I have my 240D running a two tank setup on alt fuels. I had some questionable veg oil that I now suspect may have had some water in it. When I switch back to diesel, I am finding I have a significant power loss. I am going to install a fuel pressure gauge at the IP inlet, but I suspect I have scored the plungers and barrels.

I read something in another thread about some original pumps not having hardened plunger and barrel elements. My friend who works at a Bosch fuel shop who said he has seen this as well. I am going to have him price four new stock elements for me as I am not after anything but stock performance.

Are there any companies that make elements for these pumps? I am having a hard time finding any info on parts for these pumps. Sometimes aftermarket stuff can be cheaper and still good quality. Can anyone point me in the direction of pricing some of these parts, even if a slight performance upgrade? My friend will balance the pump for me at their shop.

Mercedes usese their own part numbers for parts. If your friend works at a bosch certified shop he should be able to use the infomation stamped on the little plate to look up the parts for your particular pump.
This assumes it is the elements (plungers and barrels) are the issue.
Why the parts are not esasily avaliable is that while the elements could be replaces as a do-it-your-self job by someone that knows what they are doing after replacment the pump needs to be calibrated on a calibration machine.

Most people find it easier just to get a used Fuel Injection Pump and swap them.

You need to say if it is an M or MW type Fuel Injection Pump. The M type has a rectangular cover on the side where the Fuel Supply/Lift Pump is.

You could remove that cover and have you friend peek in and see if the Plungers sre stuck in the upward position. When it is like that as you rotate the pump you will see compressed springs that say commpressed no matter how much the pump is rotated.

I used to work in a fuel injection shop. Your friend ought to know how to unstick the plungers.

If it is an MW Fuel Injection Pump and you know which cylinders are not firering you can have your friend remove the Delivery Valves and unstick the plungers.

I kind of doubt if your plungers and barrels (Elements) are so baddly scored they will not work at all. If water got in it is more usual for the plungers to stick upwards due to rust but it can also happen due to gunky fue.

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84 300D, 82 Volvo 244Gl Diesel

911, thanks for replying. First thing I am going to do is get a fuel pressure gauge before I do anything.

I do not have a misfire or anything. Just really low on power when running on pump diesel. This has happened over a period of a couple weeks or so.

Seems unlikely to me that things could be gunked up already. I've been running this fuel about 4 weeks and drive the car everyday to work. Diesel tank always has a good dose of some kind of injector cleaner it is to clean everything out.

I'll get the fuel pressure gauge on tomorrow and report back.

Pump tag, I'm assuming this means MW pump:

That is the tag that is on the Governor. the Pump Tag is at the front left top corner.

So you symptom is actual loss of power.
Loss of Power causes and trouble shooting:

Starting with the most frequent cause/s remember there can be more then one cause.

Fuel Filters restricted- Change Fuel Filters.
Fuel Tank Screen- Remove and clean Screen or replace it.

One way to trouble shoot. Swap the positions of the Fuel Return hose with the fuel inlet hose and be sure you have 1/2 Tank of Fuel. That reverses the flow in the hoses and does not pull fuel through the tank screen but from a higher position in the Tank (which also means you would run out of fuel before the gauge shows that). If you power is restored when you do that your Tank Screen is restricted.

Plugged or restricted Fuel Tank Vent. Mud and road gunk can plug the outlet. On a WQ123 it is in front of the left rear fender.
One way to troubleshoot- Have about 1/2 tank of fuel (you don't want a full tank) and drive without the Fuel Fill Cap. Having no cap acts as the tank vent. If it drives normally with the Cap off your vent is likely plugged up.

Fuel Pressure Relief/Overflow Valve- If it is the type that can be dissembled the spring in it can be stretched back to 27mm of free length. Otherwise it needs to be replaced.

Fuel Pressure Relief/Overflow Valve- If it is the type that can be dissembled the spring in it can be stretched back to 27mm of free length. Otherwise it needs to be replaced.

Fuel Supply/Lift Pump- The Valves inside can get gunked up and the Piston can stick. There is rebuild kits for it or you can take it apart and clean it out.

