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'89 Stalls when Warmed Up - HELP!

2610 Views 13 Replies 7 Participants Last post by  90GT AOD
My '89 Mustang will stall after 15-20 minutes, once it’s warm. (It’s completely stock and has always run perfectly.) It doesn't matter if I'm driving it or not - it stalls sitting in the driveway, going 70MPH down the highway (giving it gas) and while sitting at a light (revving or not as I've tried both). Both the battery gauge needle and the tach suddenly fall to zero and it shuts off, sometimes those two gauges will drop like it’s going to stall but the engine will kick back up and keep running. But once it starts stalling, it become more and more difficult to restart. It never did this until the Mustang shop I bring it to, did some tuning, replaced the EGR sensor and adjusted my idle, leading me to believe that it is an electrical problem, maybe the work they did uncovered a problem? (The thing is, is that they keep telling me they can’t get the car to reproduce the problem - it does it without fail for me every time I drive it. So either they can’t figure it out or they just don’t want to spend the time on it. I feel like I’ve been thrown out into the cold!) I've also had the following recently replaced: alternator, voltage regulator, battery, battery cables, starter. It's not the fuel pump as I can hear this every time I start the car. And if it is a fuel problem, why doesn't it occur instantly? Why wait until the car is warm? Maybe a vacuum leak?? I am completely frustrated. I would really appreciate any suggestions!!!!
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I'd bet the module on the distributor has gone bad, it sounds like the symtoms. I haven't had to buy one in a while but I always keep an extra one in my glove box on both my Mustang and Econoline Van.

They're very easy to replace, the only "hard" part is that you might have to move the ditributor to gain access to the 5.5mm bolts or screws, you might want to buy the specail tool at the parts store to make it a bit easier. So just mark your distributor, unplus the wire plug, unscrew the mounting bolts, carefully push straight down on the module to "unplug" it from the distributor, then replace. Just make sure you use the clear delectric grease on the back of it, the new module should come with a small packet of it.
Yes, that's what I think now too. I did some research online and found a bunch of articles on the TFI module going bad. Sounds just like my problem. I'll pick up one tonight along with that tool. Thanks for the tips on replacing it!!!
I had the exact same problem before but it was not my module, if I were you I would take off the module and have it tested at an auto-parts store before you jump out and buy a $100 part. They will test it for free just make sure you ask them to run it through at least 3 times so it gets nice and hot. If it turns out to be good then I would hook a fuel pressure gauge up to it and let it warm up and as it starts to die watch the fuel pressure to see if it drops as the car dies. That is what my problem ended up being even though it really does sound like the module. I know it is kind of weird that the fuel pump would only quit when it is hot because it had me baffled too. Also if you are hearing the fuel pump when you turn the key to on and it is excessively loud that is another sign that it is the pump.
I hate to be the bearer of more bad possibilities, but I think that the pickup inside the dizzy can cause these symptoms, too. I don't know if they can test the pickup, Advance said they couldn't. They can test the TFI though.
I'd guess the ignition module. Does it start back up about 5 minutes later?
Ok, everyone, get this...I replaced the ignition module as it was original, 170K miles, I figured this is it. I warmed it up for 15 minutes, took it out, drove around, fast, slow, stopping, the works for 45 minutes, get it nice and hot. It was perfect! No stalling, no 'almost' stalling...I was very happy!

So I'm way to work today, which happens to be about 15 minutes from my house, I blast down the highway, get off and stop at the light at the end of the off-ramp, and it 'almost' stalls there.

Back to square one...
Get ahold of a fuel pressure gauge. Check your PCV valve too. I had one on my '82, which wore out, it would open too far, and stick, causing a severe lean condition. Drove me crazy, as it took months to figure it out. You might try pulling codes too.
Well the shop said they checked the codes and came up with nothing. They also said they checked the PCV value and it was good. I guess I'll pick up a fuel pressure gauge and check that next...while I'm at it, maybe I'll get a code scanner too and check that myself...
Is it any better? You said it almost stalled, so it sounds like it's a bit better, you might have multiple problems you need to chase down. You said no codes were shown, but did you pull the codes twice, once with engine running, and one with the engine off?

Did you buy a aftermarket module? Because those can sometimes not be the best of quality, that's why I bite the bullet and bought the Ford module.
I would have agreed with meangreen92 about the stator (pickup inside the distributor), but since pulling the codes revealed nothing it looks like something else. Failure of the stator generates a code, even if it is intermitten. I have seen alternators with intermitten shorts cause those symptoms. What brings that to mind is that you said the "battery guage" drops when it stalls. That sounds like an electrical short. If you can borrow an alternator to sub, that would be a good test. You can take the alternator to AutoZone or one of the others for a free test, but if it is intermitten, that might not be conclusive.
I just had another thought. Check to be sure that you electrical system has a good ground. Loss of ground shuts down the ECM. Maybe add a new/temp ground just for a test.
The tach needle falling to zero indicates a loss of the SPOUT signal. Suspecting the TFI module or the distributor stator seems like the correct course of action at first...

However, the voltage gauge also falling to zero would seem to indicate a more systemic electrical problem. If the gauge is losing power, other systems probably are too, including the PCM.

Since it seems to be receiving power from neither the battery nor the alternator, I would looks for a bad connection that would cause a loss of power from both of those sources at once. A bad chasis ground connection seems likely. Follow the thick black wires.
RMarsden said:
...Both the battery gauge needle and the tach suddenly fall to zero and it shuts off...
Good advice!! All the Fords I've owned always seemed to have a ground problem one time or another in their life.
davido30093 said:
I just had another thought. Check to be sure that you electrical system has a good ground. Loss of ground shuts down the ECM. Maybe add a new/temp ground just for a test.
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