Help Trouble shoot my 94 N/A 850 issue ;)

[luketrash]

I pulled the fuel pressure numbers just now on my lunch break (mmm, gassy smelling hands for the rest of the day.. It's like spanish fly for the gals at the office.)

When you turn the key on, fuel pressure bumps up to 40psi. When the fuel pump relay then clicks off, it falls to 10psi and sits there.

When the car is started and idling, it sits at 40psi.



When you goose the throttle cable, it'll drop to about 35psi.



When you shut the car off, pressure sits at 10psi for an indefinite time (longer than a couple of minutes that I stood there until I got bored.)




I actually learned something! All this time when starting the car, I let the fuel pump buzz until the relay clicks off before turning the key all the way to fire the engine. WRONG! At that stage, I only have 10psi. I need to immediately turn the key while the pump is making 40psi!!! However, this still doesn't explain my hard starting issue.

Do these numbers look horribly wrong, as if my fuel pressure regulator needs to be looked at?

[Ozark Lee]

The book routine calls for the relay to be jumpered while making the test. The 40 PSI is low but not that low, it could be the calibration of the gauge.

The system is supposed to hold 30 PSI for at least 20 minutes after the pump is shut off. It makes me think check valve is bad but what is weird is that it does hold 10 PSI. With a bad check valve it usually goes all the way to zero instead of stopping at 10.

Another test to do is to get a pair of pliers and squeeze the return line, the pressure should jump way up (Don't let it exceed about 80 PSI). If the pressure really doesn't jump much then the problem might be the pump itself.

...Lee

[luketrash]

I just found the check in the 850 service manual pages listed here on the site.

(the part about pinching the return line.)

I'm going to try that after work.

This gauge is borrowed and came from Harbor Freight, so it's accuracy is questionable at best. But I think it's weird pressure falls so low when shut off. Where is the check valve located? Is it part of the whole sending unit that the fuel pump is a part of or is it built into the pump itself?

[Ozark Lee]

Where is the check valve located?

It is built into the housing of the pump which makes it a problem. Changing the pump insert to a Walbro or some other aftermarket won't fix the check valve problem. I think I would waste a big can of carb cleaner trying to fix the old one before I bought a new Volvo pump assembly.

One other problem that occurs is the fuel pressure regulator fails and actually allows raw fuel to get sucked into the intake.

There are aftermarket check valves but I don't know where to source them.

...Lee

[luketrash]

I'll have to check it all out carefully now. The service manual is actually doing a dang good job of explaining what to do. The section that deals with non DTC issues and drivability/accelleration lists MAF as the first suspect. I might pull it tonight and give it a good hose down with MAF cleaner.

Just for some reference, here's some related info from the service manual that pertains to my adventure:

Code: Select all

FUEL DELIVERY
Fuel Pressure Regulator
1) Install Connector (998-9725) to Fuel Pressure Gauge (999-
5011). Using Adapter (999-5479), connect pressure gauge to valve on
fuel distribution manifold. Turn valve in direction of adapter.
Connect other gauge connection to Fuel Drainage Unit (981-2270, 2273
and 2282).
2) Remove electrical distribution unit cover in engine
compartment. Remove fuel pump relay. See Fig. 2. Connect jumper wire
between fuel pump relay terminals No. 1 and 3. Turn ignition on. Fuel
pump should start. If system pressure is 43.5 psi (300 kPa), go to
step 5).
3) If system pressure is too high, remove jumper wire.
Disconnect pressure regulator return and vacuum lines and blow through
lines. If both lines are okay, replace regulator and recheck pressure.
4) If system pressure is too low, squeeze return line and
ensure pressure rises. Do not allow pressure to exceed 87 psi (600
kPa). If pressure rises quickly, pump and line are okay. Replace
pressure regulator and recheck system pressure. If pressure rises
slowly, check for blocked fuel filter, fuel pump strainer or fuel
lines. If pressure does not rise, replace pump.
5) If system pressure was 43.5 psi (300 kPa) in step 2),
check operation of pressure regulator by connecting Vacuum Pump (999-
5843) to pressure regulator. Apply vacuum to regulator. Ensure system
pressure falls by same amount as regulator pressure.
6) Turn ignition off. Remove jumper wire between fuel pump
relay terminals No. 1 and 3. Reinstall fuel pump relay. Check fuel
system residual pressure. Pressure should not fall below 20 psi (200
kPa) in less than 20 minutes. If fuel pressure falls faster, check
injectors, pressure regulator, and fuel pump. Disconnect Pressure
Gauge (999-5011).

