Quick fuel pump electrics question...

Post Mon Mar 26, 2012 3:26 pm

Sorry got to be fast, I've already stretched my lunch break long enough.......

'91 e30 318is

fuel pump not getting 12v.

All works just fine with 12v via test wires.

No click from relay, relay swapped for one from my old car, with same numbers on the same connections - same relay, just different shape. Still no click.

Fuse 11 swapped a few times with others from the box.

Multimeter across fuse terminals reads nothing with ignition on, which is odd I thought.

Anyways.. Just posting this real quick in the hope that when I get out of work someone will have posted some magic.

Any ideas?

Thanks:)

Post Mon Mar 26, 2012 3:37 pm

Does the pump definately work?

Post Mon Mar 26, 2012 4:15 pm

I do not know the 318is but on the 318i with the M40 motor the fuel pump does not run when the ignition is turned on. When the crankshaft sensor sends pulses to the ECU the ECU powers up two relays sitting in the engine bay under the long black plastic section running under the windscreen.
What actually happens is that the most RH of the relays gets +12 volts from the ECU which then supplies ground to the injectors. This first relay also supplies ground (green/brown wire) to the second relay which then energises and supplies +12 volts to the fuel pump.
So if you have the ignition ON and you ground the Green/brown wire between the two relays the fuel pump should run without getting the engine pulses.
They use this method so that if you are in an accident and the engine stalls but ignition is still on then the fuel pump stops pumping.
So the first thing you need to check is that the ECU is picking up the crankshaft pulses.

This applies to the M40...not sure about the M42 though.

Post Mon Mar 26, 2012 5:43 pm

1) Multimeter won't give a valid reading on an unloaded circuit. Use a test bulb.

2) Fuel pump doesn't come on with just the ignition, you need to crank the engine or have it running for the fuel pump to kick in.

If you're not getting 12V under those circumstances, then chances are it's your DME relay or CPS sensor. More info available on THIS page:

http://www.e30zone.net/e30zonewiki/inde ... oubleshoot

Post Mon Mar 26, 2012 7:04 pm

Grrrmachine wrote:1) Multimeter won't give a valid reading on an unloaded circuit. Use a test bulb.

2) Fuel pump doesn't come on with just the ignition, you need to crank the engine or have it running for the fuel pump to kick in.

If you're not getting 12V under those circumstances, then chances are it's your DME relay or CPS sensor. More info available on THIS page:

http://www.e30zone.net/e30zonewiki/inde ... oubleshoot

Good comment and a good link to Wiki.

However there is nothing wrong with using a multimeter if you know what you are doing...using a test bulb is a bit basic with severe limitations.

I think the main points have been covered here...the most important being that the motor needs to be spinning before the fuel pump gets its voltage!

Post Mon Mar 26, 2012 7:21 pm

Thanks for the replies... It'll give me something to work from with the remaining sunlight:)

Duke137 wrote:Does the pump definately work?

Yup... Given 12v straight from the battery it whirs away and the car starts and runs just fine.

Billwill wrote:I do not know the 318is but on the 318i with the M40 motor the fuel pump does not run when the ignition is turned on. When the crankshaft sensor sends pulses to the ECU the ECU powers up two relays sitting in the engine bay under the long black plastic section running under the windscreen.
What actually happens is that the most RH of the relays gets +12 volts from the ECU which then supplies ground to the injectors. This first relay also supplies ground (green/brown wire) to the second relay which then energises and supplies +12 volts to the fuel pump.
So if you have the ignition ON and you ground the Green/brown wire between the two relays the fuel pump should run without getting the engine pulses.
They use this method so that if you are in an accident and the engine stalls but ignition is still on then the fuel pump stops pumping.
So the first thing you need to check is that the ECU is picking up the crankshaft pulses.

This applies to the M40...not sure about the M42 though.

Thanks.. The fuel pump does come on with the ignition, but only briefly to pressurise the system, that's why I suspected the fuel pump in the first place - No brief "hmmm" from the rear when turning the ignition on.

I have two relays under the black cover on the bulkhead, the RH one (if sat in the drivers seat) activates (well, clicks at least) when the ignition is turned on.. I assume this is the DME relay. The middle one (I presume the fuel pump relay) does nothing when the ignition is turned on, but I can't tell what either are doing when I crank the engine as there's too much vibration in the engine bay to feel for clicks. There's no relay in the far left slot.

I'll try bridging the relay like is says HERE

Grrrmachine wrote:1) Multimeter won't give a valid reading on an unloaded circuit. Use a test bulb.

2) Fuel pump doesn't come on with just the ignition, you need to crank the engine or have it running for the fuel pump to kick in.

If you're not getting 12V under those circumstances, then chances are it's your DME relay or CPS sensor. More info available on THIS page:

http://www.e30zone.net/e30zonewiki/inde ... oubleshoot

1 - Noted, ta.

2 - (see above re pump coming on briefly with ignition) - I assume the CPS sensor is ok as the engine runs just fine with the fuel pump given 12v straight from the battery.

That link is very useful, thanks.

Going to go mess with it now.

Post Mon Mar 26, 2012 7:22 pm

doubleposting.

Post Mon Mar 26, 2012 7:53 pm

Bridging the relay = no joy.

Running a wire from the back of terminal 87 to the fuel pump positive = Normal functioning fully working fuel pump, complete with that reassuring brief 'hummm' when the ignition is turned on. Car runs fine with this setup.

I assume from this that the wire (green/blue that comes out of terminal 87 and goes to (I think) the fuel pump + has broken somewhere.

Off to check wiring diagrams to confirm.

Any thoughts?

Post Mon Mar 26, 2012 9:00 pm

Having trouble finding a wiring diagram with e30 318is related stuff in there..

Think I'll download e36 manuals and try them.

Post Tue Mar 27, 2012 12:34 am

Find the aftermarket immobiliser.

Post Tue Mar 27, 2012 8:47 am

It does have an aftermarket alarm in there- which I never use as it's a pain in the ass. I hope to god it's not an immobiliser too but now you mention it that sounds about right

I'll have a look later, thanks.

Post Tue Mar 27, 2012 12:57 pm

As it turns out, it does have an immobiliser.. And a quick beep on and off of the alarm system saw everything back to normal.

It didn't even cross my mind to try that as I never use the alarm, as it's a bag of crap that goes off too often.

This is exactly why forums are great:D

Thanks Brianmoooore, that's the second time you've sorted my car out with simple observations / knowledge - you also advised I check fuse 21 a while back when my rev counter stopped working.

I appreciate it very very much:)