I have played with my cars for almost 60 years, so have a lot of experience on many different cars, but am learning all the time. I am presently helping a young lady with her '97 Volvo 840 wagon that will not start. I think it is a fuel pump problem but not sure yet. I get no fuel pressure at the engine when key is turned on, and no sound from the tank, like a pump running, but not sure yet if it is a problem with the pump, or power to the pump. Will post again when I check it out some more.
I have looked online for relevant videos but none have provided much useful info, so any help will be appreciated.

 

RobertDIY has a very complete playlist of videos on Youtube. What I'd do is start by bookmarking volvotips.com - very handy guides on the 850. Next I'd jumper the fuel pump relay to see if the fuel pump starts up and sends pressure to the rail. Robert has a vid on how to measure fuel pressure using the shraeder valve on the side of the fuel rail (under the black cap - like a tire valve). If you don't see 40 PSI or so, you probably need to replace the pump. If the pump kicks on, then you may need to replace the fuel pump relay (note - a bad FPR is an indication that the fuel pump may be ready to fail so plan on replacing the pump shortly. What happens is the pump starts to pull too much current and that fries the relay. Eventually the pump fails due to the friction building up). If you now have fuel pressure at the rail, next check is the fuel injector relay up on the cowling near the fan shroud (typically its a gray relay). Check for any wiring issues there as well. If all of those are intact, then you are probably getting fuel to the injectors and you should start thinking of testing for spark related problems.

 

I have checked the relay by shorting it out, but not sure if I shorted the correct pins (1 and 3) since they are not labeled that way at the socket. I shorted the pins that are toward the front and the back of the socket, not the side pins, and pump did not start with key turned on. But what I want to do is just find the wire in one of the 4 connectors that are found back near the pump, that sends 12 volts to the pump, then just demate that connector, put battery voltage on that wire and see if the pump starts. I have seen a lot of wiring diagrams but nothing that I can identify the 12 v supply wire that goes to the pump. I think it is one of the wires in the 4-wire connector, but not sure. Can anyone tell me which connector, by color and number of wires, and which wire on that connector, provides the 12 v supply going to pump, so I can apply 12 v to that wire and see if pump starts?

 

I was able to determine the problem was the relay, not the pump. I got it running with relay shorted and ordered a new relay. Can anyone tell me if it is OK to drive the car with the relay shorted, until I get the new relay? I assume the pump normally cycles on/off once it reaches operating pressure, so I don't want to damage the pump if it runs constantly while driving.

 

Got the new relay, put it in, and the car is running OK. Will check fuel pressure to be sure it is good.

 

Just to note on the 850s, a failed relay is usually a warning sign that the fuel pump is about to fail. Logic is that the pump is struggling so it pulls too much current and fries the relay. The new relay gets your going but don't be surprised if the pump fails within 6 months. You can test to see if your pump's current draw or have a spare ready to install :-)

 

I will check the fuel pressure; I assume about 40 psi is what it should be - is that correct?
And I could remove the relay and short the relay contacts with an ammeter to see what the current draw is. Can you tell me what it should be, so I can know if it is drawing excessive current? I already have bought a new pump and intended to return it, but if the present one is going bad I might keep the new one just in case.
Thanks for the help.