fuel pressure test gauge, 1995 850

auRum98 · Post by **auRum98** » 10 Feb 2009, 14:50

Hi

I'm attempting to troubleshoot my 1995 850, and I need to test the fuel pressure, but I'm having a hard time locating a test gauge. Advance auto carries one, but it won't fit because the throttle linkage mount is in the way. It seems like I'd need something with a 90 degree fitting.... Does anyone have any suggestions?

Thanks!

Post by **Ozark Lee** » 10 Feb 2009, 14:58

Some folks just use a tire gauge - I question the accuracy of that but it will get you in the ballpark. The standard gauges work fine on my N/As but not on my turbo so I have been looking for a solution as well.

...Lee

auRum98 · Post by **auRum98** » 10 Feb 2009, 15:15

I tried a tire gauge, and it reads 10- 15 lbs. Shouldn't it be closer to 40 lbs.? I can hear the pump when I turn the key on, but the tone changes when the engine turns over. Could the pump be working but not supplying enough pressure?

Thanks,
Ian

Post by **MadeInJapan** » 10 Feb 2009, 15:33

Certainly.

auRum98 · Post by **auRum98** » 10 Feb 2009, 15:39

Is pump replacement the only remedy, or are there other possibilities? I guess what I'm asking is, how can I tell definitively if the pump is weak before I replace it?

Post by **MadeInJapan** » 10 Feb 2009, 15:52

It could be your fuel filter...if it's clogged it will reduce pressure. If it's old it needs replacing anyway- start there...then get a good gauge to correctly measure the pressure at the fuel rail. If pressure is still low, then you need to replace your pump.

Post by **Ozark Lee** » 10 Feb 2009, 17:09

Ian,

We have a lot of variables going here. The change in tone on the fuel pump has me wondering about the battery cables. You will need your stereo code but clean up the battery connections including the secondary connections that come off of the main lugs on the battery (no cost - cheap and easy).

The fuel pump relay (103) could also be failing - when you remove it most of them have 4 terminals, 31, 31b, 15 and 87. Put a jumper wire between the socket positions associated with pins 15 and 87. If it starts and runs then you can either repair or replace the fuel pump relay.

You can fix it for a few bucks worth of Radio Shack parts - here is how I fix mine.

https://www.matthewsvolvosite.com/forums ... php?t=9681

Lastly it is the big dog, the fuel pump itself. The OEM replacements are insanely expensive but they require little more than unscrewing the cap (a tad more difficult than it sounds) and plug and playing them to replace.

Use a volt meter on the fuel pump and observe the voltage to it while listening to it. If the voltage remains and the the noise stops the pump is toast. They normally are an all or nothing proposition where they work perfectly until they completely fail but I suppose there could be variations of that scenario.

Many people use the Walbro replacement kits if the fuel pump is bad and I have not heard of bad results other than they are noisier than the OEM units and they are much cheaper. Since you had such low pressure at the start I am also questioning the check valve in the fuel pump. The stock fuel pump pressure should be around 44 PSI and it should hold that pressure for quite a while. If it bleeds of quickly after the pump stops (key off) it indicates a bad check valve and it is unfortunately built into the OEM fuel pump housing and the Walbro won't fix it.

Let us know what you find.

...Lee

Post by **rgrady** » 10 Feb 2009, 17:24

When I was having my no power issue my fuel pump was very loud. After I reconnected the loose hose inside the fuel pump assembly the pump got quiet again. I think without the backpressure of the fuel line the pump was over spinning causing the impeller to cavitate creating the louder noise. Suction and discharge head pressure are very important for the proper operation of any pump.
As far as being able to hook up a fuel pressure gausge, I bought one from autozone and when I got home discovered the issue of the throttle linkage in the way. I took a 90 deg. angled fitting off my refrigerant gauge set hose and was able to hook it up. Was still a tight fit. The refrigerant was a larger size schrader fitting so I had to use the reducing adapter that came with the pressure gauge.

Johnny78Blaze · Post by **Johnny78Blaze** » 28 Nov 2011, 16:43

Or just take out two of the three bolts holding down the throttle linkage mount and slightly loosen the third. You can then slide the whole thing away from the rail, making room for the fuel pressure tester.