Fuel pump relay... ground?

morbid · 07-08-2006, 12:13 AM

I remember time ago, I was working with a fuel pressure problem, that ended with another fuel relay. The car is doing the same thing again. Socalldriver (if I'm not wrong), at that time, told me it could be the relay or its ground. I don't think this relay went bad too. I jump between fuses to run the car, and sometimes I pull off the jumper while the car's running, and it stills running until fuel pressure drops again. I think the ground's failing... Do I need to take the relay board out to make another ground point? Where's the fuel relay's ground?

Thanks in advance...

SoCal Driver · SoCal Driver's Garage

With the DME relay in you can only get the fuel pump to run with a jumper across Aux fuse #2 to #3. Removing the jumper with the engine running will result in the engine dying in a few seconds as the fuel pressure falls off.

Pull the #2 fuse. Using the jumper figure out which side of the fuse contacts goes to the fuel pump. Pump will run connected to one side but not to the other. Inspect the fuse for damage. Could be blown. Could have an end cap bent out of shape.

With the fuse out and the jumper in place start the car. Use a test light and check the other end of the fuse holder bracket to see if the DME relay side is hot (12 vdc) or not. If it's not hot then this gets a bit more dicey.

If there is no voltage then you will have to check for the voltage coming from the DME to close the fuel pump contacts.

You will have to pull the DME relay and check the 85b pin on the relay plug (not the relay) for power when you crank the engine over. You will have to jumper between pin 30 and 87 to power the DME. This will tell IF the DME is actually powering the fuel pump circuit in the relay.

These tests will tell you for sure that the problem is the DME or the relay plug/pins/receivers and not just a bad relay or fuse.

newoldguy · 07-08-2006, 10:01 AM

Morbid,
I had a starting problem on my '87 944 n/a that was related to my fuel pump relay ground pin. If you look on the bottom side of the relay, you will see that each of the pins is numbered. The ground pin is one of the small ones and is #1. For some reason as yet undetermined, the pin on the relay itself was not making contact in the fuse/relay board below. The solution was to solder a small wire to the #1 pin on the relay (I put it close to the base so that it would plug in completely) and then run the wire out to a ground bolt on the body. I've had no starting problems since. This doesn't answer why the pin doesn't make contact in the board but at least my car is running. Let us know if this is a solution in your case.
Curtis

SoCal Driver · SoCal Driver's Garage

Early 944's have the relays under the dash next to the drivers door. The later 944's (which you have) relay and fuse panel is under the hood conveniently located. This is not to imply that the same problems can not occure with both relay sockets. It's an access thing that one as to work around until the relay/fuse block has to be dropped out from under the dash -- a real pain in the arse.

As to bad pin receivers in the sockets: Remove them, cinch them a bit tighter, reinsert them then reinsert the relay. Soldering wires to the relay then bypassing the socket makes you one of these SOB PO's.

SoCal Driver · SoCal Driver's Garage

In addition Morbid's relay ground is working as he does not have to jumper the power to the DME. It's only the fuel pump side (second set of contacts) that does not appear to be working.

newoldguy · 07-08-2006, 04:16 PM

If anyone out there can tell us later 944 owners how to access the fuse/relay block so as to pinch the female receptacle, I'm sure we would be suitably impressed. As I was unable to figure it out short of removing the dash and drivers side of the firewall, I resorted to the wire solution. I guess I could have insisted on a purist approach and enjoyed looking at my carr sit in the garage but chose to drive it instead. SOB that I am and all.

SoCal Driver · SoCal Driver's Garage

There are thumb screws at each corner of the block. Loosen them and pull the whole thing up. Once it's out there is a latching bar through the center. Brandon (Brando on this board) found he had to do this same repair to his after he jumpered it wrong.

