Please help with STRANGE electrical problem

John Pedersen · 04-30-2008, 01:47 PM

First off the car is a 1977 911S, the fuel pump relay had a jumper wire from previous owner from terminal 30 to 87a. I assume relay was bad and po did not want to buy one. I removed jumper and car will not run, put back and fuel pump works, car runs.
Now for the strange part, when I start the car it starts and runs fine, turn off key, car keeps running. The only way to stop it is remove the relay and jumper wire from 30, 87a. Also the idiot lights stay on and cdi is on and humming. I remove the neg from battery and all resets off but same problem when I start the car again. What is up?
John

2.7RACER · 04-30-2008, 02:51 PM

John,
Looks like the PO has been tinkering over and above his skill level.
The power to the CDI and dash comes from the ignition switch.
The fuel pump relay is controlled by both the ignition switch and the CIS airflow switch.
Interestingly the fuel pump relay is NOT energized when the engine is running.
I would find where the ignition power is coming from with the key off and the CDI still getting power.
Remember to NOT disconnect the battery ground wire while the engine is running. It will instantly destroy the alternator. You probably already knew that.
Should be an adventure, someone made some "improvements" without knowing what to do.

John Pedersen · 04-30-2008, 03:06 PM

My theory is the relay is bad, that is why he jumped it and second the electrical portion of the ignition switch is now bad as well?

2.7RACER · 03:53 PM

John,
You can test your theory re:bad relay by substituting any of the round black relays in it's place.
With the igniton on, engine off, the relay should click. You can feel it and maybe even hear it click.
Once the engine is running the relay is off. No click if you remove it.
If you are comfortable trouble shooting with a meter and schematic go ahead.
If you aren't comfortable chasing electrical problems, time to bite the bullet and find someone capable.

boyt911sc · boyt911sc's Garage

John,

Based from the description of your problem, the PO must have hot wired terminal #15 of your ignition switch or ignition SW is defective. Both CDI @ terminal #15 and FP relay @ terminal 87a are connected to S11 (fuse #11) power supply terminal. And would only get power when the ignition switch is turn to RUN position @15. If the RUN position has been hot wired, the CDI and FP (87a & 30 bridged) will be both running all the time plus several pilot lights of the instrument cluster.

There should be no power to fuses #11 and #12 (front fuse panel) when the key is removed or ignition switch at OFF. Determine why these two (2) fuses have power when they should NOT. If you would like to do the troubleshooting yourself, I could provide you with some pictures of the ignition switch assembly with wiring coupler.

Tony

Bench-Racing · 04-30-2008, 06:55 PM

The funny thing is 30 and 87a are already connected (internally) when the relay is not energized. When you energize the relay (latch it) 30 and 87b are then connected. Jumping 30 to 87a shouldn't do anything unless 87a is then jumped again to another accessory.

2.7RACER · 04-30-2008, 09:35 PM

Charles,
You are correct, 87a is connected to 30 when the relay is NOT energized. Known as the NC (normally closed contact).

In normal operation the red fuel pump relay is not energized when the motor is running.

Power comes from the ignition switch when it is in the run position goes to pin 87a and pin 86.

Pin 86 is the power end of the relay coil. Pin 85 is the ground end of the relay coil.

The fuel pump relay is wired to block power to the fuel pump in the event of a stalled motor.

In the start mode, separate from the run mode, power is sent to the starter and pin 87 via the now famous yellow wire.

Power is also at pin 87a and pin 86 from the ignition switch run mode.

Pin 86 energizes the red fuel pump relay and closes the circuit from Pin 87 to pin 30, then to the fuel pump.

Once the motor starts, the air flow sensing arm raises up. This motion opens a switch connected to pin 85 of the relay, breaking the ground to the red relay coil and de-energizing the fuel pump relay.

Once the relay is de-energized power to the fuel pump flows from pin 87a to pin 30 and to the fuel pump.

The jumper wire from pin 87a to pin 30, merely give the fuel pump power as soon as the ignition switch is turned to the run position.

If the engine doesn't start right away it is possible to flood the engine with a jumper across pin 87a and pin 30.

Also with the jumper in place, if the engine stalls the fuel continues to flow through the injectors and floods the engine.

It is not intuitive for the red fuel pump relay to be off with the engine running, but that is how it works.

Check page 2 of the '77 schematic. It's all there.

It takes some study to understand it for the first time.

The '74 models did not use a red fuel pump relay, from '75 to '83 the red relay was used as described.

T77911S · 05-01-2008, 03:08 AM

notice that he said when he removes the neg. from the battery, everthing resets itself. once he turns the key back on, the CD stays on.
he may have wired in a relay (or wired it on by accident), that is latching itself on until power is removed.

