So Ive been trying to figure out a certain issue that is concerning me. So at a stop my 79 240D auto trans will start to accelerate just fine for about a sec or two then suddenly bogs down a lot, then picks up speed and goes.

I've changed both under hood fuel filters and primed the lines. Checked for vacuum leaks and didnt notice any (I actually only have the brake booster and the fuel shutoff hooked up, not the door actuators or anything else to help diagnose). I also changed my rear end fluid, the trans filter and fluid. Oh and even did the newer parallel wired glow plugs.
I've been a lot of research and even seen other vids of other owners with a 240d auto and all seem to have way better take off. I know these cars are slugs but seriously this is not normal.

driving after that is just fine, even on the highway.

any thoughts?

things to check: fuel tank strainer, fuel tank vent valve, leaky fuel line

Post number 2 and Your Fuel Pressure Relief Valve/Over flow valve needs the spring stretched to a free length of 27mm. Your Fuel Supply/Lift Pump needs rebuilding.

Leaky Fuel Line can mean it is leaking in Air.

Check the linkage mount on the fire wall to see if it is falling apart.

If it is the transmission I have not read of those particular symptoms. However, when I had the transmission not working well I cleaned a drain pan and I replaced the Filter but reused the Fluid. And that worked for almost a year then my B2 Piston in the trans broke.
Which leads to another issue. Don't know if it is a B2 piston issue or not. If you cannot go forward after your mentioned symptoms I would guess your B2 Piston or the bushing and seal has issues.

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84 300D, 82 Volvo 244Gl Diesel

I did check for leaking fuel lines and did find that one of the injector hard lines was leaking (forgot to mention that) but Ive since repaired that not leaking anymore. I didnt check the vent valve or the strainer yet, and the pressure relief valve...guess I'll do those next. thanks!

If the Fuel Pressure Relief/Overflow Valve has a ball bearing in the end of it, it cannot be taken apart.
If you have one you can take apart the attached pic has the instructions on how long the free length of the spring needs to be. Also inspect the Ball Bearing that is used as a valve. If it is not round anymore or has pits in it there will be times when it won't seal.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

thanks diesel911

so i adjusted it, it was at 21mm and adjusted the spring to 27mm. It made a small difference but still bogs down. Ive got some diesel purge on order, I think Im gonna try that next.

I assume you did check the transmission fluid level as Mercedes wants it done. I remember some odd things if the level was a little low. On their automatics.


Not that this is your problem. Just something you did not mention. It may be a fuel problem as others have mentioned. If in the fuel system I might suspect air is getting in. Enough could kill off power until it was processed.

I don't diesel purge is going to do anything... Imo that Is just like changing your oil, you should do it once in a while but your notice gonna notice much of a difference.

It's definitely something simple to do with fuel tho

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yes, I did check the tranny fluid level, actually did a filter and fluid change along with the rear end. I did do a fuel filter change, both of the underhood ones. It feels likes its a fuel delivery problem which is why I'm gonna try the diesel purge. I did check, more like feel, if all cylinders are getting fuel from the hardlines and yeah they are (i know to properly check it I would need to hook it up a guage to see pressures).
I'm suspecting that maybe one or more injectors might be dirty which is why I wanted to try the diesel purge.
I do need to also look into the fuel vent valve but just havent gotten to it.

The only fuel pressure you can check on the engine is the fuel supply pressure.

What is referred to as the Fuel Injection pump has 3 systems on it. There is the Governor in a separate housing to the rear and there is the fuel supply system from the fuel tank to the fuel supply/lift pump that is bolted onto the Fuel Injection Pump Housing (the front part of the fuel injection Pump that bolts up to the block) through the spin on filter and into the fuel injection pump housing where it passes out and has the pressure regulated by the fuel pressure relief/overflow valve and on back to the tank.
You can check the fuel supply pressure but there is no easy way to tap in if you have the stock plastic tubing lines. However, there is threads on how to do that.

Then there is the high pressure part of the system that creates the high pressure that goes onto the Injectors. You don't put a gauge on that portion of the system. The Injectors are like a spring loaded pressure release valve. You check the pressure in them by removing each injector and putting it on a diesel Nozzle/pop tester.

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84 300D, 82 Volvo 244Gl Diesel

Have you replaced the 2 rubber lines between the steel fuel line and the lift pump?
steel line->rubber line->primary filter->rubber line->lift pump.

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1977 240D auto w/OM616.916 engine
2005 Matrix 5spd
2006 Prius

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Okay if you noticed a small but certain improvement when you stretched the relief vale spring. It proved that you have enough fuel pressure to open that valve.


So the problem is not a lift pump itself. It is not a dirty injector or probably not the injection pump either. You can use a cleaner if you want to but it should not get rid of this problem. Unless disturbing stuff like lines to feed the cleaner through fixes the issue.


. Start simple. Have a look at your first small clear fuel filter. There will be a constant air bubble in it and that is fine. You do not want to see a small stream of bubbles going through it as well.


Did the car have this issue when you got it? Did it develop all by itself since? If by chance it only developed after you did anything in the fuel system right after. That is where the problem will be.


Personally I suspect with no certainty. You may be accumulating air at idle. As you take off the injection pump soon may have to process that air. That may be your bogging down. Personally I would work at making sure this is not the issue first of all.


If you have the older white handle on the finger priming pump. These can be a source of air. If you can stretch a small balloon over the handle and it seals tight against the lower pump cylinder . This takes away that possibility it is the source of air.


These remember in general are very old cars now. That in most cases have not been well maintained. Over a long period of time.


Runs strong on the highway does mean something.

Subscribed to see what the end problem is....

A '79 prolly takes off in 2nd gear from a dead stop no ? . my '79 and '80 both did .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Sorry I havent checked in, been busy at work. So yes, it does have the older white handle on it. I dont know how it was driving before because the car did sit for about 2 years without starting. I did get it running but did not drive it since it first had no brakes. After I did the brakes (master cylinder), I changed the fuel filters. I did prime the system afterwards and started fine after. I havent checked to see if there is a stream of bubbles but I will check and report back.
The idea of air in the system is something I didnt think of. Oh and now I have not changed the rubber lines either.
Will be checking back.