SoCal Driver · SoCal Driver's Garage

This is the bottom of the later fuse/relay block. The arrow points to the release for the individual relay bases. You can see the end of the hold down bolt/thumb screw in the lower left corner.

morbid · 09:20 PM

Thanks People! Few months ago when I replaced the fuel relay after those test you told me to do, the problem disappeared. Now (yesterday night) I was running the car and the engine turned off while the car was running, so I had to pull over the street. Luckily the jumper I used in the past was in the glove box, and this was the first thing that came to my mind, get it and jump between fuses 2 and 3. The engine started and kept running so I could returned to my house. At my house, while the engine running, I pull the jumper (with ignition switch on), and the engine turned off. Then I sat at my PC to ask you about. Today morning I started the engine without the jumper on, and it didn't run. Put it (jumper) on and the car was able to be use. Then, after that first ride on morning, at evening, I started the engine, forgetting to put the jumper on, and the engine started and ran well until now. That's why I'm confused. Yesterday night and today on morning it wont run without the jumper, and suddenly, at evening, the car ran well without the jumper wire on... That's why I don't know where to find the problem; in the circuit and/or in the components... Tomorrow those test you told will be done, Thanks SoCal. You're the man!

morbid · 08:58 PM

Quote:

Originally posted by SoCal Driver
In addition Morbid's relay ground is working as he does not have to jumper the power to the DME. It's only the fuel pump side (second set of contacts) that does not appear to be working.

SoCall, the tests were done (few days later) and everything was right until yesterday. Now, I think my relay ground is no more working... yesterday night I was working with the cooling fan relay, socket and wires 'cause for some reason the relay burned out with the white/black-striped wire, melting part of the socket. I got another relay from my '83 944 and changed it with the whole socket. When I'm finished doing this, I started the engine to test the fans, and it didn't ran. Remembering the old fuel pump case, I jumped between fuses 2'n 3, but engine didn't run. After a some starting without engine runs, left that until today. This evening starting the car again it ran after some hard starting, but it didn't starts fast if I turn it off to start again. It needs to be hard start to run. So I decided to do the 5 min test. No spark neither pulse in injector socket, but hot in both sides of coil with ignition key on (but no pulses on the green wire while cranking). Another start and the spark jumped, the injector socket pulses and engines started to run. Now it's hard to start until DME relay clicks the DME on. This thing it's getting me mad, my friend...

SoCal Driver · SoCal Driver's Garage

Review: The ignition switch power goes to the DME relay and to the coil. The DME relay's first set of contacts provide power to the DME and to the injectors. Power at the coil but not at the injectors means the DME relays first set of contacts are not closing. No power to the coil means the ignition switch is not working.

If there is power at the coil and at the injectors then the first set of contacts have closed in the DME relay. This means that the fuel pump will run when the engine is cranked. There has to be a good speed sensor for the fuel pump to run after the engine has started as this tells the DME to close the fuel pump contacts.

It is possible that there can be power to the coil and not to the DME relay. The wires do split off from the ignition switch. The circuit going to the DME relay could be open.

With a test light check to see that pin 86 is hot with the key on. Note that pin 30 is hot all the time. Comes from the battery buss.

If you can manage it use the test light from aux fuse 3 to pin 85b. With a jumper from 86 to 87 to power the DME, crank the engine and see if the test light illuminates.

Test light from power to pin 85 will tell you if the ground to the DME relay is good.

morbid · 07-18-2006, 11:01 PM

Thanks Hugh, lets do that in the morning (2:03AM now in PR). Will get back with news later...

morbid · 10:31 PM

Hugh... The old on-off fuel pump relay-ground case, resolved! (I hope...). Checking what you told me last (testing the 85b with the light tester for good ground, with 86-87 jumped) I discovered the problem. From no light in the tester when the ignition switch is in off position, moving key to run position light comes on, but off when moved to cranking; and comes on again when you releases the key in run position. Only the second time in test, out of five, the light remained on in run/crank/run position. Then I noticed the key didn't turned back from crank to run position anymore when you releases it. I still had the switch from my '83 944, got it, put it on, tested and voila! The car is working properly now, starting and running well. I remember I bought the electric part of the switch few years ago to my '83 944, but I put the whole switch on so I can use my old key to start the car now. I hope wont have any problems so far (knock on wood).

Thanks again Hugh, you're the man... SoCal Driver!

...Now I can take time to change the timing/balance belts with tensioner, and to stop breaking more than I can fix.

SoCal Driver · SoCal Driver's Garage

Finally!