124 tach wire routing/path help... - PeachParts Mercedes-Benz Forum

locry · #1 04-01-2006, 06:48 AM

87 non turbo 300D

my tachometer currently isn't working...
i was wondering how the tach gets its signal.
I found the rpm sensor near the flywheel, traced the wire which goes to one big relay, KILMA i think, then goes thru the right side of the firewall where the battery is...

IF i were to completely bypass the wiring from the sensor directly to the tach on the cluster, what needs to be done? can i wire the rpm sensor directly to the cluster? I've read about tach amps with regards to 123 bodies, i think the 124 don't have this anymore, does this mean that i can wire it directly?

knowing the actual path of the current from the sensor to the actual tachometer would help a lot... thanks guys!

dieseldiehard · #2 04-01-2006, 03:05 PM

Welcome to the world of EDS (Electronic Diesel System - not to be confused with the company started by Ross Perot

)

the sensor (L3) that generates the tach pulses is located at the flywheel, unlike the earlier 617 engines which used a magnetic pick up at the crank damper on the front of those engines.
The 124 diesels use the ring gear (where the starter motor engages during starting) to send 144 individual pulses per revolution to the EDS module.
The interconnecting cable goes to the sensor located at the rear of the oil pan, left side. I believe it is near the ground wire that connects the engine to the frame. Look for a damaged or loose sensor.
The EDS module's primary function is to hold the idle speed at the set point value. I am pretty certain it also feeds the tach gauge eventually.

Perform a check using the EDS idle speed adjust switch. If you remove the trim plug the engine should idle down to about 570 RPM. It should be set to 630 RPM +/- 20 RPM with the trim plug. If that is working then the sensor is ok and the next route that you would trace is the AC compressor unit (N6) unfortunately that's where my experience stops

Note that I speak from experience with 603 turbos, so I hope your engine is similar. Things may be different. A FSM is helpful if you are going to work on your car because it will also include a wiring diagram. The 124 is entirely different from earlier diesels and you can't wire directly from the gauge to the sensor.

I've never seen a NA '87 diesel. Is it a grey market car? Automatic or stick (just curious, a 5-speed behind a NA 6 cyl diesel would be sweet!)

locry · #3 04-02-2006, 12:24 AM

its a euro spec 124, most of the benzs here in the Philippines are euro spec, the US version cars are the grey market ones.

it has an auto tranny, which is the rarer one here, as most of the 300Ds i know come with manual trannies.

anyway, i believe the idle circuit you speak of has been disconnected, as far as i know... got the car this way

Am i correct in assuming that the ELR black box is responsible for "translating" the pulses from the flywheel sensor to the tachometer? And that direct wiring would be pretty much futile?

locry · #4 04-02-2006, 01:16 AM

SOLVED!!!

I finally found a way to bypass all the electronics thingabobs to get the tach working DIRECTLY from the RPM sensor at the flywheel to the TACHOMETER.

Locate the connector from the RPM sensor, it should have to wires, WHITE and BROWN...

Next, locate and remove the ELR DIEZEL 6CYL box, same size as the KLIMA... use the #3 and #5 female connectors(holes), it should be the GREENw/WHITEstripe and the BLACKw/REDstripe wires. i inserted the 2 pin male connector from the RPM sensor to the those two holes, should line up ok, just bend the 3rd safety plastic prong of the 2 pin connector. I oriented the connector so that the WHITE wire from the 2 PIN connector alligns with the BLACKw/REDstripe of the ELR connector. Voila! working tach!

I know this effectively disables the compressor safety feature but mine doesn't work anyway... as is the ELR, disconnecting both the KLIMA and the ELR didn't change anything... it seems the PO bypassed the idle circuit and the A/C circuits making the car a MECHANICAL non computer controlled diesel, its a NON-TURBO anyway...

IT may be safer and easier to just replace the KLIMA and the ELR, it's just not an option for me at the moment... funds and availability issues.

Oldbeaver · #5 07-30-2007, 09:47 PM

Hello. It looks like you found what I am looking for: where are the wires that goes to the tachometer in the instrumetns panel? I am looking them below the engine hood but couldn´t find them so far.

My car is a MB 300E of 1989, a W124 chassis.

