Car mysteriously dies - second time

[thorsen]

Last night, my 1972 250C left me stranded for the second time last night. Driving down the road, the engine gradually lost power until it would not even idle. I made it to the shoulder and the car would start for just a second, then die out. Eventually, it would not even start.

I pulled the lead from the coil to the cap and it sparked to ground, and I operated the accelerator linkage and gas pumped from the acceleration jets. My initial thought was vapor-lock, but I don't think the pump jets would work if that was the case. Stumped, I called AAA and waited.

I left the hazard lights on for the 45 minutes it took to get back home, but when I made it the battery was completely flat, as in the engine would not turn over.

The first time it happened, I attributed it to a low-fuel condition and made sure to keep the tank full. Last night I had 3/4 of a tank and I could hear the (after-market) fuel pump running, so I am 99% sure that is not the problem.

Could an almost-dead battery not provide enough juice to run the ignition system? That is really the most liekly thing I can think of at this point. Obviously I will be picking up a new battery tonight.

[mbdoc]

If the original ignition module is still connected it COULD be the problem.

[thorsen]

Doc,

I haven't looked at it too deeply yet, but I think I just have the points ignition and a coil with a resistor. Would there still be an ignition module?

[ggenovez]

What's the voltage on the battery when the car is running? almost sounds like the alternator is dying and you're running on battery.

[250 Coupe]

Originally Posted by thorsen

Doc,

I haven't looked at it too deeply yet, but I think I just have the points ignition and a coil with a resistor. Would there still be an ignition module?

My 1971 250C had a ignition module. It was under the battery tray. It now has a Crane XR3000 mounted to the end of the tray.

My 250C stranded me once, turned out to be a plugged fuel filter in the fuel pump. If yours is still connected and has a bolt head in the middle of the cover, there is a filter under that cover.

My 1970 250/8 stranded the Ex once, it turned out the points were oxidized enough to kill the spark.

Michael

[thorsen]

Interesting - I have the module mounted on the front of the battery tray. I understand the principle of a points system - but what does the module do? It seems to me like you would need either one or the other.

Last night, my spark was yellow, so I am guessing low battery voltage. The battery that was in there when I bought the car was iffy when I bought it, and now it is reading 12.2 volts - time for a new one.

My Haynes manual makes no mention of the ignition module. Can anyone recommend a better manual?

Thanks everyone.

[ctaylor738]

The basic purpose of the ignition module was to allow the voltage across the points to be reduced so that the points would last longer. That's why you see the two resistors reducing the voltage. My personal experience with (I think) 10 cars has been zero ignition module failure. And I have not seen any intermittent failures in posts - they seem to die once and for all.

A weak spark could be a coil, points, condensor, wiring, or ballast resistor problem.

If your 12.2 volts is with the engine running, then that's a problem you should fix, but it's plenty to start the car.

[thorsen]

12.2 volts was engine off, and was not enough to crank the car. Battery was replaced, shows 13.4 engine off and 13.6 with engine on. Headlights on high drops it down to 13.57. I think the charging system is ok.

With the new battery, the spark is a bright blue.

I think I will replace the points, wires, and coil on general principle. I think I am going to hold off on replacing the ignition system with a Crane or Petronix for now.

[ggenovez]

Sounds like you're a volt short. Should be ~14.5 when the car is running.

[Benziger]

thorsen,

The symptoms you described are very similar to ones I experienced a little while back. I immediately suspected bad fuel / lines, but this wasn't the case, and attention turned to the distributor, which was basically just shot after 40 years of service (replacing the points did little good). I'm not sure if it could have been repaired/rebuilt, but my mechanic replaced it with a second hand unit and the problem was fixed.

All the best.

[Shab]

In my 250C, which did the same thing, the voltage regulator was the culprit. Symptoms began with flickering lighting.

[nhdoc]

Check the ground strap between the chassis and engine. On my '64 it had separated when the car was lifted on bad subframe mounts and I had to remove it and re-assmble it. My car would die when running warm and would crank very slowly, if at all until it cooled prior to this, now it is fine. Check this next as it can cause the conditions you are describing and is a cheap fix if found to be the fault.

[thorsen]

I did not find any ground cable at all - that's a cheap and easy fix.

I did repair some bodged wiring on the 3-terminal connector on the back of the alternator. It looked like new wires had been spliced in with the twist-and-tape method. Nice. I got that all cleaned up.

I am getting close to seriously needing a good wiring diagram for the car. The Haynes manual is not going to cut it. Does anyone know where I can find one?

[nhdoc]

There should be a ground strap somewhere. On mine it was off the firewall to one of the bolts on the bell housing. If you don't have one that would certainly be something you'd want to replace.

[MunichTaxi]

There should be 2 Ballast resistors, a 0.4 ohm and a 0.6 ohm.

A standard ohm meter will register 2-3 times the rated ohms, because it is not the proper way to test them.

Have you checked to see if each of their connections, are free of corrosion?