Article by: Sean
Article applies to: all models with the M70 V12 engine.
Problem: In my ongoing quest to fight the problems with rough idling, stalling when accelerating and surging I decided to replace the fuel filters to see if makes any difference.
I was still convinced it had something to do with a certain lack of fuel (pressure).
Also, the last time they where replaced was back in 1997 and 150.000 kilometer (94,000 miles) ago, so I had a good reason for it, they needed to be changed anyway.
Background: the 750 has at least two parts of everything concerning the engine, meaning also 2 fuel filters.
The fuel systems of both banks are working totally separate of each other, the only thing in common is the fuel return hose.
The filters are mounted at the outside of the car, between the right drive axle and the fuel tank and very easy to replace. You need to remove your rear right wheel to access the filters.
It’s inevitable that you will spill some fuel when disconnecting the hoses and removing the filters. Use your head and work in a well ventilated area.
Let’s start unbolting and removing parts:
Before you begin, it’s a good idea to depressurize the fuel system to prevent spraying fuel all over the place including yourself.
Pull the fuel pump relays and start the engine until it stalls completely (picture shows relay box next to right strut tower of an ’88 750 with removed fuel pump relays).
Jack car up, notice bucket to catch the fuel (remember to support the car safely):
The filters are located between the right drive axle and the fuel tank:
First remove the fuel hose clamps, and after that the remove the 10mm central bolt of the fuel filter mount. Both filters are mounted in this assembly:
Mount removed:
Replacing the filters. Mind the position of the arrow, arrow pointing towards engine fuel lines.
Notice I used 2 brands of aftermarket fuel filters, my supplier ran out of stock (from a personal point of view:
I like Mann and I dislike Fram but I didn’t had any choice at that moment):
When reinstalling, don’t be afraid to over tighten the central bolt (ending up in crushed fuel filters), that cannot happen due to the construction of the filters mount.
I suggest you use new fuel hose clamps, the old clamps can be rusty (causing leaks when tightening).
When you first start your car, the engine can stall a few seconds because the pumps must fill the filters and pressurize the fuel system first.
Don’t reinstall your wheel yet, check carefully for fuel leaks around the filters.
Total amount of time: about 1 hour
Total amount of parts and cost: about 35 euro/US dollar per piece, so expensive!
Skills needed/difficulty level: nope. Basic stuff.
Satisfactory level after the job done: clean fuel now, but original problem not solved. Bummer. But they needed to be replaced anyway. That’s what I keep telling myself.