Being a conservative man, I only acted impulsively after thinking a long time before purchasing my first BMW. She is a 1991 e34 m5, black with white dove intrior, and 127,000 miles thus far. Like many other M5's with this milage she's not perfect. Hoping to get years of driving "ZEN" out of her, my labor of love has begun.
All the basics have been replaced;filters, plugs, fluids, etc. The only thing that has cost me a few extra bucks was replacing the cats and exhaust. With a little luck I was able to find both for $350. Now the time has come to replace the fuel pump. It has hissed for the 4 months I have owned her. Being an old pump I guess this is the cause of my slight "lag" when accelerating hard. When I replace the pump do you think this will solve the slight "lag" of power? If not how do I know if I should replace the fuel regulator, injectors, or the sending unit. Also too, in order to save a few bucks I believe I can use a pump from a 735. Not sure if this is correct though. Is it possible to use a pump out of a regular e34 model or will this lead to problems? If anyone could help a newbee out, it would be greatly appreciated.
Hobby: something you go nuts about, to keep from going nuts about something else.
Hello Zen, welcome to the board.
All i can tell you is that repacing the fuel pump should make a notable differance to how well your car goes. It certainly improved how my car performed when I changed mine.
as far as using a 735i unit, I don't know if it would work or not. I would think that the M5 pump would be specific to the car. You should be able to get the right one through an independant supplier for a decent discount over the BMW genuine part. In the UK I paid around £170.00 for mine.
I'm sure someone will be able to chime in soon with more definative advice.
Part 16141181354 (FUEL PUMP) was found on the following vehicles:
E32: Details on E32
E32 735i SEDAN, U.S.
E32 735iL SEDAN, U.S.
E32 730i SEDAN, Euro
E32 730iL SEDAN, Euro
E32 735i SEDAN, Euro
E32 735iL SEDAN, Euro
E34: Details on E34
E34 525i TOURING, U.S.
E34 525i SEDAN, U.S.
E34 535i SEDAN, U.S.
E34 M5 3.6 SEDAN, U.S.
E34 518g TOURING, Euro
E34 518i TOURING, Euro
E34 518i SEDAN, Euro
E34 520i SEDAN, Euro
E34 525i SEDAN, Euro
E34 530i SEDAN, Euro
E34 535i SEDAN, Euro
E34 520i TOURING, Euro
E34 525i TOURING, Euro
E34 525ix SEDAN, Euro
E34 525ix TOURING, Euro
E34 M5 3.6 SEDAN, Euro
E34 M5 3.8 SEDAN, Euro
It makes perfect sense & is just mass production vehicle economics.
Constant pressure rate pump regulated in line to the fuel injector head.
Same thing with many common saloons.
Same pump in a 1.6 Escort as there was in an Escort RS Cosworth.
I did a little research on this ages ago & its not too scientific but could be easily proven.
Pump is common on the petrol engined vehicles from a 518i to M5 3.8
Fuel pressure at the rail & therefore the pressure at the injector head varies for each model dependant on application.
The 3.8 & the 540i have similar pressure rate regulators @ 3.5 bar but the 540i has several pressure regulator options all @ 3.5 bar.
The 3.6 has a 3.0 bar regulator
The 540i fuel pump is also I suspect common to all the other models.
There is a little grey area here over pump assembly configuration ie with suction assembly but it figures that with the std fuel duty cycle of a 540i
with its 3.5 bar regulator supporting the rail head pressure for all eight injectors & its vastly reduced fuel demand for each of its 8 cylinders & much lower rpm cycle, it would figure to be common.
It goes without saying that higher fuel delivery rates require larger bodied injectors to deliver the fuel.
The injectors as fitted on the 3.6 & 3.8 have the greatest duty rate for very obvious rpm related reasons.
Optimisation of injectors to accomodate the full spectrum of use does lead to compromise especially so with single injector per cylinder application after some years in service.
The nozzle spray pattern is very precise.
It wears & opens the nozzle internal angles eventually due to a combination of pressure & detergents in the fuel acting as a cutting compound to erode the nozzle & ruin the fuelling of the injector duty cycle @ idle dwell.
That makes the emission test harder to pass & part throttle pickup at low rpm will also suffer with greater wetting of the cylinder possibly leading to greater fouling of the plugs.
Hmmm, Maybe I should go for a replacement pump too whilst I am trying to bankrupt myself? I have noticed that when standing behind the car,regardless of how much fuel is in it,the pump is quite noisy,a hissing sound. Is this normal,never noticed it on any of the 535's I have owned? Or am I just looking for more things to spend my hard earned on?