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w124 1993 220E - ADB1240226B970861
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27 Posts
Discussion Starter #1
Hi all,

I recently ran a diagnostic on the car using HFMSCAN and sent the logs through to HFM to analyse.

The only fault that was picked up by Mike at HFMSCAN was that the ECU was not registering when the car was being put in to drive.

Is there a switch in the selector unit that relays this info to the ECU as I cant seem to locate any info about this?

Thanks
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,061 Posts
These cars don't have a transmission ECU a.k.a GSM (Gear Selector Module). They are purely hydraulically/mechanically driven.
 

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w124 1993 220E - ADB1240226B970861
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27 Posts
Discussion Starter #3
Thanks

Is it correct then that the idle is meant to drop to 650 when put into drive?
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,061 Posts
Yes, with the engine at full operating temp and depending on outside air temp a idle speed of around 700rpm is perfectly normal
 

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w124 1993 220E - ADB1240226B970861
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27 Posts
Discussion Starter #5
OK because according to the ECU read out once at operating temp its constantly idles at 750 whether in park or drive.... I was advised to have this looked at as the air / fuel mixture appeared higher then it should be
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,061 Posts
You have a late model W124. The idle is fully under ECU control. There is no fuel mix adjustment possible.
 

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w124 1993 220E - ADB1240226B970861
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27 Posts
Discussion Starter #7
I assume the air flow meter would be the cause of the fuel mixture then?
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,061 Posts
Again, the fuel mixture is regulated by the ECU based primarly on inputs from the oxygen sensor, engine temp sensor, MAF sensor, etc.

Do be aware that the above are all wear and tear items and need to be replaced at some time. Example: the oxygen sensor has a useful lifespan of about 100K km. After that, its efficiency drops. Same thing with the MAF, although they usually last longer. If your car emits has a high HC (hydrocarbons) content then that usually points to MAF. And if the engine temp sensor is beyond its sell by date, then the ECU will command the injectors to spray extra with each cycle.

On the other hand, if your idle is not stable then you need to verify your car no longer has the dreaded eco junk wiring disease (i.e. engine wiring harnesses and throttle body).

And lastly, don't discount false air (intake leaks). Sometimes can be a simple as a loose clamp, or a worn gasket or the need for new rubber intake manifold couplings.
 
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