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

Post by **luketrash** » 14 Mar 2008, 08:50

Is this only for testing a no-start issue? Or can I drive around for a bit like this to see if it fixex my power delivery problem?

Post by **Ozark Lee** » 14 Mar 2008, 09:35

You can drive it. It can become a safety issue if you got involved in a collision but it is otherwise just fine.

...Lee

Post by **luketrash** » 14 Mar 2008, 09:38

Cool, and thanks much! My 1954 Ford sedan has a glass float bowl Holley carburetor on it, so I know all about collision related fire dangers

Post by **luketrash** » 14 Mar 2008, 12:35

Jumpering the fuel pump relay circuit allows the car to run just fine, but it still runs the same, so the relay is not the issue.

Next week I hope to get ahold of someone's fuel pressure tester and see what sort of PSI I'm getting at the fuel rail as well as what happens to fuel pressure when the car is shut off.

My little 400 mile trip last weekend cost me half a quart of oil too, so I refilled my oil.

Post by **MadeInJapan** » 14 Mar 2008, 15:34

Seems like slowly you're getting things sorted. On our old 850 that burned some oil, I kept a quart of oil lodged between the front headlight and battery just for the purpose of filling up when I needed some.

Good luck figuring out your fuel deliver system.

greasefingerss · Post by **greasefingerss** » 14 Mar 2008, 20:01

Just some observations with other vehicles that I work on (not Volvo specific)

The fuel pressure regulator reduces the fuel pump pressure. It usually fails in the open position. So you should get increased pressure if it fails.

The check valve will have nothing to do with the real issue. It should only delay starting. Only a pressure gage on the rail can help. Most all vehicles specify a leak-down rate. In other words it should not hold pressure overnight. Example: my Jeep factory service manual stated that the pressure should drop at 1 psi per minute.

The gas supply is really clean these days, so the filter should not be an issue unless it is 90,000 miles old. Most fuel tanks are plastic and that helps keep rust out of the fluid. I removed a gas tank from one of my vehicles at 160,000 miles (to replace the fuel pump). When I went to wipe the tank clean with rags; where was nothing to clean. It was spotless!

Your issue is very difficult for me to resolve. Fuel delivery is the main thing that comes to mind. But being intermittent makes it so hard to single out. Your pump could get hot and bind. An electrical component could fail over time or with heat????

Post by **MadeInJapan** » 14 Mar 2008, 22:54

Heat in the fuel pump tends to happen if the car is run with a very low amount of gas (gas actually cools the pump) or if the car has actually run out of gas before, and especially during the summer months. Of course if you haven't done this, who knows what the previous owner did.

Post by **luketrash** » 17 Mar 2008, 07:44

Oddly enough, my car seems (this is just observed) to run worse when the fuel tank is completely full than it does when nearly empty.

However, it is doing the same thing at all levels of fuel.

I have a fuel pressure test kit in my posession and plan on testing it tonight.

Do any of you have fuel pressure specs for the '94 n/a cars? At idle? At throttle? At shutoff with leakdown?

I was in Omaha all weekend and started the Volvo when I got home after not having driven it for 3 days and it fired right up! So these problems are totally intermittant. The power delivery suffers at all times though, but it was running 'OK' last night when I drove it into town.

If I can't find anything in a week, I'm going to seafoam the car from all three ways (gas tank, intake, and crankcase) I might even inject a teaspoon full into my low pressure cylinder to see if it'll knock the piston ring loose overnight.

I could see the problem being related to bad or dying fuel injectors, but I don't know of a good way to bench test them really.

greasefingerss · Post by **greasefingerss** » 17 Mar 2008, 18:24

The fuel pressure regulator is manifold vacuum pressure operated. So one simple thing would be to insure that the vacuum line is intact. Anything above 44psi is diverted back to the gas tank. For leak-down, the pressure should not fall below either 20 or 30 psi after thirty minutes of shutdown (I do not remember which it should be) The pressure should be mainly constant since it is an electrical motor that operates at only one speed. It is capable of something greater than 44psi but the FPR reduces and maintains this.

My gut feeling says that your issue is not the injectors. There are so many devices that are involved with fuel management: MAF, O2 sensor, ERG, CTS, etc

Post by **luketrash** » 17 Mar 2008, 20:02

This gives me somewhere to start. Back when I tore off the intake system to do the PCV system, I am trying to remember if there was anything goofy going on.

I did get to thinking it could be a vaccum leak at the throttle body or the intake gasket, but spraying carb cleaner on both areas has no effect on the way the car runs. That's not a definitive test though.

I just wish the car would throw a DTC