'82 SC Won't run

[CMXI-SC]

Need your help with this problem. Have a stock 1982 911SC I've owned since 1984. No trouble at all until.....

1. How it happened: Driving conservitivly above the speed limit felt a small miss. Then a big miss (read complete shut down) then came back to life. While this was happening the tach and speedo were swinging wildly and the wipers started going high speed while not turned on. Finally died completely and pulled to the side of the road. Tried to re-start and heard a "pop" in the trunk. Found the battery had exploded and blew a piece of the top of the case off (lucky it was an Optima battery so no acid spill). Battery was 7 years old so guess it went short finally. Jumped it with a friend's battery and found I had no whine from the CD and no spark. Friend towed me home.

2. What I've done so far: Had the CD rebuilt through ZIMS. Installed new Optima battery. Changed out electrical section of ignition switch. Rebuilt alternator (bearings were bad however regulator and diodes still OK). After reinstalling CD unit trouble symptoms are as follows: Car starts and runs as long as the key is in the "start" position. As soon as the key is moved to the "run (on)" position the motor stops. Have checked the fuel pump and it runs fine with terms 87a & 30 jumpered at the fuel pump relay socket and the key in the run (on) position. Have cleaned as many ground points as I can locate as well as engine compartment T14 on the regulator panel. Took a resistance reading between fuel pump relay socket terms 85 & 86 with the relay removed and it read short. This i think is pointing me to the RPM limiter switch being fried. I have also lifted the air flow sensor with the key on and the fuel pump relay in but could not hear the fuel pump run but do hear fuel hissing in the fuel distributor(not certain this is a valid test). Can not locate T2a or T2e below the regulator panel per the current flow diagram to check conductivity from the air flow sensor ground. Am I on the right track? Has anyone had this problem? Is there a source for RPM limiter switches? Pelicanparts and PCNA have no record of this part.

Thanks in advance for any help you can give.
CMXI-SC

[wckrause]

Have you tested the fuel pump relay? You'd get the same symptoms if it were bad. Same thing with the fuel pump fuse. It looks like (if I'm reading the schematic right), that with the key in the START position, the fuel pump fuse is bypassed.

Electrical diagram

[Early_S_Man]

After talking to Jack on the phone this afternoon ... his alarm system isn't working, and it is the likely cantidate for DEMON that is haunting the fuel pump! My plans are to use the following 1969-vintage HP antique to identify whether the current operating the fuel pump relay is coming from the Brown/Red wire from the alarm sytem after pulling the lead from the Air Flow Sensor Contact ... which, along with the Rpm Limiter Switch, have been eliminated as problems!

[Superman]

So, Warren. Just exactly WHEN was it that this DC milliammeter sold for $825? It's not something you see every day.

[Early_S_Man]

Jim,

That page was from the '75 catalog ... and by the time it ended production around '87-'88 it had a $2895 price tag ...

So, when you find one for sale on eBay for under $100 ... you best be there at the auction end to snipe it, if you have an interest in such a machine! And, for the benefit of Mr. Z ... vacuum tubes reside under that ventilated aluminum case, and yes, it would keep roast beef sandwiches warm indefinitely!

And regarding how sensitive it is ... it can differentiate between the current drawn by three relays with the coils differing by less than 10 Ohms ... all operated by a regulated 13.8 Volt supply!!! The really amazing thing about it is how many things you can do with the buffered output as an amplifier ... including drive a plotter, A/D converter, oscilloscope, or integrator!

[Early_S_Man]

For the benefit of any SC owners, there are a few misconceptions out there about the operation of the red fuel pump relays that need to be cleared up ...

1. The fuel pump relay provides pwer to the fuel pump in two distinctly different ways during starting and 'normal' engine -running conditions. During the initial starting phase the fuel pump gets power from the Yellow #50 starter solenoid lead via the 'make' contacts #30 and #87. The fuel pump relay is operated by a set of 'break' contacts in the Air Flow Sensor Contact ... until ingested air flow is high enough to move the sensor plate ... then, power from Fuse #16 is supplied via the #30 and #87 contacts ... after the fuel pump relay releases due to the interrupted ground from the Air Flow Sensor Contact!

2. While the engine is running normally ... the fuel pump relay serves as an emergency stop device to cut off the fuel pump when a ground is provided to the relay coil terminal #85 from either the Air Flow Sensor Contact (meaning the engine has stalled -- but the ignition switch hasn't been turned off) or the Rpm Limiter Switch -- if max engine revs has been reached!

3. The factory alarm/theft-deterrent system has no schematic diagram in the factory service manual ... the one appearance being the Part I of the '82 USA 911 SC current flow diagram! In the last part of the electrical section of the manual there is a connector pinout and basic Voltage and test lamp checks ... AND an insignificant (to the writer, apparently) note saying that even without power, a failed Alarm Control Unit can DISABLE POWER TO THE FUEL PUMP, 'UNDER CERTAIN CIRCUMSTANCES!' MAYBE IT SHOULD BE CALLED THE OWNER DETERRENT SYSTEM? There is a workaround provided to disable the alarm system by jumpering both terminal #61 connectors at the alarm unit 8-pin socket ... after the unit has been disconnected!!!

Jack found that note while we were on the phone, and after I had suggested that the alarm unit was the source of the mystery ground that was keeping the fuel pump relay operated!

The following diagram may be instructive to interested SC owners ... who may want to remember this incident, and a few things about troubleshooting the fuel pump circuit!

[CMXI-SC]

Warren,

Finally got the plumbing out and found the alarm control mod. Went through the continuity checks and found the alarm didn't work when either door was opened (but we knew that, didn't we?) Guess what! Jumped the #61 terms per the work-around and low and behold the car started and ran. now to find an alarm relay (perhaps from Pelican????) What an adventure. Will call you via land-lines tomorrow. Thanks to you and everyone else for your help.

JACK

[hellblau82]

Hey guys

I have a chopped tunnel harness I'm adapting to another dash harness.

But..in my tunnel harness on the passenger side I have 3 brown red cables..

I'm guessing one of these is the air flow sensor contact..any tips how I can confirm this,?? its wuite difficult to get to the engine connector on the motor

[Vereeken]

So weird to come across the reply from Early S Man. It has happened to me a couple of times last week.

Let us all give him a moment of our thoughts.

Thank you for all your CDI and Coil schematics.

Michel