300SD stalling after exiting freeway :-( - PeachParts Mercedes-Benz Forum

michaelshu · #1 12-19-2009, 09:35 PM

Hello all,

Searched the posts, but couldn't find an answer... any help or guidance is very appreciated

I've got a 1982 300SD that stalls after exiting the freeway. Around town it's fine. I just did 30 miles on surface streets and it had a nice, even idle at each stoplight. However, if I get on the freeway for anything over 5 miles, when I exit, it will stall at the first stoplight. It will restart and bog for a bit and want to stall again, but if I hammer the accelerator, it will get past it and start running smoothly again.

Just started yesterday, but has been pretty consistent in following the above pattern.

A little extra info about the car (some might be extraneous, but too much is better than not enough, right?):

* B-100 Biodiesel for the last 10K miles or so. Fuel filters changed (both of them) about 1,000 miles after starting the BioD, then about 1000 miles ago. So, shouldn’t be the fuel filters, right? Filled up with regular diesel today to see if that made a difference, but no... BTW, my Bio-D is made commercially, not a homebrew.
* Oil changed about 2 weeks ago, maybe bumped a vacuum line? But, then again, the problem only started happening yesterday, and it's my daily driver.
* Thought it might be starved for air, so I changed the air filter last night, same problem today though.
* All fluids were changed about 1,000 miles ago (brake fluid, coolant, trans fluid, diff fluid, etc. by my mechanic)
* Drives just fine on the surface streets (I know I said it above, but just to reiterate!). It just happens after exiting the freeway.

Any ideas fellow peachparter's?

Thanks for your help...

By the way... while I was filling up with regular diesel today a guy made a U-ey and stopped to talk for awhile... he had an '83 300SD in the same color combo. It's nice to be a part of a friendly community :-)

79Mercy · #2 12-19-2009, 10:02 PM

When hot what is the idle speed?

pawoSD · #3 12-19-2009, 10:08 PM

My car had a similar issue way back when I first got it. Turned out that the rack damper bolt was in all the way (way too tight) and it would randomly stall while coasting. Adjusted it properly, issue gone.

kerry · #4 12-19-2009, 10:10 PM

I'd try removing the vacuum line from the shut off valve and see if symptoms persist.
There is at least one other thread on here with exactly the same problem. Don't recall the outcome.

Diesel911 · #5 12-19-2009, 10:56 PM

Easy to check wild guess. Try driving the same way with the Fuel Fill cap off; but not on a full tank; otherwise fue might come out on the Freeway.
What I was thinking of is Vacuum is building up in the Fuel Tank due to a partially clogged vent; whey you drive fast the Vacuum builds up faster than it can be vented but becaue you are going fast it does not show an effect on the Fuel Supply Pump.
When you return to going slow you now have a lot of vacuum and the Fuel Supply Pump may be getting effected by it.

When you drive slow no problem as there is time for the Vacuum to vent.

While you do not have the symptoms of a Fuel Filter issue; it does not matter the length of time or miles of a previous Filter Change; I have witnessed new Filters plug up within a few hours (due to contaminated Fuel) on seversl occasions.

I think the Rack Damper adjustment is also a likely cause as well as too low of an idle speed if it is below what is on the Emission Sticker.

michaelshu · #6 12-19-2009, 11:51 PM

(ORIGINAL POSTER)

It idles about 850-900 regularly. But when getting off the freeway, it starts idling there, then it idles a bit lower, then struggles for awhile, then stalls.

Thanks for all the quick replies :-)

79Mercy · #7 12-19-2009, 11:56 PM

OK your idle speed is fine.

Check for a vacuum in the the fuel tank like diesel911 said. When you get off the highway pull off the cap and listen for a loud wooshhhh sound.

michaelshu · #8 12-19-2009, 11:57 PM

(ORIGINAL POSTER)

Hello Diesel 911,

My dad guessed at a vacuum issue also...

What's the best way to clear the tank vent? Is it easily accesible?

I just put my little guys to bed so I won't be able to try the fuel filler cap off test until the morning, but I can get out to the garage tonight and try to clear that vent.

Thanks for all the great advice so far everyone, I will definitely "pay it forward" :-)

Diesel911 · #9 12-20-2009, 11:19 AM

Another thought. I had a small Air leak that had an effect on the idle but only after the Engine was warm.
It turned out that my Fuel Inlet Hoses were hard and not sealing. When the Engine compatment was hot I could twist the Hoses around the Plastic Filter Nipples even with the camps tight.
For a few dollars of fuel Hose it was cured.
I am not sure where the tank vent is. On some vehicles there is just a little Pin Hole inside of the Fuel Fill Cap.

Added: Tank Vent is item #47

GWNorris3rd · #10 12-20-2009, 04:23 PM

Isn't item # 47 the vent line and #83 the Tank Vent? I have the bell shaped vent end (#83) and it does get clogged with road dirt, just take it off and use brake cleaner on it and reinstall.

kerry · #11 12-20-2009, 05:06 PM

Are we sure the D and SD have the same tank vent?

4x4_Welder · #12 12-20-2009, 06:30 PM

Does it still have the EGR, and what's the chance that is holding open?

michaelshu · #13 12-21-2009, 12:29 PM

Hello all,

Again, thanks for all the helpful guidance.

I throughly cleaned the gas cap, but didn't see any "pinhole" that might be venting some of the vacuum suction. Was still wanting to stall after a longer-ish drive at 65+ MPH.

I got under there this morning and couldn't find the bell shaped tank vent (Item #83?). Looks like on the image (Thanks Diesel911!) it's more towards the front of the car though... not towards the rear by the tank?

I called my indie mechanic today and he said it shouldn't be a vacuum issue. More like a fuel supply issue... I tried explaining it wasn't with the vacuum system, but more so the tank not venting and creating a suction possibly... but something got lost in the German/English translation over the phone. I'll get under the front and look for the bell shaped vent (I'll let you know if my SD has it kerry) and then might run it by the mechanic later. I'll definitely follow up with any updates.

Thanks again all,

Diesel911 · #14 12-21-2009, 04:59 PM

Quote:

Originally Posted by michaelshu

Hello all,

Again, thanks for all the helpful guidance.

I throughly cleaned the gas cap, but didn't see any "pinhole" that might be venting some of the vacuum suction. Was still wanting to stall after a longer-ish drive at 65+ MPH.

I got under there this morning and couldn't find the bell shaped tank vent (Item #83?). Looks like on the image (Thanks Diesel911!) it's more towards the front of the car though... not towards the rear by the tank?

I called my indie mechanic today and he said it shouldn't be a vacuum issue. More like a fuel supply issue... I tried explaining it wasn't with the vacuum system, but more so the tank not venting and creating a suction possibly... but something got lost in the German/English translation over the phone. I'll get under the front and look for the bell shaped vent (I'll let you know if my SD has it kerry) and then might run it by the mechanic later. I'll definitely follow up with any updates.

Thanks again all,

If driving without the Fuel Fill Cap on did not help than you do not have a Vacuum in the tank Issue.
If I was trying to find the Tank Vent I would trace it from the bottom of the tank and go forward from there.

Remember the poor Venting idea was just a wild guess on my part.

bbboomer · #15 12-21-2009, 07:36 PM

Times two on the rack damper screw. Mine did the same thing. I screwed the damper screw in about a half turn and problem gone!
Mine is the old style screw so I will be replacing it soon. The miss has occasionally resurfaced so a new screw is the answer.