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  #1  
Old 01-23-2022, 04:51 PM
JHZR2's Avatar
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OM603.971 EDS Codes and Diagnosis

I pulled codes on my 93 300SD, from the 38 pin diagnostic plug.

I got the following:
Pin 4: EDS
8 - Engine coolant temperature sensor (B11/4)
9 - Intake air temperature sensor (B2/1a)
2 - Fuel rack position sensor (L7)
3 - Air flow sensor signal (B2/1)
7 - Starter ring gear speed sensor (L3)
5 - Exhaust gas recirculation valve vacuum transducer (Y31/1) or fault in exhaust gas recirculation (EGR) control circuit

Kind of surprised that I got so many codes. All I know is that I idle around 550rpm, and the cluster temperature, tachometer, and speedometer all work.

Pulling other codes, I found that the HVAC codes indicated, amongst others:
43 - Engine Coolant Temperature Sensor (B10/8)

I would assume that B11/4 and B10/8 imply two different sensors, as we know there are two.

My primary interest is, what of these are required to be fixed in order to get idling properly? I havenít tested boost levels, but the car drives very well, cruises at speed effortlessly, and now starts well (replaced GPs and cleaned the intake soot out).

I primarily bought this car because it has a factory refurbished engine and AT; and I want those. The car runs great and all systems are functional. But idle isnít high enough, and the governor overshoots to a low RPM before bouncing back to 550. When stone cold it does crank and idle at a bit higher, but as soon as itís slightly warm, and everything warmer itís always 550ish.

So, recommendations on where to start?

Thanks!

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #2  
Old 01-24-2022, 12:10 PM
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Code 7 is why you have a low idle most likely. Does the tach in the cluster work?

Now that you've pulled codes, you should clear them and see which ones come back. Some of those might be old.

The governor in the IP really should never control the idle speed, it should be the EDS.

-J
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1991 350SDL. 230,000 miles (new motor @ 150,000).

Tesla Model 3. 136,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.
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  #3  
Old 01-25-2022, 11:52 AM
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Quote:
Originally Posted by compu_85 View Post
Code 7 is why you have a low idle most likely. Does the tach in the cluster work?

Now that you've pulled codes, you should clear them and see which ones come back. Some of those might be old.

The governor in the IP really should never control the idle speed, it should be the EDS.

-J
The tach, speedometer, and MPG gauge all work fine. Thus why code 7 was suspect to me...

I suspect that the signal may make it to tach but not to someplace else (???). Im having an issue like that with the alternator light.

I do need to clear all codes and try again...

Thanks for the hint on #7. Need to find where the wiring harness goes...
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #4  
Old 01-25-2022, 01:35 PM
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Cruisin on Electric Ave.
 
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Posts: 5,210
On the W126 the Tach gets its signal from the EDS computer. So if the tach works, the pickup is good and the computer should be controlling idle speed.
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  #5  
Old 01-25-2022, 01:41 PM
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Posts: 364
Mine overshoots the governor then bounces back to 550 rpm as well. Following…
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1983 300D Midnight Blue
4 speed, W115 intake mani, non-EGR exhaust mani, KKK K26, 3 pc Euro bumpers, Lo-spec Euro headlights, AL129X, hubcaps, custom A/C

1987 300TD Smoke Silver
Euro headlights, thermostat relocation, coolant bypass mod, rebuilt Becker + Jehnert + Helix audio, OEM Oris roof boxes and surfboard racks, Euro towbar

1983 300TD Reed (Moss) Green / Dark Olive MB Tex Euro spec

1983 300TD Silver Blue / Blue cloth Euro spec, OM648 and 722.6, 15" hubcaps, W126 S2 brakes
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  #6  
Old 01-25-2022, 02:27 PM
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Quote:
Originally Posted by compu_85 View Post
On the W126 the Tach gets its signal from the EDS computer. So if the tach works, the pickup is good and the computer should be controlling idle speed.
I’m doing this on my 93, w140. Think it’s different?

