Anyone have a Smooth start on the 603 Engine 300d etc. - PeachParts Mercedes-Benz Forum

777funk · #1 05-22-2007, 08:24 AM

Hi guys,
I have a 300d from 87 with the 603 6 cylinder engine. Runs great after it's warmed up about 20 seconds or so. But when I first start it, it's just a bit rough and smokey of unburned diesel (It misses and is a little choppy). Anyone else on here with that engine have a different experience?

Deni · #2 05-22-2007, 09:09 AM

Did you check your glowplugs? My om602 (like yours less 1 cyl) runs rough when I have 1 or more bad gps. It runs very nice when turned on if the gps are working.

babymog · #3 05-22-2007, 09:36 AM

I have two '87 603s, both start smooth with no smoke.

777funk · #4 05-22-2007, 09:39 AM

Yeah they seem ok. I get a .6ohm reading or so across each one. I didn't pull them and try the jumper cable test though. I may do that. I'd think with each one reading close to 1 ohm they're ok. But that may not be the case. I don't know. I also changed the injector nozzles. I notice there's a slight seepage of fuel around threads of the two piece injector body. Also on the prechamber. So I'd assume if a bit of pressurized fuel can escape so can compression. Any thoughts on this fix?

michael cole · #5 05-22-2007, 09:42 AM

No worry.this is fairly typical of 603's.lots of posts on this issue with some remedies.try glowing for a longer period on startup

kernelpanic · #6 05-23-2007, 05:57 AM

Might want to look at this link
This little trick has made my 77 300D start more cleanly. Not sure if yours is wired the same as mine but it's worth checking into.

JimFreeh · #7 05-23-2007, 08:14 AM

Sounds like a glowplug or two is out.
I think you have to lose two before the IP glow light fails to come on.

Our old 87 300TD would exhibit the same symptom when I'd lose a glow plug.

Jim

Ken300D · #8 05-23-2007, 09:45 AM

Mine does exactly what yours does. And it did exactly the same thing after a complete replacement of all glow plugs. The engine develops a cold nature somehow over time. (I say "over time" because I can't imagine Mercedes being able to sell the car new to the typical consumer if it ran rough like that when started.)

I just live with it. After that 20 seconds the car runs so well its not worth any worry about it. I can see how it might be embarrassing to a city dweller with the smoke and all, but I live where America is still America.

Ken300D

Brian Carlton · #9 05-23-2007, 12:02 PM

The '86 does exactly as yours. It needs a full 30 seconds of glow to eliminate the characteristic missing.

The '87 can be sitting for four months and it starts in 1 second after waiting about 10 seconds for the glow light to go out. Not a hint of miss or smoke. Simply unbelievable. It does have a #22 head and angled injectors..........hmm...........

gsxr · #10 05-23-2007, 12:53 PM

Misfire or stumbling on startup for the OM603 IS NOT NORMAL. It just depends how much it bothers you, and how much you want to determine the root cause & fix it:

1) Even if the plugs measure 0.6 ohms each, that's not a guaranteed good plug. A better test is measuring the current draw, but you need a DC clamp ammeter for this. If the plugs are old, I replace them on principle. One or more may be carboned up, adding to the problem, even if the plugs are OK.

2) If the plugs are all good and not encrusted in carbon, make sure you wait until the glow light is off. Wait an extra 5 seconds before a cold start. In winter (temps below freezing), wait 10-20 seconds after the light turns off before cranking. This makes a BIG difference. (But it's a nuisance. Keep reading.)

3) Adding factory afterglow cures all of this. My blue '87 sat for 7 months while I was doing major projects on it over this past winter. I waited 5 seconds after the glow light turned off, cranked, and it fired up instantly & idled dead smooth, like it was a warm start. Incredible. My white parts car will do the same thing (without afterglow!) after sitting 6-9 months. Both have the old vertical injection and 25mm glow plugs. Click here for my writeup on the OM603 afterglow conversion.

4) The problem may not be glow related at all. You could have issues with fuel delivery. Might be delivery valve seals, or a slight air leak in the supply lines. If a 30-second preglow (or a couple of pre-glow cycles) with new plugs does nothing to cure the rough startup, the problem is almost certainly fuel related.

My 1993 300D 2.5T has factory afterglow standard, and it also starts instantly and smoothly in any weather. In sub-freezing temps I may wait 3-5 seconds after the glow light turns off before cranking, but above freezing, I don't need to. Ditto for the blue '87.

justinperkins · #11 05-23-2007, 12:54 PM

This might sound crazy, but I'd recommend changing the oil and replacing the air filter if you haven't already.

That is of course, if the GP system checks out.

Brian Carlton · #12 05-23-2007, 01:01 PM

Quote:

Originally Posted by gsxr

Misfire or stumbling on startup for the OM603 IS NOT NORMAL. It just depends how much it bothers you, and how much you want to determine the root cause & fix it:

Dave, it has to be considered somewhat normal under specific conditions........otherwise M/B would have never invented afterglow.......and nobody would have spent the money to retrofit older vehicles for afterglow.

gsxr · #13 05-23-2007, 01:09 PM

Quote:

Originally Posted by Brian Carlton

Dave, it has to be considered somewhat normal under specific conditions........otherwise M/B would have never invented afterglow.......and nobody would have spent the money to retrofit older vehicles for afterglow.

MB added afterglow mostly for emissions reasons. I should have clarified that cold weather would be the "specific condition" exception (below freezing), but a longer preglow cycle typically helps with that. It's summertime, so IMO anyone complaining about rough startups in warm weather, has an engine with a problem...!

For the record, the afterglow made almost no difference in cold starts in summertime (ambient temps above approx 50°F). It does make a noticeable difference below approx 40°F, with no need for extended preglow times.

Brian Carlton · #14 05-23-2007, 01:24 PM

Quote:

Originally Posted by gsxr

MB added afterglow mostly for emissions reasons. I should have clarified that cold weather would be the "specific condition" exception (below freezing), but a longer preglow cycle typically helps with that. It's summertime, so IMO anyone complaining about rough startups in warm weather, has an engine with a problem...!

For the record, the afterglow made almost no difference in cold starts in summertime (ambient temps above approx 50°F). It does make a noticeable difference below approx 40°F, with no need for extended preglow times.

So, would you conclude that a properly running 603 should start with no stumble (at 70° ambients) using the M/B preglow light as the indicator? The variability of this light......depending on model year........is interesting. At 70 degrees, the '86 gives about five seconds.........the '87 gives close to 10 seconds.

I'm going to pull the manifold on the '86 sometime this year and replace all the plugs........just to see the improvement.

gsxr · #15 05-23-2007, 01:35 PM

Quote:

Originally Posted by Brian Carlton

So, would you conclude that a properly running 603 should start with no stumble (at 70° ambients) using the M/B preglow light as the indicator?

Short answer: Yes, with the caveat that "properly running" also includes a properly functioning preglow relay, light, plugs, etc. None of the 603's in my family (even without afterglow) stumble on cold starts in ambients above 70°F.

Quote:

Originally Posted by Brian Carlton

The variability of this light......depending on model year........is interesting. At 70 degrees, the '86 gives about five seconds.........the '87 gives close to 10 seconds.

I think that's due to wear tolerances in the old style relays. I like the new afterglow relays, that use a separate temp sensor that screws into the head. I suspect it's more accurate.