TACHOMETER - PeachParts Mercedes-Benz Forum

DAVECAD2.0 · #1 05-13-2013, 03:03 PM

The tach on my '91 420SEL stopped working. Checked for loose connections on the gauge. What sensor/sendor does this work on and where is it located. I guessing that's the problem.
Thanks, Dave

DAVECAD2.0 · #2 05-15-2013, 10:08 AM

Blank stares. Slacked jaws. I'm hearing crickets people.
Anybody?

Ndralle · #3 05-15-2013, 07:31 PM

if its like the diesels there should be a little "trash can" looking plug on the wheel well that commonly comes loose.

check this url. www (dot) benz world (dot) org/forums/w123-e-ce-d-cd-td/1597328-w123-300td-tachometer-problem.html

i chopped up the url a little. im not sure if im supposed to post links to other sites.

pmckechnie · #4 05-15-2013, 07:59 PM

On my 84 500SEL the tach signal comes from the ignition module at the left front of the engine compartment. It is called the TD signal. If the fuel pump relay doesn't see this signal, the car wont run.
I don't know but I believe the Generation 2 gas cars are the same. Also, on the Gen 2 gas cars, the A/C won't work if it doesn't see the TD signal.
Sorry I can't be more specific.

Paul

JamesDean · #5 05-16-2013, 11:33 AM

The tach signal on the later cars (I believe) is sourced from the EZL module. It is accessible at the X11 connector on the driver's fender.

Looks like its on pin 1, based on this information.
BOSCH KE3-JETRONIC MIXTURE ADJUSTMENT

If you have signal there then the problem is upstream. Could be failed capacitors in the tachometer.

Ndralle · #6 05-18-2013, 03:35 AM

It sounds like it is different from the diesels. Well, we got this thread movin'.

germanv8 · #7 05-20-2013, 11:49 AM

Quote:

Originally Posted by pmckechnie

On my 84 500SEL the tach signal comes from the ignition module at the left front of the engine compartment. It is called the TD signal. If the fuel pump relay doesn't see this signal, the car wont run.
I don't know but I believe the Generation 2 gas cars are the same. Also, on the Gen 2 gas cars, the A/C won't work if it doesn't see the TD signal.
Sorry I can't be more specific.

Paul

On my 85 500SE, I've been having trouble with the heat on all the time, then the AC stopped working, and after the shop switched out the AC regulator, the ACs working but the tach stopped working and the heat is still flowing all the time. Do you think the AC regulator swap and the tach now not working are related?

JamesDean · #8 05-20-2013, 11:51 AM

The tachometer signal does pass through the AC relay I believe. This is so that the AC relay can kick off the ac compressor at certain speeds.

DAVECAD2.0 · #9 05-20-2013, 04:14 PM

Quote:

Originally Posted by pmckechnie

On my 84 500SEL the tach signal comes from the ignition module at the left front of the engine compartment. It is called the TD signal. If the fuel pump relay doesn't see this signal, the car wont run.
I don't know but I believe the Generation 2 gas cars are the same. Also, on the Gen 2 gas cars, the A/C won't work if it doesn't see the TD signal.
Sorry I can't be more specific.

Paul

Thanks, but no fuel or A/C problems.