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  #1  
Old 02-07-2022, 12:16 PM
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Location: New Jersey
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W140 - Flasher affecting EDS idle control

Im having some issues, and Im looking for thoughts on how/where to start.

First, all fuses are OK.

Yesterday, the seat adjustments, steering wheel controls, and mirrors all worked fine. Then all of a sudden they didnt.

Today, I had to run the flasher. I noticed that when it flashes, the idle drops enough to see it on the tach.

I cant see how these things are affected.

The alternator is performing properly (had a D+ wire failure, it is now fixed, and it works perfect).

Having a hard time seeing how this is related and why the EDS would be affected... And also how to fix my seats and wheel...

Any suggestions?

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 02-07-2022, 01:42 PM
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Has the alternator output been checked with a meter while the car is running with a fully charged battery? Were the fuses checked using a meter?

If yes to the above I'd clean and tighten every ground I could locate before replacing anything.

Good luck and please report your findings.
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  #3  
Old 02-07-2022, 01:54 PM
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Location: Springfield VA
Posts: 5,211
Sounds like you need to start checking all your grounds!
__________________
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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  #4  
Old 02-08-2022, 05:20 PM
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Quote:
Originally Posted by compu_85 View Post
Sounds like you need to start checking all your grounds!
Whatís the theory on grounds doing this? Wouldnít it be more of a potential sporadic short that brings the control signal down?

Iím not very experienced with automotive electrical troubleshooting. I can handle a multimeter and look at voltage and conductivity, but Iím not sure I understand the theory associated with a loose ground causing this.

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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  #5  
Old 02-08-2022, 08:11 PM
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Posts: 2,161
Electricity follows the path that has the lowest resistance. When a ground becomes incapable of handling the amount of electricity/load being drawn it will take the next path of least resistance through a component that was neither designed or intended to carry the electrical demand. This can cause the component (s) that is the "new" ground to either react in very strange ways and/or be damaged.

As an example, cars that had clutch cables with bad engine grounds would start with odd electrical symptoms and eventually the clutch couldn't be disengaged. The clutch cable was the next path of least resistance but was capable of continually carrying the load/current so the inner cable would weld itself to the outer casing.

Good luck!!!
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  #6  
Old 02-08-2022, 09:53 PM
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Quote:
Originally Posted by Sugar Bear View Post
Electricity follows the path that has the lowest resistance. When a ground becomes incapable of handling the amount of electricity/load being drawn it will take the next path of least resistance through a component that was neither designed or intended to carry the electrical demand. This can cause the component (s) that is the "new" ground to either react in very strange ways and/or be damaged.

As an example, cars that had clutch cables with bad engine grounds would start with odd electrical symptoms and eventually the clutch couldn't be disengaged. The clutch cable was the next path of least resistance but was capable of continually carrying the load/current so the inner cable would weld itself to the outer casing.

Good luck!!!
Thanks for that. I fundamentally understand that electricity will take the path of least resistance. I guess my curiosity lies more with the fact that a flasher is pretty far distanced from EDS, which has its own dedicated harness From the computer block, and the actuator runs on a biased signal where one of the two pins to the idle control shows battery voltage and the other has some lower value that creates a delta that is the control signal as I understand it. I am just having a hard time conceptualizing how a bad ground on a flasher circuit which would be way far forward and wait for back could put a stray voltage back into the EDS. Obviously I see something so there is something going on. Itís just hard for me to grasp how it would go in that path when none of the connectors or feeds seem to be the same. Time to review wiring diagrams in more detail again. I did watch the voltage at the cigarette lighter and it did not fluctuate when this was happening. If it was enough current to really fluctuate things I would think that a fuse would also open. ?????
__________________
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 02-09-2022, 01:49 PM
compu_85's Avatar
Cruisin on Electric Ave.
 
Join Date: May 2008
Location: Springfield VA
Posts: 5,211
The issue with bad grounds is that nothing will make sense. The current will find a way - like if the EDS computer had a bad ground, perhaps it's sending some current through the tachometer now? Or if the instrument panel has a bad ground it would be sending some current back through the EDS? Go into the repair manual and find all the main ground locations and start taking them apart, and cleaning them, one by one. There are a few which will have many wires going to them, I'd hit those first.

I've not worked on a W140; I can't offer any tips on where they might be located
__________________
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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  #8  
Old 02-09-2022, 01:54 PM
JHZR2's Avatar
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Join Date: Jan 2002
Location: New Jersey
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Quote:
Originally Posted by compu_85 View Post
The issue with bad grounds is that nothing will make sense. The current will find a way - like if the EDS computer had a bad ground, perhaps it's sending some current through the tachometer now? Or if the instrument panel has a bad ground it would be sending some current back through the EDS? Go into the repair manual and find all the main ground locations and start taking them apart, and cleaning them, one by one. There are a few which will have many wires going to them, I'd hit those first.

I've not worked on a W140; I can't offer any tips on where they might be located
I will to the extent I can get to them. The w140 is a complex beast. Far more complex than the w123 and w126.

And they used biodegradable wiring in some of it which doesnít help things.

If I see no resistance between the body, battery negative, engine, alternator case, etc. and grounds, can I assume theyíre OK?
__________________
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 02-10-2022, 01:05 PM
compu_85's Avatar
Cruisin on Electric Ave.
 
Join Date: May 2008
Location: Springfield VA
Posts: 5,211
Don't measure resistance, measure voltage under load. Say between the alternator case and the ground wire you're testing. It should be 0 when there's load on the wire (or just a few 10s of millivolts). Bad grounds will have a voltage drop compared to a good ground.

-J
__________________
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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  #10  
Old 02-10-2022, 10:07 PM
JHZR2's Avatar
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Join Date: Jan 2002
Location: New Jersey
Posts: 4,857
Quote:
Originally Posted by compu_85 View Post
Don't measure resistance, measure voltage under load. Say between the alternator case and the ground wire you're testing. It should be 0 when there's load on the wire (or just a few 10s of millivolts). Bad grounds will have a voltage drop compared to a good ground.

-J
That makes sense. Alternator case or battery negative is the better reference?
__________________
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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  #11  
Old 02-11-2022, 11:07 AM
compu_85's Avatar
Cruisin on Electric Ave.
 
Join Date: May 2008
Location: Springfield VA
Posts: 5,211
Start by comparing them. Turn a bunch of stuff on and measure the voltage drop. There should be none. If there is, inspect the main ground cable

You can do the same test from the alternator positive terminal to the battery positive. In both cases with the engine running.

-J

__________________
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.
Reply With Quote
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