Need some help
I would suggest at the minimum, having the alternator and battery tested. Not at the chain parts stores, but go to a reputable shop where they can perform a load test on the battery and check alternator output. A test like this is properly done with the battery in the car, alternator hooked up and the engine running.
It's entirely possible that the shop did not reinstall the various ground cables or didn't tighten the battery ground cable where it attaches to the engine.
One thing you may also check is to watch the displayed voltage when the problem happens again. With the ignition key still at RUN, the display should still show a voltage. What is it?
these ignition systems require so much voltage that they will not fire a spark plug without at least a good 10V AND high amps behind it. A fully charged battery will only run these ignitions at hiway speeds for about 10 minutes...and you can watch the volts drop in 10ths as you drive....
So,
if you apply ANY drain to the system in a low/minimal charge situation, that will be enough to kill the borderline voltage level to the ign system. Mine will drag the idle down 100 rpm if I bottom out the power windows as it pulls the voltage down and the alt tries to kick in briefly to compensate. Any addition load will stall a weak battery IF the ALT is not producing a charge.
The Volt meter should show you what the alt is doing....should show 14+ V after start up...and idle at 13 when normal and some things running....if the gauge shows less than 13 immediately after start up...the regulator or the alt itself is faulty.
As stated, a good shop would have tested and advised regarding the alt condition. Replace it if faulty or trace the wiring issue. Shorts, hot wires grounded out and poor connections can ALL cause this.
As far as your many grounds, none of those matter to the alt. Those are ALL engine control, fuel inj and dash display control grounds. The grounds that you care about for the alt are the one in the plug-in, the battery/frame/block and the block/frame strap by the oil filter. The "bundle" of harness grounds on the block are all ECM and display grounds. Almost each electrical servo or electrical "thing" in a C4 will have its own grounds somewhere near that part. None that I can think of are related to the charging.
Its easy to over-think these things. Get the Alt tested, and replace if necessary. If it comes down to a wiring issue that YOU cannot diagnose yourself, find an 'auto-electric' specialty shop to do that work. They only charge $75 to $90 per hr to trace shorts and harness issues like this. They will ID the problem and allow YOU to do the repairs yourself. I've used auto-elec shops several times and NEVER had to pay more
than $75 (1 hr min) for a proper diagnosis.
Your FSM will guide you thru any tracing of the system that you want to attempt yourself.









