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E34 (1989 - 1995)

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  #1  
Old 12-24-2012, 01:15 PM
Zenith86 Zenith86 is offline
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Mein Auto: 1991 BMW 535i
Fuel Pump Issues

Hello, I have a problem.

I have a 1991 535i. The fuel pump stopped working so naturally I replaced it only to discover that it wasn't the problem. After the fact i hooked up a 12v directly to the old pump and it runs just as strong as the new one. Next I hooked up a multimeter to the plug that goes to the pump/fuel level gauge, showed 11.92v. Then went to the contacts at the pump in itself. NO POWER!! The car does turn over and there is spark, it will run, but barely, off of the injector pump. Please help me!!!
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  #2  
Old 12-24-2012, 03:42 PM
BMR_LVR's Avatar
BMR_LVR BMR_LVR is offline
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Jump terminals 30 and 87 at the fuel pump relay socket. See if that makes the pump run continuously (it should) and the car should run this way, but it may throw a code for a fuel pump relay (1261). If jumping the terminals causes the pump to run and i.e., the car runs also, then you need to replace the relay.

If you jump the terminals and have 12v to the electrical connector, but the pump won't run, then the new pump is probably faulty. If that is the case, I would try the old pump again. If you have 12v at the switch with the terminals jumped, then it has to be the pump.

I donít know if you have it, but there is a searchable version of the Bentley manual here on the fest. Testing of the fuel pump is spelled out very well.

Good luck.
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It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 200K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #3  
Old 12-24-2012, 04:49 PM
Zenith86 Zenith86 is offline
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I have tested both pumps, they work fine, and i have 12v to the connector as is. but not to the pump. I also just did a continuity test on the wiring. It is fine, I dont know where to look for the relay though. This is my first BMW. I will look at that manual thank you for the help

Last edited by Zenith86; 12-24-2012 at 04:50 PM.
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  #4  
Old 12-24-2012, 05:01 PM
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BMR_LVR BMR_LVR is offline
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Quote:
Originally Posted by Zenith86 View Post
I have tested both pumps, they work fine, and i have 12v to the connector as is. but not to the pump. I also just did a continuity test on the wiring. It is fine, I dont know where to look for the relay though. This is my first BMW. I will look at that manual thank you for the help
PM sent.

Electrical stuff is not my forte, so bear with me, but I can't figure how you can have 12v at the connector and the pump not get that voltage Can you be a little more specific as to when you have voltage at the connector? I.e. is it continuously, with the key in position 2 or position 3 (cranking)?

If you have 12v at the connector, then the relay should be fine, as should the fuel pump fuse.
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Most problems are usually something simple !

Quote:
Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 200K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #5  
Old 12-24-2012, 05:05 PM
Zenith86 Zenith86 is offline
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I have 12v continuously at the connecter with key in position 2 "running" fuse is fine, i changed it to be sure. There does look to be a scorch mark on one of the solder points on the bottom side of the plate. When the connecter is plugged in there is no voltage to the solder points or to the leads that go to the pump

One note on that, Its possible that the 12v im seeing is for the Fuel level sensor which runs off the same plug.

Last edited by Zenith86; 12-24-2012 at 05:07 PM.
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  #6  
Old 12-24-2012, 05:19 PM
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BMR_LVR BMR_LVR is offline
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Quote:
Originally Posted by Zenith86 View Post
I have 12v continuously at the connecter with key in position 2 "running" fuse is fine, i changed it to be sure. There does look to be a scorch mark on one of the solder points on the bottom side of the plate. When the connecter is plugged in there is no voltage to the solder points or to the leads that go to the pump

One note on that, Its possible that the 12v im seeing is for the Fuel level sensor which runs off the same plug.
Key in position 2 should not energize the pump continuously. In fact, from what my very dependable and competent independent mechanic told me (along with my experiment on this very issue on my E36), the only time the fuel pump is energized is upon turning the key to position 3 to crank the engine.

I suspect a bad fuel pump relay. Again, jumping terminals 30 and 87 at the fuel pump relay socket will supply continuous voltage to the pump. If your pump is good, and assuming that there is not a break in the wiring somewhere, then the pump should run and so should the car. If jumping the terminals fixes the no-start, then you need a new fuel pump relay. This is a common fail item.
__________________
Most problems are usually something simple !

Quote:
Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 200K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #7  
Old 12-24-2012, 05:28 PM
kmorgan_260 kmorgan_260 is offline
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I haven't worked on an e34 but had similar problem with e36. On my car the pump and sender have separate wires. There are four wires in the plug - two go to the sender and two to the pump. I suggest you double check the pump connection since I agree with what BMR LVR said. If you have power to the connector and you know the pump works then it should run. From what you describe I would suspect the relay. If it works with the terminals jumped as BMR LVR suggested then the relay is bad. I would use a fuse on the jumper for the relay just in case you connect the wrong terminals or if there is a short somewhere. Good luck!
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  #8  
Old 12-29-2012, 01:03 AM
robertobaggio20 robertobaggio20 is offline
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Quote:
Originally Posted by BMR_LVR View Post
Key in position 2 should not energize the pump continuously. In fact, from what my very dependable and competent independent mechanic told me (along with my experiment on this very issue on my E36), the only time the fuel pump is energized is upon turning the key to position 3 to crank the engine.
If the fuel pump only runs when cranking at key3, how could the engine run after it starts up and you are back at key2 ? Can you remember how you conducted the test on your E36 ?