John Pedersen · 12:44 PM

Ok guys I need help and a a little patience, I want (WE) want to solve this. Today I removed jumper from 30 and 87A, and inserted a black relay. Car started fine and ran fine without jumper, so po must have done this because of bad relay. Now the car still will not turn off with key, when I remove fuel pump relay car dies. I check the relay plug and 86 and 87A are hot, even when you reinstall relay you can here the coil engaging on the relay. Now I pull relay and pull neg from battery and no power to 86 and 87Aand all idiot lights and cdi and off just like normal.Also 30 at the fuel pump relay is dead, all are dead. I thought 30 is hot all the time?? Is there another relay for somthing that is hangong up to keep the car running or? This is driving me to drink more beer than usual! Any ideas and thanks for your time to help!
John

John Pedersen · 05-01-2008, 03:35 PM

ttt

John Pedersen · 05-01-2008, 05:05 PM

please help!

Mysterytrain · 05-01-2008, 05:16 PM

I'm with Tony on this problem. Sounds like the relay stays energized and maintains the pin 87 to 30 connection on the fuel pump relay. If the yellow wire from the fuel pump relay was moved from terminal 50 on the ignition switch to terminal 15 you would have this condition because of the dual circuits within the switch. Additionally, The relay would fail in time and might explain why the genius PO went with the jumper. There is also the possiblity that the ignition switch has failed and is not breaking the connection between terminals although I think this would also effect the starter solenoid. Two other possiblities..the rev limiter could be defective and intermittently energizing the Fuel Pump relay and causing the engine to cut out. Hence, the jumper fix. You could remove the rev limiter and replace the relay and see how that works. Lastly, does the car have an alarm? Someone may have made some amazing modifications to the wiring. You will need a real good friend with a meter, a schematic and a bottle of JD.. So, I'm guess the PO popped the clutch to shutdown...lovely.
keep us posted.

RoninLB · 05-01-2008, 05:20 PM

John Pedersen · 05-02-2008, 03:48 AM

First off no alarm, checked for that first. The rev limiter, are you refering to rotor in the cap?
I think SC's have somthing like a rev limit device but this car is a 1977.
So are we down to the electrical portion of the ign switch?
John

Bill in OKC · 05-02-2008, 07:46 AM

This is a wild shot in the dark - have you tried a red relay instead of a black one for the fuel pump? The red ones - I have read here - have a diode in them that the black ones do not. I have seen relays latch up without this diode and there might be a reason for Porsche using the red one for the fuel pump.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by John Pedersen

Ok guys I need help and a a little patience, I want (WE) want to solve this. Today I removed jumper from 30 and 87A, and inserted a black relay. Car started fine and ran fine without jumper, so po must have done this because of bad relay. Now the car still will not turn off with key, when I remove fuel pump relay car dies. I check the relay plug and 86 and 87A are hot, even when you reinstall relay you can here the coil engaging on the relay. Now I pull relay and pull neg from battery and no power to 86 and 87Aand all idiot lights and cdi and off just like normal.Also 30 at the fuel pump relay is dead, all are dead. I thought 30 is hot all the time?? Is there another relay for somthing that is hangong up to keep the car running or? This is driving me to drink more beer than usual! Any ideas and thanks for your time to help!
John

John,

I'm a little bit confused about the situation. Could you tell us something about the following scenario (pull out FP relay):

1). Ignition switch OFF: Do you have power @ 87a (FP relay socket)?
2). Ignition switch ON : Do you have power @ 87a ?
Use a test light/lamp for the above tests and see what you have.

Install FP relay back:
1). Ignition switch OFF: Does fuel pump run? If NO, lift the air sensor plate and see if pump runs.
2). Ignition switch ON : Does fuel pump run? If NO, lift the air sensor plate and see if the pump runs.

Need to know the answers for the above and we could tell you more what causes this anomaly. Thanks.

Tony

OSI930 · 05-02-2008, 08:23 AM

1977 to 1986 911 and turbos had an generator warning light diode, Pelican part #911-617-108-00-M100, that is located in line to the generator warning light. Pop out the gauge that contains the generator warning light and you should see it. I had a turbo that would not shut off with the key although the accessories like the tachometer would. I tested the diode and I had current flow in both directions. I bought a new one from our host and the problem was solved. Does the generator warning light stay on when you turn off the key but other electrical items such as the tachometer shut down normally with the key off?

John Pedersen · 05-02-2008, 09:40 AM

Tony
1). Ignition switch OFF: Do you have power @ 87a (FP relay socket)?

No power to 87A or any on FP socket
2). Ignition switch ON : Do you have power @ 87a ?
Yes to 87A also 86
Use a test light/lamp for the above tests and see what you have.

Install FP relay back:
1). Ignition switch OFF: Does fuel pump run? If NO, lift the air sensor plate and see if pump runs.
No to both
2). Ignition switch ON : Does fuel pump run? If NO, lift the air sensor plate and see if the pump runs.
No and yes when you lift the plate
Also, re the generator lite , I don't se a diode on back and oil, gen lite egr., park brake lites stay on after key is off and the CDI is singing!
The car starts and runs fine with a good black relay in FP socket but turn key off, keeps running untill you pull FP relay out, but you need to remove the Neg from the battery to kill power to other lights or CDI, aftr you do this all is fine until you turn key on again!
John

Mysterytrain · 05-02-2008, 05:20 PM

I'm betting on the ignition switch. There are two circuits in the switch as I recall. It could be miss wired or it has failed. That would explain why the FP relay is energized and the lights stay on...but I'm still confused with the need to pull power to reset.

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