1985 300D loss of power after 20-25 mins

The majority (80 percent) of these type of power problems are due to restricted fuel flow or air in the fuel system. I would go after the tank screen first. Be sure and check the tightness of ALL your fuel hoses and clamps.

The other 20 percent turn out to be a mechanical problem. Worn lift pump, injectors, timing chain, injection pump, turbo, etc.

Report back on what you find. Kent

Good morning Kent,
I spent the weekend under both cars troubleshooting and working. On the 85' (the one that has the loss of power), I pulled the fuel strainer to find it was about 98% clear. I replaced all the fuel lines as well and found that my braided line was rotting a little but not bad enough to let air in I think. I have not had the chance to run the car yet since I'm waiting on an intake but should get the parts today.
Considering the good condition my strainer and lines were in and new fuel filters and a relatively new bosch priming pump, do you think it could be something else? One of my diesel mechanic friends suggested it could be the wastegate on the turbo sticking open after the motor heats up all the way and at high rpm's. Possible? Probable in your opinion??
Thanks much,
Brandon Oswald
Pensacola, FL

1979 300D "Red"
1985 300D Turbo "Blue"

Brandon,
Mine is a non-turbo 97 300d with about 2500 miles running on a two tank veggie system. I am having the same problem and getting it checked out today or tomorrow. My problem occurs after about 20 minutes as well. I notice minor sputtering at a constant rpm and especially on hills where it revs higher than normal and has a problem shifting to accomodate the hill. When I switch to diesel everthing works normal and when I switch back to veggie everything works normal for about 10 minutes. After noticing the problem, on idle I can feel it running rough every so often. I just changed my veg filter and all other filters have a recent change. I am not doing the mechanical work myself so I will be interesed to hear what you find out.

Thanks,

Dave

Brandon.my 82 300cdt did the same thing.After changing all fuel lines under the car,removing the lovecraft conversion kit and putting it back to the stock spin on filter, replacing the turbo,adding a rebuilt injector pump with new injectors and doing a valve job and timing chain to the tune of about $4500 it turned out to not even be an engine problem.It was the transmission all along.good luck.

Joe.

just a follow up on my 97. it looks like a very tiny amount of air is getting into the veggie line. I guess it takes a while to develop, hence the 20 minutes for the sputtering.

Dave

Joe,
Thanks for your reply and that really sucks what you had to go through to find the real problem. What was the issue with the transmission? When mine starts to lose power, it refuses to shift and then when it finally does shift it is really hard.
Thanks for any input you have.
Brandon
1979 300D "Red"
1985 300D Turbo "Blue"

Dave.

I'm driving a '98 MBZ turbo and I have the same problem of sputtering and loss of power when climbing hills. I have then removed the filter and opened the 'water outlet valve' on the 5 micron filters I am using. Out comes little specks of carbon looking stuff. I figure the WVO is not getting filtered down to 5 microns correctly and the minor sediment floating in the oil concentrates on the filter element. After a while (too much sediment accumulated) I notice the engine 'starves' for fuel. Anyway, that may be the problem, your not cleaning your WVO down to the proper micron cleanliness.

Romeo

After replacing both fuel filters again, pulling the fuel strainer (which was 98% clear), checking vacuum readings, replacing the stock airbox with a high quality aftermarket kit, cleaning banjo fitting for ALDA, adjusting ALDA in small increments, and trying different transmission throttle position cable settings, our 1985 300D is STILL doing the same sputtering and eventual dying after it gets to about 70-80*C.

I also drove it with a guage attached to the boost line that goes to the ALDA. I got 9.5 lbs of boost at full throttle and consistent readings until the engine warmed up but when it started to sputter, the boost pressure dropped correspondingly. I'm not sure, but it looked like it was dropping as the engine spooled down which would indicate to me that the turbo and the wastegate are working fine and are not the culprit.

My wife and I normally run both our 300D's on veggie oil that we thin with 10% Jet A and 5% unleaded fuel, cetane boost, and injector cleaner. We filter it down to 5 microns and run it through a water block before putting it in the tank. I do not believe this is the problem because I filled it up with regular pump diesel on Friday and it is still consistently doing the same thing.

CAN ANYONE HELP?? I'm tearing my &*$^@#* hair out because of how well it runs until it heats up. I don't get it!!!

