I just acquired my 1987 300SDL last week. It was running pretty good for the most part, but seemed to lack power. Assuming th fuel system was plugges from the car sitting a while, I have been doing the normal things (fuel filters, diesel purge, fuel additives, etc).

Well, today I got stranded and I think it is the fuel lift pump.

The engine was not getting fuel. I suspected the fuel screen in the tank, so I pulled out my diesel purge kit and rigged a small fuel tank under the hood. Upon trying to start the engine I discovered that it wasn't pulling fuel from that either.

Still hooked up to the small makeshift tank, I removed the fuel line coming out of the top of the lift pump (the one that goes to the secondary fuel filter) and tried cranking again. So all I had was my small tank with a line going to the fuel heater, from that to the lift pump, then out the top of the lift pump. Unfortunately no fuel was being pushed out the top of the pump.

Question #1: Am I correct in suspecting that this means my lift pump is shot? I mean, it couldn't be anything else, could it? If I'm not mistaken, the Injection Pump really runs my lift pump too, so is it possible my injection pump has failed? Any way to test?

Question #2: I'm thinking of putting in an in-line fuel pump as I can get one locally instead of having to wait to have another MB lift pump sent in. I'm looking at an electric pump that produces 10-14 psi. Would this work? If so, any suggestions as to where I should tap the power to run it?

Yes it does sound like your lift pump is shot. I'd stick to the OE pump. Why make your engine dependent on electricity when it's not dependent in its OE configuration?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks for the reply!

My reasoning for converting to electric is that I cannot find the OE pump locally and really can't wait to get the other shipped in as this is my only car. If I can use the electric pump I can be up and running in a few hours. I just need help determining if this solution would work. I do intend to replace the OE pump eventually, and I figure I could leave the electric pump in place as a booster pump (may help if I decide to run biodiesel in the future). If I use this electric pump, I presume I would just bypass the OE pump? Would I need any type of pressure regulator or cut-off switch?

This will work. There already is a pressure relief valve in the system on the injection pump. Gallons per hour does not want to be too great I would think. Since the pump has a rated pressure it should have a shutoff at the fourteen pound pressure point. A thirty pound pressure fuel pump would mimick the original bettter I would expect. Even grabbing a used lift pump somewhere would be better than an electric in my opinion. They simply are more reliable. I assume you have verified the injection pumps crankshaft is still turning. It is what drives the manual fuel or lift pump.

THanks Barry,

No - I have not verified this. How would I check it?

Going with the electric pump as it appears my OE lift pump is out and I can't even find a used one anywhere in the state.

I have the choice narrowed down to 2 pumps.

#1 is rated at 10-14 psi and 20gph.
#2 is rated at 45-65 psi and 35gph.

Which one should I choose (or does it matter)?

One way to check is to watch the RIV tang as the engine turns. There's a port in the side of the IP aft of the lift pump. Remove the plug with a 17mm wrench and look for the RIV tang when the engine is at 15* ATDC #1. If you see the tang come into view at 15* ATDC every other crank revolution, the IP shaft is turning and the IP is ostensibly timed correctly.





Sixto
87 300D

First things first !!!
There are 2 small one way valves in the lift pump. If either gets a bit of crud on its seat it then the lift pump doesnt work. Its easy to check them. Make sure you put them back the same way as they were or it will not work.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

This site has typically gotten parts to me within a day or two.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Wow! That would be great if it was just that. I'll pull the pump and inspect the valves. If that is not the problem, the photos posted will also help me make sure the crankshaft is turning. Wouldn't have known how to do that otherwise. It is so great there are folks like you who can share your knowledge!

As a backup, I picked-up an electric pump tonight - so 1 way or another I should be running tomorrow (that is unless I fried my IP). I will post my results.

Thank you all again for the great tips!!!

bypass the fuel t-stat completely before rebuilding / replacing the lift pump

__________________

X2

I think there is a few threads about doing the bypass.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Someone who needs instructions to bypass the thermostat shouldn't be messing with the engine

Sixto
87 300D

Importec - BMW, Jaguar, Mercedes, Porsche, Volvo, Toyota Parts...

CarQuest can have one of these or you can order it an have it by Monday. Worldpac has a warehouse in Minneapolis, World Auto 952-949-0274 can order it also and have it overnight.

__________________
Mark
========
THE WHITE FLEET
2016 GLE300d 4-MATIC 38K BROWN!
2012 S350 Bluetec==94k WHITE

2007 ML320 CDI==166K WHITE (FOR SALE)

Under new management:
2005 E320 CDI--140K--WHITE
1995 E300-Diesel-133.5K--THE CAR IS BLUE
1986 300SL--97.5K (European) AND WHITE. Back in Europe!
1991 190E 2.3-73K California Perfect.--WHITE
1995 E320-Wagon-159K--WHITE (recently scrapped)
1987 300D Turbo-213K--WHITE
1987 190D 2.5 Turbo-288K--WHITE

OK, It is running. I bypassed the mechanical pump using the electric and it seems to run great now. Thank you all for your help!

A few of you commented about bypassing the fuel T-stat. Are you referring to the fuel heater located lower and aft of the OE pump? Currently I am still running through that but could bypass it easily if recommended. What would be the purpose of bypassing it?