so, yesterday after driving 100k with no problems, 7 hours later my 850 t5 refused to start! battery good , starter motor spinning ok , plenty of fuel ! would not bump start down a 1 mile hill!.........had to be recovered !! any ideas please!

 

Fuel pressure? Spark at the right time? Compression?

 

Can you here the fuel pump running? If so, check fuel pump relay.

 

also check the injector relay - its a small gray box up front by the radiator. try giving it a tap. To test the fuel pump there's a shrader valve on the end of the fuel rail, 850s should have about 39 PSI for fuel pressure. You can jumper the fuel pump relay to see if it kicks on the pump as well.

 

ok, all of the above answers are what i was looking for! so far (daylight gone) i have no fuel pressure at the inlet end of the fuel injector rail !! and as far as i can tell no fuel pump noise !!! tomorrow will check fuel pump and relay !!! many thanks so far!! great stuff ....

 

I'm usually pretty happy to jumper the fuel pump relay right away and start there. If you have spark, then the main fuel injection relay is okay.

 

yep, that`s where we went!!.........jumping the relay gave power to the pump, but no start! took the relay apart ! working as should do!...... so relay back in, pump out ! broken wire in the pump (visible).......repair wire / clean / re-position, starts first time!........i have to say, the pump is large, and looks very vulnerable to wear and tear whilst submerged in the fuel?? interesting!?/..... so it appears if the pump is damaged/us !! >>>>then the relay also stops power to the pump, so taking the apart proved it was ok!! then almose certainly the pump is broken!!

 

I've venture to guess that every high mileage 850 has replaced the fuel pump at least once. Mine lasted about 225K miles but gave all the tell tale warning signs...