Car started missing and died

[csbush]

Was out for a nice back road drive in Chester, my 70 911S with MFI. Was running great for about an hour at normal operating temps, and then it started missing at full throttle. The missing got progressively worse to the point I could barely keep my speed up. It finally died, and would not start. Fortunately I had made it most of the way home and with a short tow, got it back to the house. Next day it started right up and seemed to run fine.

I suspect I have crud in my tank that covered the inlet screen, and it died from fuel starvation. After it sat with no suction on the screen, the crud fell off, and it was able to run.

Any other suggestions or ideas before I drain the full tank and pull the screen out? Tank is 3/4 full and I HATE draining out that much gas!

Chuck

[304065]

what ignition system? what is the voltage measured at the battery terminals with engine off? what is voltage with engine on?

[RSTarga]

Hi Chuck,
Apart from everything mentioned above... coil?
Usually crud in the tank it just dies, and if you stop a while for things to settle down,it will restart.

[Irish911]

Chuck, nice write up in the ESSES. You have a gorgeous car.

You don't mention if this has happened before. You could find out by going for the same drive and see if it happens again, provided you don't mind another tow. It will at least use up some of the fuel. As David mentions once the car dies it should restart in about 15-20 minutes if it is crud in the tank. Do you have an in-line filter you could look at to see if it has any dirt on it? This happened to me with another car and I could usually get home if I waited a bit after the car died. Ended up replacing the tank and fuel pump and have never had the problem again.

[csbush]

Thanks, and appreciate all the advice. I'll check the voltages and take another drive to see how it is acting. Coil is a possibility as I think it is original...but I havn't cleaned the tank out in a long time either.
Thanks to all for the suggestions!
I'll report on how it turns out.

[mobius911]

Bad CD? I had one that only started failing when it got hot.

I recently had a leak in the fuel going into the banjo fitting right at the tank. And like yours the tank was nearly full. I used one of those cheapy transfer pumps to pump out the tank by removing the fuel level gauge. I filled a gas can and just poured the gas into my other cars. Got all but the last gallon or so, and draining that small amount from the bottom was easy.

[Jim Breazeale]

BAD CD. End of story....................

Ciao

Jim

[Cornpanzer]

Agree with Jim that it sounds more electrical. Electrical parts often fail when they get warm. I would swap in another coil first and see what happens. You can buy a cheap VW 12v coil from your local auto parts dealer for about $10 and use it as a diagnostic tool. I wouldnt use it for a long period, but it works great as a tool. If its not that, borrow a known good CD box and try that.

If your existing coil is a silver Bosch part, I would bet a 6-pack of your favorite beer that this is the issue. I have had two fail on me on long road trips...but truth be told they usually just crap out without a period of mis-fire.

[304065]

Thanks, and appreciate all the advice. I'll check the voltages and take another drive to see how it is acting. Coil is a possibility as I think it is original...but I havn't cleaned the tank out in a long time either.
Thanks to all for the suggestions!
I'll report on how it turns out.

If the VR fails in the full-field condition the system voltage approaches 18V. The CDI box has a zener inside that is supposed to limit the voltage, but in practice, the CDI box will throw up its hands and start cutting out after a bit.

You start the car and pull the battery down a few percentage points with the starter drain. . . the VR cranks the alternator full-tilt-boogie, which pulls the voltage range down a bit while the battery charges, but as soon as it's full (a few minutes) then the system voltage goes up into the critical range, causing the CDI to give up.

Certainly check this, it's a lot easier than replacing the filter socks (which is my next guess). CDI's are pretty robust and with the $350 asking price for a three pin these days you don't want to buy one if you don't have to. They can be economically repaired.

[csbush]

Thanks. I'll try and test it out. Had not considered the CD as a possible culprit yet. Appreciate the advice. Thanks for explaining how measuring the batteries gives you insights on the condition of the CD box.