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  #1  
Old 07-04-2005, 10:53 AM
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OM 606 Question

Does anyone know if on the OM606, the engine computer enriches the diesel fuel mixture when the engine is cold, and then leans it out as it warms-up, in a similar manner that a gasoline engine does?

Would the idle speed also be different based on an either a cold, or warm engine. In other words would the idle speed be somewhat higher when the engine is cold?


Phil

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Old 07-04-2005, 11:20 AM
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Quote:
Originally Posted by pberku
Does anyone know if on the OM606, the engine computer enriches the diesel fuel mixture when the engine is cold, and then leans it out as it warms-up, in a similar manner that a gasoline engine does?

Would the idle speed also be different based on an either a cold, or warm engine. In other words would the idle speed be somewhat higher when the engine is cold?

A diesel engine is unlike a gasoline engine as the mixture is not controlled. The diesel typically gets much more air than it ever needs and the power and speed of the engine are controlled by the amount of fuel injected. The only time the fuel/air ratio becomes perfectly in balance (all fuel and all air consumed) is at maximum power conditions. Even in this case, most of our diesels are probably still a bit "lean".

I'm not sure of what the 606 does, but the computer on the 603 maintains a fixed idle speed independent of engine temperature and load variations (a/c compressor, alternator, etc.).
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  #3  
Old 07-04-2005, 11:35 AM
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With regard to cold start up...the injection timing is advanced about 5 degrees.

This is to compensate for the ignition lag time ..ie: burn start is slightly later in a cold engine.

.
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  #4  
Old 07-04-2005, 11:45 AM
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Hi Brian,

I was really hoping that the answer is that the engine does enrich the fuel mixture when cold. The reason being is that for the last year or so I noticed that my EGR system stopped working. Nor the EGR vacuum valve, nor the associated vacuum valve located in the cross over pipe near the EGR valve would open or close anymore. Simultaneously I also noticed that I took a major hit in fuel economy. I finally traced the problem to the EDS coolant sensor. That coolant sensor is really comprised of two independent thermistors. One connects to the EGR relay and the other to Relay N/8 which is part of the EDS system. I also discovered that the wiring to that sensor were completely corroded. The combination of the above made the computer THINK that the engine was always cold. Since the EGR does not activate below approximately 60C it never came on. I am not sure what was happening with the EDS system. In any case, I fixed the wiring and put in a new coolant sensor. ALl is OK now. I was just hoping that my fuel economy will now be back to normal. Its to early to tell however.

On a related matter the 4 pin round rubber plug that connects to said sensor is on its last leg. The internal wires at that plug are also corroded, but I can't get inside the plug to fix it properly. I managed to fix it but am not sure how long that repair is going to last. My Mercedes dealer said that this plug is not available separately as it forms part of engine wiring harness. Any ideas on where to get this plug.

Having gone to all the trouble of fixing my EGR system, I will now go ahead and plug the vacuum lines in order to disconnect it. I don't have a CEL, so I should be OK


Thanks

Phil
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Old 07-04-2005, 11:55 AM
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Phil,

It's possible, as mentioned by dkveuro, that the five degree timing advance was there all the time. When fully warm, this advance might have been too great and fuel economy suffered. I have no data, of course, but it could explain the drop in economy, and, hopefully, you are looking at a return to your previous numbers.

If so, please post again and confirm that 5 degrees of advance dropped the fuel economy enough to notice. It's valuable info.
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Old 07-04-2005, 12:01 PM
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Quote:
Originally Posted by pberku
Hi Brian,

Having gone to all the trouble of fixing my EGR system, I will now go ahead and plug the vacuum lines in order to disconnect it. I don't have a CEL, so I should be OK

Phil
I've been running with a golf tee in my egr vacuum hose for 40K miles. No problems so far.
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  #7  
Old 07-04-2005, 12:02 PM
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Thanks Brian, and dkveuro for both your replies. I kept meticulous records of my fuel milage, and should be able to accurately determine if indeed my fuel milage has now improved. I will wait until I go through two tankfuls and than post the results. Will than also disconnect the EGR monitor for two more tankfuls and post the results again

I am really hoping that dkveuro is right.

Thanks

Phil
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Old 07-04-2005, 12:11 PM
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Chuck,

Did you also plug the vacuum hose leading to the vacuum valve located just in front of the EGR valve on the crossover pipe, the one about a foot away from the air filter housing.

Both these vacuum pods work in unison. As the EGR opens the other vacuum pod closes, and vice versa. Hence both vacuum lines should be plugged, not just the EGR valve.

Phil
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Old 07-04-2005, 12:46 PM
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I only plugged one, the one connected to the top of the EGR, didn't know about the other hose.
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  #10  
Old 07-04-2005, 02:03 PM
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If you only blocked the EGR valve, without blocking the other vacuum valve than you end-up with a restricted air input to the engine. These two valves work in unison. when the EGR valve opens, to allow re-circulated exhaust gas in, the other valve closes to restrict an equal amount of clean air from entering the intake manifold. The total amount of intake air remains the same. If you only block the EGR vacuum, but not the other vacuum hose, than your total air intake will be restricted. That's why both vacuum hoses should be blocked, not just the EGR vaccum hose.

Phil
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Old 07-04-2005, 04:11 PM
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Be interested to see how you get on. I've read you loose a lot of power at high revs with the EGR mod- maybe I'll try disconnecting the vacuum lines when I'm in the city, then re-connect for motorway use!

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---------------------------------------------------
past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
----------------------------------------------
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  #12  
Old 07-04-2005, 05:10 PM
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You may indeed loose power if you only plug the EGR vacuum line and not the vacuum line next to it. [See my post #10 above]. Plugging only one line and not the other is equivalent to driving with a partially blocked air filter. This will make you loose power, especially at high speeds when more intake air is required by the engine.

Phil
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Last edited by pberku; 07-04-2005 at 05:19 PM.
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  #13  
Old 07-04-2005, 05:32 PM
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The IP on the 606 seems to be much more computer controlled then the 603. I bet if you pull the battery the car will shut down. Anyone want to try this? Place bets maybe?

As for the egr mod my friend is currantly working on that. In another week or two his egr may be broke, with a bit of luck.
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  #14  
Old 07-13-2005, 03:07 PM
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Plugged both vacuum lines and can't say I notice much difference.

One question, not sure if I'm talking boll*cks, but since the ball sockets + linkage that is attached to the first flap inside the air duct next to the air filter/egr is also connected to the accelerator cable/throttle linkage, does this mean that the engine could be starved of air when you put your foot down as the flap closes but the egr doesn't doesn't open with it?

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1993 320TE M104
---------------------------------------------------
past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
----------------------------------------------
"music and women I cannot but give way to, whatever my business" -Pepys
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