Fuel pump not working!bmw alarm?

[andysheep]

Iv traced my j plate 320i cabby not starting due to fuel pump not providing fuel pressure,i tryed a working relay out off my daily ,nothing, so jumped betwween pin 30 and 84,(im making it sound like i know what im doing) and hey presto its pumping fuel merrly in to a bucket,so just before i put the interia in the car it would run,so since i put carpet etc back in iv touched somthing,and pushed the alarm button on dash,just to see if it changes anything,im getting to the stage ill try anything,which is not good,its a bmw alarm and i think its the culprit,
Andy,any help would be great

[Brianmoooore]

Does your J plate cabby generate sparks at the plugs when you crank it?

[andysheep]

Yes i get spark ,first thing i tryed ,learnt that form your posts, and made sure feed and return line were unblocked,(new lines)spark plugs gapped and clean,no splits in throttle body pipes and idle valve buzing,cams turning linked to the fact iv spark,were now?
Andy

[Brianmoooore]

If an immobiliser is the problem, then jumping out 30 - 87 on the fuel pump relay doesn't defeat it, if it's been wired in the normal way. It would normally be connected somewhere between pin 87 and the pump, usually either connected inside the fusebox or behind the glovebox area.
There's a difference between powering the pump in the way you have, and it being powered when cranking the engine. It gets about 13 volts when you jump out the relay, but only about 8 volts when cranking, and this might be the difference between a failing pump working and not working. Alternatively, an immobiliser could be connected in line with 85 or 86 of the pump relay, but this would be very unusual. I've never seen it done like this.
You could try connecting a spare battery or a 12 volt power supply between body earth and pin 87 of the relay socket, with the relay removed, and then trying to start the car.
With the spare battery connected, the pump should be up and running and totally unaffected by the voltage drop that occurs when the engine is cranking.

[andysheep]

Thanks brian,will study up on the sly at work tomorro and try all of these tomorro night,your wisdom is greatly received and when i jumped the fuel pump relay it seemed to run fast,the bucket filled bloody quick like you say,
Andy

[andysheep]

Sorry to take so long to reply brian ,you were right , i jumped the fuel pump with a spare battery and it starts and runs and the fuel pump is on its last legs,just like you guessed,new one comes today thanks for the great advice once again,it stoped me tearing in thing that should be left alone,thanks again,
Andy

[Brianmoooore]

The first time I came across this was on my own car, on a camp site, in the middle of France. With the limited testing I had to hand, it took me a while, and a bit of unnecessary 'tearing apart', to work out what was going on.