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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 04-06-2013, 03:46 PM
Fabius Fabius is offline
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Low Voltage at Fuel Pump

Hello, all, I've exhausted my feeble know-how on this issue so I really hope you guys can help me out. Three months ago I purchased a 2003 330i with 126,000 miles; I've put about 2,000 miles on since. A week ago, while on the highway, the engine stuttered and shut off on me. I pulled onto the shoulder and was able to turn it on one more time before it stuttered again and shut off, after which it cranked but did not start.

I towed it home and, suspecting a fuel pump issue, the next day I pulled the back seat off and checked the voltage at the pump. I got between 4 and 5 volts, so I went to the battery and checked voltage there. Battery was putting out about 7 volts, so I took it to Autozone and they told me it wouldn't hold charge, so I replaced it and proceeded to check the voltage at the pump again. I got the same 4-to-5 volts; pump wouldn't start up, car would crank but not start. I read 4-to-5 volts regardless of whether I have key in "2" position or if I'm cranking.

I then checked the 20A and 15A fuses associated with the fuel pump, and those were fine. I then switched the horn relay with the fuel pump relay and still no luck. I then put the fuel pump relay into the horn relay slot, and horn worked. This is pretty much the limit of my know-how, but I did check voltages at the horn and fuel pump relay. I'd like to know from you guys if I did that right. I was able to measure 12 volts at both the horn and fuel pump relay, but I don't know enough about electronics to know whether my power loss to the fuel pump is between the relay and the fuel pump or between the relay and something else; is it my control unit? How do I know? I've searched everywhere for what voltage I *should* be getting at fuel pump. Some say 4-to-5, others 12V, still others only 12V when I'm cranking. But again, I only read 4-to-5 whether I'm cranking or not, and pump's not turning on.

I've attached the fuel pump relay wiring diagram from my Bentley manual and a picture of my fuel pump relay slot indicating where I measured 12 volts; the picture is oriented as though I'm looking right at from the passenger seat. I circled in red where I was able to read 12 volts; I was not able to ready any voltage everywhere else in the fuel pump. Your help is greatly appreciated.
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Last edited by Fabius; 04-06-2013 at 04:04 PM.
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  #2  
Old 04-06-2013, 03:59 PM
GoForthFast GoForthFast is offline
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Your DIY skills are ahead of many here. And logically explained!

What is the age of your fuel pump now? May be time for a new one.

I seem to remember that you won't read a full 12 volts at the pump all the time, so hence my statement just above this one.
Have the voltmeter hooked up with no hands and check the voltage AS you turn on the ignition. May jump to 12 and then cut back.

If I had your car and pump was due anyway, I'd start off with that.
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  #3  
Old 04-06-2013, 04:07 PM
Fabius Fabius is offline
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GoForthFast, my fuel pump is original. I'm ready to replace the fuel pump, but only if I've narrowed the diagnosis to that first; I hesitate to replace it without going through a process of identifying it as the problem, meanwhile actual problem goes unsolved. That my battery died makes me worried that something's going on beyond a bad fuel pump.

I did check voltage as someone's cranking the car, and voltage reads 4-to-5.
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Old 04-06-2013, 04:19 PM
GoForthFast GoForthFast is offline
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I'm saying I suspect your fuel pump to be the problem.

Check fuel pressure at the Schrader valve?

After you get the car running again, use the OBC hidden functions to check to see if your alternator is putting out.
No dash light when your battery was failing?
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  #5  
Old 04-06-2013, 04:21 PM
Fabius Fabius is offline
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No fuel pressure in fuel line based off of Schrader valve. Okay, so you think it's the pump. So 4-to-5 volts is the expected voltage at the fuel pump? Is there any danger in connecting a 12V source directly to the pump?
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  #6  
Old 04-06-2013, 06:29 PM
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SJBimmer SJBimmer is offline
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This may help you.

