Recurring power loss problem on 1984 300D (runs on WVO, has injection line heaters, in-line heater and auxiliary 12 v. pump before filter):
Power loss is worst/most noticable at high speeds (on freeway) and up long grades. Worst case it got down to 7mph on freeway shoulder.
Weird: If car rests for 20 minutes, gets going fine again for 10-20 miles.
Changed all filters more than once, bled system properly. Still happened.
Poured ATF into tank and directly into spin-on filter. Made marked difference for 20-30 miles, then problem recurs.
Had tank and tank screen cleaned out, thought it must be dirt coming form tank. No change.
Had injectors cleaned. No change.
Thought I found leaking fuel line, was just overflow line.
Asked mechanic to check all fuel lines for leaks drawing air. Factory trained MB mech for over 25 years, says significant air leak would cause car not to start at all. Saw threads here that seem to think otherwise (power loss thread started by tc art). What's the truth?
Any ideas? Could it be the main fuel pump (IP?) Is there a way to check the IP without replacing it? Why would ATF make it temporarily better if it's a failing pump? This is the part that stumps me.
Saw good thread here about power loss related to a misaligned throttle linkage, will check that too. (same, tc art thread)
p.s. hand pump doesn't seem to be leaking.
p.p.s. hand pump on my other MB, the wagon, IS leaking, has experienced occassional power loss, but after running some diesel through it, seems fine again, although still leaking.
p.p.p.s IF I got some bad (hydrogenated) oil in the system (small amount is possible), could clog and cause power loss or blockage in a fuel line I think, but could be "burned out" with diesel (and would have seen more problems in wagon, since both cars use same oil.)
appreciate any help from you guys
thanks so much
Stanya

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1982 300TD, 265k
1984 300D, 282k

How does it run on pump diesel?

If WVO od SVO oil has some water in it, IP could get cavitation of it's bores.

How are the fuel return lines?

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Can you add a clear filter or hose? I think you are getting air in the system. I use a inline fuel filter from pepboys to help detect leaks. Does it happen on grease only or diesel or both? Can you describe your system?

Mike

Hi gents, I had similiar problems on my Benz which stymied me for quite awhile recently. I started having low power alot on pull out or even at cruise. I pulled tank, cleaned it, replaced screenvery bad) and filters. Things were great for awhile, then same problem again. after much pondering I checked throttle linkage. I found that after about !/3 throttle movement the cable for boost pressure from ex. manifold would jam the link on vacuum valve against heater hose. I spot tied it to an inj. line, rechecked throttle movement thru entire range, no biding. been great ever since. After cleaning cable the last time I routed the cable inside of button on alda instead of outside towards radiator. It helps when you put problems in when fixing something, ha, ha

newagon, are you running a two tank system? If not pull the tank screen out and clean it? Make sure to put on a new o-ring, you don't want it to leak.

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thanks for replies.
rrgrassi: return lines were ok, but will check again. going to take car back from mechanic today so I can test it running on diesel. water in oil could be possible i suppose. how fast does the cavitation occur? how to fix? i'm thinking it might be something else though, because wagon didn't have same probs (although wagon has big Davco filter, maybe it does some water separating too, i'll check.)
thanks!
mike0000: i have a clear inline filter (the pre filter) and it just shows regular bubble, no extra air so far.
the conversion on this one is most basic: Vegtherm inline heater from Plantdrive, 12 v. pump before spin-on, and injection line heaters. That's it. My wagon has no inline heater, just coolant warmed Davco fuel pro filter with 10 micron big filter, then injection line heaters.
will do diesel test today and report back.
bubbazook2: thanks for throttle linkage info. had heard this before, will check today.
Biodiesel 300TD: unfortunately it's NOT the tank screen, did tank and screen clean out. even added a few extra larger holes in tank screen to allow SVO through.
ALL: will report back later after stealing car back from mechanic today to some of my own testing acc toall your thoughts.

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1982 300TD, 265k
1984 300D, 282k

of course it is difficult to diagnose online but i would look at tank vents.

The engine eventually pulls a vacuum on the tank and slows fuel causing power loss.

Shut off car and vacuum in the tank subsides, bingo-- power again till same cycle occurs.

Steve

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85 300d in progress

I do not know how fast cavitation occurs. It is caused by the rapid expansion from water to steam. I saw it mentioned in a post in this forum. Do a search for cavitation. I do know it requires either a new IP or rebuilt IP.

That is a worse case senario, so hopefully it will run great on diesel.

I run on WVO occasionally as well, but I thin it with kerosene and pump diesel. I want to mix it with bio diesel, but it still costs more than pump diesel. I use an old propane turkey fryer that I heat up to 300 degrees. I have had water boil out plenty of times. I then let it cool, cold filter into a container, cold filter again after settling, reheat to 130, then warm filter into another container, then mix with kerosene and diesel, then add it to the tank.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

.
Hello all

We had the same problem with our 300SD.

It would lose power after a half an hour of driving.

Especially when going uphill, it seemed.

If we would let it sit for 15 to 20 min it would be OK again for a while.

I also thought it may be crud settling in the bottom of my tank.

So I disconnected the fuel line just before the fuel filter.
And put the open end in a bucket.
And pressurized the fuel tank at the fuel filler cap with compressed air.

I was trying to blast out any crud that may have been at the bottom of my tank or in the fuel lines.

What I noticed was the fuel lines under the tank started dripping fuel.

The old rubber lines that are covered with a braided fabric.
( I call those fabric covered lines " Hitlers revenge " )
( I bet a lot of the old VW Beetles caught fire because of that stuff )

It was impossible to see under normal operating conditions that the lines were letting air into the fuel system under the vacuum of the fuel pump.

I replaced all of the old fabric covered lines with new rubber ones.
Including the return lines on the fuel injectors.

That solved the power loss problem for me.


By the way.

The lines directly under the tank have a pressed on metal retainer, like a hydraulic line does.

I ground the metal retainer off, and there was a hose barb underneath.

I attached the new fuel lines with regular hose clamps.


NAPA had the very small diameter fuel line in stock, to replace the return lines from the fuel injectors.


This has solved the power loss problem for me.
And I hope it will for you also.

Thank you.
Until next time I bid you peace and happiness.
RichC

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When the power of love overcomes the love of power the world will know peace.
Jimi Hendrix

Thanks again rrgrassi, RichC..
looks like we fixed it: as I suspected, it WAS a pump problem, but luckily NOT the IP. The 12 volt auxiliary pump we had installed to help pump the SVO was just too wimpy. It was clicking but not pulling hard enough. My mechanic installed a big MB pump and the car is back to full power (with SVO). What a huge relief.
Now to deal with the leaky hand pump on the wagon. Runs fine but I'll replace it ASAP.
COld starts are sitll my issue. Neither car came with a block heater, so I'm trying to decide what the next best move is. Not that we have it tough here in LA, gets down to maybe 30 when I get up to go to work at 5:30am.
For now, a dash of diesel helps.

rrgrassi: thanks for filtering/heating info. I hadn't been heating the oil after collection because I figured that whatever water might be in it would have boiled out in the hot fryers. but if you've found water in collected WVO, then maybe I oughta rethink my set-up.
thanks again,
Stanya

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1982 300TD, 265k
1984 300D, 282k