Help, what could be the reason the electric fuel pump doesn't work at startup?

[arthur_525TDS]

Hi.

At the first I would like to say that my problem is common for cars with petrol and diesel engines. The problem is the following:

I know when I put the key on ignition ( before starting the engine ) the electric fuel pump ( which is in fuel tank ) should work ( for a short time ) to supply the fuel to engine. It doesn't work. What could be the reason? I have measured the voltage on fuse N23 ( the pump's fuse. The fuse was OK ) and there was not a voltage when I switched on the key on ignition state. The relay which supplies the voltage to that fuse also was OK. I think that from a reason (I would like to know WHAT reason ) the DDE doesn't send signal to mentioned relay. Maybe by the some reason there is insufficient pressure in fuel supply system? Maybe the fuel level sensor is responsible for the mentioned signal?
My thanks to everybody who will reply to my issue.
P.S.
Just when I start the starter the pump works. But it also should work before starting the starter, when the key has put on ignition state. :(

[Karl]

I think all BMWs are made so the engine must be running or starter must be engaged to get power to the pump, but I'd appreciate a second opinion from an experienced BMW tech...

[632 Regal]

sounds like a safety issue to me, why have full pressure to the system while your sitting in a parking lot burning some buds? It doesnt take long at all for the pressure to build up since theres a check valve in the fuel system to keep some pressure in it.

thats my guess...

did i win the $10,000 prize yet?

[DueyT]

I know that some cars have a pressure accumulator in the FI system and that the boost pump/lift pump won't energize if there is still suitable pressure with which a successful start can be accomplished. That's probably in combination with what Jeff also mentioned about saftey and not having a fuel pump try and fill a line without any volumetric consumption (i.e. bypass/return 100% of what is pumped)

FWIW,
Duey

[Robert K]

I recently replaced the fuel pump on my 1991 535i. Before doing so, I ran some diagnostics using the Bentley manual. What I remember is this. First, there is a check valve in the fuel system that is supposed to maintain residual pressure in the fuel line. That way, when you do go to start the car, you have some fuel pressure already in the line. Also, to test the pump, you have to put the key in the start position and actually jump across two terminals at the fuel pump relay socket (after removing the relay). I don't exactly know why BMW made it that way, but that's the way it is. I know that in my 1986 Ford Tbird, when I turn the key to "ON," I can hear the fuel pump start up, then shut off once fuel pressure is built up. So as somebody else has said, it is most likely some type of safety feature BMW decided to incorporate into the system.

Grace and peace,

Robert K
1991 535i

[632 Regal]

The potential for accident is at least 10 fold VS not pumping fuel in circles when not needed.

[arthur_525TDS]

A lot of thanks to everybody who has replied to my issue. :)

Just I would like to add the following: when I fill the fuel tank more than 30 liter the engine starts immediately, I mean the starter works very short time ( 1 sec, even maybe less than 1 sec. I think because of in this case the fuel pressure is enough ). But when the fuel is less than 25 liter the starter works a bit longer ( more than 15 sec ) before engine is started ( low fuel pressure ). I think the reason is that the fuel pump does not work when the key has put on ignition state ( before starting the starter ). This logic of starting has been implemented in many cars ( for example in Robert_K 's Ford Tbird ).

[Bill R.]

transfer pump relay on startup, and in position 2 of your key the transfer pump should be running. I would suspect the fuel heater relay or thats what i would check next. Jumper it and see if the transfer pump runs. It looks like once the engine is running that the alternator supplies power to the transfer pump relay but on startup the fuel heater relay does.
http://www.bimmernut.com/%7Ebillr/images/dieselfuel.jpg









A lot of thanks to everybody who has replied to my issue. :)

Just I would like to add the following: when I fill the fuel tank more than 30 liter the engine starts immediately, I mean the starter works very short time ( 1 sec, even maybe less than 1 sec. I think because of in this case the fuel pressure is enough ). But when the fuel is less than 25 liter the starter works a bit longer ( more than 15 sec ) before engine is started ( low fuel pressure ). I think the reason is that the fuel pump does not work when the key has put on ignition state ( before starting the starter ). This logic of starting has been implemented in many cars ( for example in Robert_K 's Ford Tbird ).

