Once yesterday and once today I had an issue where I had been doing a lot of driving and parking and driving and parking and suddenly my car did not want to start. Both times I put a rag at the end of the schrader valve on the fuel rail and drained out some fuel and then the car started right up. The first time I did this I kept draining thinking the pressure would drop but it didn't seem like it ever did and I kept getting lots of fuel.
Does anyone have any idea what I am dealing with on this?
Kind of wondering if this is due to the fuel pressure regulator?

 

best way to sort this out is to put a pressure gauge on the valve and see exactly what you have. could be the pressure regulator, fuel pump relay, fuel pump etc.

 

I borrowed a fuel pressure gauge and the info I got was as follows.
At idle I have 35psi
Giving it some throttle it goes up to 45psi
When I shut it off it is at 35psi and slowly rises to 41psi.

What should I be getting?

My Haynes manual says "regulated fuel pressure - 4.39psi".

 

Volvo 850 basic testing service manual has a good self test suggestion

 

That the pressure goes up after engine is shut off is completely bizarre!

I would watch the fuel pump voltage at the pump and see that it is shutting off when key is off.

 

Symptoms of a failing fuel pump.

 

Hey Boxpin,

Are you referring to the fuel pressure going up after key off? If so, sounds to me more like fuel pump relay (and overload15+ and ..etc) contacts have welded or something? That's why I said very bizarre.

 

I'm on my third fuel pump since I bought the car. I ordered a spare pump relay so I'll try putting that in and re testing.

 

I put in a new fuel pump relay and it happened again. I connected a gauge and running is around 36 psi and after I shut it off it rises 2 and 3 psi. If I let the car sit for about a half an hour it starts right up. When it doesn't start I can still hear the pump run.

 

I see nothing strange or confusing about the increasing pressure or any of the fuel pressure measurements. That sounds to me like everything is working great. Any liquid closed up in piping will rise in pressure if it gets warmed up. The regulator is obviously working, and is mechanical, so it'll bleed some fuel off when the pressure gets up to the upper 40's. I don't think you should replace anything more.


I find it very strange if spraying fuel out of the Schrader valve is the secret to getting to run. If that happened, normally you might suspect vapor lock, but the fuel system is okay, so it ought not do that.


So if both those things are true, you might need to look for a hot spot. If, for instance, you are boiling fuel in a spot that is under the car, where originally there was a heat shield, that make be a possible explanation for all your observations. You might be able to do some experiments (like cooling down a part of the fuel system with water) to see if you believe this.

 

You didn't say, but I assume that pressure is at idle? If so, it's too low for a '95 850; should be about 43 or so and go up a bit when you blip the throttle. You can temporarily pinch the return line and see how high it goes; should go up to about 80 psi or so if your pump is good.

From the '95 manual:
=====================================
4) Turn ignition on. Fuel pump should start. Fuel filler
cover can be removed to determine whether main pump is operating. Fuel
pressure should be about 43.5 psi (3.06 kg/cm  ). If pressure is too
low, pinch return hose by hand and check whether pressure rises. DO
NOT allow pressure to exceed 86 psi (6 kg/cm  ).
5) If pressure rises rapidly, pump and lines are okay.
Replace pressure regulator and recheck line pressure. If pressure
rises slowly, fuel filter, fuel pump strainer or fuel lines are
blocked. If pressure does not rise, fuel pump is probably faulty.
6) If pressure is too high, remove jumper wire between relay
or fuse terminals. Remove return hose from pressure regulator. Blow in
pipe. Remove vacuum hose from pressure regulator. Blow in pipe. If
both hoses are open, pressure regulator is defective. Replace
regulator and recheck pressure.

 

[QUOTE=gdog;439103]You didn't say, but I assume that pressure is at idle? If so, it's too low for a '95 850; should be about 43 or so and go up a bit when you blip the throttle. You can temporarily pinch the return line and see how high it goes; should go up to about 80 psi or so if your pump is good.

Yes this is at idle. If I blip the throttle it goes up to the low 40s. I'll try pinching off the return and see what happens.