Hey all,
Last week I wrote in about some strange stumbling and stuttering on cold start up with clouds of blue smoke. I believe my mystery is solved. I believe I have a flaky GP relay timer. With the help of this Board and the Mercedes Benz Club Board this is what I have learned. My car is a 1986 300sdl. No afterglow on this vehicle. My glow plugs Ohmed out correctly and leaving the block heater plugged in made it start like a champ. I counted the number of seconds my GP light stayed on at 36 degrees outside. It was 8 seconds one day, 5 seconds the next, 10 seconds the third day. I counted the number of seconds until the GP relay clicked off. It was a consistent 39 seconds. I believe the timer inside this realy is flaky, so now I just ignore my light in the morning and count to 20 from the moment I turn the key and it starts just like new, with barely no smoke or stuttering.
This relay was replaced last year and it is not a German made relay, it is made in Hungary. My previous experience with a Hungarian OVP relay in my 380se tends to make me believe that these parts do not have the same quality as the original German parts.

Second issue: When cold in the AM, I get a lot of flaring in the transmission when shifting. When the car is warm all is well. By the way I plugged the vacuum line to the EGR last summer. Now hear me out with my thoughts on transmission vacuum issues. When you have a vacuum leak, your transmission will shift very HARD. When you have too much vacuum, your transmission will shift very soft or even flare. There are a bunch of these little different colored orifices plugged into the vacuum lines coming off the vacuum pump and they provide a controlled amount of vacuum to different parts of the car. With the EGR vacuum line plugged perhaps too much vaccum was in my lines and caused the flaring when cold? When I plugged my EGR vacuum hose in to its normal position, cold or warm, my transmission shifts like a charm. Does this sound crazy? I experimented by leaving the vacuum line unplugged to the EGR without a golf tee in it and the tranny shifted extremely hard.
Comments please?
John

You need to adjust the trans, you can probably get most of the flair out. There is this thing on the side of the IP (forget the name), but you move it forward or back and it firms or softens up the shifting. Play with it a bit and see what you like, most people like these cars to shift a bit harder.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Cold shifting can also be dramatically improved by switching to synthetic transmission fluid: Mobil 1 Synthetic ATF is best.

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First issue:

Your experience with the 603 is perfectly normal. The length of time that the glow plug light illuminates is dependent on the ambient temperature. However, this time is unrelated to the time the glow plugs remain engergized and it's totally unrelated to the time that the plugs need to remain energized.

Everyone with a 603 needs to let the plugs go for a minimum of 15 seconds if they expect a smooth start. These two that I have are typical of this behavior. The '86, with it's older head and glow plugs is extremely sensitive in this regard.


Second issue:

The flaring when cold is due to a circuit that specifically increases the vacuum when the engine is cold to prevent banging on shifts. Apparently, when these trans were new, the unit would offer up a very hard shift when cold. So, M/B put a circuit to soften the shift. But, as the trans ages, the characteristic changes from a proper shift when cold to flaring when cold.

To avoid this flaring, and firm up the cold shifts, simply disconnect the vacuum solenoid that is sitting right next to the amplifier. The vehicle will then perform in similar manner no matter what the temperature. The cold shifts may feel a bit firmer, but, certainly not objectionable.

Where?

I have the same issue now that I have dropped some BB's in my ARV/EGR lines.

-Jim

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

Brian,
Do you mean disconnect the electrical lead to the vacuum solenoid? or disconnect the vacuum lines themselves?

This makes total sense to me. I am looking at the service manual and in typical German engineering speak what you just put into Simple English is how this system works. In fact,I believe Mercedes changed this system for the 87 model. Correction, they changed it for the 90 and 91 350sdl models, and made a modification to the transmission itself

John

Just unplug the solenoid and the transmission will never get higher vacuum when cold. You can try it and see if it improves your situation.

To kill the shift-softener circuit, you can also unplug the electrical switch in front of the thermostat housing. It's a round switch that is closed to ground below 50°C, and opens above that temp. On my cars, I found that it would cause flaring when cold. With the circuit disconnected, cold shifts are fine, with Mobil-1 ATF anyway.

About the smoking, also check your IP timng and cam timing (chain stretch). The 1993 300D that I just bought had retarded cam and IP timing and it would smoke & misfire when cold, especially when revved above idle. Adjusting the IP timing (from 18° ATDC to proper spec of 14° ATDC) cured this. Runs great now.

__________________
Dave
Boise, ID
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I unplugged the electrical connector and my cold shifting is just fine now, no flaring. Thanks for the advice!
John

Good job.

Help is what we do here.

I almost forgot to reply to this - wooops. The item on the side of the IP is the vacuum control valve (VCV). I learned the hard way that this is not a seat-of-the-pants adjustment. It's a binary thing - it's either set properly or it's not. There's a procedure in the FSM on how to set it (outlined below). I too thought that tweaking it could firm up shifts, but it my case it actually caused odd intermittent flaring when set to full firm. Anyway - my cars are happier after the factory adjustment:

1) Loosen the two 10mm bolts enough so the VCV will rotate
2) Have a helper push the accelerator pedal to the floor and hold it there
3) Rotate the VCV clockwise until resistance is felt
4) Tighten the bolts
5) Go for a test drive

In evey car I've adjusted this on so far, it's ended up right in the middle of the adjustment range.

I followed the FSM procedure and was happy with the shifts. My trans is currantly all screwed up I need to work on that this spring. I have the vacuum unpluged and it shifts just ok. I need to figure out whats wrong.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I've tweaked it manually all the way clockwise. And, I got the vacuum down to about 9" at idle and the shifts are definitely firmer.

Now.........just in the last few days.........I get an intermittent 2-3 flare.........but, such a severe flare that the engine runs well over 4K before I lift and it shifts.

Happens when I'm down with more than 1/2 pedal...........but, not all the time.........???

I had similar oddities with it at full clockwise. Try setting it via the FSM procedure (outlined above) and see what happens. It didn't make sense to me either, but it helped in my case...

Are you actually doing that procedure with the engine running at maximum rpm?

I'm not exactly comfortable with that..............