Fuel Relay Clicks, Fuel Pump No Power

[OsoMoore]

I am tracing a lack of fuel problem on my 79 SC.
First I switched out my original fuel pump relay and tried two different new ones from PP. One didn't seat properly in the socket, so I held it in. Neither fixed the problem.

Then I pulled two different injectors, and neither had fuel.
Next I pulled the fuel line at the accumulator. No fuel came out when I cranked the car.
Next, I pulled off the belly pan and hooked my trusty multimeter up across the two fuel pump contacts. It shows 0 volts. When I crank the engine, I see -0.7 volts.

I put a finger on the relay while I turned the key. When I turn to the "ON" position (but not cranking) I feel the relay click once. When I crank, I don't feel anything from the relay.

So it appears there is an electrical issue, right? Any ideas where I should look next? My fuel pump is pretty new and looks in good shape. Its little rubber shock absorber is broken but in place, and the pump is held in place by a hose clamp. Both contacts appear reasonably clean. I pulled back their little rubber covers in order to hook up my multimeter to the two contacts.

[DRACO A5OG]

Oso, try swapping the relay and see if she will power up.

[OsoMoore]

Originally Posted by DRACO A5OG

Oso, try swapping the relay and see if she will power up.

No luck. Both spares and the original show the same behavior when watching the multimeter. I also tried using the power window relay (which I know works) and got no power.

I was curious, so I pulled out the relay and then tried. I get the same -0.7 volts with no relay as I do when I have a relay.

I guess I can try to start tracking the wires, right? Does anyone know if the fuel pump needs a ground, or is one of the two contacts a ground?

[timmy2]

Black wire is 12vdc from terminal 30 on fuel pump, brown wire is ground.

Why not jumper the relay socket like you were going to take fuel pressure measurements to ensure pump is working?

Might want to check the integrity of wire from safety air flow switch wire. It is the brown with red stripe wire that shares a 2 terminal "T" connector with a red wire near the CDI box.
Or just ground that point with a jumper to test if pump will run with ignition on...

[Royze]

I had the same issue with 930 two weeks ago & finally solved today,

There was two issues to the problem, The battery had good voltage but the ground wire was not connected right, after that I also replaced the startup cell motor and the engine started like a charm. I only need to renew my fuel accumulator & then I can call it a day.

[thumbdoctor]

Ignition switch contacts?

You mentioned to feel a "click" from the fuel pump, so I guess that it's activated wehen starting. Remember the the fuel pump is fused (#16) and draws a lot of current. That often causes burned fuse contacts. Check the fuse, clean the contacts and try again. I had similar electrical problems with my fuel pump, caused by corroded contacts on bridged terminals at the underside of the fuse box. Cleaning, soldering and protecting the soldered joints solved it and my '78 Targa didn't show the problem since the repair last summer.

To your question regarding grounding of one of the pump terminals, I can confirm that the minus-terminal is grounded.

BTW a (relatively) new pump is no guarantee for fuel supply. Debris and rust particles from the fuel tank reaching the pump, can easily damage the pump. The CIS system is a very nice fuel injection system as long as the fuel system is clean, clean and clean again. Do not just replce the pump when it's dead. Also check, clean and/or replace the fuel filters of the system. If you don't the new pump could also have a short life.

Otto

[porwolf]

I would do a systematic tracking of the wiring with the help of a schematic like the ones in the Bentley book, starting at the battery. You could disconnect the +wire on the pump, pull a temporary wire form the battery and connect it to the pump. You should be able to tell that the pump is running then. If that work you know that the pump and it's ground connection is OK. Then I would connect that temporary wire to the relay socket pin that leads to the + connection on the pump. If the pump works the problem lies further upstream. You could go in that direction until the pump stops working. Then you have located the problem. I have never needed to do that. But that is what I would try.

