Low / No Pressure at Fuel Rail 1994 850 Turbo

RABrillhart · Post by **RABrillhart** » 11 Apr 2008, 18:49

OK, this has been gone over several times, but...
I think I have a Fuel Pump issue. I went out to Harbor freight and bought a fuel pressure tester, but do I need a special Schrader valve connector to test at the fuel rail? The stupid tester did not seem to come with one. If I need an adaptor where can I obtain it. I did a quick test and got 0 pressure release after the engine was cranked. Actually I got a little vapor (Air?) released when I manually pushed the schrader valve.

Right now I can't get the car to start so I cant test while its running, but I would like to in the future so ... How do I set up to test the pressure... Beg borrow or buy an adaptor to connect to the schrader valve or is there an other way?

So, right now, my thoughts are that it is a Fuel pump. (The relay was already rebuilt). But can no fuel delivery when the relay clicks on be from some other causative agent or should I just go out and buy a fuel pump.

Post by **MadeInJapan** » 11 Apr 2008, 18:57

I would think that Harbor Freight would have the correct fitting. You do not want to test the pressure with the car running but with the key in position II (fuel pump on). Also, leak-down test is important. After you turn the car off, how quickly does it lose pressure. Low or no pressure at the shrader valve could be a bad pump or bad fuel pump relay. The repair database has a write-up on how to jumper the pins of the relay socket to see if the cause is the relay. If that is eliminated as the cause, then it's your pump.

Post by **Ozark Lee** » 11 Apr 2008, 21:11

As MIJ said, you can eliminate the relay by jumpering it. There are 4 pins on the relay (#103). If you look next to each pin there is a number molded into the plastic at the base of the relay. Those numbers should be 31, 31b, 15, and 87.

Fashion a jumper wire and jumper the relay socket positions associated with pins 15 and 87.

If the car starts and runs then the relay remains your problem. The relay rebuild I posted is a 99% fix, not 100%. Other stuff can go wrong with it that is not easily or cheaply repairable.

You can also do the listen test, with the relay jumpered and the key in position II you should be able to hear the fuel pump running. Fold down and listen behind the (US) passenger's side seat. If you don't hear a motor whirring noise then your fuel pump itself is likely bad.

One more test you can do is to take a ball bat and give the bottom of the gas tank a good whack. If the whirring starts after the whack your fuel pump is toast.

Let us know what your find.

...Lee

PS. Harbor Freight always amazes me. I will go in to buy a tool set and it will have every sized wrench except the one that I need for the specific task at hand. I have a couple of fuel pressure gauges that I bought either at Advance Auto Parts or AutoZone and they had the appropriated connector for the Volvo - Don't even ask about the Porsche fuel rail - I had to got to, of all places, Harbor Freight to buy a tap and die set and make my own adapter for it. I think the gauges that worked on the Volvo cost around $35.00 each.

RABrillhart · Post by **RABrillhart** » 11 Apr 2008, 21:29

Thanks guys,

I was able to hear the relay clicking but as you discussed that doesn't necessarily mean the contacts aren't toast. I will do the jumper and then listen for the Pump. (My old MG used to thump when it started but I have as of yet not heard my fuel pump on the Volvo. I will fold down the seat and check. The bat whack sounds like a good test. BTW, don't get me started on Harbor Freight, I am presently finishing a cam follower for a machine I am rebuilding on a Harbor Freight Mill... It has been running flawlessly for over two years. But can I get a tap or screwdriver set that doesn't have to be swapped out? NO!

RABrillhart · Post by **RABrillhart** » 12 Apr 2008, 20:09

OK, here

Post by **MadeInJapan** » 12 Apr 2008, 22:00

The reason your car didn't start right away was because there was no fuel in the line...it needed time to be primed. For those who do this, in the future, leave the key in position II for a minute or two before you try to crank it. No harm!
Glad you got it fixed! Great job.

Post by **renns** » 13 Apr 2008, 04:58

As MIJ says, the system is full of air after replacing the pump. The pump only runs for a couple seconds when the key is turned to 'run' position, so waiting a few minutes won't help much. To prime the system after such work, cycle the key to 'run', wait a few seconds, then 'off', and repeat a few times. Each key to 'run' sequence gives you that couple seconds of pump run time, and it should purge the system in short order. Three or four cycles should be adequate. In vehicles with more pump noise, you can actually hear the system purge and the pump load up as the system pressurized properly.

RABrillhart · Post by **RABrillhart** » 13 Apr 2008, 06:37

Thanks guys!
Re the priming issue...

I was prepared to have to prime the car. The main weird issue here was not having to crank the car a few times. It was not having the car crank at all. Air in the rails would not have locked up the engine, or the starter, would it? With this in mind why did the car crank well after that. Now when I say crank, I mean having the starter roll the engine over. It was reminiscent of a bad starter... oh no I hope I am not headed there...

Post by **MadeInJapan** » 13 Apr 2008, 07:15

I think the main issue here is to not over-think this. Without proper fuel a the injectors our cars do all kinds of things that makes us think of all kinds of things. Enjoy your car and try not to worry about things so much!