Idle issues, missfire, backfire, stalling

Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
Whats up guys, new to the mustang scene, only had this thing about 3 months. Its a 94 5.0 Gt. Full msd ignition. Been having issues lately. Firstly since day one, on cold starts, while putting the car in gear first time of the day and proceeding to let the clutch out, it would struggle, almost as if it was either not getting enough fuel, or getting too much and flooding out a bit. After a second it would clear up and run like a champ. Shut the car off start it up and drive away no issue. As of recently, started to get a bit of a missfire, but nothing too crazy. Than one day i went to start the car and it didnt want to start. I stopped cranking the key, than tried again and she finally ran. Since than it has intermittent stalled at idle on me. And been doing it alot more frequently. Almost undriveable. I have to keep the rpms up at stop signs/lights in order to keep it running and she will sometimes missfire pretty bad. Almost as if ignition or fuel is cutting out, than picks back up. Today she stalled and didnt want to start back up. Thought i was gonna have to call a tow truck. Would crank the key, and nothing. Noticed a couple times after i stopped cranking, there would be a delayed backfire. Like 2-3 sec after i stopped cranking, it back fired. She finally started and i kept the rpms up the whole way and made it to work. Made it home from work tonight too, but while decelerating at around 3k rpms, she backfired loud. I probably spit flame out the tails. My daily is down and depending on this as a daily for the time being. Car has been awesome, but whatever gremlins i have here are getting significantly worse. Car is almost undriveable. Since the first sign of problems, i have replaced plugs, cleaned the iat sensor, the maf, intake, throttle body, and just swapped in a new accel coil. Ive heard from a few owners the msd disty are troublesome. Also hearing that the msd6al box i have is useless. Unfortunately i have alot of priorities and cant really afford to change everything at once. I have a mustang buddy local to me with a motorcraft disty, and a tfi module he is gonna toss me cheap. Any other things you guys recommend i check? Appreciate your feedback in advance...
 
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Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
Bump...had no choice but to drive the car last couple days. I had good luck yesterday holding the throttle around 2k for a minute or two till she warmed up a bit, and ran with no misfire. Idle still surged a bit. Would drop to around 500. Today on startup, it was sputtering bad. Even with the throttle held for a bit she was struggling and tried to die. I kept it alive, but started to smell raw fuel. Even the kids noticed it. Smelt like i was sitting at a gas station
 

Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
Is the car stock besides the msd stuff? Have you verified where the timing is at with a light?
Car is mostly stock. Has cat back exhaust, bbk cold air intake. Have not checked timing. Car has been running great until a week or two ago. I dont see how ign timing would jump on its own?
 

96pushrod

Mustang Master
May 15, 2018
880
535
103
28
Savannah
Ignition wouldn’t change by itself, no, but it sounds like the car has never really been right.

The obd1 code scanners are $20 on amazon, a wise investment for the efi mustangs.

If the car is stock, then it shouldn’t be too bad to diagnose. Check basic things: such as fuel pressure mentioned above. Performing a base idle reset is also good to do on a car you have recently purchased.

If the car runs well when pedaling, the idle air control (iac) valve may be starting to go. If you unplug it and the idle doesn’t do anything, it may be faulty. They’re like $50, the bmd ones are still made in the USA.
 
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Steviesn95

Member
Sep 25, 2019
19
2
13
37
Pittston Pa
Ignition wouldn’t change by itself, no, but it sounds like the car has never really been right.

The obd1 code scanners are $20 on amazon, a wise investment for the efi mustangs.

If the car is stock, then it shouldn’t be too bad to diagnose. Check basic things: such as fuel pressure mentioned above. Performing a base idle reset is also good to do on a car you have recently purchased.

If the car runs well when pedaling, the idle air control (iac) valve may be starting to go. If you unplug it and the idle doesn’t do anything, it may be faulty. They’re like $50, the bmd ones are still made in the USA.


Ok i just came out to start tinkering. I tried unplugging the iac while car was running, and the car stalled immediately. Maybe i didnt have it warmed up enough? Trying to get it to warm up more now and idle for a bit and will try again. I also quickly threw my timing light on it. On plug wire number 1 i had no light. I hooked it to another wire and it lit up. (Just to make sure it wasmt my timing light not working) put it back on plug wire number 1 i got a 2 lights, and nothing after that. Almost as if #1 isnt firing. I tried to unokug the spout and car died. Thinking its def a spark issue at this point..
 

96pushrod

Mustang Master
May 15, 2018
880
535
103
28
Savannah
So you weren’t actually able to see where your base timing is at? Have somebody throttle up the car to 2500 rpm when you remove the spout, you should be able to set timing without it dying.

If it died with the iac disconnected you probably need to open the tb blade just a hair. I would do the base idle reset though, that should cover it.
 

