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

g23a1

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Apr 29, 2020
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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
 
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Noobz347

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You need a new Thin Film Ignition module (TFI)



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.
 
Last edited:

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
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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

Member
Apr 29, 2020
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1
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20
NY
You need a new Thin Film Ignition module (TFI)



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?

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

Slap me as well as point and laugh
May 17, 2018
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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

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Apr 29, 2020
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NY

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

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Apr 16, 2015
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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

wonder how much it would cost to ship you a pair
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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:
Do it step by step and if you have any questions post them in this thread.
 

g23a1

Member
Apr 29, 2020
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NY
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.

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:
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

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
17,816
5,781
193
polk county florida
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

Member
Apr 29, 2020
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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

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
17,816
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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

Stangnet Facilities Maint Tech... Er... Janitor
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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.
 

g23a1

Member
Apr 29, 2020
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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

Member
Apr 29, 2020
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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.