'77 930 no power to fuel pumps even with the FP relays jumpered!

G60SuperCharger · 04:51 PM

Was driving my '77 930 on a hot day and all of the sudden the engine shut off and I pulled over to the side of the road. I tried to restart, but I did not hear any fuel pumps running. AAA towed me home.

I hooked up a battery straight to both fuel pumps, and they run just fine, so the pumps aren't the problem.

I looked at the "Why my car won't start" sticky and followed this troubleshooting routine:

"Reach around and pull the connector off the AFM. as soon as the key is ON, no start needed, the FP's should run. (F)
then i would check to see if the boost pressure switch is grounded. with connector off AFM, ground the wire on the boost switch. (A1)
jumper 30 and 87a on yellow relay. (G5)
jumper pins 1 and 2 on the speed relay. (B3)
IF 1 and 2 run the pumps, check for 12v to speed relay. (M pin 7)
if 12v present, speed realy bad. bad solder joints are a problem on this relay.

jumping the FP relays really only lets you know the FP's work.
grounding (D4) just cuts the circuit in half. if the pumps run, then it is something on the left side. if they do not, then it is on the right side.

a note for the yellow relay:
unlike most realys, the yellow relay runs the pump in the de-energized mode, or "normally closed" mode. so the coil can be bad and the pumps can run.
you might consider popping the cover off and cleaning the contacts with fine sandpaper. i bet there are a LOT of good/repairable yellow relays that have been replaced.

the yellow relay and speed relay are known for bad solder joints.

the FP circuit was different for the years on the 930 from what i am told."

This last line is crucial because the '77 does not have a speed relay that I can tell. I used this wiring diagram to jumper the front fuel pump relays. I have 12v+ on pin 30 on both relays, but jumpering them to pin 87 doesn't run the pumps! 12v+ is not getting to the pumps. Any ideas what I should try next?

G60SuperCharger · 07-01-2015, 04:55 PM

Sorry here's the diagram. I also jumpered 87a and 30 on the "yellow relay" (which is a round red one on mine) and it made no difference. This was made for an '86 930...perhaps the front fuel pump relays are wired differently on my '77?

IMR-Merlin · 07-01-2015, 05:13 PM

Are you getting 12v to the 30 terminal on the relays?

G60SuperCharger · 07-01-2015, 05:19 PM

Yes, constant 12v to the 30 terminal on each relay, even with the ignition switched off.

IMR-Merlin · 07-01-2015, 05:35 PM

If you are jumping 30-87 on the relay, then according to the above diagram, you should have the pumps running.

Have you run a continuity test on the 87 to pump wire?

JFairman · 07-01-2015, 05:42 PM

Install a hidden 30 amp double pole single throw toggle switch that bypasses the relays so you can turn on the fuel pumps when the relay ground circuit takes a dump and leaves you stranded at the worst possible time or location.

It will probably happen eventually.. kinda like a flat tire.

T77911S · 07-02-2015, 06:00 AM

use a test light to check for power at pin 30. a MM does not put a load on it.
spin the fuse for the FP. make sure it is making good contact.
if you jumper both relays and neither pump runs makes me think you have a bad connection BEFORE the relays or a wiring problem and not enough current is getting to the FP.
check for power at the FP with a test light. if that is good then it i sthe ground side.
if no power to the FP then you have a wiring problem, but again, if both pumnps dont run that is very very strange.

IMR-Merlin · 07-02-2015, 06:07 AM

Quote:

Originally Posted by T77911S

use a test light to check for power at pin 30. a MM does not put a load on it.
spin the fuse for the FP. make sure it is making good contact.
if you jumper both relays and neither pump runs makes me think you have a bad connection BEFORE the relays or a wiring problem and not enough current is getting to the FP.
check for power at the FP with a test light. if that is good then it i sthe ground side.
if no power to the FP then you have a wiring problem, but again, if both pumnps dont run that is very very strange.

You can also run a 12v wire direct to the 87 terminal to test the connection from the relay back.

G60SuperCharger · 10:56 AM

Quote:

Originally Posted by IMR-Merlin

You can also run a 12v wire direct to the 87 terminal to test the connection from the relay back.

Thanks for the suggestion, I did this and the pumps worked. I decided to make a jumper from a higher gauge wire so the contacts were better, and now both pumps work with pin 30 and 87. Sorry, should have done this earlier.

With that out of the way, attention now turns to the rear relay, which in 1986 was a square yellow one but my 1977 is a round red one, same as the front FP relays. Jumping pin 30 and 87a causes both front relays to click, but fuel pumps still don't turn on. I already swapped the front relays with others (two different sets actually).

I then disconnected the green over-rev safety switch on the distributor and jumpered the two terminals on the lead wire, and it didn't click any relays at all. Should it?

There is no "speed relay" on '77s if I understand correctly. How does the over-rev system work on '77s?

