Fuel pump pressure and flow rate

[NICAT]

Hi.
W163 ML320 2002 190K KM
Fuel pump failed and was replaced before i bought it. Previous owner just got it fixed at some place in rural area. They just replaced the pump (30-40$) itself.
It is generally sold as an assembly, electronic pump + fuel level sensors, pipes and housing. MB Catalouge doesnt provide a part number for pump itself.
I made some research on the forums. Bosch fuel pumps with part number 0 580 453 431 meets the requirement. (4 Bar Pressure, 115L/H flow rate)
The issue is that too many pumps from different car brands (honda, toyota, lada, kia, fiat )both physically and electronically fits in this car. They just differ in pressure and flow rate. Most have flow rate near 60l/h
So it is possible that car has wrong fuel pump.
Even car makes a single clunk during hard acceleration which is not transmission related. (I know it may have many different causes, i will get further diagnosis to find and fix them one by one. )

I have several questions.
1. I had pressure test. It was 3.7 bar at idle. Mechanic told it is acceptible and no further test is required. But i think at idle it engine doesn't consume that much fuel. So do we need to make additional test while driving car at higher RPM-s to see if there is fuel starvation? İs that even techically possible to test fuel pressure while driving? If so how much the pressure should be that time?
2. If fuel pump pressure or flow rate exceeds the requirement, does it mean engine will run rich ? (Or will ECU adjust it automatically?)
Regards

 

[mk378]

You would know lack of fuel-- the engine will sputter and obviously starve for gas when you floor it, and keep doing that for as long as it is floored, especially as the rpm tries to rise. The worst case (i.e. the best test) is trying to climb a mountain at highway speed, if there is such a road in your area.

It would not be just a single clunk.

The pump always moves a lot more fuel than the engine needs. There is a mechanism to return the excess to the tank and maintain the design pressure. In some cases (mostly newer than what you have) that regulator is inside the pump, then you need an exact replacement. The older design has a separate line from the regulator in the engine compartment back to the tank, a so-called two pipe system.

 

[NICAT]

You would know lack of fuel-- the engine will sputter and obviously starve for gas when you floor it, and keep doing that for as long as it is floored, especially as the rpm tries to rise. The worst case (i.e. the best test) is trying to climb a mountain at highway speed, if there is such a road in your area.

It would not be just a single clunk.

The pump always moves a lot more fuel than the engine needs. There is a mechanism to return the excess to the tank and maintain the design pressure. In some cases (mostly newer than what you have) that regulator is inside the pump, then you need an exact replacement. The older design has a separate line from the regulator in the engine compartment back to the tank, a so-called two pipe system.

Yes. Thanks a lot sir. it was a great relief to know this.

 

[Dave9]

car makes a single clunk during hard acceleration which is not transmission related.

I have several questions.
1. I had pressure test. It was 3.7 bar at idle. Mechanic told it is acceptible and no further test is required. But i think at idle it engine doesn't consume that much fuel. So do we need to make additional test while driving car at higher RPM-s to see if there is fuel starvation? İs that even techically possible to test fuel pressure while driving? If so how much the pressure should be that time?
2. If fuel pump pressure or flow rate exceeds the requirement, does it mean engine will run rich ? (Or will ECU adjust it automatically?)
Regards

Single clunk seems more related to a single tranny shift than anything else. How did you rule out tranny?

1. Unlikely, as mk378 mentioned it has to be able to deliver more pressure than needed, though if only the pump was replaced, it may be due for a fuel filter too.

2. No, it always should exceed the requirement (for smooth accelerating engine), the ECU will reduce injector duty.

Just for the heck of it, I'd also run through that tank of fuel and try fresh fuel.

If you are already consulting with a mechanic, why not ask him what he thinks the problem is?

 

[NICAT]

Single clunk seems more related to a single tranny shift than anything else. How did you rule out tranny?
If you are already consulting with a mechanic, why not ask him what he thinks the problem is?

We switched to manual mode in transmission so there were no gear shifting. Even at that mode, in a single gear it clunked.

If you are already consulting with a mechanic, why not ask him what he thinks the problem is?

I am actually searching for a good mechanic. By that time i want to do my own research over the internet.
Mechanics here are not very professional. Their troubleshooting method is to replace everything one by one till they find the real culprit.
With the spare parts removed my previous cars till now, i can start a junkyard business