[Flat6pac]

remove the relay, look at the numbers on the bottom representing each pin. On the relay plug female, jump pins 30 and 87a will direct drive the pump.
Bruce

[porwolf]

Originally Posted by Otto H. Wegkamp

You mentioned to feel a "click" from the fuel pump, so I guess that it's activated when starting. Remember the the fuel pump is fused (#16) and draws a lot of current. That often causes burned fuse contacts. Check the fuse, clean the contacts and try again. I had similar electrical problems with my fuel pump, caused by corroded contacts on bridged terminals at the underside of the fuse box. Cleaning, soldering and protecting the soldered joints solved it and my '78 Targa didn't show the problem since the repair last summer.

To your question regarding grounding of one of the pump terminals, I can confirm that the minus-terminal is grounded.

BTW a (relatively) new pump is no guarantee for fuel supply. Debris and rust particles from the fuel tank reaching the pump, can easily damage the pump. The CIS system is a very nice fuel injection system as long as the fuel system is clean, clean and clean again. Do not just replace the pump when it's dead. Also check, clean and/or replace the fuel filters of the system. If you don't the new pump could also have a short life.

+1 on making sure no debris enters the pump and doing a thorough cleaning around the exit line of the fuel tank, together with inspecting and possibly replacing the in-tank mesh type fuel filter. (It is still available and less than $50.- at Pelican) Look what could be lurking in the tank:






It is very important to make sure none of that ever reaches the fuel pump. A clean, complete tank fuel filter, and a clean fuel path after that filter, at the very bottom of the tank which is double walled with only about a quarter inch spacing in between and about 4 inch diameter, is very important. It can all be accomplished with tank in place, but empty.

[ossiblue]

Originally Posted by OsoMoore

I am tracing a lack of fuel problem on my 79 SC.
First I switched out my original fuel pump relay and tried two different new ones from PP. One didn't seat properly in the socket, so I held it in. Neither fixed the problem.

Then I pulled two different injectors, and neither had fuel. Normal. No fuel because no fuel pump running.
Next I pulled the fuel line at the accumulator. No fuel came out when I cranked the car. Normal, for same reason as above.
Next, I pulled off the belly pan and hooked my trusty multimeter up across the two fuel pump contacts. It shows 0 volts. Normal for non running engine. When I crank the engine, I see -0.7 volts. Not normal. Should have 12v when cranking.

I put a finger on the relay while I turned the key. When I turn to the "ON" position (but not cranking) I feel the relay click once. When I crank, I don't feel anything from the relay. Normal. The first click is the relay switching the fuel pump power feed to the starting circuit (87). You would not feel another click while cranking, but would feel another click once the engine fired and intake vacuum opened the safety switch. The second click is the relay switching to terminal 87a.

So it appears there is an electrical issue, right? Any ideas where I should look next? My fuel pump is pretty new and looks in good shape. Its little rubber shock absorber is broken but in place, and the pump is held in place by a hose clamp. Both contacts appear reasonably clean. I pulled back their little rubber covers in order to hook up my multimeter to the two contacts.

As suggested, try jumping the sockets in the relay base, 30 and 87a, or unplug the wire for the air sensor switch. Turn on the ignition and see if the pump runs. If it doesn't, measure the voltage at the pump hot wire (disconnect it from the pump) with the relay jumped and ignition on. What do you find? No power? check the fuse box. If you jump the relay terminals and get power to the wire but the pump won't run, it's probably a faulty pump.

[OsoMoore]

Update!
Jumping 87A to 30 had no effect. I did discover, however, that both contacts of the fuel pump go to ground!
I will next remove the contacts and see if the pump itself is shorted, or just the contacts.

I certainly did not expect my continuity test to beep when testing across the contacts.

Also, my fuse box is something of a mystery - the fuel pump fuse (number 6 from the left) is not located there anymore.

[OsoMoore]

More info.
I removed both of the wires connected to the fuel pump.

The two contacts on the pump are a short circuit, to eachother as well as to the fuel pump housing.
Both of the wires, when disconnected from the pump, are shorts to ground (and thus to eachother).
When I crank the engine, I see 0.6 volts across the wires.
While cranking I see the ground wire remains shorted to ground at 0 volts.
While cranking I see the "live" wire goes to 0.6 volts compared to ground.

Obviously something is wrong in the wiring leading to the fuel pump - I should see 12 volts on the live wire when cranking.

Does this mean the fuel pump is dead as well? I'm not sure what my readings on it are supposed to be.

