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Old 10-28-2017, 06:16 AM   #1
martynstewartjones
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Fuel pump voltage gone

I'm scratching my baldy head here. What would cause no voltage to the fuel pump at prime that's not fuse or relay related? Battery is 11.5v relays swapped with horn and horn works. Changed the 20A fuse under the bonnet even though continuity was fine. Changed fuse 57(? From memory) even though continuity was fine. Fuel pump still doesn't prime.

Symptoms I'm having is crank but no start. I couldn't hear the fuel pump prime before trying to start.

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Old 10-28-2017, 08:35 AM   #2
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You do know the fuel pumps fail on these cars quite often at this age?

You do know if the battery is at 11.5 Volts, it is DEAD and while the engine may crank, the cranking Voltage is probably too low for many of he modules in the vehicle to work properly.

The fuel pump prime Voltage only lasts about 4 seconds. Then the fuel pump has about 4.5 Volts at the connector until the engine is actually cranked, when you will only see about 11.5 Volts while cranking.

Have you actually used a Voltmeter to measure for Voltage at the fuel pump connector? Have you removed the fuel pump access cover under the rear seat to inspect the wiring for rodent damage? Have you beat on the top of the fuel pump to try to get it running one more time to then determine the fuel pump has failed?

Suggest you read this thread - Fuel pump failures - https://forum.e46fanatics.com/showthread.php?t=929501
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Last edited by jfoj; 10-28-2017 at 08:36 AM.
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Old 10-28-2017, 09:07 AM   #3
martynstewartjones
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Originally Posted by jfoj View Post
You do know the fuel pumps fail on these cars quite often at this age?

You do know if the battery is at 11.5 Volts, it is DEAD and while the engine may crank, the cranking Voltage is probably too low for many of he modules in the vehicle to work properly.

The fuel pump prime Voltage only lasts about 4 seconds. Then the fuel pump has about 4.5 Volts at the connector until the engine is actually cranked, when you will only see about 11.5 Volts while cranking.

Have you actually used a Voltmeter to measure for Voltage at the fuel pump connector? Have you removed the fuel pump access cover under the rear seat to inspect the wiring for rodent damage? Have you beat on the top of the fuel pump to try to get it running one more time to then determine the fuel pump has failed?

Suggest you read this thread - Fuel pump failures - https://forum.e46fanatics.com/showthread.php?t=929501
That was kind of my next stage. I tried to hook up my booster under the hood but it was giving me a red light meaning something is wrong. 11.5 is after charging too but I wasn't too sure how picky the system was. I've seen other cars run fine on that as after crank it will go above 14 when firing. I have a great fluke multimeter that I use for my auto electrics and that's what I used after taking the connector off the fuel pump and checking the pins closest together. Actually I tried all pins and both wires on both sides of the tank - guessing one is sender and one is pump? I've got a pump on order as a back up after I read that thread last week. I was wondering if there was any other way that there would be a no voltage at pump other than fuse or relay. Thanks.

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Old 10-28-2017, 09:40 AM   #4
markusmarkus
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Fuel pump voltage gone

Check the fuel pump relay in the relay panel above the fuse panel. Go to www.bmwgm5.com to see the picture of the relay panel with designations. You can swap the horn relay for the fuel pump relay.

The battery is dead, as jfoj noted. The lead plates of lead acid batteries are permanently damaged when the voltage gets that low.

Last edited by markusmarkus; 10-28-2017 at 09:41 AM.
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Old 10-28-2017, 11:06 AM   #5
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Originally Posted by markusmarkus View Post
Check the fuel pump relay in the relay panel above the fuse panel. Go to www.bmwgm5.com to see the picture of the relay panel with designations. You can swap the horn relay for the fuel pump relay.

The battery is dead, as jfoj noted. The lead plates of lead acid batteries are permanently damaged when the voltage gets that low.
Yep already did that. Horn works when swapped. Battery is my next step.

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Old 10-28-2017, 11:16 AM   #6
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Just test for Voltage at the fuel pump or apply 12 Volts to the fuel pump.

Chances are the fuel pump has failed not a relay or circuit problem.

But the battery is a problem either way. Needs to be properly charged and/or replaced.
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Old 10-28-2017, 11:27 AM   #7
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Originally Posted by jfoj View Post
Just test for Voltage at the fuel pump or apply 12 Volts to the fuel pump.

Chances are the fuel pump has failed not a relay or circuit problem.

But the battery is a problem either way. Needs to be properly charged and/or replaced.
Yes. I tested for voltage at the fuel pump.... I removed the back seats.. I took the four nuts off the metal cover... I removed the metal cover.. I pulled back the clip to take off the connector... I put my fluke multimeter set to dc volts across the fuel pump supply terminals and then I turned the key on... nothing.. how would a new fuel pump fix this?

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Old 10-28-2017, 12:02 PM   #8
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Ews?
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Old 10-28-2017, 12:14 PM   #9
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Ews?
Wouldn't that stop the engine from cranking?

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Old 10-28-2017, 12:32 PM   #10
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Originally Posted by martynstewartjones View Post
Wouldn't that stop the engine from cranking?
Seen a lot of bad keys lately that would allow the engine to crank, but would not provide injector pulse and fuel pump power.

If you have another key, try it.

I see you indicated you did check for Voltage AT the fuel pump connector, this was not clearly stated from the beginning. Do you measure between 4-5 Volts at the fuel pump connector to the larger wires in the 4 wire connector with the key in the on position?? If you get 4-5 Volts at the fuel pump connector, then the relay is probably good.

