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#4534740 - 10/05/17 04:15 PM 98 Mustang GT stalls out
EricF Offline


Registered: 07/14/09
Posts: 1645
Loc: SF Bay Area
I am trying to diagnose a friends 98 Mustang GT 4.6L, VIN: X, around 148k miles.

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).
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 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 expereienced 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 guage 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..

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 replacemnt 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
_________________________
1993 Ford Ranger XLT 4.0L 4x4 (240k) 5W-30 Synpower
2006 Saturn Relay-3 3.5L (85k) 5W-30 Synpower
2012 Ford Fusion SE 2.5L (39k) 5W20 M/C Semi Syn

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#4534747 - 10/05/17 04:31 PM Re: 98 Mustang GT stalls out [Re: EricF]
SubieRubyRoo Online   content


Registered: 05/14/12
Posts: 1128
Loc: Winchester, Indiana
Does it sputter and get really weak or just die? It's been years since I've worked on 4.6s, but it still sounds like you are losing either voltage or ground for the two spark coils near the drive belt. Either that or the PCM has something going on... bad ground from harness or from engine. Might have been on it's way out anyways, and the impact of the wreck jarred it loose.

Does it stall while idling too, or just while in motion?

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#4534776 - 10/05/17 05:08 PM Re: 98 Mustang GT stalls out [Re: EricF]
Kuato Offline


Registered: 10/23/05
Posts: 7094
Loc: Colorado
Agree....check all electrical connections. Wonder if it is possible for the inertia switch to be intermittent?
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#4534804 - 10/05/17 05:47 PM Re: 98 Mustang GT stalls out [Re: EricF]
bioburner Offline


Registered: 09/19/16
Posts: 1418
Loc: Minnesota
A failing CPS? I know I have had the exact issue but on the diesel
I would post it on a Mustang forum. I've Been over at SVTPerformance doing a lot of reading on a possible purchase of a pony car and there is a lot of serious gearheads there that modify Ford ponies.


Edited by bioburner (10/05/17 05:48 PM)
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#4534819 - 10/05/17 06:06 PM Re: 98 Mustang GT stalls out [Re: EricF]
mechjames Offline


Registered: 01/16/08
Posts: 516
Loc: Richmond, BC, Canada
A failed/failing speed sensor will cause a Mass air equipped foxbody mustang to stall out during deacceleration and coming to a stop sometimes. As the ecu doesn't know if you are moving or not, I believe the threshold is 7mph where it uses the IAC valve and adjusts ignition timing to idle. Not sure about the newer ones cause it can use ABS sensors as backup, but maybe the ABS and PCM arne't connected.


Edited by mechjames (10/05/17 06:08 PM)
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#4534827 - 10/05/17 06:11 PM Re: 98 Mustang GT stalls out [Re: EricF]
EricF Offline


Registered: 07/14/09
Posts: 1645
Loc: SF Bay Area
So far, it's only been stalling when driving. I had it idling for a half hour or so, put in drive, chocked the wheels, set ebrake and it idled there for 15min with no problems. But as soon as I began to drive, about halfway down the block it just died, put it in Neutral, fired right up, back in drive and it was fine.

It does sputter, but not like it's out of fuel struggling to keep going. the sputtering isn't even noticable. When it's going to die out, the idle just starts going down to zero and the engine is dead.
The strangest part is.. it starts right back up. It hasn't not started immediately after it dies.
I would think if it were a loose wire or ground somwewhere that it would possibly at times NOT start back up.

The idea of losing voltage does make sense, the weakened battery theory is starting to make some sense. But I'm really not sure how.
I've looked on electrical diagrams via AllData and they're not exactly thorough enough to say whether or not this could be something.
Then again, the alldata isn't giving a lot of theory about this either.


Before the accident, the car running 100% perfectly.

I've thought about crankshaft sensor, but I would think it would've set a code? It does fit the issue however. The impact wasn't near the engine bay, but like I said, the battery popped out of the built in hold-down. the puck kept it from moving more.

intermittant inertia switch came to mind too. I moved the wires around when it was idling. Nothing changed.. kept idling. But unfortunately the stalling only happens when driving.

It's blowing my mind!
_________________________
1993 Ford Ranger XLT 4.0L 4x4 (240k) 5W-30 Synpower
2006 Saturn Relay-3 3.5L (85k) 5W-30 Synpower
2012 Ford Fusion SE 2.5L (39k) 5W20 M/C Semi Syn

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#4534833 - 10/05/17 06:20 PM Re: 98 Mustang GT stalls out [Re: EricF]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
Run the tank dry, drop fuel tank, and pull the sender pump assembly.

