How much fuel pressure (from the lift pump) is acceptable. Is there a point where it reaches a threshold of too much pressure supplying fuel to the injector pump?

The reason I ask, is I have an OM617 transplanted into my Dodge Dakota and she’s equipped with Dual Fuel Tanks. I’ve been running it on just the Primary Tank, by removing the Fuel Pump from inside the tank (has a pickup tube installed in place of the pump) and bypassing the selector valves for the tanks.

If I put the fuel pump back in (outputs roughly 65psi), connect the selector valves and bypass the lift pump on the engine, will I need to plumb in an adjustable fuel pressure regulator to drop the pressure down or will the Injector Pump be fine receiving pressure that high?

__________________
'92 Dakota : OM617 Swap
'73 Duster : 8-71 Blown 426

The mechanical lift pump on the side of the OM617 is designed to give between 0.6 and 0.8 bar pressure at idle (according to the FSM)


Google says that's about 8 to 11 PSI (do you trust google to convert it?)


Anyway seems like you've got way way way way too much pressure being applied to the injector pump.


If I were you I've just run a line directly to the mechanical lift pump and see it works with out the electrickery pumps

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

The factory manual may be wrong .Or the interpretation of what is quoted might be. This low of a pressure would not even open the relief valve if it was in decent condition. Filter pressure reductions alone might have an effect on the useable base pressure of the injection pump as well. Setting the relief valve to 19 pounds opening pressure is not uncommon by some injection pump rebuilders.

On deadheading the lift pumps .Thirty psi is not uncommon I believe. Anyways the regulating of fuel pressure. Is determined by the spring in the lift pump. As far as the lift pump is concerned.

Where the actual operational pressure overall is determined by the setting of the relief valve pressure on the injection pump it opens at. This to me is a pretty solid indication that at least the system designers had two things in mind. The first was to provide adequate pressure to keep the the relief valve functional all of the time. Plus as filter obstruction increased with use the pressure in the injection pump remained constant.

The mechanical lift pump should be the fuel pump of choice in almost all situations. It is both very reliable and easy and cheap to rebuild on the 616 and 617 engines.

If one supplied 60 psi to the injection pump at too high a volume. The relief valve could not keep the fuel pressure in the base of the injection pump low enough. This may or may not have an effect on the sequential timing of the injection pump or even the actual timing.

Experiments that I have conducted on the Volkswagon diesels. Basically advancing the timing. Would result in the loosening of the damper pulley. Mercedes diesels. At least the 616 and 617 do not have a really robust damper attachment system either. So caution is advised. As in some cases when it loosens off it damages the nose of the crankshaft on these engines. There is really no fix for this in many cases other than replacing the crankshaft.

Actually calibration of the injection pump must be done at the pressure the relief valve is set for when the injection pumps where initially calibrated and when being rebuilt as well.

Anyways the lift pump has a much greater capacity to create pressures well beyond what that fsm night quote. A common sense approach to testing a lift pump in service. Is simply to run the engine with the return line from the injection pump closed. With a pressure gauge temporarily installed anywhere between the lift pump and the close off of the output. You can judge the condition the lift pump is still in. I would think anything below twenty pounds it should be rebuilt. After you establish the low pressure output you are seeing is not from another cause.

Actually if you established the pressure was that low by test. It would be advisable to feed the lift pump from a container of fuel. If the results were similar the lift pump may be well on the way to ultimate failure. There are all kinds of changes when these engines are running with not enough fuel pressure present to keep the relief valve functional.

If you read the service manual in depth. A reference to periodically checking the fuel pressure should be present. I suspect every thirty K. I do know it was a required part and parcel of the dealers periodic service of these engines. My guess is some did it and others not. What is fairly reasonable to me is that in all too many cases. It has not been checked in decades on the vast majority of these cars.

Mercedes did not design or manufacture this fuel system. So the writers of the service manuals at the time may have lacked insight on exactly what was going on totally and made some written errors in the fsm. Yes the 8 to 11 pounds pressure is a valid figure. Only when present in the base of the injection pump though. Personally I think it is relatively safe to adjust the relief valve spring to as high as 19 pounds operational pressure. If the lift pump is in really good condition. Plus the fuel filters are in reasonable condition. There are many, many benefits of having this system in good condition. Quicker cold starts, Less engine noise at both idle and highway speeds. More apparent power plus even better fuel milage. I base the last comment on at least a few mentions of the fuel milage increasing about 1-2 miles per gallon after only a secondary fuel filter change.