But with a battery at 11.5 Volts this is something that needs to be sorted FIRST.

What happens when you put the key in the ignition, turn it on and open the door? Do you get a key beep for the key being in the ignition?
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Old 10-28-2017, 01:14 PM   #11
martynstewartjones
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Originally Posted by jfoj View Post
Seen a lot of bad keys lately that would allow the engine to crank, but would not provide injector pulse and fuel pump power.

If you have another key, try it.

I see you indicated you did check for Voltage AT the fuel pump connector, this was not clearly stated from the beginning. Do you measure between 4-5 Volts at the fuel pump connector to the larger wires in the 4 wire connector with the key in the on position?? If you get 4-5 Volts at the fuel pump connector, then the relay is probably good.

But with a battery at 11.5 Volts this is something that needs to be sorted FIRST.

What happens when you put the key in the ignition, turn it on and open the door? Do you get a key beep for the key being in the ignition?
I'm going to have to recheck Monday. Car is stuck in work at the moment and they close shop on Sundays. Is the beep just one beep or is it a constant chime? I've got a spare but it doesn't have the buttons on it. It's a bmw branded one. Would that have the chip? Forgive the newbie question but I don't know the nuances of E46's but I've been working on engines for 30 years.

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Old 10-28-2017, 01:20 PM   #12
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Originally Posted by martynstewartjones View Post
I'm going to have to recheck Monday. Car is stuck in work at the moment and they close shop on Sundays. Is the beep just one beep or is it a constant chime? I've got a spare but it doesn't have the buttons on it. It's a bmw branded one. Would that have the chip? Forgive the newbie question but I don't know the nuances of E46's but I've been working on engines for 30 years.

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The spare key should work perfectly fine. I think as long as the door is open, the beeping won't stop
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Old 10-28-2017, 01:30 PM   #13
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The spare key should work perfectly fine. I think as long as the door is open, the beeping won't stop
Well I had the drivers door open and I don't remember a beeping. I'll try the spare thanks.

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Old 10-30-2017, 08:46 AM   #14
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Ok. No voltage at the pump with key off or key on - I mean trace volts around .03. No beeping with the key in or the spare.

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Old 10-30-2017, 09:38 AM   #15
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Might be a bad key or problem with the EWS system. Usually getting another key is easier than dealing with software and hoping the key is not the problem.

All BMW keys have the EWS chip in them. If no beeping with the spare key, then there is a problem with the EWS or the antenna around the ignition cylinder.

May sure you have checked ALL fuses to include the fuses in the DME box. I recall there is one fuse in the glove box area that can impact the EWS.

Check fuses Check fuses 27, 29, 30, 14, 67, 30 & 43. Pay careful attention to fuse 30.
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Old 10-30-2017, 09:47 AM   #16
martynstewartjones
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Might be a bad key or problem with the EWS system. Usually getting another key is easier than dealing with software and hoping the key is not the problem.

All BMW keys have the EWS chip in them. If no beeping with the spare key, then there is a problem with the EWS or the antenna around the ignition cylinder.

May sure you have checked ALL fuses to include the fuses in the DME box. I recall there is one fuse in the glove box area that can impact the EWS.
Will do. I'm moving the car back home tomorrow so I can spend more time tracing continuity and voltages. I'm picking up a new battery tomorrow. Is there any way to turn off the EWS check temporarily so I can rule the key out. I have bmw tools.

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Old 10-30-2017, 09:50 AM   #17
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See notes about the fuses I just added.

DO NOT try to disable the EWS, not sure this can be done. But you could check for EWS and key errors, but check fuses first and make sure you get the beeping when the key is in the ignition and the door is open. BUT you need to turn the key on for the EWS to read the key.
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Old 10-30-2017, 09:54 AM   #18
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Will do. I'm moving the car back home tomorrow so I can spend more time tracing continuity and voltages. I'm picking up a new battery tomorrow. Is there any way to turn off the EWS check temporarily so I can rule the key out. I have bmw tools.

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By BMW tools do you mean inpa or pa soft?
With either one, you can check the status on the ews. Check the errors and report back

The only way to disable ews is using the ews delete from the MS43 tuning thread, but your car has to be older than 2003 and you have to be very careful. I don't recommend you do it. For me it was very easy and I did it on my second DME that I bought from eBay.

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Old 10-30-2017, 10:27 AM   #19
martynstewartjones
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By BMW tools do you mean inpa or pa soft?
With either one, you can check the status on the ews. Check the errors and report back

The only way to disable ews is using the ews delete from the MS43 tuning thread, but your car has to be older than 2003 and you have to be very careful. I don't recommend you do it. For me it was very easy and I did it on my second DME that I bought from eBay.
INPA. I need to see if it works with my Delphi OBD Interface first. It doesn't throw any codes through Delphi but I guess INPA goes deeper.

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Old 10-30-2017, 10:28 AM   #20
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I had the exact problem last week. I had previously swapped the horn and FP relays thinking this was my problem. In the end it turned out that the horn relay had an intermittent problem as well and just bought me a couple of weeks of false security.

A new relay cured the problem. I wouldn't trust any 14 year old relay wherever it came from to perform consistently under load. A new FP relay and DME relay cured my problem with the added benefit that I fitted a new FP for peace of mind. The old FP still works and wasn't the cause of my original problem.
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