Fuel Pump Not Running Topic is solved

turboman850 · Post by **turboman850** » 15 Oct 2019, 15:27

Hello Fellow Volvo 850 Sportwagon Owners
For near 3 weeks now I have been troubleshooting my 850 Turbo Wagon concerning a crank but no start situation.
The fuel pump motor doesn't run when try start, turn key on or when fuel pump relay is jumped or replaced w a good one.
I have unplugged the fuel filter and blown it out...it is functional.
I took my 12v jump box and hooked it to the pos. and neg. points of the fuel pump wiring at the rear of car. The fuel pump runs when this is done. So I know the pump itself is not faulty. But, this is the Only way it does run. After it runs I have good fuel pressure that is continuous after 30 minutes.
My question is: What within the wiring system could possibly cause this condition?

Post by **kranz** » 15 Oct 2019, 16:52

check the fuse

turboman850 · Post by **turboman850** » 16 Oct 2019, 05:03

Fuses are all good.
There is a Main Fuel Relay at radiator next to fan relay. No one seems to speak of this and I have,read plus watched many videos on fuel system operation this car, but this relay is never mentioned. Only reason I found out about it is looking at relay locations in repair manual, but no mention of function. What is its purpose in the fuel electrical system?

Post by **abscate** » 16 Oct 2019, 06:22

You have to check the wiring diagram (see the thread in the Major Topics Forum above to find) but I think the fuel pump is directly wired to the fuel pump relay. If the fuel pump relay is good, and the motor is good, the fault is in a wiring run between the two.

turboman850 · Post by **turboman850** » 16 Oct 2019, 09:11

There are three connectors according to schematic. Believe check ground at pump to start as most likely first to be bad, then ohm out from pin 87 to Red positive on fuel pump connector wires.

shegarty · Post by **shegarty** » 16 Oct 2019, 10:32

turboman850 wrote: ↑16 Oct 2019, 09:11 check ground at pump to start.

This could be an easy fix before tearing apart the car looking for a bad connection. Also, check continuity of the 12V supply, you should be able to do that at the pump relay fairly easily.

Post by **erikv11** » 16 Oct 2019, 11:10

turboman850 wrote: ↑16 Oct 2019, 05:03 ... There is a Main Fuel Relay at radiator next to fan relay. No one seems to speak of this and I have,read plus watched many videos on fuel system operation this car, but this relay is never mentioned. Only reason I found out about it is looking at relay locations in repair manual, but no mention of function. What is its purpose in the fuel electrical system?

On the 850, the main fuel relay fires the injectors. There are many posts about this relay here at MVS, especially noting that this relay's connector and wiring tends to fail and can be a cause of no-start due to injectors not firing.

turboman850 · Post by **turboman850** » 16 Oct 2019, 15:20

Checked ALL wiring to schematics. All voltages good except at fuel pump when key turned on. Main fuel Relay check good. Pin 30, 85, and 87 all register 12v as should. Battery is 12.1v. Ohm'd from fuel pump relay pin 87 to Red pos. on pump connector and good wiring. Blk neg to grnd at pump connector good. Pin 15 fpr to fuse ohm good. Fuse good. So a mystery why fuel pump Not run?
Decided to go ahead and check ignition coil for spark plugs...No Spark!!
New mystery: Is there ANY reason computer or another system would shut down my pump and ingnition coil (No spark when place grnd near wire or coil) to keep car from starting?? Or do I just have bad coil and it shutting down my "start sequencing" at computer???

Post by **abscate** » 16 Oct 2019, 19:34

Charge battery

12.1 volts is dead

shegarty · Post by **shegarty** » 17 Oct 2019, 05:07

A faulty cam or crank sensor will limit either spark or fuel to prevent startup. They will also limit spark or fuel if they sense a timing error, have you checked your timing belt to see if it has slipped a tooth, or two?