Car randomly switches off

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Hi everyone,

My 2003 Mitsubishi Diamante 3.5L 6G74 randomly switches off sometimes.

It's a rare occurrence, usually happens every few thousand miles.
When it does happen though it may happen 3 times within 100 miles, then disappear for another 1,000 miles.

All but once this happened while the car was driving, so it feels like the AC compressor kicking in but harsher. It doesn't actually turn off though as I believe the car "jump starts" itself as it is moving.

Once it happened while idling, it was exactly as if I had turned off the ignition.

Car has had fuel filter, plugs, leads, distributor etc changed with no difference.

Any ideas what this could be?
 
Do any of the dash lights light up when this happens?

Is it just the engine cutting out, or is everything turning off (fan, radio, etc.)?

I bought an Accord with a faulty ignition switch... it would die randomly but it was everything turning off.
 
It could be so many things. Loose connection somewhere, bad sensor, etc etc.

I don't know anything about this car specifically, but I wonder how much a person could learn if you could happen to capture data while it happens.
 
Some causes for stalling:

- Dirty throttle body
- Bad cam/crank sensors
- Bad Ignition switch
 
Fuel pump going bad if it does it going down the road like it's turned off, and then magically comes right back like nothing has happened. Had it happen on a Jeep, and it was very random.

Next time it does it. See if it feels like it's running out of fuel. It may or may not sound like it's running out of fuel.. It took my Jeep almost a year or more before it started sounding like it was running out of fuel, and that's how I finally figured out it was the fuel pump.

I was having stalls on the same Jeep randomly. Most of the time coming to stops or taking off. It would just die, but would crank right back up. Then it got to the point I would have to wait a minute or two before it would crank. That was a crank sensor.
 
I'm not sure if this is a drive by wire throttle body system or not but if it is it could be a dead spot in the gas pedal sensor. When you let off the gas in modern vehicles they go open loop and shut off the injectors. If you are hitting a dead-spot it could be doing this thinking you let off the pedal.

Alternatively it could be loosing the crank signal from the crank sensor intermittently and then regain. As the engine is still spinning it would feel like it shut-off and re-started.

Or it could be a fault with the ignition switch loosing power intermittently so it turns off the ECM, then turns it back on and the ECM sees the engine spinning over so it fires back up the injectors / coils for spark and resumes running restarting itself.

Do you have a way to see if it goes open loop when this happens with a scan tool?

Also can you could hook up a test light to the ECM fuse and see if it looses power to the test light at anytime while you are driving and the problem occurs indicating that it might be the ignition switch.

Intermittent problems can be hard to pin down because they don't happen often and can have multiple causes.
 
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Had the same issue with my 6G72, and it drove me crazy. The throttle body and IAC valve were clean, the injectors had just come off an ASNU machine, new fuel filter, plugs/distributor rotor/cap and wires, no vacuum leaks. Turned out to be the IAC valve, which wasn't cheap to replace, but it did have a ton of miles on it and was 17 years old at the time of replacement.
 
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