Sounds like you are convinced it is the IP. I don't think so. One bad batch of veg with water in it is not going to cause the problem you are seeing, especially on the Mercedes inline pump, where most of the moving parts are lubricated by engine oil, not diesel fuel. Usually you have less power on veg, not the other way around. Maybe you have an air leak when running on diesel? That could cause low power too. One way to diagnose that easily is to install a temporary clear pvc return line at the secondary fuel filter housing that returns to the tank. It should have clear, non foamy, no bubble fuel at all times, on veg or on diesel, engine running or not (as in overnight- where you should not see even a small bubble there).

I gave you 2 easy things to try first. Of course you can do the difficult thing first, like changing the IP.

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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

The power loss is becoming more noticeable on the aux tank as well. I like the idea of the clear return line. I will do that. If I don't see any indication of an issue there either, I will run the fuel suction directly into a fuel tank under the hood or something - eliminate all the plumbing outside of the engine bay.

I don't mean to be dismissive, and you're right - those two things are absolutely easy enough to try before swapping the IP. Thanks.

The fuel feed hole on the side of the Elements are small enough that any sort of stuff that restricts the holes has the potential to not allow enough time for the Element to fill.


This is only something you would notice over time but if the Plungers and Barrels were scored Diesel Fuel would pass by them and mix with engine oil. But, a leaking fuel supply/lift pump can do the same so smelling fuel in your engine oil or having your oil level rise is not so definitive as to the cause.

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84 300D, 82 Volvo 244Gl Diesel

Fuel Feed Hole in the Element of an MW Fuel Injectin Pump.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Yesterday it stalled when I parked it in the driveway. Wouldn't restart. Started up tonight and pulled it in the garage. No air in the return. Connected hoses to jug of diesel under the hood and once it was warmed up, it continued to run worse until it wouldn't start at all.

Planning to move forward with replacing the IP tomorrow.

Installed new-to-me pump and all is well again. Thanks for everyone's help.

Ah, good. Now how about opening up the pump and posting pics?

__________________
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

If he has any idea of one cylinder being worse then the rest he only has to pull on Element out.

However, I posted in 2 threads how it is possible to take an Element out and stand a good chance of getting it back in and have it run OK.

I would be more interested to know how he plans to keep the same thing from happening again. And to top that off we are running out of summer meaning that there is going to be a greater chance to plug up another Fuel Injection Pump in the up coming winter.

You can't see much of the inside of an MW Fuel Injection Pump when the element is out. But, you can view stuff on the bottom of the element.

I was unable to get the Plunger out by just pulling the element. That is where you would look for scoring.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

I was assuming the pump would need a rebuild to be any use so tearing into it wouldn't hurt a thing

__________________
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

I would like to pull that out and take a look sometime. I will post pics when I do.

I had an 85 wagon rotbox with over 400k on it a couple years ago that I sold after running 400+ gallons of homemade fuel through between September and May in a pretty cold winter without any issues. I had a coolant heat exchanger for the fuel and my blend was mostly waste oil and stale gasoline. Not long before I sold it, I started running the nasty blend of veg oil that I recently started out my 240D on. I was upfront about having run the wagon on alternative fuels to the buyer. He messaged me a few weeks after getting it that he had very similar symptoms to what I found my 240D having and eventually replaced the IP and all was well after. I chocked that failure up to high mileage and the fact that it had been run in WVO for some time previous to my ownership as well. I now realize that it was likely fine up until the point where this batch of fuel started to get run through it.

I have gotten rid of all the oil I had that was contaminated with that batch of veg oil. From here on out, I will have little to no veg oil in my fuel blend.

Alternative fuels are not entirely about saving money. If you don't find the idea of driving your car on fuel you made satisfying, the amount of money saved to effort and experimentation invested will never be worth it. If something like this happens again, I will likely call it quits but I still believe the one batch of fuel is what caused my issues.

Again, thanks for the help.

First, congrats replacing it with another IP fixed it.
Did you determine what that one batch of veg was contaminated with that took out your IP? I am still surprised by that so it must be potent stuff.

Can you describe your filtering process? FYI I've been running veg in a 2 tank system in both inline and rotary Bosch IP's for 12 years now without any problems with the fuel system or engine other than a main shaft seal on a rotary pump, which started to leak ever so slightly but ran fine. I replaced the seal and no more leaks.

__________________
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

I have a centrifuge and finish with a 2 micron Caterpillar filter.

This veg oil was applesauce at 50*F and I blended it with a small amount of gas which turned it golden liquid brown in the summer. I then mixed it with other oil and centrifuged it and it seemed to clean up well enough, so I ran it. I don't de-water as most of my fuel is waste oil which doesn't really hold water like veg, plus I wouldn't have dared heat a gas blended liquid like that anyway. I have seen Bosch inline pumps of my own and from close friends run on many different types of oil with 10-15% gasoline with no issues so I suspect it must have had a lot of water absorbed into it.

WVO and WMO together I hear is a recipe for sludge, was WMO what you mixed in with it?

__________________
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

Yes. Mixed beforehand, they do form a sludge that drops out of the oil. It is thick like tar, but still flows like a liquid. My blend has to pass through a 2 micron filter before it goes into the car.

Well I can't comment as I've never done it before but seems like that may be a possible cause of your issue, if chemical reactions were still happening well after mixing when sitting inside the IP?

__________________
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