1985 MB 300DT problems over problems - Page 2 - PeachParts Mercedes-Benz Forum

siral3x · #16 02-09-2008, 03:45 PM

Quote:

Originally Posted by zeke

x2 - I had rough and inconsistent idle on my 240D and on my 300TD, and in both cases, air in the system was at least partly to blame. I changed the fuel lines and tinkered until I stopped seeing air bubbling into the primary filter and until I was sure that there was no air in the secondary filter, and it made a world of difference in both cars!

I thought I needed new motor mount (still do), but getting the air out of the system and getting the idle right smoothed it out enough for me to justify putting off the motor mount for a few more months!

My rough idle is only for 30sec MAX, every time I start the car COLD. Even if I start it and rev it up to 1k rpm I can still feel a stumble and miss here and there. After the car runs for 1 min or so...no more stuble miss whatsoever, and idle stabilizes itself at about 700rpm. The previous owner told me he had the same problem and couldn't figure out for years.
What fuel lines are you talking about?? From the tank to the IP??
I always glow in the winter at least 15 sec more after the gp light goes off.
How would I check to see if I got air in the lines???or if I have a bad hand pump??etc??

zeke · #17 02-09-2008, 03:59 PM

I have a water separator in the 240D - changed lines to and from that, also from steel line to primary filter, primary filter to pump - THAT's where my problem was - I think it was just weeping. Maybe just enough leak to let air in while car is off, but not bad enough to cause a problem when car is drawing fuel through?

Could also be the fuel line from tank to steel line - that is on my to do list, but I have to wait until the tank is mostly empty, and will clean strainer at the same time....

If you can see diesel on any of the fuel lines, they are leaking. The braided ones are apparently tricky cause they can weep but not look wet. If they are 20+ years old, might not be a bad idea to change them.

Air in the lines seem to have caused the opposite problem in our 300TD - I am sure Brian will let me know if I am off base here

but the car was dieseling after shutoff....I thought it was a vacuum leak...but once when it happened, I got out to shut it down with the STOP lever, and saw air bubbling through the primary filter. After I reseated the fuel lines (and saw no air coming into in the filter when it was running) haven't had the shutdown problem since. I think the vacuum was ok, but the car was getting enough air through the fuel line to keep on going!

Anyway, all this is just speculation, but it seems like an easy thing to try without have to take the engine/IP apart?

toomany MBZ · #18 02-09-2008, 04:04 PM

Quote:

Originally Posted by siral3x

If it was a air leak then it would do that all the time. It only does it on a cold start. I'm sure the compression is not perfect but still I'm worried.
btw thx for the pic!

Enough pressure on the go pedal will over come a leak.
No prob on the pic, they speak a thousand words!

tobybul · #19 02-09-2008, 05:22 PM

Quote:

Originally Posted by siral3x

I have tried diesel purge and it did improve somewhat my idle, but it did not fix it. Yep, I'm having the injectors rebuilt back in Europe since I'm visiting soon. I'm willing to call a diesel service shop here too...any recomendation?? I drive from Ludington to Holland MI, every weekend, any shops around??

Your profile did not show your location....... but anyway, in Grand Rapids, I used Diesel Service once at 54th st just east of US-131. They charged about $35 each for testing and replacing my nozzles.

Yes, your idle may be low but that does not explain the missing after a few minutes. If its low - its low, period. It should be around 750-850.

Are you using B20 or any B-fuel by chance? This caused my 84D to exhibit the same symptoms. After 2 fillups, I switched back to regular diesel.

Only other possibilities are dirty filters. If you have air in the line or inside the IP, the car will NOT start no matter...well, may be eventually after xxx starts.

How about using synthetic motor oil? This has improved all of my D's running. Cheapest out there is Rotella 5w40 from Walmart which I know you have at Lundington.

blackestate · #20 02-09-2008, 05:49 PM

[QUOTE=siral3x;1757516]I. It runs nice and smooth for about 5 more sec after I start it and then it starts too MISS, shake, and idle loops erratically, eventualy stalls. It seems like the engine is not receiving enough fuel OR maibe to much??? I glow again, car starts fine..KEEP my FOOT on the throttle and keep it at around 1k rpm for 30-40 sec and then NO more shaking, looping, stalling! ]

Sorry, I am no expert, new to these, but to me if it is running normal for 5sec or so, then dies, I think you have air close to the IP. the short run time would bleed the fuel from the injector lines. Just my thought.

On my old ford idi, we would be able to find this by looping a piece of clear tube into the fuel return line when warm, runing it so it was full of fuel. Then after it had cooled down having someone start it, and watch the clear line for air bubbles.Should see some around the time it starts to stumble.
There is a return from the filter you could check, and a return from the injectors to the filter, and then you could check between the lift pump and the IP, a pain, but probably where I would start.

tobybul · #21 02-09-2008, 08:35 PM

[QUOTE=blackestate;1758228
Sorry, I am no expert, new to these, but to me if it is running normal for 5sec or so, then dies, I think you have air close to the IP. the short run time would bleed the fuel from the injector lines. Just my thought.

On my old ford idi, we would be able to find this by looping a piece of clear tube into the fuel return line when warm, runing it so it was full of fuel. Then after it had cooled down having someone start it, and watch the clear line for air bubbles.Should see some around the time it starts to stumble.
There is a return from the filter you could check, and a return from the injectors to the filter, and then you could check between the lift pump and the IP, a pain, but probably where I would start.[/QUOTE]

Theres some merit to this suggestion... however, my only problem with it is that it should have difficulty starting from the the get-go if there is any air at all in tje lines. But its probably worth a try to do as suggested.

siral3x · #22 02-10-2008, 10:52 AM

Quote:

Originally Posted by tobybul

Theres some merit to this suggestion... however, my only problem with it is that it should have difficulty starting from the the get-go if there is any air at all in tje lines. But its probably worth a try to do as suggested.

-All fuel filters changed 2 months ago;(didn;t fix the problem);
-The prefilter looks clean and has maybe 1 air buble in it...is that normal???