Mystery hesitation and low volts..

Dear all 328/308 experts. I have been chasing a mystery hesitation. 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. Any ideas would be most welcome....

 

I am far from an expert when it comes to these cars, I have had my 308 about a year. It sounds like something is braking down under heat. I would check to make sure all your grounds are good. Make sure your fans are not pulling too many amps or voltage. My X1/9 has a problem not too far removed. It would drop to 10.5v and die. I found the problem in the ignition switch. It was an high load wire not making good contact. Easy fix. Check and make sure you don't have any plugs showing signs of overheating.

 

An interesting option, which I did, is to purchase a voltmeter that includes an induction based amp-meter (for DC circuits). They are available on Amazon and other places. I got a nice one for like $35. Serves as a voltmeter but also clamp-on amp-meter -- the wire you want to measure the amp-draw you just clamp over (simple!). This way you can easily tell how many amps your fan is drawing, amongst other things.

I don't want to be yelled at for placing a product link here, but basically if you enter "AstroAI Digital Clamp Meter Multimeter 4000" in Amazon, you will get the tool I am mentioning. BTW, I have no link or benefit to this product.

Just a thought...

 

Have you considered the problem being fuel pressure or the accumulator?

 

Grounds clean and tighten, tighten your battery cables, check all the connections. Check your starter at the terminals - the plastic goes brittle and crumbles, causing a weak connection. It might be time to check the resistance on your cables. look for any parasitic draws. the voltage bounce back up is interesting to me - something is sucking it dry while under load.

 

I changed the filter and pump, but have not measured the fuel pressure (I agree I should do this). I'm keen to figure out the voltage drop first, as this could effect lots of things, including fuel pressure....

 

I understand that but its still above 12V. I'm just thinking you might want to look at perhaps 2 things wrong, not one. At least if you check the fuel pressure and regulator you know you can rule that out.

Lastly, what's the condition of the battery itself?

 

A bit more info: when i measure voltage I have the car running and everything connected as normal. I connect multimeter B+ (at starter) to Batt -, and get 14.4 volts before fans start, then 12.4 volts after fans kick in, then remains at 12.4 volts after fans turn off. Connect multimeter between B+ (at starter) to Batt + and see a voltage drop of 0.1 volts, which is normal.

 

Do you have any suggestion for a fuel pressure gauge that comes with the necessary adapters? Will the Autozone loaner suffice? And yes, I should have checked the battery by now….it does seem to hold charge OK, currently at about 12.5 volts after sitting for 2 days…

 

As long as it fits Bosch K Jetronic should be OK. But I have never done the actual test of the fuel regulator. Its measured over time. This Fi system was the most widely used in German cars of the 1980's.