

PiP in the distributor
Weak Ignition coil
Bad Fuel Pump
Bad Fuel Regulator
Intermittent Wiring
Ignition Switch in the Steering Column

g23a1 · Apr 29, 2020

Noobz347 said:
You need a new Thin Film Ignition module (TFI)

Fox Body TFI Module - Manual Transmission | 1986-93 Mustang

This TFI module fits your 1986-93 Ford Mustang with a Manual transmission. Shop for a Fox Body TFI module from Late Model Restoration today!

lmr.com

Have you pulled codes? Drop by Amazon and pickup an OBD1 code reader. We also have instructions on pulling codes with a paperclip if you are interested in that.

I looked up TFI and saw it was called "Thick" and you mentioned "Thin" I didn't see anything called "Thin" so I just want to make sure I'm looking at the correct item.

I don't have an OBD1 reader, I'll have to get one, but I'll probably try the paperclip method in the mean time. Do you have the link that?

Noobz347 said:
Other possibilities include but are not limited to:

PiP in the distributor
Weak Ignition coil
Bad Fuel Pump
Bad Fuel Regulator
Intermittent Wiring
Ignition Switch in the Steering Column

Thanks for this list, I'll check some of these too.

Olivethefet · Apr 29, 2020

Electrical - How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs

@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it... Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on. Dumping the computer diagnostic codes on 86-95 Mustangs Revised 26-July-2011. Added need to make sure the clutch is...

www.stangnet.com

As for the TFI. I think they only make one for the fox, so if you search for 93 Mustang TFI it should take you to the right spot.

g23a1 · Apr 29, 2020

Olivethefet said:
Electrical - How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs

@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it... Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on. Dumping the computer diagnostic codes on 86-95 Mustangs Revised 26-July-2011. Added need to make sure the clutch is...

www.stangnet.com

As for the TFI. I think they only make one for the fox, so if you search for 93 Mustang TFI it should take you to the right spot.

Ok, thanks.

KRUISR · Apr 29, 2020

Is it low on fuel (gauge may not be reading the most accurate). I had an issue with mine staying running back in the fall ( I was around 1/4 tank on the gauge). Put some gas in the tank, runs great.

General karthief · Apr 29, 2020

You can't 'assume' anything with these cars 'cept they are old and need work. If you do you will waste time and money, I feel tou likely have more than one problem with it.
here is a place to start:

Help me create the "Surging Idle Checklist"

Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...

forums.stangnet.com

Do it step by step and if you have any questions post them in this thread.

g23a1 · Apr 30, 2020

KRUISR said:
Is it low on fuel (gauge may not be reading the most accurate). I had an issue with mine staying running back in the fall ( I was around 1/4 tank on the gauge). Put some gas in the tank, runs great.

I was thinking it might be that, or it could be older bad gas. The previous owner didn't use it much so who knows when it was last filled up. Since it isn't registered I haven't been able to take it to a gas station and I don't have a jerry can.

General karthief said:
You can't 'assume' anything with these cars 'cept they are old and need work. If you do you will waste time and money, I feel tou likely have more than one problem with it.
here is a place to start:

Help me create the "Surging Idle Checklist"

Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...

forums.stangnet.com

Do it step by step and if you have any questions post them in this thread.

Thanks for the link to that, but I don't think that's the issue. Yesterday I was disconnecting and reconnecting some of the wires in the engine bay and it seems to be running better and for longer now. It's not surging idle anymore, just runs for a bit then dies.

General karthief · Apr 30, 2020

g23a1 said:
I was thinking it might be that, or it could be older bad gas. The previous owner didn't use it much so who knows when it was last filled up. Since it isn't registered I haven't been able to take it to a gas station and I don't have a jerry can.

Thanks for the link to that, but I don't think that's the issue. Yesterday I was disconnecting and reconnecting some of the wires in the engine bay and it seems to be running better and for longer now. It's not surging idle anymore, just runs for a bit then dies.

You don't know what the issue is.
You have to be methodical when dealing with these computer controlled cars.
OR you can waste time and money wiggling this and replacing that. Your call.

g23a1 · Apr 30, 2020

General karthief said:
You don't know what the issue is.
You have to be methodical when dealing with these computer controlled cars.
OR you can waste time and money wiggling this and replacing that. Your call.

That's fair, I might as well try it, I have nothing to lose.

g23a1 · May 1, 2020

So I bought a code reader and when doing the KOEO test I got 15 C a two times, which means the test failed. Not sure if that was me screwing something up, but it may need to be looked at.

More important is that on the times it worked I got 66 C, which if for MAF voltage being low. I don't have the tools on hand for me to test the MAF voltage, but I'm assuming that's what is causing the engine to stall, if that's even possible. I took off the air filter and looked down the MAF and it was clean, I also disconnected and reconnected the MAF cable to no avail.

I also tried doing a KOER test in which the cylinder count didn't happen and I got code 98 R, then 66 R (I'm assuming it was R since the car was running, maybe it was C, but 66 R and 66 C mean the same thing so it really doesn't matter). After the test, the engine stalled.

I saw this thread about someone else who had both 66 and 98, so I'm assuming 98 was caused by 66. They mention stalling too, so I'm assuming stalling is possible from the MAF sensor. Unfortunately the thread never got a confirmed fix.

General karthief · May 1, 2020

Post #2 tells you how to test the maf.
Unfortunately many do not post the end results, I suspect many times it was found to be operator error or they gave up and it was cobbled together enough to sell off.

Noobz347 · May 2, 2020

If you run the checklist and are thorough, you will find the issue.

Nobody has ever come back and stated that they couldn't find the problem after running the checklist. It's been updated several times over that 20+ years to reflect discoveries.

General karthief · May 5, 2020

Update?

g23a1 · May 28, 2020

General karthief said:
Update?

Finally I have an update. I was busy the past few weeks due to finals, sorry for such a delayed response. Good news and possibly bad news. Good news is the Mustang runs fine now. The bad news is I still have code 66 and the MAF sensor may not be getting any power.

After a while I kept passing the KOEO test, and after running a few KOER tests, the car started running fine. The last KOER test I did, the car ran in test mode for a while, but after it finished it sounded different. The idle was smoother too. Ever since then the car runs fine.

However, I finally borrowed a multimeter from my job and just tested the pins. I tried both the V with the ~ and the V with the - above it. I'm not sure what the difference is or which one I should be using. Here is a picture for reference. I was measuring the pins like this but I only got 0.002 volts. However, I get the same reading when touching the plastic on the MAF, and it doesn't look like the pins are being touched. I checked the multimeter on the battery terminals to make sure it worked, which is does. So either it isn't getting power or I'm not fully touching the pins.

g23a1 · May 28, 2020

Got another update, I tried attached the the multimeter to the pins from the back like this: 1 2

I got between 0.9 and 1.02 volts this way when measuring with in the V with the - above it mode. This was at idle. The idle voltage is supposed to be 0.6 V, so despite getting the low or no voltage issue, I'm getting high voltage.

Engine 1993 GT keeps stalling after 30 seconds to a minute when sitting

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