'98 V70 VERY HIGH Fuel Pressure

Felix_saenz · Post by **Felix_saenz** » 13 Nov 2012, 18:19

I have a persistent p0171 code on a '98 V70 AWD B5254T--long term fuel trim bank 1 lean, at something like -23% to -25%.

After checking for vacuum leaks and doing a homemade smoke test, I decided to check fuel pressure. Performance on the car is NOT too severely affected--little hesitations and surges here and there when accelerating, but the idle is steady.

I checked FP twice, two Saturdays ago and last Saturday. BOTH TIMES I GOT A READING OF 93-95 PSI.

I don't know a whole lot about fuel pumps, but I know that this is incredibly high.. and can't it deadhead?

I thought maybe it had something to with the gauge--it was an Evertough set rented from O'Reillys, but the gauge tested fine on another car.

At this point, I'm imagining one of two things:

1) Bad fuel pressure regulator? It holds a vacuum okay (checked with a vacuum gun), so it should be opening okay? Unless it is stuck in the closed position.. any way to check this?

2) Clogged fuel return line? But with that amount of pressure I would imagine that the clog would be pushed through. Or, that the fuel return line somehow isn't correctly attached? I'm don't like the thought of removing the rear end to drop the tank..

Other fuel related issues: trouble starting when around 1/8 tank of gas. Also, for some reason when I fill up, the tank doesn't hold any more than 15 gallons, while the gauge indicates that the tank holds 18.

Its frustrating that with such a high fuel pressure, there is such a lean condition... and that there are no other codes, nor is performance really too affected.

I thought maybe bad O2 sensor, but wouldn't that turn up greater performance problems? Same thing with clogged injectors?

Do you guys have any advice for me? I'm pretty young and though I have some experience and feel comfortable working on cars, this thing has me confused. I'm thinking that I'll order the pressure regulator and if there is no change after installing it, I'll return it.

Thanks, Felix

[EDIT] I noticed today that there isn't a hiss when loosening the gas cap after the car's been ran. No pressure in the fuel tank?

Post by **cn90** » 14 Nov 2012, 16:40

Usually the fuel pressure is about 45-55 psi in most cars.
I guess you can replace the FPR, and see what happens next.
Check your VIN number and ask dealer for the PN (there are a few versions of FPR).

Post by **rmmagow** » 14 Nov 2012, 19:01

I'd bring the car to a Volvo specialist and even maybe a dealer to have that fuel pressure tested again. That's awful high and should cause a different set of issues I think. Before doing the FPR make 100% sure it's really high pressure. I'm fighting the same P0171 code in my 98 V70, that and a P0455. My car runs very well, just CEL at least once a week.

Felix_saenz · Post by **Felix_saenz** » 14 Nov 2012, 22:13

Thanks for the feedback.

I ordered the FPR from FCPeuro. Its behind the block on the passenger side for this model.

I got a different FP tester from O'Reilly tonight and tested again to be sure. Again ~96psi. I'm in Corpus Christi, TX... the closest dealership is 120mi away in San Antonio and there aren't any Volvo specialists here, just plain ol' mechanics. I don't even think there is a European import shop here.. Honestly, I'm surprised that other set of problems hasn't shown up.

Post by **jblackburn** » 14 Nov 2012, 22:18

I believe the XC is set up with a fuel pressure regulator at the tank and a non-return fuel system. I can't ever remember if that's just the later years or does include the 98 though. Some 98's (NA I believe) had a different fuel system then others.

In that case, if you had a non-return fuel system...your regulator would be bad.

Easy way to tell?

Do you have these TWO fuel lines on your engine?

Felix_saenz · Post by **Felix_saenz** » 14 Nov 2012, 22:39

I'm guessing it is a later year.. maybe this is an intermediary between the FPR on the rail itself in the 850 and what you describe, at the tank, in the XC70.

jblackburn wrote: In that case, if you had a non-return fuel system...your regulator would be bad.

Is it the same case if it is a return system?

Felix_saenz · Post by **Felix_saenz** » 14 Nov 2012, 22:42

I have two lines coming across the valve cover, but one is the fuel supply and the other is vacuum line 1 in the picture, it runs to the intake manifold.

Post by **jimmy57** » 14 Nov 2012, 23:26

I agree it's deadheading. The integral relief valve on the pump is limiting it to the mid-90's fuel pressure.
Take the FPR out of the vessel on the line and check to see if the return line is free.

Felix_saenz · Post by **Felix_saenz** » 15 Nov 2012, 15:03

Thanks for the feedback Jimmy. It is relief valve that is preventing the pump from failing, then. Would this affect the tank's pressurization? When I turn the gas cap, there is no hiss and so I assume no tank pressurization.

My father suggested something similar but I didn't execute it very well. I couldn't figure out how to put air ONLY into the return line, and what I ended up doing was putting the air compressor needle down into the return with someone standing at the tank to listen. I might try this time around to fit a rubber or plastic hose down into the pipe and blow on it. That seems like the only way without being able to access the other end of the line. Unless you have any other suggestions?

Post by **jimmy57** » 15 Nov 2012, 15:06

The tank will not pressurize the vent is open all the time through the canister.
I normally use some piece of hose I don't mind putting my mouth on and using that to blow through a line to check for it being blocked. That return line will have some obstruction but you should be able to blow through it.