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Steve van hool

528i won't start

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My 528i been stood for a while, fired up ok once warm, it ran rough, now no joy. I disconected the fuel pipe from the fuel rail, am I right in assuming that a constant flow of fuel should come through with the ignition on?

 

At the moment thinking along the lines of fuel pump relay, or the fuel pump itself, arn't there two pumps on these?

 

Any advice on ascertaining the problem gratefully received folks, will turn over, but not fire up, it's not even trying to fire up now.

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There is only one pump on the drivers side just above the trailing arm behind the wheel, the filter is mounted side by side with the pump.

 

Can you here the pump running?

 

Try pulling the crankcase breather of and squirt some petrol in the air intake using a washing up liquid bottle, if there is spark it will fire or spray some easy start in there as it has a lower flash point just in case your spark is weak. If you have spark then you are looking at fuel regulator, pump, pump control, filter or if the tank is at low level you may suck muck up onto the pickup snode which will stay there or fall off after a while, put a couple of gallons in there it will wash any muck off the pick up.

 

Check for a leak on the fuel line it will drag air in and lose pressure

 

Also it maybe condensation in the dizzy cap which would form when the engine gets warm after a long time laid up, it will give you a miss then can fail to start

 

 

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1 hour ago, Steve van hool said:

am I right in assuming that a constant flow of fuel should come through with the ignition on?

 

No you are wrong. With LE jetronic, the pump should kick over for half a second when the key is turned Run. This primes the fuel rail. The pump wont start running again until the engine reaches 300-400 rpm. 

 

Maybe the in tank fuel filter is gummed up, or the external one.

 

You should workout how to run the pump by jumping the fuel relay. I believe this has be discussed before. 

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Sounds like i should take it off your hands ;)

 

Obvious question is whether its seeing a spark?

 

You might have a lift pump in the tank too but if that fails it tends to cause issues when fuel levels are low or cornering. It does supposedly cause the main pump to work harder and fail sooner but if the cars been sat the dizzy cap seems a good place to start.

 

 

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32 minutes ago, Captain Beaky said:

No lift pump in the tank on an E28

 Err yes there is  - have a look in the tank of the M535i!

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1 hour ago, duncan-uk said:

 Err yes there is  - have a look in the tank of the M535i!

 

Well you learn something everyday! 

 

That's a head scratcher!! so there are two pumps and 2 relays?

 

 I've never come across this when I done LPG conversions on E28's and there's quite a few of them, I used the change over signal from the LPG ECU to cut the power to the fuel pump relay so it would not run while on gas.

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12 hours ago, Steve van hool said:

 

What does the fuel tank pump actually do, is it a back up for the chassis pump.

 

Its a lift pump, i believe it gives the main pump an easier life but does run without it.

 

Some cars don't have them but failure is a documented issue IIRC.

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Sounds like the fuel pump relay. This also triggers the injectors. It's a tall black relay next to the fuse box with seven pins. Get three bits of wire and with the relay removed, bridge the relay socket terminals 87 (red/white, injectors),  30 (red, 12 volts) and 87b (green/violet, fuel pump). That will activate the pump and power up the injectors. 

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24 minutes ago, Sir Anthony Regents-Park said:

Sounds like the fuel pump relay. This also triggers the injectors. It's a tall black relay next to the fuse box with seven pins. Get three bits of wire and with the relay removed, bridge the relay socket terminals 87 (red/white, injectors),  30 (red, 12 volts) and 87b (green/violet, fuel pump). That will activate the pump and power up the injectors. 

 

+1

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41 minutes ago, Sir Anthony Regents-Park said:

Sounds like the fuel pump relay. This also triggers the injectors. It's a tall black relay next to the fuse box with seven pins. Get three bits of wire and with the relay removed, bridge the relay socket terminals 87 (red/white, injectors),  30 (red, 12 volts) and 87b (green/violet, fuel pump). That will activate the pump and power up the injectors. 

 

I have heard that a faulty pump relay is a common E28 fault, to the extent that some even carry a spare relay, can you explain precisely which three terminals are bridged with the three pieces of wire, 87, 87b, and 30, and bridged to where?

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You are joining all three wires together so that 87 (red/white, injectors) and 87b (green/violet, fuel pump) are powered by 12v from T30.

 

If the car now starts after the distributor cap has been cleaned, it's probably not the relay. My E32 developed a bad misfire last year due to the cap and rotor being shagged out. 

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To update, the car will fire up, then cut out after about 5 secs every time now, I  sprayed  carb cleaner into the AFM, and it ran normally, so the ignition side of things would appear OK.

 

Will now have to investigate the fuel side of things, filter? pump? which one? injectors? As advised I jumped the connections on the fuel relay, and it made no difference, advice gratefully received.

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Do you think maybe its priming with the ignition, then firing but not then switching on the pump? so dies when the primed fuel is spent?

 

I'd be looking at the relays i think.

 

Other thought is there an immobilizer?

 

A long time ago my brother-in-law had a 993, i borrowed it to meet some friends for lunch in London.

 

After lunch i went to fire up the car and it ran, then died. Did same thing over and over. Called AA. when patrol man arrived i was sat in car showing him what was happening and i saw a fuse on the mat.

 

Nosing about i found an empty fuse slot roughly above.

 

I suggested we put it back in, AA man not keen but i did and problem solved.

 

Seemed the immobilizer had two circuits, start and run and the run fuse had dropped out.

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You could have something there re: priming, then cutting out once the primed fuel is spent. 

The trouble is that I have tried bridging the fuel pump relay to no avail, are there any other relays to check.

 

 Yes there is an OE immobilser built into the on board computers, but it is not currently activated.

 

The joys of looking after a 35 year old car, it is a good job I don't do this for a living.

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It's getting plenty of fuel, when turning it over, undoing the fuel feed, and return pipes on the fuel rail proved this.

 

So injectors not firing, massive air leak or blockage somewhere, ignition switch, cruise control, AFM?

 

I believe L jetronic have a crank sensor fitted.

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Is there a sensor/ relay that tells the ecu to fire the pump as the car is running?

 

On the Motronic its the two induction pick ups in the bell housing.

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