How to depressurize the fuel system when removing fuel pump fuse does not work?

[martinxue]

Hi,

I have a problem to depressurize the fuel system for my 1988 240GL
sedan as I need to check the in-tank fuel pump. According to Haynes
manual, I need to take off the fuel pump fuse and start the engine, let
it stall and proceed to the rest of fuel system depressurization.

But after I took out the fuses (even all the 16 fuses in the fuse
panel), the engine still could not be stopped. I post the question a
few days ago and from the information that I gathered, I suspect that
someone has modified the electric wiring for the fuel pump, as this car
was bought from someone else and it had been serviced by several
mechanics.

So are there any other ways to depressurize the fuel system?

Any suggestions will be greatly appreicated.

Thanks very much.

Regards

Martin

 

[M-gineering]

Hi,

I have a problem to depressurize the fuel system for my 1988 240GL
sedan as I need to check the in-tank fuel pump. According to Haynes
manual, I need to take off the fuel pump fuse and start the engine, let
it stall and proceed to the rest of fuel system depressurization.

But after I took out the fuses (even all the 16 fuses in the fuse
panel), the engine still could not be stopped. I post the question a
few days ago and from the information that I gathered, I suspect that
someone has modified the electric wiring for the fuel pump, as this car
was bought from someone else and it had been serviced by several
mechanics.

So are there any other ways to depressurize the fuel system?

Any suggestions will be greatly appreicated.

Thanks very much.

1 somebody hotwired the relay: restore to factoryspecs, as the current
situation isn't safe
2 Ignore Haynes and unscrew a connection wearing goggles and with a rag
wrapped around it.
--

 

[Peter Ziobrzynski]

1 somebody hotwired the relay: restore to factoryspecs, as the current
situation isn't safe
2 Ignore Haynes and unscrew a connection wearing goggles and with a rag
wrapped around it.

I was following the same advice for my 1999 V70 and probably stumbled over the
same problem. The fix for me was to find the correct fuse. In V70 there is two
sets of fuses: main and secondary - two locations - main is inside the engine
compartment. In the main there is a fuel pump fuse.

 

[Johan Plane]

I was following the same advice for my 1999 V70 and probably stumbled over the
same problem. The fix for me was to find the correct fuse. In V70 there is two
sets of fuses: main and secondary - two locations - main is inside the engine
compartment. In the main there is a fuel pump fuse.

Hi,

Sorry, but I can't see the problem. In my 265, there never was any pressure in the
rear, i.e. the fuel lines to/from the tank. I just popped of the hoses and got the
pump out of the tank. Came a trickle just as the hoses came off, bot that's all.
Remember that the in-tank pump is just a pre-pump to the main pump located just in
front of left rear wheel. It's after the main pump the pressure builds, but that
pressure is contained from main pump and forward and doesn't kick back, and the
return hose is pressureless - more or less anyway. When the main pump stops, the
pressure drops quickly to nada..

Johan

 

[Michael Pardee]

Hi,

Sorry, but I can't see the problem. In my 265, there never was any
pressure in the
rear, i.e. the fuel lines to/from the tank. I just popped of the hoses and
got the
pump out of the tank. Came a trickle just as the hoses came off, bot
that's all.
Remember that the in-tank pump is just a pre-pump to the main pump located
just in
front of left rear wheel. It's after the main pump the pressure builds,
but that
pressure is contained from main pump and forward and doesn't kick back,
and the
return hose is pressureless - more or less anyway. When the main pump
stops, the
pressure drops quickly to nada..

Johan

How did we miss that? True - the lines at the tank have no pressure.
Depressurization applies only to the fuel system between the main pump
output and the engine.

Mike