2000 XC high fuel pressure overnight

ron-powell · Post by **ron-powell** » 17 Nov 2011, 11:45

Hello:

Car has 175K miles. Had a hard starting problem about 6 months ago and I installed an external in line fuel check valve. Car only hard started once since then. Two weeks ago, I had a hard start, eventually starting and running OK. After some research, replaced the camshaft position sensor.

Secondary to that, had a small fuel drip under fuel rail, creating fumes in cabin. Last week, an indepenedent volvo shop replaced injector seals and possibly tightened the fuel line fitting. All OK until yesterday morning.

After 2 minutes of idle, major fuel smell. Raised hood and fuel was spraying over top of engine later determined from around the fuel line to rail fitting.

Had car towed back to the independent shop where they idenified the leak. This is when they discovered that fuel pressure is normal when the car is running, but it sat overnight with a fuel pressure gauge on the rail and the pressure this morning was over 100psi.

The initial thoughs of the shop are that the leak was caused by the overnight fuel pressure increase bending some bracket attached to the rail, flexing something(?) and then the rail leaks. The night before the leak, the car sat outside in 30F temps, so why would pressure increase that dramatically in a closed system when temps are decreasing?

I told them about the external check valve and am positive I did install it on the correct line having traced it backwards from the fuel rail to the tank. Why else would it run normally for 6 months?

They want to dig into the tank and replace the pressure regulator, apparently something else that helps hold pressure in the system, and while they're in there, replace the pump and the rest. That, of course, is around $1700.

As of right now, the car cranks and runs with normal fuel pressure but the shop is concerned about the same thing happening again. The shop is a good one. They've taken care of 3 of our wagons for 9 years, so I trust them.

Has anyone seen anything like this before?

TIA, Ron

Post by **jblackburn** » 17 Nov 2011, 11:58

I've seen stories of people having this happen.

My theory behind it is that the check valve is put in the line AFTER the fuel pressure regulator on these AWD models. The regulator is supposed to keep high pressure out of the fuel rail that is created when it sits there in a hot engine and vaporizes (and can create vapor lock on hot days). With a check valve holding the pressure up in front of that and not allowing it to flow back, the regulator can't do anything like that.

On a FWD where that regulator is up near the engine itself, it releases that pressure back into the fuel tank, while the check valve in the pump keeps gas in the line up to the point from the fuel tank up to the area of the front wheel.

https://www.matthewsvolvosite.com/forums ... =1&t=38593

ron-powell · Post by **ron-powell** » 17 Nov 2011, 15:23

jblackburn:

Thanks for the fast reply.

So is the answer here to remove my in line check valve, because of its location in the system, as a test? I have access to a fuel pressure gauge to duplicate what the shop is doing Re watching the pressure overnight.

The hard starting earlier could have been caused by the camshaft position sensor instead of a faulty tank check valve. The shop guys did mention the CPS when I quizzed them about the hard starting months ago.

And I can live with waiting a second or two at start up if it is the tank check valve.

Ron

Post by **jblackburn** » 17 Nov 2011, 19:00

If you can still do that where you spliced the fuel line I would give that a try for sure. Put the gauge on there and see what it says in the morning.

ron-powell · Post by **ron-powell** » 17 Nov 2011, 21:30

jblackburn:

Had an interesting conversation tonight with our helicopter mechanic. He's spent quite a lot of time on newer model cars as well.

He's of the opinion this vehicle has a "returnless" (no return line) fuel system. I thought the second line I was seeing under the car was the return line, but the mech thinks it's probably a vent line. He also reiterated your earlier comment about the location of the pressure regulator.

My in line check valve is probably not allowing a pressure bleed off to some lower pressure after shutdown, while normal pressure is registered at the fuel rail when the car is running. I never did check the pressure after installing the check valve. I suppose it's taken a few months for the additional pressure to finally create the original seep and noticeable smell a month or so back and the spray under pressure yesterday morning.

I'm picking up the car tomorrow morning and will remove the check valve and see what's what.

When researching the hard start problem months ago, I never read any indication that with this type fuel system, over pressure is a potential result when installing an additional check valve.

Thanks for getting me on the right path,
Ron

Post by **JRL** » 18 Nov 2011, 06:15

Exactly where did you install the CV?
The correct location is right behind (to the rear of) the fuel filter
In fact we now attach them to the rear side of the fuel filter

ron-powell · Post by **ron-powell** » 18 Nov 2011, 16:46

Hey JRL:

The check valve ended up right in front of the tank, a couple inches into the soft line.

jblackburn: I ended up punching out the valve plunger, since there was no way to get it apart and just put the body back in line to keep the length intact.

I've not been able to get my friend's fuel pressure gauge yet, but tried a old tire gauge. Running, the car showed 59psi. After a 10 minute period after shutdown, I got 14-15psi. I'm still interested in a proper pressure gauge just to see what the shop was seeing.

Academically, I would also like to understand the system a bit better. How the components line up, etc. At this point, I think it's the tank, pump and then the pressure regulator with integrated check valve. I also think the high pressure is always there after shutdown, even though running pressure is lower. Maybe the pressure regulator allows it to bleed down to a reasonable level, so the system isn't over-pressurized like what I ended up with, but holds some for the next start.

I originally installed the valve in May, so it took perhaps 4 months for the initial seep to manifest itself and another month before it blew the fuel line fitting at the rail. My mistakes were not understanding the system and not checking residual pressure after installing the valve.

BTW, the shop put a few hours into diagnosing the car, but didn't charge me anything. Independent Volvo Services in Albuquerque NM. A great bunch of guys.