Mystery hesitation and low volts

Dear all Mondial/328/308 experts. I have been chasing a mystery hesitation. Dear all Mondial/328/308 experts. I have been chasing a mystery hesitation on my '86 Mondial since I bought it in back in June. Symptoms are a strong hestation when warmed up, when under load. gradually gets worse until car stops running. Restarts fine after 1/2 hour. I have done quite a bit, changing fuel filter and pump, plugs, coils, coil transistors. Checked the ignition with an oscilloscope.

Just this week I've noticed the battery voltage drops from 14 volts to 12.3 volts when the cooling fans engage, then remains there even after the fans stop turning! Then the voltage gradually drops down to about 12.1 volts after 15 minutes watching it, so it may even go lower than that. Its like the alternator has stopped functioning and the battery is just draining. Battery recovers to 12.6 volts after sitting. I have checked the alternator belt tightness, and checked the B+ cable to the starter. I also checked the quick-release B+ cable connector by the firewall (I bolted the ends together as the plastic clip was broken and it was loose). Today took the alternator to a repair place. They bench tested it under a load and told me it output about 13.9 volts under an 80 amp load, so they dont think there is anything wrong with it. However, they did not heat the alternator while testing, so conditions not exactly the same as when I am driving it, getting it warm and getting the issue.

 

I am chasing an occasional limp mode on my T that seems to pop up mostly from cold. may not be much help, but I have been through many bits like O2 sensors, ignition module, cleaning stuff, but have just noticed that my smaller batt cable on the battery is loose and maybe the ground on the engine subframe is not as good as it could be. I also noticed the connector in the engine bay is not great. One thing I have noticed on my car is the indicators and fog lights are not working again, now I know the connections are not bad, but it does seem that many issues are just dodgy connections.

 

Check the associated relays after you confirm your grounds are okay.
Alden

 

I'd definitely start with the earthing points.
I had a slow starter motor issue and wasted an afternoon removing and stripping it down to find out that it was very clean inside, and the problem remained. I turned my attention to the big ground lead from the engine block to the rear subframe. It looked clean, but on removing it I could see paint and corrosion hidden between the two surfaces. 5 minutes with a small wire brush cleaning the surfaces up and the motor spins just like it should...