Throttle linkages from the Pedal to the Fuel Injection Pump out of adjustment or parts worn or broken.

Plugged Air Filter or air inlet system.
.

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84 300D, 82 Volvo 244Gl Diesel

MW Fuel Injection Pumps have 13mm Nuts on oppsite sides of the Elements.

In the next pic in the upper left the Plate with numbers you need to tell what parts are inside of the Fuel Injection Pump outlined in red.

Attached Thumbnails

   

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84 300D, 82 Volvo 244Gl Diesel

I will have a fuel pressure gauge on in the next day or so and that should identify if I am having a filter, overflow, or lift pump problem.

This morning is a good example of what happens. Starts great. Takes foot to floor in all gears for normal acceleration. Switch to waste oil tank and power seems more reasonable. Drive for an hour and switch back to diesel a few miles before my destination, foot to floor acceleration is sub par even by 240D standards.

Fuel filters are new. Recently got a diesel purge with Marvel Mystery Oil after it was starting to haze, cleared it up nicely. Valves adjusted. Air filter is new. I have not tested for the vent, I will pull the full cap off and see how it goes. I checked and pedal linkage extends further than IP linkage will go with linkage popped off the ball.

I have a line on an 80k mile pump from a 240D on CL locally for $100. I may milk this as long as I can and swap it in.

Pic below of tag circled in red. I sent this over to my buddy at the Bosch shop.

Thanks again for the replies.

I have a used pump I could pull off an engine.

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CC: NSA

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82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

Is your twin tank setup got switchover valve for the return? Maybe veg oil getting in your diesel tank? As others have said you may be jumping to conclusions here. New elements virtually mean a pump rebuild, which will probably cost more than the car is worth. If it really does turn out to be a clogged up IP then just swap a used one on?

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

It might be a good time to do some thinking as to if using an unrefined alternative Fuel is really saving you money.

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84 300D, 82 Volvo 244Gl Diesel

10psi at the IP supply at idle, 9 at full load. It's not the tank screen, filters, overflow or lift pump I don't think.

I have a looped return and single switchover valve so almost zero chance I am contaminating one tank with contents of the other.

Grabbing $100 80k mile MW pump locally tomorrow.

And yes, I have been doing a little soul searching on the alternative fuel. I have several friends who have been doing this for a long time in 12 valves and this vintage Mercedes with great results. I don't think I'm ready to give up yet as I really believe my current issues are caused by a bad batch of veg oil. If I can't get it right with fuel I have more confidence in, I'll probably throw in the towel.

This is a $500 kinda rusty car. Big reason I bought it was to experiment with this stuff. I knew things like this were a risk, but I also enjoy the learning process (even if it does ultimately mean I'm better off running pump fuel.)

x2, the real cost includes not only parts, but also all of the time invested in maintenance and repair of the alternative fuel system. Not to mention the time spent collecting and preparing the fuel. To do unrefined alternative fuels "correctly", you have to dump a pretty hefty amount of your time into it. Which is why so many who attempt it, end up taking short cuts, resulting in a dead car that won't run well or at all.

IMO it's simply not worth it.

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

It depends on where you T ed in the pressure gauge. If you did that between the lift pump and the Spin on Filter if the filter is plugged the pressure will be high.
In order to take the filter out of the picture you need to put the gauge between the Spin on Filter and the Fuel Injection Pump Housing or install a new filter right before the test.

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84 300D, 82 Volvo 244Gl Diesel

Yes, pressure gauge is plumbed into hose on "out" port of filter housing and IP.

If I were you, before doing any major work, I'd run dry the veg tank and put diesel in it and see if you still have the significant power loss running on diesel out of the veg tank. If not, then is a plumbing / clogging issue in you switch over valves. Clamp off one of the veg coolant heater lines so you are not heating the diesel. For short runs, you don't need to do that.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

If I am not losing fuel pressure to the IP under load, I don't see how it could be anything but the IP failing to inject enough fuel.

I would like to buy the timing pin to lock the pump during install but it appears to be NLA. Anyone know of a replacement or have one laying around? P/N I have is 900 589 86 73 00

Setting injection pump timing after rebuild OM616