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#1
11-10-2009, 08:23 PM
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91 350sdl tach amp
Can anybody post me a pic of where my tach amp lives. It's not on the left fender well like earlier models.
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#2
11-10-2009, 10:19 PM
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There isn't one.
Does the engine idle at the correct RPM? If you unplug the electrical connector form the ELR on the injection pump does the speed change? -Jason
__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket  Tesla Model 3. 205,000 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
11-10-2009, 10:53 PM
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No it idles low. Not sure what the ELR on the I/P is.
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#4
11-10-2009, 11:26 PM
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Your model does not have a separate or modular tach amp as older models do - it is in the EDS - electronic diesel system.
The ELR is the trimmer for idle speed control - an assortment of metal film resistors in a 7 position adjustable control by the fuse box. Position four I think is the normal setting.
__________________
1986 300SDL 201K Daily Driver 1984 300D In Progress 1989 240GL 196K Swedish Brick 1984 300SD -- Sold 289K ------------------------------
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#5
11-11-2009, 07:07 AM
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350s don't have the little trimmer dial. The computer just does what it wants to. Is the actuator on the injection pump not called the ELR as well? It's the round looking thing on the back of the pump, facing the firewall, with a two pin connector on the top.
-Jason
__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket Tesla Model 3. 205,000 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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#6
11-11-2009, 08:24 AM
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To start with...is the ABS lamp stay on as well?
If yes, then most likely the over-voltage relay is at fault. If not? does the a/c compressor come on? If no then possibly the crank sensor is at fault.
__________________
MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator
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#7
11-11-2009, 09:46 AM
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Thanks for the update of info. No the abs light does not stay on. Yes the a/c comp operates correctly. I don't believe I have the round adjuster by the fuse box. I even swapped out the pickup that mounts above the flywheel.
Keep the suggestions coming. When the car warms up the idle will surge up and down; don't know if this is a result of anything related.
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#8
11-11-2009, 11:03 AM
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EDS control unit processes the a/c voltage signal from the flywheel sensor & sends DC voltage signal to tach & Klima relay.
EDS also controls the voltage signal to the idle solenoid on the injection pump. You would need to see if voltage signal was getting to the tach w/ volt meter. Should be the same voltage signal at the TD pin of the klima relay connector.
__________________
MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator
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#9
11-11-2009, 12:54 PM
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If the A/C is operating normally it is my understanding that there is a proper RPM signal from the flywheel sensor or the Kilma would drop out the compressor clutch.
__________________
 Gone to the dark side - Jeff
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#10
11-11-2009, 02:23 PM
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Yes the a/c clutch works correctly. Where is the klima relay? Would it be easier to check voltage there?
Since my idle surges up and down could that be an indication? Can I do a voltage check at the idle solenoid?
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