• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 2.3L (N/A & Turbo) Tech

89 Mustang 2.3 Occasional Misfire/Stall

  • Thread starter Thread starter Alex129
  • Start date Start date Dec 4, 2018
A

Alex129

Member
Nov 19, 2018
17
4
13
Layton, UT
Dec 4, 2018
#1
  • Dec 4, 2018
  • #1
So, I have a bit of a mystery for you guys. My car likes to stall every now and then, and I'm stumped as to why. From a cold start, it starts out fine. Once it's fully warmed up, it's also fine. However, in between then, it occasionally bucks and stalls like it has a misfire. It idles and runs just fine until it gets into these fits, it's the strangest thing. Here's the list of things I've learned so far:
-Fuses are all good.
-Battery cables/terminals are clean and free of cracks/corrosion.
-IAC is clean and functioning normally. I can hold the throttle open, and the problem persists.
-I'm reasonably sure the injectors are working normally, but I don't possess a noid light.
-TFI module is new, as is the coil, spark plugs, and wires. These were replaced since the car had been sitting and wouldn't start when I bought it. They are off brand; however, the car didn't run at all until i replaced the TFI module specifically, so I'm fairly sure it's doing what it needs to do.
-I could not find a vacuum leak, though that doesn't necessarily mean there isn't one :/
-There are no outstanding power draws, but i did notice the battery voltage hangs out around 13.2 at idle with the alternator loaded (lights on, etc.). Alternator tested good at my local parts store, battery is 3 years old. I also noticed loading the alternator tends to exacerbate the problem.
-I pulled the KOEO codes. I got 11 at first, and an 18 that was stored. This is my only real lead. That being said, the battery has been disconnected, and hasn't been driven much since then, so it really doesn't have a chance to store any other codes right now.
-Fuel pressure checks out, have 40 psi with the regulator disconnected and vacuum line plugged. It also isn't leaking fuel anywhere I can find.

I'm stumped. Like I said, it starts just fine, and runs smooth cold and after fully warmed up. Just that in between stage... I suppose my first question is how long can the computer take to calibrate? Could this be a thing I need to drive out of it? Otherwise, what should I check? My mind says PIP sensor, but it isn't really exhibiting the typical problems that would cause. Any help would be greatly appreciated.
 

General karthief

wonder how much it would cost to ship you a pair
20+ Year Stangneter
Aug 25, 2016
27,942
10,582
203
polk county florida
Dec 5, 2018
#2
  • Dec 5, 2018
  • #2
First thing I would do is get a fuel pressure gauge and mount it to a wiper arm temporarily with zip ties and monitor the pressure when the stumbling occurs. Did you get the koer codes?
 
A

Alex129

Member
Nov 19, 2018
17
4
13
Layton, UT
Dec 5, 2018
#3
  • Dec 5, 2018
  • #3
KOER didn't show anything unordinary. I ran it on the road for a good while, ran the codes again, and got 31 added to KOEO though. I pulled the EVP sensor and gave it a good clean, along with the connector.
I'll try your suggestion with the fuel pressure gauge, should I leave the regulator disconnected as I do this? I also noticed that I oopsed and added too much transmission fluid, could that cause a problem like this? It leaks anyways, so that would fix itself i presume
 

General karthief

wonder how much it would cost to ship you a pair
20+ Year Stangneter
Aug 25, 2016
27,942
10,582
203
polk county florida
Dec 5, 2018
#4
  • Dec 5, 2018
  • #4
Trans fluid level has no effect on how the engine runs. Leave the vacuum line hooked up when driving around monitoring the fpg, pay attention when the car acts up.
 
A

Alex129

Member
Nov 19, 2018
17
4
13
Layton, UT
Dec 7, 2018
#5
  • Dec 7, 2018
  • #5
Okay, bit of an update: I ended up testing the fuel pressure, but it seems to check out. It fluxuates with engine vacuum as it's supposed to, and never got below 26-30 psi. So, the code 18 got me looking into the timing and ignition system. When it started having a fit, I disconnected the MAP and the SPOUT at separate times. The MAP raised RPM a bit, but didn't otherwise affect the problem. However, the SPOUT made it stop. Applied throttle, turned on lights and A/C, and it runs just fine, if a little bit faster. Plug it back in, acts up again. Timing shows 10 BTDC. This leads me to believe the PIP is acting up as the engine heats up, but it doesn't explain why it evens out completely after being fully warmed up. Could the computer be on the fritz, not able to adjust timing like it's supposed to? Or, could it be that the new TFI isn't jiving with the PIP sensor?
Also, I searched again for vacuum leaks, as I thought of more places to check. Still nothing.
 
1

1984 Carburetor'd 2.3

Member
Nov 28, 2018
32
7
18
Hewitt,Texas
Dec 8, 2018
#6
  • Dec 8, 2018
  • #6
I bought a brand new TFI last week and it made mine run worse than the one I took out>>> I took it back to AutoZone>>>
they tested it and said it was Fupped right out of the box and gave me a replacement
 
A

Alex129

Member
Nov 19, 2018
17
4
13
Layton, UT
Dec 9, 2018
#7
  • Dec 9, 2018
  • #7
Final update! The car is fixed! On a hunch, i went ahead and swapped out the MAP sensor for a newer one that was in a buddy's 88 Ranger. It ran a little rough after that, but we couldn't get it to stall anymore. I checked the timing, however, and it was 16 degrees too advanced. Yikes! Base timing was still fine though, so we just reset the computer and let it relearn the timing curve. It's running like a dream. So, combination of a bad MAP, and the computer overcompensating to keep the car alive. Thanks for the help!
 
Reactions: General karthief
You must log in or register to reply here.

Similar threads

E
2007 GT Stalls when lights or a/c turned on
  • ejscarfo
  • Jun 22, 2026
  • 2005 - 2009 Specific Tech
Replies
2
Views
140
2005 - 2009 Specific Tech Jun 29, 2026
ejscarfo
E
I
98 Mustang GT dying
  • ItsMason
  • May 14, 2026
  • 1996 - 2004 SN95 Mustang -General/Talk-
Replies
3
Views
132
1996 - 2004 SN95 Mustang -General/Talk- Jun 25, 2026
lenzgt
L
L
Help with 1986 GT 5 Speed Please
  • Lcasada1999
  • Mar 20, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
7
Views
267
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Jun 21, 2026
CAMTWO1070
F
Alternator Not Charging
  • Fri Guy
  • Aug 29, 2025
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
7
Views
435
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Aug 31, 2025
AeroCoupe
C
Engine Idle cuts out
  • claypoolxx
  • Mar 7, 2026
  • Fox 5.0 Mustang Tech
  • 2
Replies
25
Views
778
Fox 5.0 Mustang Tech Jul 24, 2026
alutwon
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 2.3L (N/A & Turbo) Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?