Check step 11 here. Note wire colors and pins might not correspond to what you have.

http://blog.bavauto.com/3562/no-start-1989-325i-e30/

This info is for an M3, but the diagnostic info might apply.

http://forums.bimmerforums.com/forum...uel-Pump-Relay

This is from an E30, but some diagnostic info may apply.

http://forums.bimmerforums.com/forum...uel-Pump-Relay

read 3rd post down here:

http://en.allexperts.com/q/BMW-Repai...on-t-Start.htm

These are all just for reference. It seems that you tried everything in a logical way. Have you tried bypassing the ignition switch? At the mileage you have, it would not be a waste to replace the fuel pump, fuel filter and fuel pump relay. Just because your relay blows the horn does not mean it will run the pump from what I have read. Supposedly 4-5 volts is to prime the pump, and power the sending init, but I do not have wiring diagrams to verify. If you find the answer, PLEASE post back as you may help someone else in the future. Wish I had more to offer. Note that on one of the links I posted it mentions a fusible link that had continuity, but would only allow low voltage to pass. Don't know if this applies or not. If I find anything that more directly applies to your situation, I will post it. Good luck!
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Old 04-06-2013, 08:13 PM
GoForthFast GoForthFast is offline
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Here is what SJB found that answers some of your questions and echos some of the facts that I mentioned:

12: Test for 12-volts at the fuel pump electrical connections. Using a voltmeter, test for 12-volts between the positive and negative wires for the fuel pump (on most external pumps this can be done with the wire terminals still connected to the pump, on applications that use a harness plug, remove the plug and test the wires in the plug terminals). You should have 12-volts, for a few seconds, when the key is turned to RUN (Ignition). If you repeat the test, you should wait a minute or two between tests, for the fuel pump output to reset (this is because the fuel pump output will turn-off if the engine is not running, as a safety measure).

YES, 12-volts You likely have a faulty fuel pump. Apply 12-volts directly to the pump to verify that it does not run.


So if it were me, I'd give the fuel pump a 12v shot and see what you get.
And I'd replace the pump even if it was working BTW. I already have on my own car!

Last edited by GoForthFast; 04-06-2013 at 08:15 PM.
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  #8  
Old 04-06-2013, 09:13 PM
Fabius Fabius is offline
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Thanks, guys. Since it's a maintenance item anyway, I will replace the pump, as well as the fuel filter. If that fixes my issue it it seems like the source of the problem will remain an X file. I'm a total lay person when it comes to electricity, but it would seem like a working fuel pump sends a signal to the relay or control unit to release the full 12 volts; only way I can make sense of it. Tomorrow I'm going to hook up a direct 12 volt source to the pump, see if it kicks on (since I'm replacing it anyway). I'll get back to you guys.
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Old 04-06-2013, 09:37 PM
chansta chansta is offline
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replacing the pump is not going to magically give you source voltage at the terminal for pump. you are only reading 5-7v because you are experiencing a voltage drop within the circuit between the relay and fuel pump.

you are going to have to gain access to the wiring and using either voltage drop or continuity test determine the point of unwanted resistance.
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Old 04-06-2013, 09:42 PM
Fabius Fabius is offline
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chansta, this is my suspicion as well. I'm not sure how to test the wiring from the relay to the pump--are there access points along that wiring that I can post up on with multi-meter leads? Where is the wiring stuffed?

Last edited by Fabius; 04-06-2013 at 09:43 PM.
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Old 04-06-2013, 10:15 PM
chansta chansta is offline
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rip and tear. looking at the wiring diagram, based on everything you've said and tested for the unwanted resistance would be between the relay terminal #2 and connector x638.

there aren't any access points besides the pin and connector, but once you've been isolate the problem area you can just rewire it by de-pinning the terminals.
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Old 04-07-2013, 12:18 AM
GoForthFast GoForthFast is offline
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Quote:
Originally Posted by chansta View Post
replacing the pump is not going to magically give you source voltage at the terminal for pump. you are only reading 5-7v because you are experiencing a voltage drop within the circuit between the relay and fuel pump.

you are going to have to gain access to the wiring and using either voltage drop or continuity test determine the point of unwanted resistance.

This is incorrect and a simplistic way of looking at things. This system is so much more sophisticated than that. You'll need more than Ohm's law to diagnose this one.
Replace the pump before you waste time on anything else.
Repeat after me; this one is counterintuitive.

PS, if you want a really nasty job, just try accessing the wiring harness along the way from the relay back to the pump!

Last edited by GoForthFast; 04-07-2013 at 12:20 AM.
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  #13  
Old 04-07-2013, 12:46 AM
chansta chansta is offline
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Originally Posted by GoForthFast View Post
This is incorrect and a simplistic way of looking at things. This system is so much more sophisticated than that. You'll need more than Ohm's law to diagnose this one.
Replace the pump before you waste time on anything else.
Repeat after me; this one is counterintuitive.