Surf rider · Surf rider's Garage

Just some input from a '76 owner. The design is terrible. Both fuel pumps run off the same fuse. Should that fuse blow the car dies, mine did on a freeway. Further, that fuse gets so hot that the fuse block deteriorates and adds to the problem. On the advice of well learned Porsche mechanic I separately wired that fuse to an isolated fuse with a small aluminum heat sink, no problems now in 15 years. When I want to hear the pumps run I find it much easier to reach behind the air cleaner and just disconnect the relay connecter (blue connector on the top of the CSI unit). The car can also be run in this condition as you can hear the pumps run and then fire it up. On another issue this method will also tell you if your fuel accumulator is going bad as you can hear the pumps run and then change tone as the pressure reaches where it should be and then you can start it. If you do disconnect the blue connector take care the connector and wire do not fall down into the air pump belt. It will not stop the engine or pumps but it is a hassle to replace the connector.

T77911S · 07-02-2015, 11:21 AM

there is nothing else for the FP's on the 77.
2 FP relays
AFM sw
boost sw
AFM relay
pumps.

its best to look at this as 2 seperate circuits.
1 is the FP and FP relay
2 is the circuit that controls the FP relays

for both FP relays:
you have power at pin 30
you jumper pin 30 to 87 the FP runs
you are jumpering pins 30 and 87a at the AFM relay and you hear the FP relay energize.

check power on pin 86 with key on. i would remove the connector on the AFM and check for power from pin 86 to 85

then i would pop the covers off the FP relays to make sure they energize. i would also clean the contacts with 600 grit paper. then i would close the contacts by hand to see if the pumps ran.
i would also remove the relay and close it and ohm 30-87 to make sure the relay is good.

if it still does not work you tested something incorrectly.

T77911S · 07-02-2015, 11:26 AM

Quote:

Originally Posted by Surf rider

Just some input from a '76 owner. The design is terrible. Both fuel pumps run off the same fuse. Should that fuse blow the car dies, mine did on a freeway. Further, that fuse gets so hot that the fuse block deteriorates and adds to the problem. On the advice of well learned Porsche mechanic I separately wired that fuse to an isolated fuse with a small aluminum heat sink, no problems now in 15 years. When I want to hear the pumps run I find it much easier to reach behind the air cleaner and just disconnect the relay connecter (blue connector on the top of the CSI unit). The car can also be run in this condition as you can hear the pumps run and then fire it up. On another issue this method will also tell you if your fuel accumulator is going bad as you can hear the pumps run and then change tone as the pressure reaches where it should be and then you can start it. If you do disconnect the blue connector take care the connector and wire do not fall down into the air pump belt. It will not stop the engine or pumps but it is a hassle to replace the connector.

there is a better way.
short version
cut the wire between the 2 FP relays. run the other wire to a spare fuse if you have one, in my case i have no fog lights. now when you look at the fuse block it looks original, the 2 relays are on seperate fuses.

G60SuperCharger · 07-02-2015, 12:47 PM

I took a closer look at the front pump pin 30 female connector, and it looks like it expanded due to heat! Closed up the connector, plugged in the relays, both pumps work!

I didn't think to check that earlier because I assumed since both pumps didn't work that it couldn't be a loose connector in ONE relay! But I guess the second relay depends on the first one to have a good contact.

I will add another fuse to the relays so they will have an individual power source and won't heat up so much.

Thanks for your help everyone!!!

IMR-Merlin · 07-02-2015, 12:53 PM

woot woot, another 930 back to running status!!

G60SuperCharger · 02:54 PM

...not so fast. Fuel pumps work but now there is no ignition! I noticed that Whenever the fuel pumps are running, the CDI box does not whine. If I pull the FP relays, CDI whine is back. Straight wired the fuel pumps direct to battery, still whenever the fuel pumps are operating, the CDI box shuts off. Is there some kind of fuel pressure cutoff for the ignition?

T77911S · 07-04-2015, 05:52 PM

no.

pin 30 should being lose would not keep both pumps from working. you may of had or still have a bad connection on the crimp side the pin. the wires are tied together where they are crimped. (based on the 86, yours should not be different).

there is a delayed relay that feeds power to the CD. power to this relay comes from one of the FP relays. later this was moved to the ignition switch. a better design.
i bet someone has been into the wiring of the relay sockets and wired the power to the CD unit to pin 87a, i would also check the crimp for pin 30. i bet you just moved it and it now makes a connection.

Surf rider · Surf rider's Garage

Quote:

Originally Posted by T77911S

there is a better way.
short version
cut the wire between the 2 FP relays. run the other wire to a spare fuse if you have one, in my case i have no fog lights. now when you look at the fuse block it looks original, the 2 relays are on seperate fuses.

That sounds like it would also work well. Whatever, the single fuse on the fuse block needs to be modified or as you state, made into two. Trust me the last thing you want is the fuse going bad on the freeway.