[timmy2]

Oh boy!, somebody has changed a few things on you....
Try to trace the wires from the fuel pump back to the fuse box area, disconnect them at both ends and then test each on to ground and to each other. They should not be grounded or have continuity to each other.

The pump may have an internal winding shorted to ground. the only way to check is to apply a fused 12 volts directly to it. 10 amp fuse in line on the supply side, if it blows the fuse you know your pump is gone.

Try to trace out the wires from the relay socket at the fuse panel and see where they are landed. then try to put them all back in their normal location.

The schematic for the '78 SC shows the colors and fuse locations for the wiring. (once you decipher the code of European wiring diagrams...)

Understanding European DIN Wiring


Pelican Parts - Porsche 911 Parts Listings & Diagrams

[OsoMoore]

Originally Posted by timmy2

Oh boy!, somebody has changed a few things on you....
Try to trace the wires from the fuel pump back to the fuse box area, disconnect them at both ends and then test each on to ground and to each other. They should not be grounded or have continuity to each other.

The pump may have an internal winding shorted to ground. the only way to check is to apply a fused 12 volts directly to it. 10 amp fuse in line on the supply side, if it blows the fuse you know your pump is gone.

Try to trace out the wires from the relay socket at the fuse panel and see where they are landed. then try to put them all back in their normal location.

The schematic for the '78 SC shows the colors and fuse locations for the wiring. (once you decipher the code of European wiring diagrams...)

Understanding European DIN Wiring


Pelican Parts - Porsche 911 Parts Listings & Diagrams

I ran to the auto store, bought a length of 12 gauge wire, some alligator clips, and an inline fuse holder w/ 10amp fuse. 10 minutes later I had a test wire (I'm proud of myself!)
I tested the pump directly off the battery and the pump runs just fine. So now I will begin tracing the wires back and testing continuity, as you indicate.

EDIT: It looks like the black wire on the pump should go to pin 30 on the fuel pump relay. Checking now!

[OsoMoore]

So here is the relevant part of the car wiring schematic.
G6 is the fuel pump. The hot wire comes from pin 30 on the relay (J16). I checked and both ends of this wire (fuel pump relay socket pin and wire at the fuel pump) go to ground.

I am thinking that, because pin 30 also leads off into the warmup regulator area, I should check around there. Fun times!

[OsoMoore]

I separated the line at T1d - the wire from pin 30 (fuel pump relay) to the warm-up regulator.
Once the line was disconnected there, pin 30/fuel pump black no longer went to ground.

So the issue is now isolated to a short between T1d and the warmup regulator! On to the next stop... T14 on the regulator panel.

Uhhhh.... Does anyone know where that is? And where is the warmup regulator?

[ossiblue]

The warm up regulator is on the left side of the engine, near the intake for( #5)correction, #3--thanks timmy2. It is a rectangular metal box with fuel lines coming from one side. Easy way: find your fuel distributor, find the center fuel line and follow it to the WUR. There is an electrical connector on the wur that can be unplugged. Try unplugging the connector and reconnect T-1d and see if you still have a good connection to the fuel pump (no short). If so, then the electrical component of your wur is shorting out.

[OsoMoore]

Originally Posted by ossiblue

The warm up regulator is on the left side of the engine, near the intake for #5. It is a rectangular metal box with fuel lines coming from one side. Easy way: find your fuel distributor, find the center fuel line and follow it to the WUR. There is an electrical connector on the wur that can be unplugged. Try unplugging the connector and reconnect T-1d and see if you still have a good connection to the fuel pump (no short). If so, then the electrical component of your wur is shorting out.

Ok, I will go after WUR next.
I did some other testing and found that T1d connects to the 14 pin connector on the regulator panel. Specifically, it connects to the 3rd pin from the top right. When that connector is disconnected, T1d does not short to ground. When I plug the 14 pin connector in, then T1d shorts to ground again.

I'm going to check on the WUR now.

[Targalid]

Warm up regulator (WUR) is that little silver rectangular box in front of the distributor that feeds fuel to your fuel distributor in the engine compartment. It has a little heater in it that requires current during engine warm up.