fuel pump, engine won't start 7/1994, 525it, M50TU

[werminghausen]

The engine doesn't start.
Story My wife was driving and all seemed normal. Then she was parking and then after 2 hours the car did start but the engine was starving and died..didn't start again.
The starter is strong but the engine won't start. I pulled the car home and it is sitting in my driveway.
History: I have replaced the starter one week ago. I took off the air intake and I had the battery out.

Today I was starting with some analysis:
1) I was measuring the fuel pressure before the fuel rail. I installed a pressure gauge and turned key to position 2. result: 0.2PSI, no pressure. If there is no fuel the engine can't start.

2) I was opening the access panel to the fuel pump (wow was it rusty under neath!) and pulled the 5 prong connector.
I measured if there is 12V at Socket/Pin 4 (-, ground) and 5 (for +) with key in position 2: NO VOLTAGE!
I checked Fuse 23 and it was GOOD.
I was trying to find the Fuelpump Relay in order to jumper the Relay to see if I can get voltage at the fuel pump socket at least.
I pulled an orange relay (not sure at all if this was the fuelpump relay) next to a white relay... and I jumped Socket/Pin 30 and 87 (of the icecube relay) but with no result. I still got no voltage at the fuel pump connector.
My guess is that it was the wrong relay?
How can I identify the fuel pump relay?

3) Then I was applying power directly from the battery to the pump (Ground to Pin 4 and Battery + to Pin 5) and NOTHING! If these are the correct pins to run the pump - then my pump is dead!

Questions:
a) Why do I have no voltage at the fuel pump socket with key in position 2 and relays in original position.
b)Is there a timing issue that the pump does just produce a small pressure, the 0.2PSI and the shuts off unless the engine is running?
c) It is not quite logical to me that 2 electrical problems occur at exactly the same time:the pump is dying and at the same time another electrical component as part of the power delivery to the pump. What do you think?
d) could there be any connection with the previous air intake R/R and starter exchange or battery exchange? did I damage some wires?
But..why did the car run without any trouble for a week?


Can you guys help me out to solve the problem?
Martin

[Dave M]

I was trying to find the Fuelpump Relay in order to jumper the Relay to see if I can get voltage at the fuel pump socket at least.
I pulled an orange relay (not sure at all if this was the fuelpump relay) next to a white relay... and I jumped Socket/Pin 30 and 87 (of the icecube relay) but with no result. I still got no voltage at the fuel pump connector.

My guess is that it was the wrong relay?
How can I identify the fuel pump relay?

3) Then I was applying power directly from the battery to the pump (Ground to Pin 4 and Battery + to Pin 5) and NOTHING! If these are the correct pins to run the pump - then my pump is dead!

Questions:
a) Why do I have no voltage at the fuel pump socket with key in position 2 and relays in original position.
b)Is there a timing issue that the pump does just produce a small pressure, the 0.2PSI and the shuts off unless the engine is running?
c) It is not quite logical to me that 2 electrical problems occur at exactly the same time:the pump is dying and at the same time another electrical component as part of the power delivery to the pump. What do you think?
d) could there be any connection with the previous air intake R/R and starter exchange or battery exchange? did I damage some wires?
But..why did the car run without any trouble for a week?


Can you guys help me out to solve the problem?
Martin

I have a good old post about this problem, but the search function doesn't work for me and Google isn't helping either. So back to square one:

First, the relay is easy to find. See below. I assume pins 30 and 87 are the ones I have jumped with my homejob switch.


Regarding applying power directly to the pump, by "fuel pump socket" are you referring to the electrical connector in the trunk as shown below??



If you've properly identified the power source wires (double check Bentley for details-I don't have mine handy to verify your pins) and directly applied 12V, then you pump is pooched.

Questions:

a) Disregarding applying 12V direct to pump, this is a classic bad fuse or relay. Regarless of your pumps health, you should still have 12V at the connecter. Sounds like you've checked the fuse, so lets rule out the relay (which the above photo should help do).

b) Not sure I entirely understand the question, but IF properly jumped (again, see first photo), the pump will run all day or untill the battery dies (ask me how I know). When jumped, its more than loud enough to hear with the engine off.

c) I think you're dead on, it does sound fishy, which is why I would verify everything you've done so far. Then, if you're lucky, you only replace one, preferrably the cheap relay!!

d) Highly doubtfull.

Good luck and keep us posted.

Dave M

[werminghausen]

I have a good old post about this problem, but the search function doesn't work for me and Google isn't helping either. So back to square one:

First, the relay is easy to find. See below. I assume pins 30 and 87 are the ones I have jumped with my homejob switch.


Regarding applying power directly to the pump, by "fuel pump socket" are you referring to the electrical connector in the trunk as shown below??



If you've properly identified the power source wires (double check Bentley for details-I don't have mine handy to verify your pins) and directly applied 12V, then you pump is pooched.