I have checked it out on my car and there is current at the fp's connector in the trunk when at key2. The current disappears when the relay is pulled, but reappears when the relay sockets are jumped, which means that the pump keeps running whether the key is in the car or not. I had to drive for around 10 miles once, many moons ago, with a jumped fuel relay socket, and each time I shut off the engine I had to remove the jumped relay wires to prevent the battery from being drained down, and replace them when I wanted to drive again. Gosh that was not a nice 2 days.


rgds,
Roberto

Last edited by robertobaggio20; 12-29-2012 at 01:54 AM.
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  #9  
Old 12-29-2012, 06:01 AM
kmorgan_260 kmorgan_260 is offline
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My e36 stays energized with key in position 2. Every car that I have ever owned worked this way.
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  #10  
Old 12-29-2012, 06:05 AM
robertobaggio20 robertobaggio20 is offline
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Your cat's paint scheme would likely look good on your car too.

Wait...wasn't there a picture of a camo E34 seen here recently ?
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  #11  
Old 12-29-2012, 06:28 AM
kmorgan_260 kmorgan_260 is offline
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Originally Posted by robertobaggio20 View Post
Your cat's paint scheme would likely look good on your car too.

Wait...wasn't there a picture of a camo E34 seen here recently ?
I've been thinking of getting my e36 painted. Maybe ...
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  #12  
Old 12-29-2012, 11:58 AM
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BMR_LVR BMR_LVR is offline
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Quote:
Originally Posted by robertobaggio20 View Post
If the fuel pump only runs when cranking at key3, how could the engine run after it starts up and you are back at key2 ? Can you remember how you conducted the test on your E36 ?

I have checked it out on my car and there is current at the fp's connector in the trunk when at key2. The current disappears when the relay is pulled, but reappears when the relay sockets are jumped, which means that the pump keeps running whether the key is in the car or not. I had to drive for around 10 miles once, many moons ago, with a jumped fuel relay socket, and each time I shut off the engine I had to remove the jumped relay wires to prevent the battery from being drained down, and replace them when I wanted to drive again. Gosh that was not a nice 2 days.


rgds,
Roberto
Okay. Let me clarify. When the engine is not running, the fp is only energized for a short duration by turning the key to position 2 (for priming and pressurizing the fuel system) and then it is de-energized once the pressure builds up. In a properly functioning system, this usually takes less than 1 second. The fuel pump is energized when the key is put to position 3 so that it can crank the engine and keep supplying fuel to the engine. It then remains energized when the key is released to position 2 as long as the engine is running.

I tested this by removing my rear seat on the E36. The pump was easily heard when it was running. With the engine off, I put the key to position 2 and the pump only ran for just a second. It then stopped. Once the key was turned to position 3, the car cranked and the pump continued to run as expected with the key in position 2.

Just to be sure that the E34 operates the same way, I repeated the experiment just moments ago with an assistant to manipulate the key. However, the fp on my E34 is unbelievably quiet so I actually had to remove the carpet flooring in the trunk, remove the fp cover and then place my ear over the fp in order to hear it running. Upon repeating the experiment, I got the exact same results: key to position 2 and the pump ran for less than one second and turned off. Turned it to position 3 and the engine cranked and ran as expected. I tried to repeat the process and capture it on video, but the fuel system was now pressurized and therefore the pump did not energize in key position 2 so I could not capture it on video.

If you have 12v at the fuel pump all the time (not the fuel level sender Ė you must make sure you are checking the correct terminals) in key position 2 without the engine running, then you have a problem in the system somewhere. Feel free to repeat the experiment on your car. Nothing has to be disconnected and it does not even require a multi meter, just the human ear and an assistant to manipulate the key (unless of course you have a very noisy pump). In fact, because of the possibility of checking for voltage the wrong point (fuel level sender), my method is probably better because it eliminates the possibility of the error.

This is the very reason that the fp checks can't be done by simply putting the key in position 2. That's why terminals 30 and 87 have to be jumped. This supplies constant voltage to the fp regardless of the ignition key presence or position thereby allowing one to test the fp.

And yes, you can run your car with the fp relay removed and terminals 30 and 87 jumped. However, that will cause a fault code to be generated and stored in the DME. Once the new fp relay is put in, then you can simply erase the fault code.

I hope this clarifies it and sorry if I caused any confusion.
__________________
Most problems are usually something simple !

Quote:
Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 200K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #13  
Old 12-30-2012, 07:20 PM
robertobaggio20 robertobaggio20 is offline
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Thanks for the writeup Steve. I think you and your indy is right.. Just read through the manual and it says this :

Residual pressure, checking
For quick restarts and to avoid vapor lock when the engine
is hot, the system is designed to retain fuel pressure after the
engine has been turned off. This residual pressure is primarily
maintained by a check valve at the fuel pump outlet and the
fuel pressure regulator. The fuel pump check valve is not serviceable
as an individual part.

So there is a check valve at the fuel pump. I believe that when fuel return pressure disappears, as when a hose somewhere bursts or is disconnected, the check valve notices this and stops the fuel pump from functioning. This is probably a safety measure. However i should think that the current to the pump remains live. And I am a little surprised that this happens when we are at key2. Perhaps because the fuel pressure regulator does not function because the engine is not running (the fpregulator needs engine vacuum to function), there may be some version of pressure detection that kicks in at the pump and causes it to go into standby mode or stop functioning altogether..



rgds,
Roberto

Last edited by robertobaggio20; 12-30-2012 at 07:21 PM.
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  #14  
Old 12-30-2012, 07:20 PM
robertobaggio20 robertobaggio20 is offline
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Deleted, repeat post.
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