Here's a link to the FSM data

https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/617/07_1-145.pdf

Just in case Barry thinks the interpretation might be a problem

Note the points of measurement and the values at which the by-pass valve is meant to operate

In my experience I've know Haynes to cock up numbers but not the FSM

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Ok, so definitely too much pressure to be safe without installing an adjustable regulator with a return port.

__________________
'92 Dakota : OM617 Swap
'73 Duster : 8-71 Blown 426

Pumps don't build pressure, they move volume. Pressure is built when that movement of volume is restricted.

The overflow valve in the injection pump is what sets the pressure. As long as the overflow valve in the IP can flow as much as your pump, a 3000psi pump will only generate the 15psi or whatever the overflow valve allows.

Ever run your pressure washer with out the nozzle in the end? All you got was the same as garden hose stream. Same idea, despite your pressure washer being capable of 3000psi or whatever.

So you're probably just fine. Try runnin the EFI pump into a bucket and see how fast it fills the bucket, and try the same with the factory 617 lift pump. If they're anywhere close to similar, you're probably good to go.

I personally wouldn't, as the stock 617 lift pump lasts nearly forever and requires no electrical power. It can also be rebuilt for much less $$ and hassle than an in tank EFI pump can be replaced for.

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

How's your truck going? Perhaps a link to your thread will help the OP?

Here it is =>

My Official OM617 Toyota Pickup Repower Thread

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

FSM data only pertains to the whole operational system. Semi deadheading the system by closing off the relief valve output does show the lift pumps true pressure capability. .

This is a good test to judge the condition the lift pump is in. Plus various other tests at the same time employing the pressure gauge. I have heard different quotes. About thirty pounds was the most common. With a semi deadheaded fuel supply system with the engine running. On the turbo engines.

The non turbo engines have a weaker lift pump regulating spring. So they will be on average produce less output pressure when semi dead headed.

It was suggested by Mercedes that at least the operational pressure of the fuel system be checked every thirty thousand miles I believe. I have felt that many of these systems have not been checked for decades. Yet it is relatively cheap to do this and if there is an issue fairly easy and cheap to correct it.

There are many possible effects possible when the fuel supply system has deteriorated with age. As a general rule anything man makes does eventually deteriorate. I have always thought the Mercedes service information might be a little thin on this system anyways. . At least on describing how to service it. As they did not manufacturer it.

I felt lets say a little uncomfortable with what I posted much earlier this morning and earlier. In my opinion Mercedes should have collaborated a little more with the fuel system designer and manufacturer.

Or the writers of the service manual should have included more information about the importance and methology of servicing this fuel system.

By the time the type 123 came along this fundamental system had been used by Mercedes since the late 1930s. Then again they were not really considering these cars would be on the road as long as they have been.

Also something was bothering me besides my unintentional slight of a very respected member on site. I never wanted to leave any impression that I had. Or meant to. I was apprehensive he would take me to bits.

Now down to what was bothering me in the back of my mind or what is left of it. Number one is I have no ideal of how the vicious pulses the injection pump generates would be dealt with long term by an electric fuel pump. I assume it depends on the design of it.

What I do know is those pulses will reflect hydraulically way back to it is absolutely certain. Plus any form of fuel pressure regulator used with any electric fuel pump will probably fail. Based on they are not very likely to have been designed to cope with this pulsing type issue.

Next item. Years ago it was assumed I knew something about these old diesels locally. So on occasion I got phone calls from some local owners.

One guy asked me if I could help determine why his 240d topped out at 50 mph. I of course initially told him the throttle linkage was the most common cause even them. It still is I suppose.

Got another call that was not his problem. So being on the way to the cottage I asked him if I could stop by for a quick look. As soon as I saw the 3-6 pound electric fuel pump in the system bypassing the lift pump. I suggested he replace the real fuel or lift pump or rebuild it.

Explaining that it had to be known if that engine was starving for fuel. He wanted to know if I was certain. I said no but there was no sense in going on to other things until it was dealt with. Plus in my opinion it could easily be the total issue.

Those earlier electric fuel pumps where 3-6 pound self pressure regulating. Designed to service conventional carbs. What I missed back then was I did not understand how these heavy pulses played into the picture if at all on that type of unreliable electric fuel pump. Anyways He sold the car not repaired. It was a decent example from the southern states. Perhaps in hindsight I should have offered to repair it for him.

