Hello-

I'm looking for advice on the lift pump for a 300D. The car lacks power and is really hard to start. When it does run I can see lots of air in the return line. I've replaced the primer pump with the new style already but I'm wondering if the lift pump is bad because when I pump the primer it only seems to add more air into the line. The primer pump won't pump fuel, just adds more air into the return line? Thanks for your help.

Replaced my lift pump and all the lines this past week. Had lots of bubbles. It would run and quit and not able to restart. I would suggest replacing all the plastic and rubber fuel lines. Mine was sucking air around one of the pump lines. I really don't think the pump wouldn't pump, the lines just would not seal.

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Ricali

03 C240 4matic wagon
95 300E 234,000
7 prior 240;s 5 still going
81 300sd gone
65 230sl gone
49 Studebaker Champion
90BMW convert.167,000
60 Dodge D-100

Do you see air in the plastic primary filter?(I don't know how you could see it in the cloth & rubber return lines) A little foaming/air is normal(at least on my car it is),but a lot is indicative of cracked or dry rotted fuel lines from the tank. I would look under the car at the fuel lines for any wetness or leaking of diesel fuel, and you can even run the engine off a can of fuel with a hose ran directly to the injector pump to test it. I am kinda new to these cars, but I've heard IP failures are not very common. Good luck.

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1982 300DT 190K (Diesel Purge + synthetic oil=smoothness at last!!!)
2004 Ford E-350 6.0 L PSD 227K
2006 Dodge Ram 3500 SRW HO Cummins 4X4 48RE 42K (brute force tow vehicle)
2005 Scion xB wife's rolling pop can
1993 GMC Sierra C3500 6.2 142K

He's not talking about the IP but the lift pump aka mechanical fuel pump aka primer pump assembly. I am thinking about swapping my wifes out due to a simlar problem. Although I haven't actually replaced the primer pump yet, but it appears that the air leak is actually in the lift pump and not the primer.

That said, the other questions posed are good ones. Where is it that you are seeing the air bubbles? If they are in the primary filter (small clear one going into the lift pump) then the air is coming from the lines or the tank not the primer.

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'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.

I'm seeing air in the plastic return line from the IP, the one that goes to the top of the fuel filter. There is also air in the plastic prefilter but it is mostly full of fuel. I've replaced all the metal fuel lines and all the rubber hose. As it is right now the primer pump, which is was recently replaced, won't pump any fuel. There is no resistance when it is pumped and I can see more air coming out of the return line off the IP when I do pump it.

1. Replace the rubber fuel line between the perfilter and lift pump.
2. Pump and recheck for air in plastic fuel line going to main fuel filter.
If no air is being sucked into the lift pump from the fuel tank or fuel lines (you would see air in the perfilter displacing fuel) and air is being pumped by the lift pump then you have a problem in the lift pump.
Check the tightness of the primer and plumbing connections and replace any suspect copper washers before replacing the lift pump.
The washers are much cheaper than the pump.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

I noticed you are running a two tank kit for WVO. I've got this car setup on a two tank also. So the lift pump is now sucking through the the stock fuel filter on diesel. I've checked and replaced every possible piece of fuel line and also I can't even get the primper pump to move any fuel. Originally I thought that the lift pump was having trouble sucking fuel through the filter so I installed an electric fuel pump just before the the lift pump to help it out. It's a low psi facet pump. It didn't help. So I've ordered a lift pump and will try that.

How do you have your fuel system setup for the two tank?

That is the wrong place for the electric pump. Pumps push well, they do not pull well. Put the electric pump back by the fuel tank. That whole idea of putting the filters before the pump is poor engineering.

Put the pusher pump at the WVO tank, not at the lift pump.My 2 tank system is not a kit. I cobbled the system together myself.
I have retained the stock fuel system, with the only changes being related to the looping of the return from the injectors and IP to the IP inlet and the addition of the solenoid valve to switch the WVO. The stock lift pump still has a return line to the stock fuel tank and continues to filter the main tank fuel while I am using WVO. This does not take IP return line fuel as it is looped.
I have a Holley Blue electric fuel pump which is capable of pushing diesel at 15 psi. On WVO it can barely manage to keep up with the engine usage while accelerating, if the oil is warm in my WVO tank, or I mix ~10% biodiesel with it, otherwise the restriction in using the OE fuel line is too great.
The Holley is situated at the WVO tank and pushes the WVO thru an OE fuel line from my spare parts car. I plan to replace the OE fuel line with a larger bore, heated, fuel line in the near future.

