Fuel pressure relief valve adjustment - Page 35 - PeachParts Mercedes-Benz Forum

Diesel911 · #**511** 11-05-2014, 05:23 PM

Quote:

Originally Posted by oldsinner111

30 psi,mine must be weak.I couldn't afford,a new one so I went with assiting it.You say it can be rebuilt?Does it ride off the cam? Is it easy to put this kit in,and will it have gaskets.

A generic Kit for the Fuel Supply/Lift Pump is with shipping included about $15. The real Bosch one is arount $30-35.

The 617.952 with the MW Fuel Injection Pump is a diffrent Kit then the MW Fuel Injection Pumps. (There is instructions for rebuilding both in the DIY Repair Links.)

Mercedes sells a Valve Kit for less but it lacks the tiny O-ring and the Lift Pump to Fuel Injection Pump gasket.

barry12345 · #**512** 11-05-2014, 06:02 PM

Quote:

Originally Posted by oldsinner111

30 psi,mine must be weak.I couldn't afford,a new one so I went with assiting it.You say it can be rebuilt?Does it ride off the cam? Is it easy to put this kit in,and will it have gaskets.

The lift pump is powered by a lobe on the injection pumps cam. There are plastic valves in the pump that wear and the seats get dirty. Generally speaking these are the common failure points.

That they survive so long at all is remarkable. They also act to reduce back flow of any fuel when tight from the filters etc .

At the same time a decision to rebuild them should be based on their output pressure. Some seem to be almost as good as new and eventual failure is usually a long term proposition I think.

Being the output pressure gradually fails with time until it becomes a problem. In those cases the engine still runs but not as well as it should for a long time as well I suspect.

Now if the fuel tank filter is obstructed will reduce the pressure as well. So it has to be eliminated during a lift pump test if the output pressure is weak .

What it all amounts to is the complete fuel supply system should be checked and tuned up where indicated. Most all of this is a labor issue rather than an expensive parts journey.

Diesel911 · #**513** 11-06-2014, 11:21 PM

In order to see what the acutal Fuel Supply/Lift Pump Pressure is you would have to do something like clamp of and close the Cigar Hose for an extremly short period; get your Gauge reading and relese it.

Id you not do the above the Pressure is controled by the Fuel Pressure Relief/Overflow valve wich for My Year and Model is supposed to have a max Pressure of 18 psi at I think it is 3000 rpms.

mottati · #**514** 01-19-2017, 07:21 PM

Bumping an old thread with a question:

If the spring tension is too tight, could that cause a no start condition? Maybe trap air in the IP?

Here's why i ask. I have a recently acquired euro 83 300td turbo, i also have a california spec 84 td, and a spare factory rebuilt engine from a junkyard.

Last night, i wanted to check the spring in my new euro car, it smokes a bit, and feels down on power compared to my US spec 84.

The spring in the euro car measured 25mm, and was a much heavier spring than the one in both my US car and spare engine (both measured 20mm, and were a much softer spring).

I stretched the spring in the euro car to 27mm. Reassembled. Primed the pump and tried to start. No start. Cracked open the injector lines at the injectors, i put 2 new fuel filters in, so thought maybe air in the system. Cranked engine, multiple times, no fuel from injector lines.

When i was priming with the hand pump, i did not hear the squeak sound, that i think is the check valve.

So i put one of the spare, untouched valves in (at 20mm, soft spring) and car started.

If i'm understanding this, the valve is for return flow, so too tight should just increase the pressure in the pump. Unless i had air trapped in there, i can't understand why the car wouldn't start.
Thanks for any thoughts.
Mike

Stevo · #**515** 01-19-2017, 08:37 PM

As I said in one of those posts way back there. When I rebuilt another engine for my 79 240D I just hooked up that fuel line with only the check valve. no spring. I drove the car for years that way, it ran great. I read this thread, checked the pressure put the spring in (parts car). The car didn't run any different, Thats my story and I'm sticken to it.

So I don't think thats your starting problem, at least it didn't effect my car.

mottati · #**516** 01-19-2017, 09:48 PM

maybe i just had some air stuck in there. At any rate, it starts and runs fine with the softer/shorter spring. And when i pump the hand primer pump i can hear the squeak noise, which i think comes from the check valve (that i didn't hear with the stretched spring).

barry12345 · #**517** 01-20-2017, 11:27 AM

Quote:

Originally Posted by Stevo

As I said in one of those posts way back there. When I rebuilt another engine for my 79 240D I just hooked up that fuel line with only the check valve. no spring. I drove the car for years that way, it ran great. I read this thread, checked the pressure put the spring in (parts car). The car didn't run any different, Thats my story and I'm sticken to it.

So I don't think thats your starting problem, at least it didn't effect my car.

Second case that not having a relief valve functional the car still ran. The last case I am aware of was also a 240d.

To me the 240ds fuel supply and pressure should have more attention paid to it then the turbo 300ds. For starters it has a weaker lift pump from the factory. Although that can be cured by installing the heavy regulator spring from the stronger lift pump.

Stronger output pressure enables more fuel filter resistance to be overcome. I still believe low fuel pressure has a seriously detrimental effect with time. Especially in the 240ds.

As for the gentleman that did not hear his overflow or relief valve open after increasing the spring pressure. You could not pump air with the fuel through the relief valve as the primer pump could not reach enough pressure to open the relief valve. Instead you were just pumping fuel against a static pocket of air to some extent I believe.

mottati · #**518** 01-20-2017, 12:56 PM

Quote:

Originally Posted by barry12345

As for the gentleman that did not hear his overflow or relief valve open after increasing the spring pressure. You could not pump air with the fuel through the relief valve as the primer pump could not reach enough pressure to open the relief valve. Instead you were just pumping fuel against a static pocket of air to some extent I believe.

yes that is what i think also.