Questions:

a) Disregarding applying 12V direct to pump, this is a classic bad fuse or relay. Regarless of your pumps health, you should still have 12V at the connecter. Sounds like you've checked the fuse, so lets rule out the relay (which the above photo should help do).

b) Not sure I entirely understand the question, but IF properly jumped (again, see first photo), the pump will run all day or untill the battery dies (ask me how I know). When jumped, its more than loud enough to hear with the engine off.

c) I think you're dead on, it does sound fishy, which is why I would verify everything you've done so far. Then, if you're lucky, you only replace one, preferrably the cheap relay!!

d) Highly doubtfull.

Good luck and keep us posted.

Dave M

Dave, Thanks
I have just 2 relays in my junction box, one is white (oriented toward the engine) and another is orange or the color of your O2 relay (toward the fender). Which one is the fuel relay and which one the DME ?
As mentioned I pulled the orange one and did exactly what you did , jumped 30 and 87 with a 15A fuse in between- and key in position 2: NOTHING
I used the Bentley information about the Socket/Pins at the top of the fuelpump in the the back. If I applied 12 V to the pins I described: PUMP IS DEAD

Again, I ruled out the fuse (I tested it numerous times)
I don't know which one of my 2 relays is the fuel relay. The socket of the orange relay I tested had no continuity to fuse 23 and therefore I believe this is not the fuel relay.
Can someone help me identify the 2 relays I have?
Your top of the fuel tank looks as rusty as mine: I painted it yesterday

[shogun]

check here in the wiring diagrams by production year, all relais and fuses and their locations are shown
http://shark.armchair.mb.ca/~dave/BMW/e34/

[werminghausen]

check here in the wiring diagrams by production year, all relais and fuses and their locations are shown
http://shark.armchair.mb.ca/~dave/BMW/e34/

I guess for my 7/94 I'll go with the 95 diagrams?
I still want to identify: which of the 2 relays is the Fuelpump and which the DME relay? Any idea?

[werminghausen]

I have again measured voltage at the socket to the fuelpump (which is off right now). There is NO voltage at any time when key is turned into position 2. I measured between socket 4 (ground) and 5 (+).
The I measured resistance between Pin 4 and 5 (of the pump side) and there were 5KOhm. What does this tell?
I also pulled both relays. The orange one is definetely the pump relay (4 prong) and the white one is the DME relay (5 prong). I have ordered both relays new in order to eliminate this potential problem.
Martin

[alex 1993 525i auto]

Another way to check without removing the relay is to check voltage at the fuel pump connector while you're cranking the engine (need a helper obviously). If no voltage when cranking (with all relays and fuses installed), then the problem is between the key and the fuel pump.
If voltage on the connector, then it is the pump or the fuel level sender. In my case it was the fuel level sender which was worn, not the pump, neither the relay. When the fuel level sender is worn, the pump doesn't receive the power and doesn't run.

(the fuel level sender is the place where the connector plugs in and tells how much fuel remains in the fuel tank, but the pump is under the sender, connected to it, so if the sender doesn't work the pump can't work)
Unless I'm wrong...

[werminghausen]

Another way to check without removing the relay is to check voltage at the fuel pump connector while you're cranking the engine (need a helper obviously). If no voltage when cranking (with all relays and fuses installed), then the problem is between the key and the fuel pump.
If voltage on the connector, then it is the pump or the fuel level sender. In my case it was the fuel level sender which was worn, not the pump, neither the relay. When the fuel level sender is worn, the pump doesn't receive the power and doesn't run.

(the fuel level sender is the place where the connector plugs in and tells how much fuel remains in the fuel tank, but the pump is under the sender, connected to it, so if the sender doesn't work the pump can't work)
Unless I'm wrong...

Thanks
Do you have another electrical
diagram?
According the electrical diagram Shogun sent for the '95 there should be power at the pump all the times with key in pos.2 when socket 30 and 87 are bridged at the fuel relay (with fuel relay removed) but this is not the case.... (if I measure at socket 4 and 5 at the pump)

[genphreak]

NonNononon

No power at relay or pump unless the engine is cranking. Standard safety feature on most modern EFI cars, to stop fuel pump in the event the engine stops cranking- reducing the risk of fire after accidents, etc.

Only test when cranking. If still no power, upstream one must check the Crank Position Sensor as this tells the ECU when the engine is cranking.

[werminghausen]

NonNononon

No power at relay or pump unless the engine is cranking. Standard safety feature on most modern EFI cars, to stop fuel pump in the event the engine stops cranking- reducing the risk of fire after accidents, etc.

Only test when cranking. If still no power, upstream one must check the Crank Position Sensor as this tells the ECU when the engine is cranking.

Thanks for the info. Someone mentioned before that the pump is priming for a short period of time when key is in psoition 2 and then pump (DME) turns it off if engine is not cranking.
I didn't get any signal for 'priming' at the pump connector though.
In theory I can jump the pump relay by connecting Pin 30(always hot) and Pin 87 at the socket? Then there must be power at the pump connector?

Test o f the pump itself without removing it: If I apply power directly at the pump connector, pin 4 (minus) and Pin 5 (plus) then the pump should run- correct?
If not the pump is dead. Am I correct? Martin