Should I maybe splice in a fuel pressure guage and monitor that?? Wouldn't air getting in my fuel lines affect perfmormance regardless of temperature?

I feel like I'm missing something obvious but everytime I stand there looking at the engine everything looks and checks fine.

Thanks very much for anything you can contribute,
Brandon and Megan Oswald
Pensacola, FL

1979 300D "Red"
1985 300D Turbo "Blue"

I forgot to mention also that when we came to a stop today after test driving, the car was in neutal but the driveshaft was making a banging noise. I got under the car and sure enough the driveshaft looked like it was trying to engage the rear end but was just rotating 1/8 of a turn and contacting it. I had my wife put it in park and it continued to do it there as well. It also got slightly louder as she stepped on the gas. It was idling roughly and I noticed it does this sometimes when the sputtering occurs and I bring it to a full stop.
Think this has anything to do with the sputtering and dying problem?? I does shift somewhat firmly but doesn't seem too bad. Also, when it starts to sputter it won't shift up or down at all.

Thanks again,
Brandon Oswald
1979 300D "Red"
1985 300D Turbo "Blue"

If your intake pressure readings were low after the engine warmed up at 55 mph, then you could have a turbo or waste gate problem or maybe clamps or hoses on the pressure side of the turbo that let air leak out. From what I understand, ou have to have that pressure to activate the ADLA sensor to send more fuel to the injectors. How many miles on the car? Sounds like you have checked the fuel system for restrictions and possible air introduction, but the description sounds like air getting into the fuel when the temp changes. Those air leaks are hard to find because there is vacuum on the hoses and no pressure to force the fuel out. Do you have a boost pump back at the tank?
I am curious now!
Al

You did not mention if your 85 has a trap oxidizer. If so I would consider the possibility that it is causing a restriction after heating up. If no trap still consider the possibility your exhaust system.

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Thanks for all the replies and I'm truly sorry for anyone experiencing something like this. I feel like we've replaced all the parts on the car except the one that is causing the fuel starvation symptoms.
I put some pump diesel in our 1985 300D yesterday and it ran ok the rest of the 20 miles home after dying on the way into the gas station from the same sputtering as I've previously described.
We looked back last night and realized that we had not tried running the car with the gas tank full since these issues have surfaced. We're trying that today.
In addition, I started the car last night in the dark and held a flashlight to the clear inline filter before the injection pump while I revved the engine. To my surprise (and hopefully a specific diagnosis) there are obvious bubbles that go through the filter when I rev the engine fairly high. They are probably only about 2-3mm in diameter but I'm sure at sustained high speeds or hills these could build up and cause my injectors to vapor lock. Is that a fair analysis?? Like the previous post, my hair is about to be gone as well except I don't have a beard to turn gray.
Thanks to anyone who donates their knowledge.
Brandon Oswald
Pensaocola, FL
1979 300D "Red"
1985 300D Turbo "Blue"

I converted my 82 300sd in May and have been thrilled. I recently read about the power loss some people were experiancing and have just now began experiancing the same problem. I changed the rear fuel filter to no avail. I am in the process of looking for air leaks and will let you know. Thanks for the information. Lets stay in touch.

Before I converted,I added a electric boost pump at the rear.I can bleed air in seconds.It will pump wvo and wmo.

brandon,

i was wondering if you fixed this problem? I have the same problem on a 1990 300d and was thinking it could be a tired fuel pump. Let me know.

Mac

Haven't fixed it yet. This problem is truly mysterious and frustrating. I have now replaced every fuel line, checked for ANY restrictions, changed the fuel filters, swapped the fuel lines from supply and return a couple times, new primer pump, different fuel, cleaned fuel strainer, driven at all kinds of speeds and loads all to no avail.
When I rev the engine really high from under the hood I can see a froth of tiny air bubbles develop in the primary fuel filter going into the lift pump. I don't think it should be doing this. I have checked and rechcecked EVERY fuel hose and fitting and can find no leaks or even questionable areas. My wife and I are going to take the car to a guy that is an injection pump specialist next week.
I really don't think it's the turbo either.
I just feel stupid with this since usually I'm ok at dealing with mechanical issues. (not so much with electrical)
Thanks,
Brandon and Megan

1979 300D "Red"
1985 300D Turbo "Blue"

how about the manual pump.