M20B25 No fuel coming through....

Sat Apr 23, 2011 11:14 am

Went to start the car yesterday to go to work and it wouldnt start.

Pulled the fuel pipe off the rail and noticed nothing coming through.

What ive done so far:

1. Put a wire across pins 30 and 87 on the fuel pump relay (fuel pump doesnt kick in)
2. Pulled the two pin plug off the fuel pmup and found to have voltage coming through when cranking the engine
3. Changed the fuel pump for a good used item.

Can anybody suggest what to do next?

Any replies much appreciated

Sat Apr 23, 2011 11:17 am

Fuse 11 is sound?

Next thing is crank position sensor,if the engine ECU does not think that the engine is turning,it will not switch the fuel pump on.

Sat Apr 23, 2011 11:20 am

Yes mate sorry fuse 11 is sound.

Ive checked on the web and tested the crank sensor by:

. Cleaning it and connecting an ohmeter to it and having a resistance of 300ohms
. then i bolted the sensor back on the car with the ohmeter attached and set to ac volts, it showed i had just over a volt whilst cranking the engine.

Does this proove the crank sensor is ok?

Much appreciated for the swift reply mate

Sat Apr 23, 2011 12:28 pm

According to my bentley manual,early CPS should give an ohm reading of about 960 ohms.Later systems should give about 540ohms....

May just be worthwhile trying a new one,methinks.

Sat Apr 23, 2011 12:32 pm

Ok mate much appreciated. Is there anything else it could possibly be from stopping the fuel pump working?

I thought i may aswell check before getting a new CPS.

Sat Apr 23, 2011 12:39 pm

By bridging the FPR you should be able to get the pump running full time,as I understand the system,this eliminates the engine ECU from it's switching duties.

So if you still have no fuel pump even with the relay bridged,this makes the pump and it's wiring suspect,a bulb across the pump terminals is the reccommended way of testing for current,the bulb should light with either the engine cranking or the relay bridged.

Sat Apr 23, 2011 1:43 pm

daimlerman wrote:a bulb across the pump terminals is the reccommended way of testing for current,the bulb should light with either the engine cranking or the relay bridged.

If you originally tested at the pump with a meter, the results are meaningless. Use a bulb.
If bridging 30 and 87 of the pump relay doesn't make the bulb light, don't start disturbing the crank position sensor.
The result of random parts swapping and testing are usually you end up with six faults or so as well as the one you started with!

Sat Apr 23, 2011 5:55 pm

Ok, so just to confirm i have now bridged pin 30 and 87 with a wire on the fuel pump relay (middle relay of the 3) and put a bulb across the 2 pin connector that plugs onto the fuel pump and the bulb DOES NOT light up.

Where to go from here?

Sat Apr 23, 2011 6:07 pm

Connect the bulb between pin 30 of the relay socket and earth. If it lights, connect the bulb between the inner socket of fuse 11 (or the wire of the fuse with the fuse in place) and earth.
Apart from having a 2.5 M20 engine, you haven't told us what car!

Sat Apr 23, 2011 6:13 pm

Oh i do apologise! Its a totally factory spec 'G' Reg 325i Touring E30!

Going out to the car now to do those tests!

Sat Apr 23, 2011 6:21 pm

When i connect the bulb between pin 30 of the FPR and earth, the bulb lit, so i then put the bulb between fuse 11 fitted and earth but the bulb didnt light up.

Sat Apr 23, 2011 6:26 pm

Are you certain you have the fuel pump relay - usually orange, and with a green/purple wire connected to 87.
Bulb between fuse 11 and earth is with the wire link in place, BTW.

Sat Apr 23, 2011 6:43 pm

Yes i can confirm it is the correct fuel pump relay. Just put the wire between pin 30 and 87, then put the bulb between fuse 11 and earth and the bulb lit up?!

Sat Apr 23, 2011 6:57 pm

If the bulb lights at fuse 11, but not at the pump plug, then the chances are that someone has connected an immobiliser between the outside pin of the fuse and the pump.
Wire is green/purple, goes down through the duct under the fusebox into the back of the glovebox area, down in the corner behind the speaker panel, all the way back the LH sill, across the back seat to a plug and socket on the RH side, down through the seat pan, and over the tank to the pump.

Sat Apr 23, 2011 7:11 pm

What an awesome bloke you are! Im going to call it a day today but going to tackle it tomorrow morning.

So i need to trace that green/purple wire off the fuel pump relay all the way back to where it connects to the fuel pump?

If i do find this immobiliser wire, is it a simple case of disconnecting it and making sure it cant touch metal?

Again much appreciated for all your help!

Sat Apr 23, 2011 7:29 pm

If there is an immobiliser, it will be cut into the pump wire. Cut one wire where it connects to the (usually) black immobiliser wire, and cut the immobiliser wire on the other connection, leaving enough of this wire to reach the green/purple you've just cut, solder them together and insulate.