A potential suspect in my car's "spoof-spoof" phenomenon is the fuel pump. It only spoof-spoofs at 3500RPM and above, and anything below that, it works fine. My question is, is there such a thing as a partially-faulty fuel pump, which operates fine at certain range of RPM, and starts to fail at higher RPMs?

My mechanic commented that it is impossible to even drive a car with a faulty fuel pump, how true is that? What are the usual symtoms of a faulty fuel pump?

Will appreciate all your advice, thank you!


Mervyn
W126 (280SEL)
Singapore

If I thought my car was running low on fuel pressure, I would check fuel delivery from pump under system pressure!!
MB figure is 1 liter in 25-30 seconds ON the return line!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

As it turns out my 1985 190e 2.3 was running on a partially faulty fuel pump for some time. The sound of my fuel pump was rather loud and the flow of fuel was erratic (outside the silent hum of a small electric motor that it should have). I eventually burnt out 2 fuel pump relays. Once the pump was replaced, it ran perfect, and the replacement of the fuel pump relays ceased.

My fuel pump was $122.00 at Fastlane when every other place I checked locally wanted close to $300.00. My mechanic received it the very next day. (No I'm not affilialted with Fastlane. But I've done my research, and they have the best prices).

1985 190e 2.3
1990 BMW 325i
1981 Mazda RX7

MBDoc - how do you run a fuel delivery test?

__________________
... Kerry

126 tailed by a 203, 129 leading the pack.

In 1959, I drove our '56 Chevy 1500 mi from Lincoln, NE to Rocky Mount, NC, with faulty fuel pump. First noticed it in Iowa; when wife would accelerate to pass a car, we would get up beside the other car & engine would quit. I could drive it and accelerate very slowly, keeping it running. Drove it all the way myself, nonstop, except for fuel, etc., 30 hours - Sat., Sat. night & most of Sun. I absolutely could not drive so long now. Very dangerous trip, of course. We were very lucky. Installed new pump on Mon.

Vadrill, how does the faulty fuel pump sound like? And you mentioned that you'd 2 fuel pump relays burnt out. Could the car still be driven with a burnt-out relay? I'm asking this because I wanted to know if I should replace my fuel pump relay together with the fuel pump.

MBDoc, you never fail to impress me with the figures and technical know-how. Sadly, our mechs here do not go by such systematic diagnosis. Even if I forward those numbers to them, they might either not have the equipment to do the fuel delivery test, or they lack the know-how. Nevertheless, I will, do or die, find a more competent workshop that knows their stuff.

Lastly, I would also like to know for myself,how to run a fuel delivery test?

Thanks!

Mervyn

MB Doc really knows his stuff. I have heard the solutions to many a problem from MB Doc. THanks MB doc for your time and expertise!
I enjoy reading what you have to say in your posts.

__________________
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T

Fuel delivery test is done at the fuel return line from the fuel distributor. Two large fuel lines go to the distributor
OPEN FUEL in the engine area is dangerous!! Have your technician disconnect this hose & insert into suitable 1 liter or qt bottle & run until 25-30 seconds are up OR bottle fills!! IF it's full in the 25 second area then the pump & filter are OK,

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Mervyn. A normal fuel pump should have a quite, uninterrupted hum like a small electric motor. When failing it becomes noticably louder and erratic. The tone of noise coming from the fuel pump would go up and down and get louder, as though it was laboring to pump fuel. I could hear mine while driving the car. It shouldn't be that loud. You can listen to it by climbing under the car. Mine is located under the car, directly beneath the back seat. If it is louder than a humming electric motor, it's may be a good indication that it is going south on you.

You can replace the fuel pump without having to replace the fuel pump relay. If the fuel pump is bad, replace that first. If the car runs normally then your fuel pump relay is most likely OK.

Brian

'85 190e 2.3
'90 BMW 325i
"81 Mazda RX7

MBDoc, I cant wait to get my mech to run the fuel delivery test! It doesnt sound too complicated, I'm really glad!

Brian, I will go listen to my fuel pump the first thing in the morning, and as for the advice on the relay, it couldnt get any better!

I'm really enjoying all this "community spirit" in this forum! Dont know what to say, except I'm grateful.

Cheers everyone!

Mervyn
Singapore
1983 W126 (280SEL)