Back to your problem.
Relocate the Facet pump to the WVO tank. (you should be able to mount it under the car near the Main fuel tank which IIRC you are using for WVO). Apply power to the Facet and remove the outlet of the prefilter. WVO should start to flow from the filter. If not, check the fuel line for blockages.
You may wish to try the Facet pump with a less viscous fuel (diesel?) so that the viscosity does not confuse the issues.

Please keep us informed of your progress.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

So here's what I did-

Checked tank screen by removing the fuel line below the tank. Fuel ran out very quickly so the screen is fine.

Changed both fuel filters.

Moved the location of the Facet fuel pump so that the fuel line from the tank goes to the inlet of the Facet pump and then to to the prefilter-filter-lift pump-I.P.

Replaced lift pump. When I removed the inlet fitting on the old lift pump I found the strangest thing. There was what looked like a piece of a metal pot scrubber pad stuck in there? I'm thinking it must have been from when I replaced the metal fuel lines. I used brake line to do the job and it must have been a metal shaving from a cut piece? Anyways, since I already had the old pump off and the new one in hand I went ahead and replaced the pump.

All fixed! Power has been restored and the new lift pump is pulling fuel just fine. My only question is about my placement of the plastic fuel prefilter. I have it placed just after the electric Facet pump. This pump is a low psi, 1.5-4psi, pump. Do you think there is any concern about the prefilter and pressure? Should I move it to just after the pump?

How's my old 123 doing?

Sounds like you've got the fuel situation corrected.

Did you ever do a timing chain?

How many miles on it now?

It always was a fine vehicle.

Brian-

The 123 is doing well. Has about 242K on it now. Converted it to a two tank vege kit at the beginning of last summer. Just drove it across the country, from N.H. to Northern California with no major issues other then the one above which I seem to have solved. Never did a timing chain because I had a trusted tech in Maryland check it out about 10K ago. Said it was fine and in no need of a replacement any time soon. Must have been all those frequent oil changes you treated it to!

Thinking that I may replace the injectors at some point. Also need to replace the rear window seal as it's leaking quite a bit during heavy rains. The tranny is getting old as it slips a little on the 2-3 when cold and downshifts with a slight clunk on the 4-3 when hot. I've tried everything for that including "trans-x" and having a trusted tech check it out. It's not a big deal though, just drive it accordingly. Otherwise it's a great car!

That's good to hear! Yes, it always was a good vehicle. The timing chain is interesting. That vehicle had dino oil changes with Castrol 15W-40 every 4K from 108K until 200K. Just goes to show you that it is every bit as good as the synthetic if you change it frequently.

The 2-3 flare was something that I would get every so often. I was convinced that it was a vacuum issue and had solved it by changing the vacuum routing in a random way. Did you ever try it with no trans vacuum and see if it still flares? The shifts might be neck snapping, but at least you could confirm if the flare could be eliminated with some vacuum tweaking.

Do you remember what part of the vacuum system you changed? That may help me to figure it out, assuming you left it that way when I bought the car?
The 2-3 flare really isn't that bad at all. Only happens when the tranny is cold and quickly goes away. What I would really like to solve is the 4-3 clunk, as it really bothers me when driving on country roads where the tranny is downshifting frequently.

So far I've replaced the two white vacumm switches on top of the valve cover. Replaced the bleed valve at the back of the I.P. Have kept the EGR plugged before the thermoswitch as that switch was a huge vacuum leak. Replaced some hoses and connectors. Cleaned the main booster line since I had found it to be plugged up with carbon. Replaced the modualtor cap.Treated the tranny with "trans-x" and replaced fluid and filter with Mobil 1. The trans-X and mobil 1 made a very noticable difference as did adjusting the ALDA. I also had a tech fool with it and he adjusted the throttle rods which made a huge improvement. As far as I'm concerned all I can do now is play with the modulator and the bowden cable until it's time for a rebuild.

I cannot remember exactly what I changed, but, I'm sure it had the effect of reducing vacuum to the trans. I did not leave it in this condition. I simply rerouted some hoses, for a single test, in a valiant attempt to reduce the 2-3 flare.

If you have a vacuum gauge, tee the guage into the line down to the trans and drive the vehicle. The guage should start out at a high vacuum (12-15 or so) and gradually move lower as you step into the pedal. At full pedal, the vacuum should be close to zero.

If you have a Mityvac, you can hook this up to the trans line and drive the vehicle with your own Mityvac control of the transmission. You can set the vacuum at various points and see how the trans behaves. This would tell you, immediately, if you could be successful with some vacuum tweaking, or whether it would be a waste of time. I'm currently doing the exact same thing with the SDL.