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  #1  
Old 05-14-2014, 10:25 PM
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Rough Starting Question

Ok folks, I am having an issue that is starting to stump me….. rough starting first thing in the morning regardless of cold or warm weather. About a month ago I noticed the 300D suddenly starting rough, and when I mean rough I mean once the glow plug light goes out it will crank and fire within about a second after turning the key but then it runs like it has air in the system or is missing on a couple cylinders. It will knock kind of hard and stumble for about 3-5 seconds with noticeable medium gray smoke out the back then it will suddenly smooth out and will rev and idles fine and purrs like a kitten. It runs like a scared dog on the open road and idles smoothly when stopping. Warm starts are not an issue at all, just turn the key , and bang…. away she goes nice and smooth. It only seems to start rough after it has cooled way down i.e. sat overnight.

So far, I have tried fresh fuel, checked and adjusted the valves, done a diesel purge, changed the fuel filters, checked and tightened all fuel line fittings, and checked the lines at the injectors but it still starts roughly in the morning.

As far as the glow plug system, here is what I have done. I pulled all 5 glow plugs and bench checked them with a jump box. They all glow cherry red at the tip within about 3 seconds of voltage being applied. Next I metered out the wires from the glow plug relay connector to each plug and all the wires are fine (no opens or shorts). I put the glow plugs back in, hooked them up and checked them for resistance from the glow plug relay connector to the plug connector, and all of them read between .04 and .06 ohms…..so that seems ok. Lastly I checked for 12 volts at both sides of the glow plug relay strip fuse and that is ok, so I turned on the key and each glow plug is getting 12.5 or so volts until the relay clicks off……in a nutshell, the glow plug system seems to be functioning properly.

So why would it suddenly start rough when cold, but then run better than ever on the open road? The injector nozzles were professionally re-done about 5000 miles ago and they have been working fine. I suppose I could re-tighten the lines at the IP and/or see if an injector is loose, but wouldn’t that cause it to run rough all the time, not for just 3-5 seconds first thing?
Any suggestions greatly appreciated

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)
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  #2  
Old 05-15-2014, 01:06 AM
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I'm in for the same info. Mine does the same thing, but it's getting worse. I also have adjusted the valves, new glow plugs, brand new injector nozzles... Running out of things to adjust or replace. Mine also runs perfectly once warmed up and I have no complaints on the open road.

-Rog
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  #3  
Old 05-15-2014, 01:46 AM
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"..runs like it has air in the system.."

Start there. Specifically in the engine bay.

Some bad connection perhaps letting in too much air. Could be bad banjo fuel lines - old and tired not holding a seal - drip oil on them during cold start. Or the washers on the banjo.

poor connection to fuel supply near lift pump and clear pre-filter.

What style hand primer pump do you have?
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Old 05-15-2014, 08:27 AM
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My bet: air leak via the primer pump. It really sounds like an air leak somewhere in the fuel system.
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  #5  
Old 05-15-2014, 08:37 AM
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I assume this is your 123? Do you know if it has the updated glow plug relay. The updated one has an after glow period where the original never did and that was to remove smoking. It sure seems to be glow related to me. When you removed the glow plugs did you ream out the carbon? You seem to have conducted extensive testing of the glow circuitry but the to truly verify operation is to measure current flow to each glow plug which could be up to 15 amps each. Maybe an infrared thermometer coud be used? Antiseise is a poor conductor of electricity and should be used only on the inner threads if you had used any and not on the seating portion of the glow plugs. One mechanic over tightened the electrical nuts and the glow plugs would seem ok on the bench but installed they did not work any longer as tightening the nuts broke a connection within the glow plug.
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  #6  
Old 05-15-2014, 09:03 AM
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Yes, it is on the W123.......sorry about that. It has a newer glow plug relay.....replaced it last year with one that has the afterglow feature. I have the black hand primer pump. Reamed out the glow plugs and did NOT use antisieze at all.

I'll double check all banjo fittings and connections and also current test the glow plugs. Probably be on the weekend as I still have to use the car.

Please keep the suggestions coming as I want to nail this down.

Thanks,

Glenn
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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)
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  #7  
Old 05-15-2014, 11:26 AM
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May be worth trying to have someone pumping the primer pump just before and during start up. Any improvement and I would suspect drain back of fuel or air.
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  #8  
Old 05-15-2014, 11:48 PM
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Worth a try! I'll keep everyone posted as I get time to work on it.

Glenn
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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)
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  #9  
Old 05-15-2014, 11:49 PM
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Rogviler,

PLEASE keep us (or me) posted as to what you are trying and if you eventually find a solution to the issue. I will do the same.

Thanks,

Glenn
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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)
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  #10  
Old 05-16-2014, 01:37 AM
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Quote:
Originally Posted by psaboic View Post
Rogviler,

PLEASE keep us (or me) posted as to what you are trying and if you eventually find a solution to the issue. I will do the same.
I will for sure. It really seems to have gotten worse since I installed the rebuilt injectors, which is what puzzles me the most. The only other thing I did at the time was to ream the glow plug holes, which should have helped if anything.

