740 fueling issue solved

Finally think I figured out the problem I've been having with my 740T.
It started out as a rough idle and noisy fuel pump and eventually seemed
to get a bit worse. I noticed power loss, increased fuel consumption,
and the acceleration was not smooth. Curiously, it would normally run
fine when first started then after driving around for a bit it would
start acting up. Sometimes it was very difficult to start, requiring 20+
seconds of cranking. Replaced the torn hose between the pre pump and
pickup, didn't help. Replaced the main pump with a good used one and
again the same issues. Went in again and replaced the pickup sock since
I noticed it was torn, double checked operation of the pre pump but
still the problem remained. Figuring there wasn't much left, I swapped
the fuel pressure regulator and everything seems to be back to normal.
Smooth, strong acceleration all the way up to the redline, smooth idle,
nice to have everything back to normal. Now that I once again have
dependable transportation I can start playing with the 240.

 

I think I have some of those symptoms - but not as severe. After
replacing my fuel pump, filter, in tank pump and sock - there's still
something that I can barely detect as off. I think I might swap out
my fuel pressure regulator as well.

I know what you mean about going from car to car. I've been
alternating between 740 and 245.

Next on this list will be a 1991-1995 E34 M50 BMW 525i 5spd.
Should make for a nice garage. LOL

 

Not a bad idea to tighten down the nuts on the wiring that is on the inlet
manifold as they are earths for the pump.

 

The prepump is grounded to the body in the trunk of the car, as I recall the
grounds on the manifold are for the various sensors on the engine but it's
been a while since I've dug into it. I rewired the whole harness about a
year ago so all that is in good shape.

 

I noticed when my car misbehaved the wires connected to the manifold were
not tight and the main pump worked once the wires were grounded properly .I
was once warned by a Volvo Tech to check these connections .Just in case it
doesnt harm to check it out .

 

BMW 525? Man you DO like to work on cars. LOL