Additionally, either someone had already replaced my relief spring with a heavier/stiffer spring, or mercedes used different springs. The one in my euro turbodiesel measured 25mm as it came out of the valve, and was stiffer than the spring that came from both my US turbodiesel, the the Td spare engine i have (both US spec). Both of those measured 20mm upon removal, and were similar, but softer than the spring in the euro car.

Dieseldemon1 · #**519** 01-22-2017, 11:47 PM

I am new to this forum I am a cummins mechanic in the Dodge Ram we have what cummins calls an overflow valve which is the same valve that MB uses but larger the idle flow in the 5.9 12 valve is 18 psi and 32 psi at 2700 I have purchased a 1987 MB with the 6 cyl engine which is sloooow on take off I put a gage in the line out of the filter at idle the psi is 0 at higher rpm it went to 8 psi I took a pair of vice grips and shut off the return line completely the pressure went to 15psi at idle and 20psi at higher rpm I dont know what the RPM is as the tach does not work anyway I am thinking that the lift pump needs rebuilding also drove it with the return clamped made very little diff in power Where can I buy the lift pump rebuild kit also the overflow valve has a place to adjust the pressure but it is hard to get to Just starting to work on this and maybe some of you will chime in with some suggestions.
Thanks for your time

JHZR2 · #**520** 07-13-2019, 03:55 PM

Quote:

Originally Posted by deniss

I have to say I'm confused by how the FSM indicates their tester is connected.

In the FSM, the gauge is teed off from a line connecting to fuel filter housing OUTLET (before the IP, using a double-bango bolt) on one end and fuel filter INLET (from the lift pump)? ForcedInduction posted those pages from the FSM, I think in Page 2 of this thread.

So I'm wondering if deviation from their method of measurement will yield very different feed pressures?

They way they hook it, their tester line to the gauge will split the pressure from the filter housing OUT to the IP, so if I'm looking at it correctly, they are not exactly measuring inline pressure in the line feeding the IP.

This could be why people who install a gauge on the banjo bolt at the filter housing OUT going to the IP get higher pressure readings than what doing it the FSM way would otherwise produce.

Am I totally off base here?

I am confused here too. Is there a “shopping list” of parts one should get to do this test? The hose is a hard type, so it’s not as straightforward as cutting into a rubber hose. So do I need to source banjo bolts with barb fittings and then some fuel hose to tee in a gauge?

I’ve flipped through 35 pages here, and saw a good pic where a gauge was permanently tapped into one of the banjos at the secondary filter. But it’s not clear to me to see how to make a test kit that I can use on my 616, 617 and perhaps 603 cars.

Any recommendations?

Mark123 · #**521** 07-13-2019, 08:58 PM

I think there are other old posts about this. but I made mine from a banjo bolt from the pick-n-pull. The bolt on the outlet of the main fuel filter. I wanted to test the pressures just before the injection pump. I bought an 1/8"-27 NPT tap and the appropriate 11/32" tap drill. I drilled and tapped into the top of the banjo bolt. I bought a 0-30 psi liquid filled gauge. It had an 1/8" male NPT connector. An 1/8"X2" nipple and an 1/8" coupling. Both just galvanized steel.
Assembled the pieces and voila! I could test my lift pump and overflow valve.
My factory manual says 0.6 to 0.8 bar minimum at idle [the pressure retained by the OFV] and 0.8 bar minimum at 3000rpm. With a OFV and lift pump from Greazer, the values on my OM616 are double that at idle. And the gauge pegs at 3000rpm. It runs great and does 25 to 26 mpg mostly city driving.

JHZR2 · #**522** 07-13-2019, 09:53 PM

I recall seeing some discussion about getting banjos from a pick n pull. I don’t have the time/availability of cars to do that by me.

Thought others certainly must have done it other ways. Threaded barbed fittings perhaps for example.

whunter · #**523** 07-14-2019, 02:52 AM

follow the procedure to stretch the spring, until it is 29-30mm, or on a staked top bypass valve replace it with a new one.
Install new lift pump valves and springs.
Assure that your primer pump is good, replace if there is any doubt.
Verify that your fuel tank vent valve works = no vacuum or pressure when the fuel cap is removed.
Look over ALL fuel lines/hoses for age cracking/leaks, they will leak air into the fuel system before diesel will drip out = MPG and performance issues.

Enjoy driving, not making superfluous diagnostic tools or tests.

Have a great day.

JHZR2 · #**524** 07-14-2019, 09:50 AM

Quote:

Originally Posted by whunter

follow the procedure to stretch the spring, until it is 29-30mm, or on a staked top bypass valve replace it with a new one.
Install new lift pump valves and springs.
Assure that your primer pump is good, replace if there is any doubt.
Verify that your fuel tank vent valve works = no vacuum or pressure when the fuel cap is removed.
Look over ALL fuel lines/hoses for age cracking/leaks, they will leak air into the fuel system before diesel will drip out = MPG and performance issues.

Enjoy driving, not making superfluous diagnostic tools or tests.

Have a great day.

All done except lift pump, still have a hot idle side to side shake with new mounts and shocks. Only at idle, smooths beautifully with any throttle. No signs of air anywhere.

Was under the impression that a gauge inline per the FSM would give indication if the lift pump and overflow were working properly to ensure IP has the right flow and pressure.

Diseasel300 · #**525** 07-14-2019, 09:57 AM

Hot idle shakes are more likely to be injector or delivery-valve related. If you had fuel pressure or flow issues they'd be far more obvious when under load than at idle.