Please explain 95 e300d lift pump to me

[connerm]

Would someone please explain what makes the lift pump work, its purpose, any failure signs, etc?

I read the excellent thread on how to rebuild one.

Thanks.

[Zulfiqar]

Its the exact same pump as the old 60x engines, its on the side of the IP and sucks fuel from the tank and provides to the Injection pump.

If you remove the cross over from the manifold, you can see the lift pump on side of the injection pump near the bottom. It will have two plastic fuel pipes attached to it, both going to the fuel filter holder. One is hidden a little below the holder, its the primary filter outlet, the other would be the IN of the secondary fuel filter and is one of the two plastic fuel lines on top of the holder.

[Diesel911]

Can't give an exact explination (ignore the arrows in the pic they point to disc Valves).

The Fuel Injection Pump has a Lobe on the Cam inside of it to push on a Rod (to the righ in the Pic). The Rod interns pushes on a Piston and compresses a Spring; at the same time it also pumps Fuel.
When the Rod moves away the Spring pushes the Piston back and at the same time also pumps Fuel.
While the above is going on the Disc Valves route the Fuel in the proper direction.
Apparently the Disc Valves do not hold up as well as the Plastic Valve on the 617 type Lift Pumps.

The Overflow/Bypass valve on the opposite side of the Fuel Injection Pump regulates the Pressure and bleeds out the Air.
Some Members have found the Plastic part inside to be messed up.

[connerm]

Thanks Diesel911 and Zulfiqar. I'm about to do some more work including reinstalling my rebuilt MB fuel injectors, installing a new throttle cable and replacing orings on oil level sensor. I've got the lift pump rebuild kit and I'm half tempted to go ahead and rebuild it while the crossover is off.

Symptom is really slow start from cold engine - like I have to floor the acellerator pedal for a couple of seconds until things get moving. I fully expect that replacing the injectors (with new Bosio nozzles from DriveByWire) will solve my problem, but if it doesn't, I've got to remove the crossover and intake again. Just not sure if the lift pump is weak, broken, leaking or what. At this mileage I know what other plastic parts in the engine compartment look like so maybe the plastic parts in the pump are shot.

[Zulfiqar]

Hard start from cold is usually some air leak, If your plastic fuel lines are really muddy brown and cooked - best would be to change them to new, if they are newish looking but you have air bubbles moving up and down them replace their O rings with Viton items. It would solve your hard start from cold issues.

There is also a fuel drain back problem that was solved by MB by adding a one way valve in the return line at the fuel filter holder.

Bad lift pump would show a very weak running engine, but frothy fuel will cause the same too. Someone with experience with such diesel pumps would guide you perfectly of lift pump symptoms.

[Diesel911]

Originally Posted by connerm

Thanks Diesel911 and Zulfiqar. I'm about to do some more work including reinstalling my rebuilt MB fuel injectors, installing a new throttle cable and replacing orings on oil level sensor. I've got the lift pump rebuild kit and I'm half tempted to go ahead and rebuild it while the crossover is off.

Symptom is really slow start from cold engine - like I have to floor the acellerator pedal for a couple of seconds until things get moving. I fully expect that replacing the injectors (with new Bosio nozzles from DriveByWire) will solve my problem, but if it doesn't, I've got to remove the crossover and intake again. Just not sure if the lift pump is weak, broken, leaking or what. At this mileage I know what other plastic parts in the engine compartment look like so maybe the plastic parts in the pump are shot.

The plastic part I was speaking of is inside of the Overflow Valve.
The thread below mosly concerns the 617s. The vOverflow Valves on them do not have the same Air Bleeding capability as your system does.

Long Fuel Pressure Relief Valve/Overflow Valve Thread
http://www.peachparts.com/shopforum/showthread.php?t=234609

[connerm]

Replaced all fuel pipe orings in January. Cleaned tank, tank screen, replaced fuel filters, changed vacuum relief valve in tank, new filler cap. Car starts super easy, idles perfectly with no shake or shimmy - no smoke. Its when I hit the accelerator that things don't really happen quickly. Its like there is a long delay. I put 80% of my money on the cause being cheap India bosch rebuilt injectors that are now 40,000 miles old.

[Zulfiqar]

Originally Posted by Diesel911

The plastic part I was speaking of is inside of the Overflow Valve.
The thread below mosly concerns the 617s. The vOverflow Valves on them do not have the same Air Bleeding capability as your system does.

Long Fuel Pressure Relief Valve/Overflow Valve Thread
http://www.peachparts.com/shopforum/showthread.php?t=234609

speaking of this relief valve, yes I know the later ones have a plastic plunger inside them that do go bad, but what exactly are the running symptoms of such a valve going bad.

[Diesel911]

Originally Posted by Zulfiqar

speaking of this relief valve, yes I know the later ones have a plastic plunger inside them that do go bad, but what exactly are the running symptoms of such a valve going bad.

Never read an exact description. But, if the Plastic piece is not keeping the Spring under tension it is going to relieve the pressure at a lower pressure.
In the that thread on the Overflow Valve when some people stretched the spring (allowed on 617s) they said their idle improved. That would make it seem like the Overflow Valve was not holding back enough pressure to Fill the Elemets properly at low speeds; stretching the Spring increased the pressure the Overflow Valve opened at.

You need that pressure to properly fill the Elements inside of the Fuel Injection Pump.

At cranking speed there might not be enough pressure to fill the Elements due to the low volume of Fuel being moved. Once the Engine is started the Fuel volume shoots up and it is more likely the overflow pressure relief valve would hold back enough pressure and the Elements would get filled properly.

[Shrumsjs]

I have air in my clear lines going to the fuel filter canister.
as i trace the lines they seem to be coming from the lift pump.
this pump although it is attached to the injector pump delivers fuel from the tank to the filters, then to the injectors.
I do not want to mess with the injectors but replacing the lift pump or seals may be an option for me.
I am assuming that air in the lines into and out of the filter have nothing to to with the injector pump as that is after the canister filter.
Am i correct.
thx to anyone anwering.
Sid

[Zulfiqar]

Air in the lines is leaking O rings on the plastic line flanges, You will also see air in the lines if the rubber fuel hose to the fuel feed thermostat type heater is rotten. It can rot specially with biofuel.

You should also inspect the overflow hoses of the injectors at this time too.

[Diesel911]

Originally Posted by Shrumsjs

I have air in my clear lines going to the fuel filter canister.
as i trace the lines they seem to be coming from the lift pump.
this pump although it is attached to the injector pump delivers fuel from the tank to the filters, then to the injectors.
I do not want to mess with the injectors but replacing the lift pump or seals may be an option for me.
I am assuming that air in the lines into and out of the filter have nothing to to with the injector pump as that is after the canister filter.
Am i correct.
thx to anyone anwering.
Sid

Not exactly. The Fuel Supply Pump delivers Fuel to the Fuel Injection Pump Housing.
Most of the Fuel goes though the Fuel Injection Pump Housing and out of the Fuel Pressure Relief/Overflow Valve and eventurally back to the Fuel Tank. That Fuel is used to cool the Fuel Injection Pump.
A small portion of the Fuel goes into the Fuel Injection Pump Elements that create the high pressure for Injection and that is the Fuel that goes to the Injectors.

X2 on the Line Seals and the other Seal.