Fuel pressure diagnosis

[Andrew Ebbern]

I'm trying to resolve what I believe is a fuel pressure problem with
my '88 240. The car will barely idle and has no power. I replaced the
in-tank pump (was definitely bad) and the fuel filter. Main fuel pump
is working, and passes the volume test (1L @ 30 seconds).

When I pinch off the return line from the pressure regulator, car runs
fine. This suggested to me that the regulator was a dud (not holding
pressure). I replaced the regulator - problem still there, but
everything is fine with the return line pinched off.

I checked the current draw on my main pump. 3.5 Amps without the
return line pinched, 8 Amps with the return line pinched.

Any ideas... perhaps my replacement regulator was a dud too?

Thanks,
Andrew

 

[Stewart Hargrave]

From a point at sea, to the circles of your mind, this is Andrew
Ebbern:

I'm trying to resolve what I believe is a fuel pressure problem with
my '88 240. The car will barely idle and has no power. I replaced the
in-tank pump (was definitely bad) and the fuel filter. Main fuel pump
is working, and passes the volume test (1L @ 30 seconds).

When I pinch off the return line from the pressure regulator, car runs
fine. This suggested to me that the regulator was a dud (not holding
pressure). I replaced the regulator - problem still there, but
everything is fine with the return line pinched off.

I checked the current draw on my main pump. 3.5 Amps without the
return line pinched, 8 Amps with the return line pinched.

Any ideas... perhaps my replacement regulator was a dud too?

What type of fuel system do you have?

Different countries got different fuel systems at different times, and
without knowing what system you have, or where you are posting from,
you may not be able to make much sense of the replies you get.


--

Stewart Hargrave

A lot faster than public transport


For email, replace 'SpamOnlyToHere' with my name

 

[Andrew Ebbern]

What type of fuel system do you have?

Different countries got different fuel systems at different times, and
without knowing what system you have, or where you are posting from,
you may not be able to make much sense of the replies you get.

It is an LH 2.2 system... 1988 240DL, Canadian .

Thanks,
Andrew

 

[Mike F]

I'm trying to resolve what I believe is a fuel pressure problem with
my '88 240. The car will barely idle and has no power. I replaced the
in-tank pump (was definitely bad) and the fuel filter. Main fuel pump
is working, and passes the volume test (1L @ 30 seconds).

When I pinch off the return line from the pressure regulator, car runs
fine. This suggested to me that the regulator was a dud (not holding
pressure). I replaced the regulator - problem still there, but
everything is fine with the return line pinched off.

I checked the current draw on my main pump. 3.5 Amps without the
return line pinched, 8 Amps with the return line pinched.

Any ideas... perhaps my replacement regulator was a dud too?

Thanks,
Andrew

Sounds like bad pressure still. When you did the volume test, did you
do it right at the pump? If you do the test it should be after the
pressure regulator. If the line is clogged (eg filter) the volume may
be good at the pump output, but not good at the engine, where it counts.

 

[Andrew Ebbern]

Sounds like bad pressure still. When you did the volume test, did you
do it right at the pump? If you do the test it should be after the
pressure regulator. If the line is clogged (eg filter) the volume may
be good at the pump output, but not good at the engine, where it counts.

Mike - I tested the volume output right at the return line from the
regulator. Operated the main pump by jumpering the appropriate
terminal at the pump relay, collected 1L with 30 secs operation.

At the suggestion of someone on brickboard, I checked operation with
the AMM disconnected. Engine started and ran fairly well in the "limp
home" mode, without the return line being pinched.

So now I'm thinking that perhaps all I did by pinching the return line
was raise the pressure well beyond normal (e.g. regulator was okay)
and this offset a problem with the AMM (or its electrical connection).
Will do some testing on the AMM later today.

Andrew