Weird!..hit a bump and car dead!!!

[damiarosyrn 911]

1983 911sc.
Wow it has been awhile since ive been on here and posting but I figured I had a weird enough incident that it was worth posting for an answer and help.
Well I was basically driving and I hit a small bump in the road and the car just dead and I pulled it off to the side. I checked all the basic fuses and relays right away and it would not fire up and I couldn't smell any gas either. Got it home and later rechecked the relays and then learned I have fire to the plugs and did that test where I placed a light meter in the fuel pump relay plug and when the rear fuel distributor plugger is lifted the light meter does go off so I guess I got power going to the rear. Now if I haven't thoroughly confused you basically Ive learned I don't have power going to my fuel pump after checking it with a 12v light meter, and the pump is good ive checked it , it works, and ive got a good ground to the pump, it seems just no power to the positive.
1. My question is to yall electrical guys, what wires can I follow up from the fuel pump to its nearest power source?
2. Is there something that could of come loose under the dash that could of knocked out the power to the fuel pump, I haven't look there yet?

Any help would be greatly appreciated.

Damian

[pmax]

Originally Posted by damiarosyrn 911

... did that test where I placed a light meter in the fuel pump relay plug ... I don't have power going to my fuel pump ...

The relay pins may not be contacting the plug. Try spreading the "petals" of the pins apart.

You can also bypass the relay and see if it starts.

[964TargaC2]

a light meter?

[Paulporsche]

There are round black plugs under the dash, below the steering wheel, on the bulkhead. Make sure they are fully seated.

[damiarosyrn 911]

sorry a 12v light volt circuit tester. Im assuming the relay is good because as im removing the fuel pump fuse I can feel and hear the relay clicking, and ive replaced the old fuse and relay with new ones with no difference, still no power to the pump.
I just checked the round plugs under the dash and they all seem to be seated fully...

[tirwin]

Damian,

Here’s how the fuel pump circuit works.

If there is a ground on pin 85 of the relay, there is no power to the fuel pump. Car will start but FP shuts off in RUN state.

There are 3 things that can put a ground on pin 85.

1) air pressure plate sensor on the engine (part of CIS)
2) rev limiter behind the dash. you can access it from the trunk
3) alarm

You can place a jumper wire with a fuse between pins 87a and 30 of the fuel pump relay socket to see if the engine will crank and run.

I believe if you hear the relay click that means that something is putting a ground on pin 85.

I had the same problem and it was a faulty alarm module. Didn’t even know my car had a factory alarm.

If there is a ground on pin 85, the next step is to isolate the culprit.

[kwyjibo]

long shot -- exactly the same thing happened to me, and I found that a previous owner had put in a kill switch for the fuel pump as a security system. I checked the wiring because I didn't hear the fuel pump and found a hidden toggle. Somehow the big bump I hit flipped the switch.

[tmadden2]

Probably not your particular issue, but I once hit a big speed bump and actually knocked the negative cable clamp right off the battery terminal. That was an embarrassing discovery.

[crashmy911]

Is motor turning when you turn ignition switch?

[Trackrash]

Originally Posted by paulporsche

there are round black plugs under the dash, below the steering wheel, on the bulkhead. Make sure they are fully seated.

+1 and not corroded.

[damiarosyrn 911]

Thanks so much for the responses but if its not something or another just haven't had time to get back on the 911, but im eager to get this issue resolved its kinda driving me nuts.
Up to now yes the car does turn over but I do not hear the pump whizzing.
Ive done a test where ive place the 12v light tester and connected it in the relay socket in the appropriate place I think it was the 87a and 30 and I went to the back and depressed the air pressure plate just slightly in and the light meter would blink off and on, I forgot the name of this test.
I have place a toggle and wire in the fuel pump relay socket also and jumped it and still to no avail. no whizzing.
I'm guessing a ground to pin 85 is a bad thing...lol?
I've looked at some of the plugs under the dash and the 2 or 3 I saw looked to be flush is there one in particular I need to zero in on?
Im going to look at the rev limiter like you said Tirwin maybe this might be the issue.
Also, this looks like it may have had an alarm system in it at some time or other I do see extra wires scattered throughout, some leading to nowhere.

