Did you have any measurements of fuel pressure with this vs. a normal 27mm spring?

__________________
Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

I'm curious about this as well. It has been suggested by some who are very knowledgeable that OM606 knock/rattle/nailing is caused by insufficient element filling. This may be poor lift pump performance or low pressure due to the weakened regulator spring.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

I did some pretesting with the valve a while ago.
My stock fuel pressure with OM617 Turbo engine was ~15psi. With the valve from Greazzer it did not fall below ~36psi....!

Gruß
Volker

At that pressure with the stock pump spring, how much by pass fuel are you seeing?

You are right, the overflow volume decreases a little bit, but not that much.
Tested with my old untouched presupply pump with 130k miles on it I had like 10%less overflow volume.

Or to give an example. This August I had some fuel with ~50% gasoline in my car.
After I went shopping (I drove the car for 1hour before) the car would not start when I wanted to leave after 20min shopping because of vapor bubbles in the fuel system.

1. cranking 2 seconds long - nothing happened
2. cranking - after 5 seconds I already heard a few cylinders reporting for duty and stopped
I did wait 5 seconds
3. cranking - after 5 more seconds the engine ran, not nice, but it ran.
And after hitting the gas once the idle was normal.

What I want to illustrate with the example, the overflow volume is still quite sufficient. Even with the wrong fuel.

Be careful with stronger springs. Too strong springs in the presupply pump can cause bad engine behaviour.

Diesel fuel canīt be compressed and so it does not store any pressure. The spring in the presupply pump can store the pressure so to say.
If the spring in the presupply pump is too strong the pump stroke is finished earlier through the bigger spring force, but the time until the pump-cam loads the spring again is too long then. In that case the oscillating pressure can cause uneven fuel loading of the elements.
I donīt say it will, but it can.

Gruß
Volker

One issue I found after installing a stronger pump spring was that the fuel pressure was erratic because the pump could not fill fast enough. i opened up the check valve passage ways which helped a little, but I found that installing a large prefilter vertically so it had an air pocket in it solved the problem. The air in the filter would act as an elastic of sorts, allowing the fuel pump to draw in a charge quickly and then the lower pressure in the filter would draw fuel in slower, like a capacitor does for an electrical circuit.

When I put the engine in the 201 chassis, I used the electric fuel pump to supply the lift pump. I made a pressure regulator to control the pre lift pump pressure, that really made a difference on the top end fuel supply. The stronger pump spring makes the lift pump really want to pump a lot of fuel so I am able to maintain a high pressure with more return flow that OEM. I can see the pressure pulses being at a higher frequency if the return flow was restricted, (not allowing the piston to follow the cam and bouncing off the top of the lobe). I am running a higher volume bypass as well and my thinking is in order to have increased volume, the piston must be following the cam profile closer on the return side, so it could then be argued that the pump frequency should be lower that OEM.. All theory of course..

My goal was to increase fuel supply and pressure, pressure frequencies were not a consideration really, but worth keeping in mind should any strange performance be experienced..

I am keeping close hold the specs. Obviously, one could meaure the PSI. I can say that the pressure is increased. However, it's not just simply adding a more robust spring to increase PSI. That is why I commented on the R&D aspect of this.

Right on. Sounds pretty cool. I'd try one.

__________________
Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

Fuel pressure relief valve adjustment

Some related info on the most recent commentary

More than 1.5 Years ago Funola was selling an Overflow/Pressure Relief Valve that was Adjustable.

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84 300D, 82 Volvo 244Gl Diesel

I hope you have one next month,I'm on a fixed income,and can't afford this month.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

Hi Greazzer,

I'll take one.

Peter

The lift pump is a positive displacement pump, it will bypass exactly the same volume of fuel that it did at 15psi, just maintain a higher pressure in the fuel gallery of the IP.

__________________
617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

Yes it is a positive displacement pump, BUT, it is the piston return spring that generates the pressure, the cam only moves the piston back, compressing the spring, (actually when the piston goes back, it transfers the fuel on the outboard side of the piston to the inboard side of the piston), and the spring tries to move the piston back (drawing in fuel on the outboard side, and pushes against the fuel creating pressure on the inboard side. If the fuel is able to flow freely then no pressure. If you dead head the pump output line then the fuel pressure will be what ever the pump spring tension is.

As I recall, the pump on a NA will generate just above 15 psi dead headed, and a dead headed turbo pump will generate just over 30psi. I installed a stronger pump spring in my pumps and am running 30/36 psi with a good amount of bypass fuel.

What about for OM606 Turbo engines?