Mentioning the primer pump, I had forgotten that I basically glued mine together since it was leaking like crazy. I haven't noticed any more leaking, but I should get around to replacing it. Sounds like it won't help since you already did that, but it would be nice to have it back for the next filter change if nothing else.

-Rog
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  #11  
Old 05-16-2014, 02:06 AM
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Was the copper crush washer under the primer pump removed before the new one was installed?

Hows the fuel pressure relief valve?

Engine dampers?

Transmission mount?

Injection pump timing?

Throttle pivot mount?

O rings on the spin on filter bolt?

Under the tank rubber lines?

Fuel tank strainer?

There are a lot and I mean a lot of things that can contribute to rough idle.

Before you go digging in, you really want to make sure you have two good lemforder/phoenix engine mounts and transmission mounts and then move on from there...
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Old 05-16-2014, 02:42 AM
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Yeah, but if his is anything like mine then it's not really a "rough idle" we're talking about, it's a narrow window before the engine warms up where it goes bonkers and then after that it's fine. It's frustrating because the searches I've run almost all point to an engine shaking/vibration problem that happens ALL the time at idle, which I get is usually mounts and all that. My engine doesn't shake, though the whole car does when it's galloping and spitting smoke on a cold start. Nor are there any problems with power or acceleration, such as I've read you get with fuel starvation or linkage slop.

Hopefully that makes it clearer.

Also, mine started with the 3-5 seconds of this that the OP is having, but is now up to 10-20, depending on how cold it is outside and how long it's been since I drove it. And it will even do a small amount of this after I go into the grocery store for half an hour (probably the 3-5 seconds it started with originally). I'm afraid he may be in for the same fate if the mystery isn't solved. This is over about a 3-year time period for me. So it seems as if something is wearing out. I don't know, anyone ever had a glow plug relay cause this? That's about all I can think of, since it seems so tied to the warmth of the engine. But I could also see it being related to such a tiny leak somewhere that it only manifests itself when enough fuel has leaked out or air leaked in, and only seems like it's correlated with the engine warming up. That sounds exhausting to figure out.

-Rog

Last edited by Rogviler; 05-16-2014 at 02:57 AM.
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  #13  
Old 05-16-2014, 03:35 AM
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Metal shrinks when it is cold and expands when it is hot.....if you have issues with blow by....it is very possible that the rings have shrunk because of the cold, thus causing the rough idle when cold as soon as the engine is warn, it runs fine because the metal has expanded to take up the worn spaces..
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  #14  
Old 05-16-2014, 10:11 PM
WillW
 
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Funny,
I've been having a similar problem all winter. I thought it was a "cold" issue, but now that it has warmed up it's still doing it. The longer the car sits the worse it gets.

So tonight I checked the priming pump and found that when I pushed it diesel squirted out around the push cap. Well I pumped it about 20-30 times and then tried to start after a single GP cycle and it started. It hadn't ran in about 4 days so maybe air in the system is the problem.

More work for tomorrow :-)
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  #15  
Old 05-17-2014, 10:43 AM
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Quote:
Originally Posted by Rogviler View Post
Yeah, but if his is anything like mine then it's not really a "rough idle" we're talking about, it's a narrow window before the engine warms up where it goes bonkers and then after that it's fine. It's frustrating because the searches I've run almost all point to an engine shaking/vibration problem that happens ALL the time at idle, which I get is usually mounts and all that. My engine doesn't shake, though the whole car does when it's galloping and spitting smoke on a cold start. Nor are there any problems with power or acceleration, such as I've read you get with fuel starvation or linkage slop.

Hopefully that makes it clearer.

Also, mine started with the 3-5 seconds of this that the OP is having, but is now up to 10-20, depending on how cold it is outside and how long it's been since I drove it. And it will even do a small amount of this after I go into the grocery store for half an hour (probably the 3-5 seconds it started with originally). I'm afraid he may be in for the same fate if the mystery isn't solved. This is over about a 3-year time period for me. So it seems as if something is wearing out. I don't know, anyone ever had a glow plug relay cause this? That's about all I can think of, since it seems so tied to the warmth of the engine. But I could also see it being related to such a tiny leak somewhere that it only manifests itself when enough fuel has leaked out or air leaked in, and only seems like it's correlated with the engine warming up. That sounds exhausting to figure out.

-Rog
Rog......that is EXACTLY the perfect description of what mine is doing. I'm thinking either a glow plug issue since mine only does it on a cold start (though I do not know how) since I checked my system completely. Or air getting in the system as the car sits overnight, but that also puzzles me because if air was getting into the system it would have power/stuttering issues on the open road and mine runs like a scared cat on the open road. Also about 10 -15 seconds after a cold start the idle smooths right out......I'm scratching my head on this one.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)
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