There are two wires coming out from the tachometer at the instruments cluster, one is red/black and the other is green/yellow. They go together into a plastic tube isolation to the firewall, but I cannot find them at the other side of it.

Can you give me an idea of how they look like, where they are, etc?

I need to find them.

Thank you in advance.

Quote:

Originally Posted by locry

SOLVED!!!

I finally found a way to bypass all the electronics thingabobs to get the tach working DIRECTLY from the RPM sensor at the flywheel to the TACHOMETER.

Locate the connector from the RPM sensor, it should have to wires, WHITE and BROWN...

Next, locate and remove the ELR DIEZEL 6CYL box, same size as the KLIMA... use the #3 and #5 female connectors(holes), it should be the GREENw/WHITEstripe and the BLACKw/REDstripe wires. i inserted the 2 pin male connector from the RPM sensor to the those two holes, should line up ok, just bend the 3rd safety plastic prong of the 2 pin connector. I oriented the connector so that the WHITE wire from the 2 PIN connector alligns with the BLACKw/REDstripe of the ELR connector. Voila! working tach!

I know this effectively disables the compressor safety feature but mine doesn't work anyway... as is the ELR, disconnecting both the KLIMA and the ELR didn't change anything... it seems the PO bypassed the idle circuit and the A/C circuits making the car a MECHANICAL non computer controlled diesel, its a NON-TURBO anyway...

IT may be safer and easier to just replace the KLIMA and the ELR, it's just not an option for me at the moment... funds and availability issues.

Oldbeaver · #6 08-03-2007, 06:45 PM

Can you help me a little finding the complete path of the tach signal until the instruments cluster?

A pair of cables (signal) go out from the tach through the firewall but I cannot see where they land in the engine compartment.

Do you know? Have a picture?

Your help would be nice.

Quote:

Originally Posted by dieseldiehard

Welcome to the world of EDS (Electronic Diesel System - not to be confused with the company started by Ross Perot

)

the sensor (L3) that generates the tach pulses is located at the flywheel, unlike the earlier 617 engines which used a magnetic pick up at the crank damper on the front of those engines.
The 124 diesels use the ring gear (where the starter motor engages during starting) to send 144 individual pulses per revolution to the EDS module.
The interconnecting cable goes to the sensor located at the rear of the oil pan, left side. I believe it is near the ground wire that connects the engine to the frame. Look for a damaged or loose sensor.
The EDS module's primary function is to hold the idle speed at the set point value. I am pretty certain it also feeds the tach gauge eventually.

Perform a check using the EDS idle speed adjust switch. If you remove the trim plug the engine should idle down to about 570 RPM. It should be set to 630 RPM +/- 20 RPM with the trim plug. If that is working then the sensor is ok and the next route that you would trace is the AC compressor unit (N6) unfortunately that's where my experience stops

Note that I speak from experience with 603 turbos, so I hope your engine is similar. Things may be different. A FSM is helpful if you are going to work on your car because it will also include a wiring diagram. The 124 is entirely different from earlier diesels and you can't wire directly from the gauge to the sensor.

I've never seen a NA '87 diesel. Is it a grey market car? Automatic or stick (just curious, a 5-speed behind a NA 6 cyl diesel would be sweet!)

joro · #7 09-03-2007, 02:49 AM

Where is the sending unit located on a 603.

locry · #8 09-03-2007, 06:01 AM

at the bellhousing, its that black plastic thing with the wire snaking-up. i can access it at the driver's side(left). behind the front wheel. i can squeeze under the car just enough to unscrew it. but that's me.

88300D · #9 11-17-2007, 02:46 AM

Hi I have a 87-88 300D W124 with the 603 donk the tac is intermitaant and it takes the AC out.

I have tested the tac sender as another contributer kindly told me to. its ok

Read your thread and thought great way to test the instrument.
if the sender and instrument are sweet it should be the relay or another sender to it.

My relay ERL PN 004 545 3632. has blanked pin 5 and now wires of the same coluor but my D-Klima PN 001545 80 50 does.

Any one know what i've got wrong or is it just because we drive different rides?

Any one know the if then equation and pin outs for my ride?

thanks for your time and contibutions