If she got hit in the rear like that and spun 170*, the connections on the fuel pump are bad.
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#4534835 - 10/05/17 06:21 PM Re: 98 Mustang GT stalls out [Re: EricF]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
OH, may as well put a new pump in there while you are at it.
_________________________
"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

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#4534846 - 10/05/17 06:35 PM Re: 98 Mustang GT stalls out [Re: EricF]
EricF Offline


Registered: 07/14/09
Posts: 1645
Loc: SF Bay Area
I did forget to mention, the fuel guage is stuck on full, and there's probably a half tank in it.

So if the connections got loosened up.. why does the car restart every single time it dies out? Wouldn't the connection that got loose, stay loose?
why would the car idle for almost an hour, but die as soon as I start actually moving the car??

I like that idea however! That fits the issue as well.
Thank You!
_________________________
1993 Ford Ranger XLT 4.0L 4x4 (240k) 5W-30 Synpower
2006 Saturn Relay-3 3.5L (85k) 5W-30 Synpower
2012 Ford Fusion SE 2.5L (39k) 5W20 M/C Semi Syn

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#4534865 - 10/05/17 07:01 PM Re: 98 Mustang GT stalls out [Re: mechjames]
Merkava_4 Offline


Registered: 01/30/07
Posts: 17501
Loc: Clovis, CA
Originally Posted By: mechjames
A failed/failing speed sensor will cause a Mass air equipped foxbody mustang to stall out during deacceleration and coming to a stop sometimes. As the ecu doesn't know if you are moving or not, I believe the threshold is 7mph where it uses the IAC valve and adjusts ignition timing to idle. Not sure about the newer ones cause it can use ABS sensors as backup, but maybe the ABS and PCM arne't connected.


A 1998 will be between the fox body and the retro body; whatever that body is called.

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#4534871 - 10/05/17 07:11 PM Re: 98 Mustang GT stalls out [Re: EricF]
Nick1994 Offline


Registered: 02/19/13
Posts: 10108
Loc: Phoenix, AZ
I had the same sort of issue with my old Chevy truck. Turned out to be a bad relay for the ful pump. Well the connection was bad and it was starting to burn it up.

Was the fuel gauge stuck on full before the accident? Sounds to me the inertia from the accident made something bend or break on the fuel pump assembly. Or a hose to a charcoal canister popped off or tore or something.
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#4534873 - 10/05/17 07:15 PM Re: 98 Mustang GT stalls out [Re: EricF]
DdDd Offline


Registered: 06/08/17
Posts: 189
Loc: NY
Definitely fuel pump related. Especially if you have improper fuel gauge readings.

I'm willing to bet the harness got mangled/damaged somewhat. It restarts because it's still connected. But driving over bumps turns the pump off. Engine dies a trillionth of a second later.

Exact same symptoms on a old Jeep, including non functioning fuel gauge. Wiring harness in left rear had gotten nicked by rubbing tires. Found break fixed. They usually share circuit with pump and sender.

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#4534946 - 10/05/17 08:48 PM Re: 98 Mustang GT stalls out [Re: EricF]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
Originally Posted By: EricF
I did forget to mention, the fuel gauge is stuck on full, and there's probably a half tank in it. I like that idea however! That fits the issue as well.
Thank You!


You are welcome.

Somethings is DEFINITELY ganked inside the fuel tank.
If it's having that many issues, you may just want to drop in a new sender/pump assembly.

The fuel pump is relatively HEAVY (copper and magnets), and there isn't much for it to "hang onto", inside there. Give the rear of the car a swift kick sideways like that, and there you go.
_________________________
"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

Top
#4534947 - 10/05/17 08:49 PM Re: 98 Mustang GT stalls out [Re: DdDd]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
Originally Posted By: DdDd
Engine dies a trillionth of a second later.


hahahhaha! Not quite, it takes several seconds.
_________________________
"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

Top
#4534959 - 10/05/17 08:59 PM Re: 98 Mustang GT stalls out [Re: EricF]
EricF Offline


Registered: 07/14/09
Posts: 1645
Loc: SF Bay Area
It's just strange the fuel pump pressure is dead on, I would've thought it would fluctuate.
I guess I could reconnect the fuel pressure gauge and kick the tank or something..
But it's making more and more sense as you guys are explaining it.
the fuel pump assembly would need to come out eventually anyway because of the arm.
_________________________
1993 Ford Ranger XLT 4.0L 4x4 (240k) 5W-30 Synpower
2006 Saturn Relay-3 3.5L (85k) 5W-30 Synpower
2012 Ford Fusion SE 2.5L (39k) 5W20 M/C Semi Syn

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