Other thing is no guarantee the wife from the tach (or engine harness) to the computer is good. Need to figure out that diagram.
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #7  
Old 01-25-2022, 02:43 PM
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Location: Calgary Alberta Canada
Posts: 1,777
Dieseal300 had a thread where he replaced the caps in the ECU to get his idle operating correctly.
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92 e300d2.5t
01 e320
05 cdi
85 chev c10
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  #8  
Old 01-25-2022, 03:17 PM
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Quote:
Originally Posted by dieselbenz1 View Post
Dieseal300 had a thread where he replaced the caps in the ECU to get his idle operating correctly.
Yes Im aware. But I dont think blindly recapping the board is the right first step. Diagnosis of the causes and issues is prudent. Thats what Id like to be able to do....
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #9  
Old 01-25-2022, 05:03 PM
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Cruisin on Electric Ave.
 
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Location: Springfield VA
Posts: 5,210
I tried to look up W140 wiring diagrams, but could't find one in an easily readable format. I'll be able to look more later.
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  #10  
Old 01-25-2022, 05:12 PM
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Quote:
Originally Posted by JHZR2 View Post
Yes Im aware. But I dont think blindly recapping the board is the right first step. Diagnosis of the causes and issues is prudent. Thats what Id like to be able to do....
Why not test it before blindly changing the caps?
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92 e300d2.5t
01 e320
05 cdi
85 chev c10
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  #11  
Old 01-26-2022, 11:57 AM
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Quote:
Originally Posted by dieselbenz1 View Post
Why not test it before blindly changing the caps?
That's what Im trying to do!

Thus why I pulled codes from the w140 38 pin connector and posted above.

I would assume that those codes help with the test. If there's another basis of testing that you recommend, I'm all ears!
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #12  
Old 01-31-2022, 12:06 PM
compu_85's Avatar
Cruisin on Electric Ave.
 
Join Date: May 2008
Location: Springfield VA
Posts: 5,210
Now that you know what the codes are, clear them and see if they come back. Then you'll know what the computer is currently upset about.
__________________
1991 350SDL. 230,000 miles (new motor @ 150,000).

Tesla Model 3. 136,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.
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  #13  
Old 02-01-2022, 12:35 AM
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Quote:
Originally Posted by compu_85 View Post
Now that you know what the codes are, clear them and see if they come back. Then you'll know what the computer is currently upset about.
Thatís the plan once the snow clears a bitÖ
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #14  
Old 02-02-2022, 08:23 PM
JHZR2's Avatar
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Join Date: Jan 2002
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Quote:
Originally Posted by compu_85 View Post
Now that you know what the codes are, clear them and see if they come back. Then you'll know what the computer is currently upset about.
I started to diagnose.

My codes were:
Pin 4: EDS
8 - Engine coolant temperature sensor (B11/4)
9 - Intake air temperature sensor (B2/1a)
2 - Fuel rack position sensor (L7)
3 - Air flow sensor signal (B2/1)
7 - Starter ring gear speed sensor (L3)
5 - Exhaust gas recirculation valve vacuum transducer (Y31/1) or fault in exhaust gas recirculation (EGR) control circuit

I figure code 7 and 8 are critical. 7 supports the RPM control loop, and 8 may make some decisions.

I went through the FSM, somewhat out of order. The pin out on the connector seems to be straight across with #1-10 being the group all in a row, and then it just keeps going and continues below.



I first checked the main fuses which are all fine.



Then I checked the EDS to the IP wiring which was fine. 3.5 ohms.



Then I check code 8, and it checks out fine.







So code 8 seems like a fluke.

Then I try to diagnose code 7, and I cannot get conductivity between the pins for the speed sensor L3. The pins the FSM say to check don’t give any resistance in the range for the Bosch or Beru sensor.

But here’s the thing… the tachometer works perfectly. And it seems like the tachometer gets its signal from the N39 connector which is the EDS.

How can my tachometer work, and the EDS not have a speed signal?

Harnesses all look perfect.



After cleaning and checking everything, I still get:

Pin 4: EDS
9 - Intake air temperature sensor (B2/1a)
3 - Air flow sensor signal (B2/1)
7 - Starter ring gear speed sensor (L3)

How does my tach work, yet I can’t measure the right resistance on the pins to diagnose code 7?

Any ideas?
__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Last edited by JHZR2; 02-02-2022 at 08:52 PM.
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  #15  
Old 02-02-2022, 09:31 PM
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Location: Calgary Alberta Canada
Posts: 1,777
How does my tach work, yet I canít measure the right resistance on the pins to diagnose code 7?

Operator error measuring signal?
You should get 150 to 300 ohms but it's a shielded signal measure ohms between the pin and ground.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10
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