PS, if you want a really nasty job, just try accessing the wiring harness along the way from the relay back to the pump!
dont start this with me again. learn to read the wiring diagram. when you do you'll realize it is that simple. dme supplies ground to energize relay and battery voltage is supplied to the fuel pump via the relay. it might be too "sophisticated" for you so i dont expect you to understand.

please stop making things so confusing for people who are trying to figure out a simple problem.

you see the 30 circuit with the fuse? meaning its battery voltage to the relay. once relay is energized the fuel pump receives battery voltage. if hes not getting battery voltage at the connector of the fuel pump than hes got a corrosion/unwanted resistance causing a voltage drop before it gets to the fuel pump.

what your telling him to do is to replace a part that hes not even sure is the problem. if you were working as a technician you'd be trying to figure out problems at the cost of the customer. very counter-intuitive.

Quote:
Originally Posted by GoForthFast View Post
I seem to remember that you won't read a full 12 volts at the pump all the time, so hence my statement just above this one.
Have the voltmeter hooked up with no hands and check the voltage AS you turn on the ignition. May jump to 12 and then cut back.
wrong. learn to read the wiring diagram.
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Last edited by chansta; 04-07-2013 at 12:53 AM.
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  #14  
Old 04-07-2013, 08:11 AM
boltaction boltaction is offline
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Man you are so right ^^
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Old 04-07-2013, 09:34 AM
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Man you are so right ^^
Actually, he is so wrong. Fuel pumps on an E46 are known to fail at about 150K. I would much rather replace a part at my leisure, than have to be flat bedded to the local rip off artist if I am out of town. How many posts have you seen where the poster has had to rip up the wiring between the fuel pump relay and the pump? MAYBE 1 out of 10,000? Electric fuel pumps can also run intermittently when failing. Why not replace a part that will have to be replaced soon anyway? I just laugh at guys that try to get the last mile out of everything, and I see them standing by the side of the road all the time. chansta likes to pop up from time to time and tell someone how wrong they are, then he slinks away for a few months, presumably to put a larger fart can on his 89 Civic. A major part of helping service customers is called "preventative maintenance". This means replacing a part that is known to fail, before it actually fails, thus preventing the customer from being stranded.
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Old 04-07-2013, 10:04 AM
boltaction boltaction is offline
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Actually that wasn't the part I was agreeing to, as far as replacing parts that aren't broken and chasing issues with said parts, go ahead. You guys should buy a tank of gas and go enjoy your car. I don't worry about being stranded, as I don't need a you-tube video to be able to work on my ****.
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Old 04-07-2013, 06:23 PM
Fabius Fabius is offline
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Well I fed the pump 12 volts directly and it wouldn't kick on. I cranked the car while giving the pump 12 volts directly, and car wouldn't start. No fuel pressure as indicated by Schrader valve. New pump will be here in three days--we'll see what happens!
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Old 04-07-2013, 07:41 PM
Fabius Fabius is offline
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I did also buy a filter. Can't wait to install and see what happens.
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Old 04-07-2013, 07:48 PM
GoForthFast GoForthFast is offline
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I found the filter harder to put in than the pump because of access. Plus at 80K miles my filter was almost untouched when I hacksawed the case open.

So you can get away with only doing the pump first just to get the car running.
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Old 04-10-2013, 10:30 PM
Fabius Fabius is offline
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Well I hooked up the pump electrical line to the new pump before installing it, and it kicked on, so then I went ahead and installed the new pump. Installation complete and car starts and runs! So thanks, guys, for helping me take the most plausible solution! For those who find this thread later on, note that I never read more than 4 to 5 volts at the pump, and a new pump solved my problem.

I appreciate the time you guys took to help me out.
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Old 04-10-2013, 11:33 PM
chansta chansta is offline
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then the values you provided were tested for incorrectly. did you test for power with the cable disconnected or did u back probe it? did you have good ground?

wiring diagram specifically shows that you are supposed to have battery voltage to the pump. if u can learn to read a bosch style wiring diagram you will understand that the 30 circuit which provides power through the fuse, the relay, and ultimately the pump, is a 12v circuit.

i still stick to everything i've said. i know how the circuit works and the values you should be getting based on the wiring diagram.
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Last edited by chansta; 04-11-2013 at 07:19 PM.
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Old 04-11-2013, 04:07 AM
Fabius Fabius is offline
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Well as I dove into this effort I didn't want my conclusions to be undone by improperly measuring voltages, so when it came to the four wired sockets at the end of the electrical cable that hooks up to the pump's four pins, I tried every combination of two with my probes with these four sockets, repeatedly, also using the metallic attachment region as ground, and never got more than 4 to 5 volts.

