Poor/No acceleration

[mark82]

When starting out the initial acceleration is OK for about 10', then there is a very noticable, spill your coffee, decrease in acceleration, perhaps a 2/3 decrease, as if the e-brake was partially engaged. Once it gets into that sub mode nothing you do with the accel pedal makes a difference except to completely remove your foot. Sometimes if I time it correctly I can get the downshift to engage about the same time as the sub mode and it restores maybe half the acceleration (still less than full normal). Those times I cannot get the downshift it crawls away very slowly at a walking pace while traffic backs up.

Mech has set the valves, replaced injector tips, timed the IP and claims there is nothing else wrong with the motor. I suspect he is just out of ideas. He said it must be the transmission. I though perhaps some sort of torque converter problem, but the trans shop says theres nothing wrong with the trans, its the motor.

It has become hazardous to drive as this occures about 95% of the time. Also has rough idle about 50% of the time and wont keep running in gear with a/c on. You get either a/c on in neutral or in gear with a/c off, not both. I am wondering if its a bad IP or bad compression in one cyl.

Any other ideas?


(79, 240d, auto)

[junqueyardjim]

Well there is probably nothing wrong there as that is the way the machine is built. It had no acceleration from new, and now at almost 40 years it is really tired and it is really difficult to take away something from nothing and still have something left. And then the darn thing has AC and an automatic. I do have a good 4 speed and other parts you would need to install it, that would make it easier to run the AC. If it has a good body, that is a great upgrade!

[Quahog]

fuel filters?

[Father Of Giants]

You have a 240d...it really isn't all that fast
I've watched people "flog" the throttle on youtube...I'm talking about foot to the floor and the thing will just cruise on by.

[Junkman]

What happens when you manually shift starting in 1st? Yes, that car is slow but not in the way you describe.

[Diesel911]

If you ever went to an interview for a Desel Mechanics Job one of the first questions they are going to as is if there is a lose of power what is the most likely cause. The answer is the Fuel Filters are plugged or there is some other issuel with the fuel supply system.
In your case that includes the Filters, Fuel Tank Screen, the Fuel Supply/Lift Pump and the Fue Pressure Relief Overflow Valve.
Additionally the Fuel Tank Vent could be restricted our plugged.

For the Fuel Tank Vent have about 1/2 tank of Fuel and see if driving without the Fuel Tank Fill Cap on. If it runs better it is you tank vent clogged.

Again you need at least 1/2 tank of fuel. Swap the position of the Fuel Supply Hose with the Fuel Inlet Hose. If that fixes the Issue your Fuel Tank Screen is plugged. (Don't drive it like this as you will run out of fuel before it shows that on the gauge.)

If your Fuel Pressure Relief/Overflow Valve is they type you can take apart you can take it apart and stretch the spring inside till it has a free length of 27mm.

You can rebuild the Fuel Supply Lift Pump for about $32 for the Kit.

When I first got my Car the throttle Linkages were messed up and out of adjustment and my Car was deadly slow. But in miy case once it got going it ran normal.

Besides the linkage there is that part on the fire wall that the pedal and throttle linkages pivot off of. The Rubber and plastic parts on that fall apart.

[Diesel911]

A plugged air intake sustem can also cuase similar symptoms. However, you did not menting any smoke.

[mark82]

Well no, its not normal acceleration. The initial 10' is normal. I have two other cars to compare to. And it is a definate, noticable, obvious, rapid change in acceleration, as if the engine just shifted into a submode.

New filters (fuel and air), did the diesel purge thing. When purchased I got fairly steady 23 mpg; after the tune up items mentioned it was very rock steady at 26.x mpg for several months. Now its back to 23-25. Dont know if thats due to whatever is wrong or the need to be frequently forcing downshifts to accelerate.

Other fuel items I will look into. Interestingly, it leaks fuel from the filler cap just enough to leave streaks outside the door a few inches long. The cap fits tightly but I guess the rubber seal is worn.

[t walgamuth]

Originally Posted by mark82

Well no, its not normal acceleration. The initial 10' is normal. I have two other cars to compare to. And it is a definate, noticable, obvious, rapid change in acceleration, as if the engine just shifted into a submode.

New filters (fuel and air), did the diesel purge thing. When purchased I got fairly steady 23 mpg; after the tune up items mentioned it was very rock steady at 26.x mpg for several months. Now its back to 23-25. Dont know if thats due to whatever is wrong or the need to be frequently forcing downshifts to accelerate.

Other fuel items I will look into. Interestingly, it leaks fuel from the filler cap just enough to leave streaks outside the door a few inches long. The cap fits tightly but I guess the rubber seal is worn.

Have you treated for bacteria lately? Could be a bad batch. Biocide...

[Diseasel300]

So the obvious question - is it shifting up into a high gear as soon as you start moving? If so, fix the transmission issue. If it won't stay in a low enough gear to gain any RPM, you'll just bog down.

[mark82]

Originally Posted by Diseasel300

So the obvious question - is it shifting up into a high gear as soon as you start moving? If so, fix the transmission issue. If it won't stay in a low enough gear to gain any RPM, you'll just bog down.

No, the trans is in the correct gears as selected by my foot. Can start in 2nd or select 1st with further push. Thats how I reduce the problem rather than staying in 2nd. When considering the trans problem I thought maybe a bad TC that is locking too soon and perhaps not fully slipping when stopped (stalling) but trans shop said thats not how it works.

This has been going on for many months now, along with mentioned filter/purge, I dont think that biocide is necessary?

Still suspicious of the IP.

[Diesel911]

Originally Posted by mark82

No, the trans is in the correct gears as selected by my foot. Can start in 2nd or select 1st with further push. Thats how I reduce the problem rather than staying in 2nd. When considering the trans problem I thought maybe a bad TC that is locking too soon and perhaps not fully slipping when stopped (stalling) but trans shop said thats not how it works.

This has been going on for many months now, along with mentioned filter/purge, I dont think that biocide is necessary?

Still suspicious of the IP.

The least undersood item is the one that often get suspected.

You can change your Fuel Filters and go straight to the Gas Station and get a bad load of fuel and within 30 minutes you new Filters did their job and are plugged up completely.
The same if something is growing inside of your tank.