The lift pump design of these cars has a form of inertia involved. The vicious spikes generated inside the injection pump do not bother it. As for reliability and function. The pulses swing from a negative to positive range of perhaps eighty or more pounds of very rapid short duration pulses when the engine is running.

Might be even higher as an undamped fuel pressure gauge cannot be read. The needle instead will be slamming hard from one side of the pressure gauge to the other at idle. The pulses have no issue in destroying those pressure gauges. Even the fluid dampened ones if installed in a constant reading fashion will be destroyed in less than an average weeks running. Unfortunatly this has been proven by at least one member.

You do have to use a fluid filled gauge to read the fuel pressure anyways. Harbor freight sells a decent one for this purpose cheap enough.

For those that can stand my extended posts. Plus long threads. For a long time I have looked at this fuel system. I think it is time to post some of my abstract thoughts on a method of increasing power and fuel milage. I think of it as stirring the pot.

At the same time it was always my principle drive. How do you make these engines really do what I feel they might? In some form of manageable fashion. So it may be time to start a thread on it. Contributions to my insanity are welcome and expected. So off to post the initial ideal I have developed.

It may or may not be practical yet it is a start I suspect. It may at least be worth examining. Try to remember it has taken a lot of mental thought to arrive at this. As the sands in my personal hourglass at 76 years of age are running down. I felt I should not delay much longer anyways.

I have no issue with exposing myself to ridicule. I got involved with women for decades so I have had my share. Knowing they think it more times than actually expressing it. Perhaps a form of compassion to a lesser creature. Who knows?

I'm thinking the factory lift pump should be fine as long as there are no air leaks in the system. Mine is supporting 220+ HP with zero issues.

Dan

Let's all remember how the lift/supply pump works on a mechanical injection pump. Its entire purpose is to fill the fuel rack with fuel. That's pretty well it. It maintains a positive pressure to ensure timely filling of the fuel pumping elements, but more is not going to do anything for you. Likewise, low pressure isn't going to affect much either, mainly top end due to slower element filling.

If the OP's overflow valve is the original 617 style that's "serviceable", I don't think he'll have an issue. The port is relatively large and will flow a considerable amount of fuel. If it's the later "drilled orifice" style with the pressed in BB, that's another story.

The ultimate tell would be to plumb in a fuel pressure gauge. If you're doing 10-15PSI, you'll be fine running the electric pump.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Parts of you post are really unknown territory. The danger although I am not certain. Is the change in injection timing. Not being dealt with.


Thirty pounds constant pressure supply has been done. Really increasing power but exactly how is unknown. I have thought it probably advanced the timing.


Because of the damper or balancer weakness I perceive exists with these engines. Long term it may cost you. Unfortunatly that poster dropped off the site before what he had in service had accumulated many miles.


The percieved by me damper issue just may be the different vibration factor inherent with advancing the timing has a tendency to loosen up the bolt rather than a structural weakness of the attachment system to the crank. Loosening it up can and does destroy the crank end. Or almost always damaging it to some extent.


If a person wants to go out on that limb. It may be prudent to red locktight that bolt in. Or design a safety method for that bolt. I have never tended to over tension the belts on these engines although I do not think it really contributes to the issue.

After the two big hurricanes last year I was helping family that live in the Caribbean. Many people have IDI diesel gensets, with a setup not unlike the 616/617 family. Many were having issues with sporadic shutdown.

Usually the setup is tank in the base underneath, dip tube, racor, lift pump, spin on filter, IP, etc.

The service folks would put little electric inline pumps and it solved the issues. I guess the lift pumps just couldn’t quite get enough flow on these engines. Just a tiny rattle type pump.

So there’s something behind giving some help.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Thank you thank you, truck's doing great. Been pulling loads of firewood out of the woods with it, liking the small maneuverability, offroad ability, and fuel efficiency quite a bit. Latest work has all been non-diesel-related, so I haven't posted about it.

I don't agree, at least not when it comes to the 616/617. I can't speak to the gensets, but with our engines where the stock mechanical lift pump is well and truly proven, I don't think there's any benefit to adding anything else. If the stock lift pump is having issues, I would fix that, not add anything extra.

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

Wicked truck - a real life saver / member of the family eh? Like a faithful dog.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!