Idle issues, missfire, backfire, stalling

Steviesn95

Member
Sep 25, 2019
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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?
What do you think the odds are of it just being the filter though? I can hear the pump prime, and run everytime
 
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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
I doubt it is the filter but change it along with the pump.
Pressure should be like 42 with vacuum line off and 34 lbs vacuum line on. Also sniff the vacuum line, if you smell gas change it too.
get a 155 or a 190 lph pump. No need for anything bigger.
 
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Steviesn95

Member
Sep 25, 2019
19
2
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37
Pittston Pa
I doubt it is the filter but change it along with the pump.
Pressure should be like 42 with vacuum line off and 34 lbs vacuum line on. Also sniff the vacuum line, if you smell gas change it too.
get a 155 or a 190 lph pump. No need for anything bigger.

This car will be getting boosted. Hopefully by next year. So i was thinking of throwing the aeromotive stealth 340 in it so o dont have to drop the tank again. But my buddy has a parts car with complete tank already pulled. So we may just swap tanks
 
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Steviesn95

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Sep 25, 2019
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Pittston Pa
So verified fuel pressure this morning. Keeping in mind, when i hooked the tester to the shrader valve, it bled the pressure from the rail. But i went and turned key on, engine off to see where pressure was at before cranking, and there was only 10psi after the pump primed 1 time. So i went and cycled the key 15 times, and the pressure was now at 30psi. Car fired right up and didnt seem to studder. With vacuum line on the fpr, it hit 30psi at idle. With vacuum off, it was around 38psi. Returned the test kit to autozone, and cycled the key a few times before starting to let the pump prime a few times, and car ran great after that. Could be coincidence, or i guess the pump is in fact weak and not building enough pressure when it primes. Or possibly bad fuel pressure regulator bleeding some of the pressure off. I did remove the vacuum line when i first started having issues, and let the car run for sometime with it unplugged to see if any gas leaked past the diaphragm in the regulator and didnt get anything.
 

Steviesn95

Member
Sep 25, 2019
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Pittston Pa
Anyone have any input on this? Fuel pressure too low? The only 10psi after i primed the pump worried me. But as i said, pressure was bled off when i hooked the tester to shrader. So im honestly not sure if that would be normal or not. The other numbers weren't that far off both with, and without vacuum line on the pressure regulator. And its either mere coincidence, or me priming the pump multiple times before i start the car is in fact helping. Car has run almost problem free the last couple days with me priming the pump a few times before cranking. Did grab a new filter today, but have yet to install..
 

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
I don't mean to be mean but think about it. :chin
put a new fuel pump in it, if you want to go over board with a 340 lph pump ok, you may or may not have problems with it. I would put a 155 or a 190 in it till I did the boost upgrade but that's me.
 
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Xkuzme1

Member
Sep 21, 2019
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Kansas City, MO
Did you have any luck yet?
I was thinking plug wires actually. Seems simple, but the backfire thing was making me thing. One cylinder down would cause the backfire you speak of. Keeping the idle up would help the e tea voltage jump a broken wire. A hot wire would get worse. A cold wore would be bad because the shrinkage would widen the gap.
 

ShagsSN95

New Member
Jul 22, 2020
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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.
How does one accomplish this "Base IDLE Reset"? Thats the first ive heard it mentioned and I am pretty sure I need to do this to my SN95 V6