The early cars use the contacts in the ignition switch to pick the solenoid on the starter. With ~10M of #4 wire, several connectors and a jumper block, the voltage at the solenoid (50) is getting too low to push the solenoid when hot. I've tried to verify this with a 928sRUS test mule.

The car is a 79 with a fairly new starter. After driving in TX heat for 20 minutes, the car won't crank. On the diagnosis, I was able to crank the car after turning off the AC, blower and radio, thus lessening the demand on the 50 circuit.

Since we have a good source of current right at the starter in the 000 gauge feed from the battery, I decided to put a relay in at the starter location. The relay is picked by the 50 circuit that used to go to the solenoid and then the high current leads are from the 000 gauge wire over to the solenoid on the starter housing.

If it runs for a week, we'll do another car, then I'll discuss with Roger about putting a kit together for early cars that suffer from hot-crank problems.

I'm using a simple 53 relay rated at 40 amps, but it's not suitable for underhood use, so it's just a test setup. The kit will offer a suitable underhood relay, wiring, connectors and instructions should it fix the issue.

 

I have an even better solution for you.

Take the wire going to the starter and put it on a Ford solinoid as used on tons of their vehicles. Then run off the other big post a wire and connect this to the big and small post of the starter. Then take the 50 wire and put it onto the activation port of the solinoid. These also have a 2nd smaller pin which you can use to power the other items which are run off the 2nd small connector on the starter.



The reason this is better is that this box rarely fails, and is designed to be run in extreme environments.

 

Looking at the image,
big post left goes to starter,
big post right goes to battery/alt.
Small post left is circuit 15,
small post right is cicuit 50 (activation wire).

I had to do this to numerous 924s as their starter is right under the exhaust manifold. Fixed it everytime!

 

Well, that's real nice, but what picks the solenoid on the starter chief? IIRC, the wire from the battery to the starter lug is a solid section, always on 12V. But I don't have a WSM handy right now. I suppose you could also have the big post on the right also feed pin 50 on the starter, which is the same as I'm doing.

 

The ford option was often used on 914s as well to fix hot crank problems....exhaust pipes cooked the starter.

 

I documented this condition and repair awhile back:

http://www.nichols.nu/hotstart.jpg

 

Doc,

you tag the small line 50 on the starter to the big post. This cuts all power to the starter, then supplies full power to it and terminal 50 on the starter for cranking

 

I even use these solenoids my ride on mowers, can be had for about $10 and last a very very long time.

 

Yeah, I'd rather not do that.

 

Kewl. I kinda figured this had been a problem before with some kind of fix. I think your relay is a bit massive, I'm sure it gets the job done. 40 Amps should do it, if not I can go up to 50 for a few bucks.

 

This is so great. I am hoping this is my answer -> Nichols Hot - Fix
Does it sound like I could be on the right track?

Last night after a 1 hour very spirited ride in the mountains (pushed this old shark a little) I pulled off the side of the road to watch for some deer, tried to start the 928 a few minutes later, no start. After checking the obvious (battery connections, power = yes, lights, windows, no cranky after many attempts) I decided to bump start in reverse since I was still heading up the mountain. Yahoo, worked, fired right up, on second attempt and hardly any backward motion.

All dash lights are on, I think I read somewhere the lights all are lite since it was bumped started, not sure if this was a dream I was reading in or not.

Got home, turned her off and re-started a few times no problem.

Anyways, this matches my issue possibly. My 928 was definitely hot from the run but weather was cool, in high 60's. Never happened before in the year I have been driving her (5k miles).

I have not checked every single ground but have checked / cleaned some of them in the past.

I feel like I am in some kind of a test car at times, now what?