Sudden Shutdown

[davekp]

A few times recently I've experienced a sudden engine shutdown. It always restarts immediately. Last year I replaced the TFI and remotely located it after the first incident. Engine is '91 Mustang 302 with Ford A9L ECU. The issue persists.
ECU capacitors? Ignition switch?

[videodude]

The capacitors in the A9L should be replaced regardless. They are can electrolytic and are over 30 years old, way beyond their expected life cycle. Even if they look good externally, they could be bad internally, and will be subject to catastrophic failure. Plenty of info on how to do the change on the internet, along with the values needed; it's not a terribly difficult job assuming you have decent soldering/de-soldering skills.

Video

[Xkuzme1]

I was having a near identical problem. Normally I’m not a “throw parts at it” kind of guy... but I was at the end of my rope. I replaced the distributor, coil, battery and I havnt seen any problems since. I went through 3 coils in a couple weeks. I was getting no spark from the coil after just a few mins of running. Honestly, it may have just been a weak battery that wasn’t producing enough amps to both crank the battery and give spark at the same time.

[CraigS]

I think there are now some newly built, more modern ECUs made to replace the A9L. I'd be looking for one.

[davekp]

I think there are now some newly built, more modern ECUs made to replace the A9L. I'd be looking for one.

Yes, but VERY pricey!

[Old Timer]

They make a MS3 that is plug and play with the fox body harness.
They have a map that will get you started, then you will have to fine tune it yourself.
The software has an auto learn that is very easy to use. Some tuners will use team viewer
to log into your PC while you are driving and tune on the go.
Or can have a shop with a dyno finish it up if you are not comfortable with it.

You can build it yourself if you are good at electronics, or buy one.
http://megasquirt.info/products/diy-kits/diy-pnp/

Install
http://www.megasquirtpnp.com/docs/mspnp_g2_eec4a8.php?isModel=1

[mburger]

+1 what videodude said. I don't think the ECU is causing your car to suddenly die, but almost guaranteed removing the cover of the A9L, you will see the three leaking and/or swollen capacitors. Been there done that. If you're staying with the A9L, might as well just change them. There's a possibility it's your PIP sensor, but likely easier to replace the distributor instead of the sensor. Maybe swap in a borrowed distributor to test with?

[Jeff Kleiner]

Dave,
I don't know how many miles you've put on the car but I can tell you that within 12 months and a couple thousand miles before you purchased it the A9L was refurbished with new capacitors and both the PIP and TFI module were replaced. I know that new (or in this case <3 years old) doesn't necessarily mean good but this will at least be a bit of history for you to go forward with.

Jeff

[Jstanding]

start with the basics. check all your grounds

[davekp]

Dave,
I don't know how many miles you've put on the car but I can tell you that within 12 months and a couple thousand miles before you purchased it the A9L was refurbished with new capacitors and both the PIP and TFI module were replaced. I know that new (or in this case <3 years old) doesn't necessarily mean good but this will at least be a bit of history for you to go forward with.

Jeff

Not that many miles.
Replaced the TFI last year when the first shutdown occurred- seemed to solve it for a few months.
Pulled the ecu today and the caps look good.
Possible ignition switch issue? (since it starts immediately after turning off, then on- no cooldown necessary)

[frankeeski]

Dave, if the ignition switch is suspect I can tell you that I've been using this switch in place of the F5R supplied switch for the last few customer builds. Seems like a much better quality switch.
https://www.amazon.com/POLLAK-31-180P-Pollak-Ignition-Switch/dp/B004BTFIZS

[seagull81]

Dave you have a PM

[AdamIsAdam]

I too am recently having a scenario where the engine will suddenly turn off. It's happened once with each drive in the last 4 drives. Initially, the car was idling and now even if I'm just driving along, it will just turn off. The tach goes to 0 RPM and it's dead until I switch the ignition off and then on again. If I'm stopped, I'll have to restart it. If I'm cruising along, I have to turn the key to OFF and then to ON and then I can let the clutch out and it will start up and keep driving.

All the grounds look good unless I'm missing some under the dash. It's a 347cid with an MSD Digital 6AL, an MDS distributor, and a new MSD coil. The car is new to me; I didn't build it.

Do these switches go bad? Car is a 7 year old build but only has 1,600 miles.

What about the main starter relay? Can that somehow interrupt the power supply? The ground and power at that junction box seems good.

I'm at a bit of a loss. Open to suggestions.

[RBachman]

I had a very similar problem with my ignition switch, except mine would sometimes fall back to the run mode and I'd get a slight backfire. I found it after trying to figure why the gauges sometimes stayed energized, and where the intermittent backfire was coming from. I did all the hard stuff before I found it. Crank em' up and wiggle the key to see if you can identify an issue. Also check the connections on the switch and make sure they are tight. Don't over tighten, they strip easily.

[swwebb]

Maybe the coil? Situation seems similar to what I experienced. See

https://www.ffcars.com/threads/coil-failure.638544/#post-6067846

[davekp]

I'm the OP for this thread.
I replaced the capacitors on the ignition module and all has been well so far, but I haven't put that many miles on since. It's been about 3 months.