Steviesn95

Member
Sep 25, 2019
19
2
13
37
Pittston Pa
So you weren’t actually able to see where your base timing is at? Have somebody throttle up the car to 2500 rpm when you remove the spout, you should be able to set timing without it dying.

If it died with the iac disconnected you probably need to open the tb blade just a hair. I would do the base idle reset though, that should cover it.
I let the car warm up a bit more. It ran with the iac and the spout unolugged (at seperate times) waiting on another more knowledgeable owner to come by and help me figure it out. Supposedly has a ford disty and a new tfi for me. I was getting a bit more light with spout unplugged and running this time. But it doesnt seem consistent. And i cant see the marks on the pulley when its lighting. Hopefully its just off and in need of the base idle reset.
 

96pushrod

Mustang Master
May 15, 2018
880
535
103
28
Savannah
When you check base timing the spout will need to be out. Make sure it’s out after you stab the new distributor in.

How’s your cap and rotor look on the distributor now?

When doing the base idle reset it’s a good idea to have the battery disconnected.
 

Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
Well we didnt get too far. Swapped the tfi, put a new cap and rotor in. Dont have the proper fitting for the fuel pressure check. Going to try and rent one in the morning. He doesnt think it was holding enough pressure at the rail. Can hear the pump prime. And there is some pressure at the rail, but only a tiny bit squirting out. Car stalled at one point and would not start back up. Battery almost died trying to start it. Turned the key and primed it 10 times before cranking. It sputtered finally. Tried cranking one more time and it started. Sputtered a bit but was able to keep it running. Honestly kind of lost at that point
 

Shuttleman83

Active Member
Jun 30, 2019
102
9
28
USA
MSD could be the problem...also check for oil leak from bad valve cover gasket, check compression, reset computer KAM for 1-2 hours and re learn, could definitely be coils / plug wires.
 
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Steviesn95

Member
Sep 25, 2019
19
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Pittston Pa
MSD could be the problem...also check for oil leak from bad valve cover gasket, check compression, reset computer KAM for 1-2 hours and re learn, could definitely be coils / plug wires.

I was thinking of pulling the terminals. My buddy suggested it too. Im honestly afraid that with these issues, and the ecu does a reset, and has to go through a relearn process, she might not start again. I just installed brand new accel coil, brand new motorcraft plugs. Changed rotor and cap for a known good one. Although its not a msd rotor, and it is an msd disty. Would that cause issues? The rotor we pulled out of the disty was old, rusted, and also not msd even though its in an msd disty. I have what appears to be a brand new msd rotor in my spare msd disty.
 

Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
MSD could be the problem...also check for oil leak from bad valve cover gasket, check compression, reset computer KAM for 1-2 hours and re learn, could definitely be coils / plug wires.

The vc gaskets dont seem to be leaking. I checked for vac leaks and found nothing. Were also considering maybe the msd 6al box is crapping out on me. He suggested i bypass it. The green and white wire attached to the hack job they did on the 6al install, seems to be missing from the harness though, so essentially if i try to bypass the 6al, i cant hook that wire back to oem harness. We cant find the original wire anywhere near the oem harness. Random thought i just had. Car was missing the pcv valve when i got it. I installed a new pcv and grommet. However it didnt come with the screen for the pcv. Been running it like that for probably 2-3 months. Could the missing screen have caused the pcv to get gunked and create these issues? I kinda doubt it. But random thought
 

Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
We did check timing. Mark lines up, but we cant see the number. So not sure if its at 10btdc, or 12, 14 etc. But car ran great for months, just started giving me issues that are getting drastically worse aboit 2 weeks ago. The car is also running lean. Which could be from blocked fuel filter, or weak pump i suppose. I really need to verify fuel pressure..
 

Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
I should note, that for some reason if i give it a bit more than usual gas when in reverse it will misfire or backfire. Its seemed to have always done that. Wth could that be about?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
You gonna find a weak fuel pump.
Oh, and lose the msd crap. The rotor don't matter, if it fits use it.
you also need to install the pcv screen and check the pcv in case it's clogged.
did you check for vacuum leaks while the engine was running?
 
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Steviesn95

Member
Sep 25, 2019
19
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Pittston Pa
You gonna find a weak fuel pump.
Oh, and lose the msd crap. The rotor don't matter, if it fits use it.
you also need to install the pcv screen and check the pcv in case it's clogged.
did you check for vacuum leaks while the engine was running?
Yes i sprayed everything down with carb and choke cleaner while running. And nothing changed at all. I do want to loose all the msd stuff. Seems like all the guys that really know about these cars say that it tends to cause trouble. And is unecesarry with our tfi setup. I will just buy another pcv with the screen this time. Like i said only been in the car 2 months or so. Maybe 3. But without the screen maybe i ruined it. If the car will make it to autozone in the am im gonna rent the fpr tester and see if it holds the 38psi