So, this just happened. Damned electricals...

So sorry to here that thorn, I had a similar problem in the past where it turns out to be one of my Digiplex were bad. Hopefully yours have a simpler and cheaper problem. Glad you and your car are safe though.

 

Not an expert, but when I hear it struggles to run at idle I think first of fuel. Start with fuel pump and filter, i.e., proper flow and pressure (injected not carbed, right?).

 

A few weeks ago, my V1 was cycling like crazy. The engine was running terrible. Sometimes it was fine. It was great until warmedup and then the trouble would start.
Then the RPM guage was flaky. Then sometimes monitoring the battery while running the voltage would drop to 10.5v I've seen behavior like that in the past when the alternator was failing. I took it to a shop where he went to check it out & couldn't find anything wrong with it. Put it back together & it's been fine since. He thought - Bad connection brought on by the heat.

But I feel your pain on the confidence factor. Pray every time you turn the key

 

When you have no idea, go back to the last thing you did. In this case, it is the alternator, that is highly suspect.

Did you do it yourself? Did you have someone else do it?

 

Bouncing tach needle suggests voltage regulator to me.


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Tell me more about this. Do you mean the tachometer was bouncing all over the place or the engine was actually revving up and down with consistent pedal input?

 

Maybe a diode failing when it gets hot? Might be a case of bad quality control which is not unusual nowadays. Not an electrical expert but could connect a multimeter to the 4-way connector taking power from the alternator to the fuse panel? It is on fuses 6 & 7 on left hand fuse box on a GT4, but not sure on later cars. Watching voltmeter while tach floats might at least rule out VR.


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I don't think this is a charging/alternator issue. When an alternator stops charging the car will continue to run until the battery voltage is too low to power the circuits. Typically the car will start to lose power, pop/backfire as fuel pressures drop, spark gets weak etc. Given that in the original post it describes shutting off and then being able to crank it back up again, run for 20 to 30 seconds and shut off again, that doesn't sound like a discharged battery.

I'm not familiar with the XDI ignition system, but the symptoms described sound more like an ignition module /crank sensor failing

 

The erratic tachometer seems like a pretty strong indication of an ignition fault. And it would be on the low voltage side.

 

There is nothing more frustrating to troubleshoot than an intermittent issue!

I agree with the two posts above suggesting that it's a primary ignition problem, unrelated to the alternator.

Pretty much any electrical component - from a wire connection to a sensor/computer module can fail in a way where it will function 'properly' in one temperature range and fail at a (usually higher) temp range. I don't know anything about the XDI system but if the crank sensors are still used as per OEM, I'd probably look there first. The ignition coil(s) are also on the list - coils are famous for failing in 'odd' ways. I have posted here before that I worked on a car where the coil failed under hard left turns - worked fine in any other driving mode! I've worked on marine systems where a wire was internally corroded and would carry the load initially but as the components heated up/drew more current, it could not deliver the necessary power and the system shut down.

You could try doing some resistance checks on various suspect items while heating them with a hair dryer to see if there are any sudden changes. Not saying this will positively identify a problem but I have seen it work often enough to be useful.

Good luck - hope it turns out NOT to be a big PITA to find/sort out, but be prepared to exhaust quite a few swear words in the search...

 

I’ve had coils fail this way when hot. It could also be marginal connections that drop below the threshold when hot. You could check for any AC voltage when the problem occurs to rule out failing diodes in the alternator. An AC pulse may mess with the XDI.

 

This is the type of thing that scares me about pulling off perfectly good, proven reliable and very boring factory ignition systems and using something like this.

 

A trick Bob Norwood taught me to determine if its the ignition is to connect a timing light and run the wire inside the car. Watch the light when you car starts to act up and see if the lights stops flashing or flashes erratically.

 

Sounds like a good plan. Hope its a simple fix.


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ALWAYS start with the most basic of basics and go from there.

There is a thread here from a couple of years ago about my car and a issue with it stalling out randomly. It would just shut off. I could start it while I was moving and keep driving. Craziest thing. I was on a club drive and had it towed home and then towed to Atlanta for repairs. Everyone was talking to me about all the usual possibilities and I was about to send off the boxes to that guy that rebuilds and upgrades them.

Turned out it was the spade connector on the fuse box for the fuel pump. It was loose. 2 seconds with a pair of needle nose pliers was all that was needed.

 

Actually It may have been a 1 minute repair because I think we just clipped off the old connector and soldered on a new one. My 12 year old stepdaughter could have fixed it.