98 GT 4.6 stalling out randomly
10-05-2017, 06:46 PM
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Join Date: Oct 2017
Location: CA
Posts: 1
98 GT 4.6 stalling out randomly
I am trying to diagnose a friends 98 Mustang GT 4.6L, VIN: X, around 148k miles.
I have read a lot of articles pertaining to stalling out for this era Mustang. Most of the solutions were based on the IAC, which isn';t the case here. (yes, I did replace it with a new Motorcraft IAC to no avail)
A week ago the Mustang was hit right rear quarter panel. the Inertia switch flipped like it was supposed to. It was towed away. I got to the car and pushed the button in and Car fired right up. Purrs like a kitten! (the mercedes, totaled, crunched and mangled). Before the impact, the Mustang ran perfectly, there were no issues aside from the speed sensor acting up.
Only damage to Mustang is quarter panel, bumper scraped up and trunk a bit off, but still locks. the right rear shock damper has a huge dent in it, but it couldn't be from this accident, the tires are fine, rims are perfect, nothing is bent, car drives straight.
The Mustang slid 170 degrees from the impact (according to cop on scene), no airbags deployed.
My friend had her foot on brake. so rear of car slid, front tires didn't move much according to her.
No fuel leaks, fuel line looks like there's no bends or crimps in it, fuel filters connectors are in 1 piece.
The gas guage is reading Full, however we're estimating about a half tank of fuel in it.
The stalling out problem arises at random, as you're driving, any speed actually, but typically it's been under 45, as since it was first experienced I won't take it on the freeway. So as you're driving, at random, engine will just die. put car in neutral and it fires right up and you're off.
Your foot can be on or off the accelerator.
There are no codes, I use an Actron scanner that can read live PID's. oxygen sensor voltages and fuel trims are going up & down like normal.
I tested fuel pump pressure, it sits at 31psi. according to what I found, it should be 32psi. I'm saying it's within spec due to my pressure guage setup is about oh 20yrs old and hasn't been used in 10 years and has been banged around over the years.. I idled this car for 45 minutes, it never left 31psi, I revved engine, pressure would jump up to 40 for a split second and go back to 31. All vacuum hoses are in good shape.
I blocked the front wheel and put in drive with e-brake tight. 15minutes of that, it didn't die.
my hoses weren't long enough to put gauge on windshield so I can read it. But i went for a drive, made it halfway down the block and card died out. put
it in neutral, fired right back up.
There is no ignition module, has individual coil packs..
The engine sputters, but it's barely noticable. i had it at 40mph and watched the idle just go down to zero and the engine died out. But put it in neutral and it fired right up and kept driving.
A loose electrical conneciton, perhaps the fuel pump connector is loose? But if so, why does the car fire right back up with no hesitation or struggle?
Wouldn't a loose connection, stay loose and get worse?
There was 1 code in computer, but CEL is off. the code was VSS sensor. I was told a few months ago that the speedometer wouldn't work at times, then would come back to life. So the code pointed to the speed sensor, which I havent't had time to replace. The CEL went off and hadn't returned.
Sorry I forgot to mention that! I doubt the speed sensor would stall the engine out.
The battery, tested good, alternator diode's tested good as well. voltage output was 14.4 volts. The battery is a little over a year old, it was in Arizona last year, and I know how the Arizona heat can kill a car battery.
I also heard that a weak or questionable battery can make it so the alternator field doesn't engage and can stall the car out as well.
I am not against replacing the battery, it's within the free replacement period. I'm using a Deka battery in it. I trust these batteries.
But also when I opened the hood, the battery wasn't tucked into its mount. the puck was still tight, but the battery was sitting on top of the hold down with the puck still holding the other side down.
Cables are tight and no corrosion.
I have swapped in a new IAC valve just to see because initially this was happening it seemed at low speed with foot of accelerator. That wasn't the cause. I also swapped the TPS and no change.
I did test the IAC and TPS and they worked fine, but I'm starting to run out of things to diagnose.
