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  #1  
Old 11-10-2009, 09:23 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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Old 11-10-2009, 11:19 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
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1991 350SDL. 230,000 miles (new motor @ 150,000).

2013 Fiat 500E. 20,000 miles, 80 miles at a time.
2012 Passat TDI. 95,000 miles. More space, power, and fuel economy than the Benz
2004 Touareg V10 TDI. 150,000 miles. One of 450.
1999 Jetta TDI. 310,000 miles.
1992 Jetta ECOdiesel. 156,000 miles. 1 of 48. Sold.
1991 Jetta ECOdiesel. 430,000 miles. 1 of 700. Sold to VeeDubTDI, totaled in front of our house
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  #3  
Old 11-10-2009, 11:53 PM
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No it idles low. Not sure what the ELR on the I/P is.
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  #4  
Old 11-11-2009, 12:26 AM
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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.
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Old 11-11-2009, 08:07 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
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1991 350SDL. 230,000 miles (new motor @ 150,000).

2013 Fiat 500E. 20,000 miles, 80 miles at a time.
2012 Passat TDI. 95,000 miles. More space, power, and fuel economy than the Benz
2004 Touareg V10 TDI. 150,000 miles. One of 450.
1999 Jetta TDI. 310,000 miles.
1992 Jetta ECOdiesel. 156,000 miles. 1 of 48. Sold.
1991 Jetta ECOdiesel. 430,000 miles. 1 of 700. Sold to VeeDubTDI, totaled in front of our house
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  #6  
Old 11-11-2009, 09:24 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.
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  #7  
Old 11-11-2009, 10:46 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  
Old 11-11-2009, 12:03 PM
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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.
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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)
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  #9  
Old 11-11-2009, 01:54 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.
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  #10  
Old 11-11-2009, 03:23 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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