Thanks for the help....

[tirwin]

Do you have access to a wiring diagram? That would help.

Maybe this helps.

Let’s decode the meaning of the pin numbers. 30 means direct to battery +. 87a means that contact is normally closed. When the key is in ON or ACC, that circuit should be closed, meaning the FP has power.

If there is a ground on pin 85, the relay opens. You should hear/feel it click. Basically, there is no power to the FP in this case.

If you jump 87a and 30 there should be power to the FP. If not, then you need to trace pin 30 out to the battery. Do you see 12v on pin 30?

Try to isolate whether you have power where you’re supposed to and then figure out if the relay is working properly. Also look at the start circuit through the ignition switch.

Two common failure modes: 1) FP isn’t getting power during cranking and 2) car cranks but then dies.

#1 usually points to something in the ignition switch circuit. #2 means something is putting a ground on pin 85 which opens the relay and cuts power to the FP after starting.

I’m trying to type this in a hurry so I hope it makes sense!

[tirwin]

When you jump 87a and 30, remove the FP relay entirely. Good idea to use a fused wire just in case there is a short to ground someplace. Key needs to be in ON position.

The test with the pressure plate is fine. The idea there is if the car wrecks and the engine dies, there is no air going through the pressure plate. No air, plate is at rest. That completes a ground back to pin 85. If the ground shows up on 85, FP shuts off so it doesn’t keep pumping fuel. Raising the plate breaks the contact, no ground. Letting the plate go closes the contact, ground is present.

[damiarosyrn 911]

Just checked sir, there is ground to pin 85 and there is no power to 30.
Ive jumped the two pins with a wire and toggle with no difference , my relay was in though, ill try it tomorrow without the relay.
When u say trace the 30 pin I guessing that wire behind the pin30 should exit the fuse box and eventually go straight to the battery?
On ur #1 cause of failure the FP not getting power, I do have a MSD ignition?
Does this eliminate my rev limiter behind the brake booster as a problem?
Thanks Tirwin.

[timmy2]

Wire from pin 30 runs directly to the fuel pump.
The jumper from 87a to 30 provides direct power to the pump motor.

[tirwin]

Take the FP relay out completely. Jump 30 to 87a. Does the FP run? It should.

If the ground is on pin 85, it’s probably because the air pressure plate is closed. If you have an MSD ignition then you don’t need the factory rev limiter connected — ASSUMING that your rev limit is set correctly on the MSD.

Dennis, I’m sure you’re right! So where does 87a go to? I’m on the road and can’t look at the diagrams.

[timmy2]

87a is switched power from the ignition switch.
Ignition needs to be in the on position to do the jumper test.

To the OP:
Easiest quick test is with everything in place on the car, turn ignition on, take airbox cover off, lift metering plate and listen for pump and injector squeal.
Then start troubleshooting.

[tirwin]

The DIN wiring standard says that 30 means “from battery +, direct”. Not arguing. But you can why I was thinking that.

Link: https://en.m.wikipedia.org/wiki/DIN_72552

[timmy2]

30 Is directly to the battery at the starter in this screenshot of the ‘78 color schematic
But in the fuel pump relay:
Red to the fuse feeding 87a comes from ignition switch.
Fuel pump relay is on the left side.
Relay terminal 30 with the black wire goes directly to the fuel pump.
The red/white goes to the WUR and other devices.
86 feeds the speed relay power
85 goes to the speed relay and the air flow safety switch.

[boyt911sc]

Go search DKLever48’s thread about FP relay socket tests. Everything you need to know and understand how the system works. The five (5) terminals namely 87, 87a, 86, 85, and 30 are individually tested with the ignition switch ON or OFF and FP relay removed. These are the basic tests to identify the culprit/s. Without knowing what is going on with these 5 terminals, you are just doing guess-work troubleshooting.

Tony