924Board.org

[juha_teuvonnen]

I have a 931 that was made in the late fall of 1981.

A week ago the car died in the driveway and refused to start. It has spark, so the issue seems to be fuel delivery. I pulled the fuel pump relay and jumped 30+87. Still nothing.

I am suspecting fuel pump, fuel accumulator and etc. Before I go and spend a hundred bucks on manometer and fittings, is there an easy way to check the pump? I am thinking:
- Measure voltage
- Measure current draw (amperage)
- Measure how much fuel gets pumped out per minute (should be something to the tune of 750 ml IIRC)

Also, had anybody here had any experience swapping the in-tank pump to aftermarket, like a Walbro? I had Walbros on my DSMs, they are reasonably priced and pretty darn close to indestructible, when rigged correctly. I looked at the Bosch pumps and they seem pricey. Any alternatives?


A curious little thing I discovered:

When I took a close look, I realized that for some reason the fuel pump relay is 944 615 113 00. Basically it's the same number as 931, except with 944 instead of 931. In any event The fuel pump relay is marked "10 sho 81" 899635 12V, 2x25A

Does this mean that this is an original relay from 1981? I was not aware that Porsche used 944 relays in late 931s. May be somebody swapped it?

[morghen]

if it started before, the relay you have should work...unless it got magically burned.

I'd do the following:

take the ground wire off the battery, take a can of contact spray and spray it all on all electrical connections. Then dry it out with compressed air or let it dry out before putting the ground wire back on.

Check if you have fuel, you're right about what you should measure...but first make sure the pump even runs by listening to it.

Check for vacum leaks, i was frustrated for weeks after rebuilding my engine that it did not start, i checked the timing 100 times, everything was at its place, except the pop-off valve hoose
_________________
Supercharger and EFI kits
https://www.the924.com

[Paul]

Run jumper from the battery to the + post of the pump, if it does not run, replace the pump.

Pull the fuel pump relay and check pole 30 with a 12V test light. This post is fed directly from the postive terminal of the battery (red/blue wire)

Check 16 amp fuse at postion 2 on the small fuse panel.

Check for continuity from pole 87 of the fuel relay socket to the +wire at the pump.

Make sure the wire on your overboost switch is connected.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[ideola]

[juha_teuvonnen]

Measured the flw:

battery voltage (ignition off): 12.4 v

battery voltage (ignition on): 12.36 v

terminal 30 of fuel pump relay to the ground: 10.36 (WTF?)

terminals of the fuel pump with fuel pump relay installed, ignition on: 0v

terminals of the fuel pump with fuel pump relay removed, 30 and 87 connected by wire, ignition on/off: 0v

There are no noises coming from the fuel pump (not a surprise, given 0 volts).

I left battery is on trickle charger for a few hours. It cranks like a champ.

Here is the kicker: with the relay reinstalled, I tried to crank the car a few times. The car fired a couple of times, like it was trying to start but ultimately didn't. I will try to measure the voltage at the pump with car cranking next.

There are 2 wires that go to the pump, back with green stripe and brown. Somebody connected a gage 16 red wire to the back/green terminal that seems to go to the front of the car (I haven't traced it yet). Does not appear like a factory job to me. Looks like someone has mucked with the fuel pump wiring before me...

[ideola]

Did you bypass the boost cutoff switch as suggested above???
_________________
erstwhile owner of just about every 924 variant ever made

[Paul]

Don't use a voltmeter, use a test light and do the tests again. Also check the 16 amp fuse at position 2 in the small fuse box.

The fact that you got less than battery voltage at socket 30 tells me the problem is between there and the battery post. My guess is a 12V test light will not light when plugged into socket 30.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Paul]

[juha_teuvonnen]

[morghen]

i'd check the fuse pannel, take it out, clean it put it back before starting to hunt for bad wires.
_________________
Supercharger and EFI kits
https://www.the924.com