[luketrash]

I found this elsewhere, which was interesting to me:

ROTTEN EGG SMELL FROM CATALYTIC CONVERTER


The sulphur smell from the exhaust, is actually caused by running the engine/cat convertor slightly lean for long periods and then running under a rich condition (ie going up a hill under heavy load) This is when the sulphur smell (rotten egg) is produced.


Under relatively lean conditions, the sulphur found in gasoline is converted to sulphur trioxide, then during the rich running condition the sulfur trioxide is converted into hydrogen sulphide (rotten egg smell) within the catalytic converter.


Audi of America issued a service bulletin Group 24, #92-04 which detailed this problem. They list the cause as : the gasoline sulphur content and the characteristic of catalytic convertor to store sulphur compounds and release them during rich engine running conditions.


Switching gasoline brands may help. The Oxygen sensor may also need to be replaced to correct a fuel injection mixture problem.

My car has always had this issue when I get on it (not really BEATING it, but foot to the floor accelleration)

Once it warms up, I really need to get around to testing every FI related sensor on the car since I think it has always had mixture issues.

[luketrash]

OK, tonight the fuel pump is testing out as bad. Fuel pressure struggles to climb to 38psi. There is no spike in fuel pressure when you turn the key on (like earlier when I tested the car cold.)

Pinching the rubber return line off of the back of the fuel pressure regulator with needle nose pliers has zero effect on fuel pressure. It doesn't climb at all.

SO....

I accessed the fuel pump door in the back of my wagon and now need your help to figure out how to get it out peacefully without breaking anything.

How:

-do you break loose the black plastic ring that holds the fuel pump assembly in place without breaking it? Does it unscrew or does it simply turn 30 degrees and pop off?

-do you pull the rubber fuel lines loose that are connected to the pump with some sort of 90 degree connector?

-do you pull the pump assembly out of the car with such limited amount of space?

[Ozark Lee]

-do you break loose the black plastic ring that holds the fuel pump assembly in place without breaking it? Does it unscrew or does it simply turn 30 degrees and pop off?

It is threaded on and it takes a few turns - on the similar setup on the Porsche I used a big pair of channel lock pliers. On other cars I have tapped it off with a screwdriver until it is loose and then just spun the ring off by hand.

-do you pull the rubber fuel lines loose that are connected to the pump with some sort of 90 degree connector?

Good for me but bad for you I haven't had to do it yet, my understanding is that it takes 2 screwdrivers to release the tabs and the connector just pops off (relieve the fuel pressure at the Schrader valve so as to not soak your carpets with gas).

-do you pull the pump assembly out of the car with such limited amount of space?

So long as the back seat is out of your way (folded down) it should lift right out.

...Lee

[greasefingerss]

That large threaded ring/plastic nut can be damaged easily if tapping it with a very large screwdriver and hammer. I got my wife to help me. She tapped on it at the same time I did. The second tap-point was of course 180 degrees from mine. It came right off on two of my vehicles that way.

[MadeInJapan]

Seems like you guys are on top of it. If you need to see diagrams or how-to's from VADIS, just let me know: badger36-at-knology.net or call me at 865-696-4163 (my cell phone). I can look things up and maybe be of help. I'm up for awhile.
Dave