I have also seen other forum-documented accounts of folks saying they saw only 4 to 5 volts, so I think it more likely that you are mistaken than not, but until someone can provide documentation about what voltage the pump should see, I think it remains an open question. I appreciate your help.

Last edited by Fabius; 04-11-2013 at 04:09 AM.
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Old 04-11-2013, 05:29 AM
Fabius Fabius is offline
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A more plausible explanation may be that 12 volts are sent to the pump only when car is running. If I really wanted to put this question to rest I should've measured voltage at the pump with car running, but I forgot in my excitement of having the car come to life. Perhaps the relay has logic in it to accomplish this? Alas, everything is put together now so my opportunity is lost.
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Old 04-11-2013, 03:18 PM
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Quote:
Originally Posted by chansta View Post
then the values you provided were tested for incorrectly. did you test for power with the cable disconnected or did u back probe it? did you have good ground?

wiring diagram specifically shows that you are supposed to have battery voltage to the pump. if u can learn to read a bosch style wiring diagram you will understand that the 30 circuit which provides power through the fuse, the relay, and ultimately the pump, is a 12v circuit.

i still stick to everything i've said. i know how the circuit works and the values you should be getting based on the wiring diagram.

newer bmw's with EKP modules have varying voltages for different engine speeds but not e46's.
You stand by everything you said? Even though you were totally wrong? Unbelievable. I think it is time for chansta to pack up and move on. Who hangs on a BMW board, even though they do not own the brand? I get the feeling that you have been booted from every Civic forum you joined, and now you are here to display your lack of knowledge and breeding. You like to throw the words moron and idiot around, and display your lack of character and education. I can only assume that you have realized that you are all you are ever going to be, and this is the source of your frustration and anger. I suggest you get back inside the Quick Lube because your break is over, the manager is looking for you, and the oil change customers are backing up.
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Old 04-11-2013, 07:14 PM
chansta chansta is offline
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Originally Posted by Fabius View Post
Well as I dove into this effort I didn't want my conclusions to be undone by improperly measuring voltages, so when it came to the four wired sockets at the end of the electrical cable that hooks up to the pump's four pins, I tried every combination of two with my probes with these four sockets, repeatedly, also using the metallic attachment region as ground, and never got more than 4 to 5 volts.

I have also seen other forum-documented accounts of folks saying they saw only 4 to 5 volts, so I think it more likely that you are mistaken than not, but until someone can provide documentation about what voltage the pump should see, I think it remains an open question. I appreciate your help.
the wiring diagram is the documentation which proves pump should be seeing 12v... theres is only 1 power line that receives power from the relay, and that relay receives power from the fuse which is on a 30 circuit (battery power).

Quote:
Originally Posted by SJBimmer View Post
You stand by everything you said? Even though you were totally wrong? Unbelievable. I think it is time for chansta to pack up and move on. Who hangs on a BMW board, even though they do not own the brand? I get the feeling that you have been booted from every Civic forum you joined, and now you are here to display your lack of knowledge and breeding. You like to throw the words moron and idiot around, and display your lack of character and education. I can only assume that you have realized that you are all you are ever going to be, and this is the source of your frustration and anger. I suggest you get back inside the Quick Lube because your break is over, the manager is looking for you, and the oil change customers are backing up.
you dont know anything about cars. you're just goforthfast's little sidekick whose only here to support everything he says.

**HERE IS THE PROBLEM**


this is the correct wiring diagram which changes everything. the wiring diagram OP posted was wrong. i just found that on alldata for his specific year & model. my fault for relying on information given by someone who has no expertise in automotive repairs (no offense). as you probably know wiring diagram is a map of the electrical system and having the wrong map, obviously lead me to a different diagnostic path. diagnosing a vehicle online/over the phone is a guess at best.
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Last edited by chansta; 04-11-2013 at 07:31 PM.
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