The results (WAS: Differential Pressure Regulator Checking

rob hod rob3 at
Thu Nov 28 13:39:23 EST 2002

    Hi Tigran,

    the air plate will get harder to move as the engine warms, its just a
question of how much is too much.
    Remember that system pressure as such has *No bearing* on the air plate

    I don't know if you;ve been following a spin off discussion that's been
going on regarding control pressure, but I think it's time you checked it on
your car. the reason I say this is because system pressure has no bearing on
resistance to movement of the air plate, only control pressure.

 Plumb a two legged gauge into the feed to the warm up reg (valve open if
the gauge has one). The port on top of the fuel dist it the supply side to
the warm up reg.   Monitor the reading from start. It should be (very
roughly) around  1 Bar at cold start, rising to around 3.8 bar warm.  The
higher the reading the harder the plate is to move.

    you may want to repeat this test with the electric feed to the warm up
reg disconnected (should lead to a much slower rise in control pressure).

    If the pressure is exceeding 4.5 bar then you've found a sympton. the
problem itself is likely to be with the wam-up regulator or with the return
flow from the regulator back into the fuel dist, and thence the return fuel


----- Original Message ----- >
> Message: 12
> From: "Tigran Varosyan" <tigran at>
> To: <quattro at>
> Cc: "'Paul R. Cole'" <bdssprc at>,
> "'Huw Powell'" <human747 at>
> Subject: The results (WAS: Differential Pressure Regulator Checking)
> Date: Wed, 27 Nov 2002 17:45:19 -0800
> Well, took my DPR to Schucks today, the guy there happened to be an
> Electrical Engineering student so he helped me test for ohms. The DPR
> resistance came out at 18.6 ohms, within spec....
> Went home, hooked it back in and started the car again. Yanked the
> out, plugged the intake manifold hole with my finger and watched what
> happened. This time I got a pretty nice cone shape out of the spray and
> spray increased as I revved... The engine ran pretty nice (on 4
> Then all of the sudden flow stopped and the engine died... I was like
> Felt the plate, it was not stiff (for the first time ever!!) and I stood
> there wondering what happened. On my way back to the cabin to start the
> again I noticed a stream of gas coming from below the car. Looked under
> there and the line going to the fuel reservoir had come mostly lose.
> My explanation is that the line must have been coming lose and spraying
> of the fuel out under the car. The car ran fine at this time. Then when
> line moved farther off the connection due to the pressure it popped off
> fuel flow to the engine stopped. This is one snafu that I think helps us
> troubleshoot the problem a great deal.... I will elaborate towards the
> let me finish recounting the events...
> So I hooked the line back up, this time put a hose clamp on it and went
> to crank the motor. Engine started up, ran for about a minute and stopped,
> just like it has been doing the entire time. While it was running I
> to make sure that the hose was on tightly and that I had no more fuel
> under the car. I went to feel the plate and yet again it was VERY stiff.
> Back to our original problem...
> I then went ahead to check the return line as someone recommended. I took
> the braided return line that comes from a cylindrical shaped piece and
> behind the firewall. I took that off, put it in a bottle and started the
> again. This time with all injectors in the car. (I ran out of hands... If
> took the injector out I would need to hold the manifold hole plugged, the
> injector in a bottle and the return line in a bottle too.) Anyhow, the
> engine ran like crap for about a minute and then started to sputter and
> By this time my 2L bottle was getting full so I shut the motor off by
> myself, but had I left it running another few seconds I am sure it would
> have died. With the return line still unplugged in my hand I checked the
> sensor plate. Again, VERY stiff!
> I cannot check the harness going to the DPR for 2 reasons. #1 I do not
> a tool to measure duty cycle, and Schucks wants $80 for one. #2 I cannot
> the engine to run long enough to reach operating temp anyway, so even if I
> had the tool to measure duty cycle of the harness I cant get the engine
> enough to where I could.
> My theory:
> Due to the resistance we know that the DPR is good, right? However the car
> ran perfect when the fuel line was slipping off the reservoir dumping half
> of the fuel on the ground. What this tells me is that the fuel pump is
> out-flowing the main Fuel Pressure Regulator. I do not know if this car
> one, or where it is but all other injected cars I have seen have a main
> mechanical FPR. I can see a cylindrical thingy with 2 lines going to it
> the Fuel distributor and a single line coming out (which becomes the
> line). From the shape of it, it looks like the main FPR to me. As you may
> recall I bought a generic fuel pump that says it will specifically work
> my car. Normally I would suspect that, however the stock pump did the same
> thing before it died! Nothing changed between the time I had the working
> stock pump and this one. This leads me to believe that there is simply too
> much fuel volume going to the fuel distributor and whatever is supposed to
> get rid of that fuel (like a main FPR) is not working correctly. Again, we
> know its not the return line as the same problem happened with the return
> line in a bottle.
> Ideas, more tests, feedback wanted very badly.
> Thanks,

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