The battery makes some sense, but on the flip side, it doesn't.
I am lost and need help with what to check next.
Thank You for any ideas/tips/solutions.
--Eric
I have read a lot of articles pertaining to stalling out for this era Mustang. Most of the solutions were based on the IAC, which isn';t the case here. (yes, I did replace it with a new Motorcraft IAC to no avail)
A week ago the Mustang was hit right rear quarter panel. the Inertia switch flipped like it was supposed to. It was towed away. I got to the car and pushed the button in and Car fired right up. Purrs like a kitten! (the mercedes, totaled, crunched and mangled). Before the impact, the Mustang ran perfectly, there were no issues aside from the speed sensor acting up.
Only damage to Mustang is quarter panel, bumper scraped up and trunk a bit off, but still locks. the right rear shock damper has a huge dent in it, but it couldn't be from this accident, the tires are fine, rims are perfect, nothing is bent, car drives straight.
The Mustang slid 170 degrees from the impact (according to cop on scene), no airbags deployed.
My friend had her foot on brake. so rear of car slid, front tires didn't move much according to her.
No fuel leaks, fuel line looks like there's no bends or crimps in it, fuel filters connectors are in 1 piece.
The gas guage is reading Full, however we're estimating about a half tank of fuel in it.
The stalling out problem arises at random, as you're driving, any speed actually, but typically it's been under 45, as since it was first experienced I won't take it on the freeway. So as you're driving, at random, engine will just die. put car in neutral and it fires right up and you're off.
Your foot can be on or off the accelerator.
There are no codes, I use an Actron scanner that can read live PID's. oxygen sensor voltages and fuel trims are going up & down like normal.
I tested fuel pump pressure, it sits at 31psi. according to what I found, it should be 32psi. I'm saying it's within spec due to my pressure guage setup is about oh 20yrs old and hasn't been used in 10 years and has been banged around over the years.. I idled this car for 45 minutes, it never left 31psi, I revved engine, pressure would jump up to 40 for a split second and go back to 31. All vacuum hoses are in good shape.
I blocked the front wheel and put in drive with e-brake tight. 15minutes of that, it didn't die.
my hoses weren't long enough to put gauge on windshield so I can read it. But i went for a drive, made it halfway down the block and card died out. put
it in neutral, fired right back up.
There is no ignition module, has individual coil packs..
The engine sputters, but it's barely noticable. i had it at 40mph and watched the idle just go down to zero and the engine died out. But put it in neutral and it fired right up and kept driving.
A loose electrical conneciton, perhaps the fuel pump connector is loose? But if so, why does the car fire right back up with no hesitation or struggle?
Wouldn't a loose connection, stay loose and get worse?
There was 1 code in computer, but CEL is off. the code was VSS sensor. I was told a few months ago that the speedometer wouldn't work at times, then would come back to life. So the code pointed to the speed sensor, which I havent't had time to replace. The CEL went off and hadn't returned.
Sorry I forgot to mention that! I doubt the speed sensor would stall the engine out.
The battery, tested good, alternator diode's tested good as well. voltage output was 14.4 volts. The battery is a little over a year old, it was in Arizona last year, and I know how the Arizona heat can kill a car battery.
I also heard that a weak or questionable battery can make it so the alternator field doesn't engage and can stall the car out as well.
I am not against replacing the battery, it's within the free replacement period. I'm using a Deka battery in it. I trust these batteries.
But also when I opened the hood, the battery wasn't tucked into its mount. the puck was still tight, but the battery was sitting on top of the hold down with the puck still holding the other side down.
Cables are tight and no corrosion.
I have swapped in a new IAC valve just to see because initially this was happening it seemed at low speed with foot of accelerator. That wasn't the cause. I also swapped the TPS and no change.
I did test the IAC and TPS and they worked fine, but I'm starting to run out of things to diagnose.
The battery makes some sense, but on the flip side, it doesn't.
I am lost and need help with what to check next.
Thank You for any ideas/tips/solutions.
--Eric
