1994 850 na fuel pressure trouble

Jwestlind · Post by **Jwestlind** » 27 Aug 2014, 10:17

Hey all, i'm having an impossible time getting a proper fuel pressure reading on my '94 850 na AT 164k miles.

Firstly, the issue i'm trying to diagnose: Baby doesn't like to start right up after sitting long enough for the engine to cool to ambient temp (overnight, for instance). I'll crank her for about 5-7 seconds and she coughs and sputters a little, acts like she's flooding, then I'll back off and and try again immediately, and she fires right up, shoots up to about 1700 RPM for a second, and then levels off at 900. She runs just a teeny bit rough regardless of where she is in the RPM range. I notice a very slight hesitation on acceleration. She hasn't tried to stall, hasn't had any surging or hunting for idle, and ALWAYS turns right over on the second shot, usually on the first shot if she's been on in the last couple of hours. I suspect a fuel issue.

Which brings me to the reason for my post: I cant seem to get a pressure reading from the fuel rail, or from the valve behind the fuel filter. I've tried with the key in run position, even after cycling a few times, and I get nothing on the pressure gauge. I get a tiny bit of air hissing out of the valve on the rail when I depress it with a screwdriver, and same thing with the valve behind the filter. I can't hear the fuel pump going at all. This strikes me as odd, since she runs without issue.

any ideas are greatly appreciated.

Joseph.

Post by **abscate** » 27 Aug 2014, 19:23

It sure sounds like you have a bad fuel pump. The valve on the rail should spurt fuel, not air

Post by **Ozark Lee** » 27 Aug 2014, 20:47

There is a check valve built into the housing on 850 fuel pumps that has been known to fail. I causes the hard start conditions that you describe but even then you really shouldn't have air in the line since the fuel pump pressurizes the rail and then has a fuel return line after the fuel pressure regulator. Any air in the system would be purged back through the return line quickly. The way to test the check valve is with a fuel pressure gauge (which you say won't register but that can't be true if it is working and the car is running).

What you do is observe the fuel pressure with the car running and then continue to watch it after the car is turned off. It should hold the bulk of its pressure for 15 or 20 minutes at least. There is actually a spec for the pressure and the time but if it quickly drops to zero then either the check valve is bad or you have a problem with a leaky injector or a bad fuel pressure regulator. The latter two problems cause the car to run very rich and flood.

...Lee

Jwestlind · Post by **Jwestlind** » 02 Sep 2014, 01:36

Thanks for the details, lee. It seemed odd to me that i wasn't able to get a reading. Is there a specific "fuel pressure gauge?" I read somewhere that a basic tire gauge would be adequate. If this is wrong, then that could be my issue. I'm a relative newbie at this kind of thing.

Joe

Jwestlind · Post by **Jwestlind** » 02 Sep 2014, 01:41

Since my original post, I discovered that's airbox thermostat was bad, since replacing it, I no longer feel what I described as hesitation. Also I noticed that the rough idle seems to be noticeably mostly when the transmission is in park with the engine running, regardless of temp.

Post by **Ozark Lee** » 02 Sep 2014, 08:52

Jwestlind wrote:Thanks for the details, lee. It seemed odd to me that i wasn't able to get a reading. Is there a specific "fuel pressure gauge?" I read somewhere that a basic tire gauge would be adequate. If this is wrong, then that could be my issue. I'm a relative newbie at this kind of thing.

Joe

Joe,

There is a specific fuel pressure gauge but most tire pressure gauges will work to an extent. The problem with the tire gauges are that the seals in the gauge were never designed to be used for fuel and they can rapidly turn to mush. I have used a tire pressure gauge in a pinch and it was 10 or 15 PSI off from my real gauge but it did show that I had fuel pressure which was the point of the test. If you do use a tire gauge just throw it away when you are done, it will never be accurate for tires again.

The Volvo Schrader valve on the fuel rail is not a standard size in the fuel pressure world and many of the gauges won't thread on properly. The cheap Actron gauge has a proper adapter, they call it a Ford adapter.

http://www.actron.com/product_detail.php?pid=16174

You should be able to get that gauge at one of the auto parts stores for under $40.00 and for around $25.00 online.

The problem that you run into, particularly with the turbos, is that there really isn't enough room to get the gauge threaded onto the fuel rail without removing things like the throttle cable cam or the intercooler line. What I have done is just rigged up a fuel line and a small hose clamp to the gauge and I remove the Schrader valve core and then clamp my small section of fuel line onto the Schrader valve stem. I keep looking for a 90 degree adapter but I can't seem to find one.

...Lee