No power at the fuel pump, relays have been checked, help !

[dogsharks]

Hello guys,

I'm an old forum member, lost my login, had to re-up with a different name so I'm coming back as a newbie!


In any case, I'm back working on my water cooled p-cars after some major distractions and I'm having a heck of a time getting the 1984 944 started.

I went for the obvious, the relays. I've swapped out relays, and I can feel the DME relay click when I turn the ignition key so that appears to be working. However, I don't hear the fuel pump making any noise.

I was tapping relays and at one time I actually thought I heard the fuel pump kick on for a moment, but never heard it come back on.

No matter what I tried in the fuse/relay box (the guy who designed the early model 944 relay box is not my friend today) I could not get the fuel pump activated.

I turned the ignition key over to the running position, where the car would be running if it started, then I went back and put a meter on the fuel pump, and I could never get any reading off the wires leading to the fuel pump. Hmmm, wonder if I could hot wire it.

Looking at the manual I see the brown wire is the ground. Therefore why not put a positive charge on the other lead and see what happens. I did and the fuel pump ran but it would not shut off. I tried starting the car while the pump was running but no results.

so now I'm stumped. Relay seems to be working, I have two tried em both. Fuel pump does not seem to be getting any hot power.

Since I'm in there now, with the car jacked up and wheel off, fuel pump dangling on the fuel line and electric line, I guess I should replace it as it is probably the original pump. I'll do the filter too. However, I am stumped why I am not getting any juice to the fuel pump now.

Help !

Regards,

Dogsharks


1984 944
1990 944 S2 Cabriolet
1983 928S 5-speed

[John_AZ]

Did you try a Clarks relay "jumper" instead of a relay?

DME Relay Information and Testing

B4 you replace the pump, disconnect the fuel pump wires and run a direct 12V line from the battery to see if the pump works-----keep + and - correct.

Could be the ignition switch????

GL
John

[Pops944]

There's a procedure on Clark's Garage for jumpering the DME relay. Try that to get the fuel pump checked. If the fuel pump kicks on using that procedure then you may need to borrow a known good relay to test your circuit. Since tapping the relays created a "possible" start, it sounds like a relay may be at fault. The DME is a dual contact relay and one could be picking up but the other doesn't. If after the Clark's Garage procedure you don't get the fuel pump to start, you'll need to check the wiring from the relay to the fuel pump itself.
Good luck.

[dogsharks]

John_AZ yes I did run a wire directly from the battery and the fuel pump did run. I am going to do the jumper thing, thanks for the tip. We'll see how it goes, but tomorrow now because it's dark outside, sheesh. Sure would be nice if I had a garage that didn't have something already in it that won't run, ha.

Regards,

Dogsharks

[Arizona_928]

Are you getting 12+ volts for the hot wire at the relay board it's like 30. then jump it to 87b

[dogsharks]

AHH-HAAAAA !!

I made up the three prong jumper and then thought I may as well just wire the spare relay like shown in the photo, and what do you know? I am getting fuel pump action. Now I'm charging the battery, too low to crank the car. Yes sadly that's the way I must work with all that is going on in my life, last week end we had to deal with one of our old dogs we had to put down, and we all cried a bucket of tears, then buried him here on the farm on nice high ground with a view. So I have an excuse, and I'll let you know how the hot battery works.

Regards, best,

Dogsharks

[dogsharks]

Okay guys, I jumped the fuel pump relay and the fuel pump is humming along. I can also hear fuel being run through the top of the motor within the fuel system so I know there is some flow there.

Odd thing: None of my spare relays or new relay will work for the fuel pump, and it is unlikely all of them are bad. Strange..... The jumper works

Even with the old and new relays installed, I can feel them as I turn the ignition key and I can feel all of them click.

Just with a little (small amount) of starting fluid into the intake system on the motor side of the MAF sensor, caused the motor to sputter a bit. That's it, nothing else to report for sweating in the hot sun today !

Dogsharks

[dogsharks]

Got fire to the coil but not sure the coil itself is putting out, couldn't test that by myself very well, will try again tomorrow. I can touch a wire to the coil terminals and to a ground, and it will spark so at least I know I have electricity to the coil. I looked at the distributor and all looks good, I lightly sanded the rotor edge with 1000 grit sandpaper.

The fuel pump jumper works, as fuel is circulating. I eased off one of the fittings with a rag handy and yes I do have fuel pressure.

Is the fuel pump supposed to run continuously with the jumper in, or is it supposed to shut off if pressure builds up.

I'm starting to think faulty ignition switch on this one, I wonder why. Is anyone else wondering this too?

Regards,

Dogsharks

[jpk]

It's a common misconception that turning the ignition to the run position should immediately provide power to the fuel pump. It doesn't. The fuel pump is controlled by the DME. It gets power under either of two conditions:
1) key is turned to the start position (engine cranking)
2) engine speed sensor signal reads over 300 rpm or so with the key in the run position.
The idea behind doing it that way is that in the event of a collision, the engine will stall and power to the fuel pump is cut off.
The fuel pump does not cycle; it runs continuously. Any extra fuel flow is dumped back to the tank via the fuel pressure regulators.

[desertt5]

Mine was doing the same thing as your realy. Turned out to be the DME wasn't sending the ground to turn on the fuel pump part of the relay.

[dogsharks]

You may be onto something here, how did you correct your grounding issue on the DME? Is it just a fuse box or relay issue, or grounding the DME itself, or what?

Dogsharks

[desertt5]

I first verified it using a DMM by checking for the ground while crnaking the motor. Right now I simply put in my extra DME. I plan to take the bad one to work, if I can ever figure out which line is dead. We have a killer circuit board repair shop.