[arthur_525TDS]

I would like to pass my grateful thanks to Bill R. Thank you very much Bill for your response with detailed illustrations :p .
Just could you tell me please where has installed the fuel heater relay ( what number is it in picture or where it has located? ) ? I know the number 2 is the fuel transfer pump's relay. I would like to test according to your recommendations. Thanks.

With best regards,
Arthur.

[Bill R.]

your case i can't really help much since we don't get the diesels in the US and I haven't worked on one...http://www.bimmernut.com/%7Ebillr/images/dieselpreheaterrelay.jpg








I would like to pass my grateful thanks to Bill R. Thank you very much Bill for your response with detailed illustrations :p .
Just could you tell me please where has installed the fuel heater relay ( what number is it in picture or where it has located? ) ? I know the number 2 is the fuel transfer pump's relay. I would like to test according to your recommendations. Thanks.

With best regards,
Arthur.

[arthur_525TDS]

I am from Yerevan (Armenia) and here there is just one BMW dealer (Euro Motors Armenia ) which does not serving the BMW cars with diesel engines.
By this reason I have not any way to solve my problem here. The single way is remote help, consulting ( via Internet ). I would like to get contact to BMW companies Customer's Support Group. It would be fine to get it from Germany.
Could somebody help me with getting a contact to BMW companies Customer's Support Group? Thanks.

[Nickhlx]

I am from Yerevan (Armenia) and here there is just one BMW dealer (Euro Motors Armenia ) which does not serving the BMW cars with diesel engines.
By this reason I have not any way to solve my problem here. The single way is remote help, consulting ( via Internet ). I would like to get contact to BMW companies Customer's Support Group. It would be fine to get it from Germany.
Could somebody help me with getting a contact to BMW companies Customer's Support Group? Thanks.

Hi Arthur,
I am Nick in England with problem in same area of starting and am looking at
glow plug relay as a possible faulty unit, when I saw your post.
I also have the 525TDS 1995 model
Nick

[Nickhlx]

I think all BMWs are made so the engine must be running or starter must be engaged to get power to the pump, but I'd appreciate a second opinion from an experienced BMW tech...

No - On my 525TDS the fuel tank pump runs for approx 20 seconds after switching on the ignition - if the engine does not start it will switch off.
Nick

[Nickhlx]

Hi.

At the first I would like to say that my problem is common for cars with petrol and diesel engines. The problem is the following:

I know when I put the key on ignition ( before starting the engine ) the electric fuel pump ( which is in fuel tank ) should work ( for a short time ) to supply the fuel to engine. It doesn't work. What could be the reason? I have measured the voltage on fuse N23 ( the pump's fuse. The fuse was OK ) and there was not a voltage when I switched on the key on ignition state. The relay which supplies the voltage to that fuse also was OK. I think that from a reason (I would like to know WHAT reason ) the DDE doesn't send signal to mentioned relay. Maybe by the some reason there is insufficient pressure in fuel supply system? Maybe the fuel level sensor is responsible for the mentioned signal?
My thanks to everybody who will reply to my issue.
P.S.
Just when I start the starter the pump works. But it also should work before starting the starter, when the key has put on ignition state. :(


You are right - it should come on before the engine starts so the injector pump has a good supply of fuel to inject.
Nick

[iainand]

i too seem to have a similar problem, when my engine is warmed up the engine turns over sometimes for a good 20 seconds before starting.


the in tank pump doesnt seem to work when turning on the ignition if the engine is warmed up, until the engine is running!

if the engine is cold, the pump runs with ignition on before starting engine.

does this seem to be a similar problem to yours???

[calibra]

Ok been reading a lot of posts about this as im having the same prob if there is a heat sensor where would it be? my pump gets a low volt but thinking about it i have only tried with the engine warm is will try and get a reading first thing in the morning see if its higher

cheers