w123 tach - what is under that cap?
szcz
reads 1000 RPM no matter what the engine speed. It will vary sometimes,
especially if I let off the accelerator.
I found the unit on the fender that has the amplifier. But, I don't
think my car has the circuit board people have spoken of. I unscrew the
cap and the part that is still attached to the fender has a number of
female electrical contacts. Under the cap is nothing at all. Where is
this amplifier unit? Could my tach work at all without it? I am
confused...
Thanks
Richard Sexton
Yours is missing apparanly.
--
Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net
633CSi 250SE/C 300SD | http://aquaria.net http://killi.net
T.G. Lambach
online by M-B parts vendors.
Then you'll KNOW the engine rpms - idles at 700 maximum 4,500 and
transmission shifts in between.
Karl
rear adapter plate and the rpm is read off the flywheel.
"T.G. Lambach" <tlam...@NoSpamcomcastOrHam.net> wrote in message
news:lOKdnaqO8uJqHY3Y...@comcast.com...
T.G. Lambach
the cap!
Karl knows, always.
szcz
so, I'm looking in the wrong place?
szcz
szcz wrote:
> Sorry... it is a 1984
>
> so, I'm looking in the wrong place?
oh, yeah, by the way - there is a small (thing?) mounted on the front
of the engine with a sensor that is adjacent - I am pretty sure this is
the tach sensor. that has a wire that goes to the cap like thing and
then into the firewall. Is that consistent for an '84?
Karl
the fire wall. Middle, near the alarm switch.
You will see a 2 wire black flat plastic connector. That is it. The 2 wires to the right go to the
sensor. The 2 wires to the right go the large EGR control unit behind the right front kick panel.
Have you had to jump a dead battery lately?
Remove the lower dash cover below the glove box. Remove the right kick panel. Next to the large
black ECU is a silver relay with a red lid on it. Lift up the lid and pull out the 10 amp fuse. Is
it blown? If yes, replace it. The tach should work now.
"szcz" <michael_s...@yahoo.com> wrote in message
news:1158722782.3...@e3g2000cwe.googlegroups.com...
Karl
the fire wall. Middle, near the alarm switch.
You will see a 2 wire black flat plastic connector. That is it. The 2 wires to the right go to the
tra...@optonline.net
>I found the unit on the fender that has the amplifier. But, I don't
>think my car has the circuit board people have spoken of. I unscrew the
>cap and the part that is still attached to the fender has a number of
>female electrical contacts. Under the cap is nothing at all. Where is
>this amplifier unit? Could my tach work at all without it? I am
>confused...
Not sure which model you have, but on many the amplifier/electronics is
contained and sealed in the screw on top of that diagnostic connector.
The electronics only consists of a few components and it's just sealed
up is some sort of plastic or epoxy in the test cap, with nothing
visible That was exactly what was wrong when my tach went whacko on
my 116 300SD. I replaced it with one from the stealership and voila,
tach fixed.
PS: I think you guys talking about this made it go again. Three days
ago, it started acting erratically again, just like last time. The
original lasted over 20 years, the new one maybe 5, so I guess the
Germans still can't make electronics. Which reminds me of an old
episode of All in the Family, where Archie was arguing with the
meathead. He told him the only mistake Nixon made with Watergate was
using Germans for anything to do with bugging and electronics, because
everyone knows the Japanese are much better
Robert S. Carroll
> Wrong place. The sensor is down on the drivers side of the rear of the engine. Look up at the top of
> the fire wall. Middle, near the alarm switch.
> You will see a 2 wire black flat plastic connector. That is it. The 2 wires to the right go to the
> sensor. The 2 wires to the leftt go the large EGR control unit behind the right front kick panel.
>
> Have you had to jump a dead battery lately?
>
> Remove the lower dash cover below the glove box. Remove the right kick panel. Next to the large
> black ECU is a silver relay with a red lid on it. Lift up the lid and pull out the 10 amp fuse. Is
> it blown? If yes, replace it. The tach should work now.
>
>
I also have a non-working tach. I have an '85 300d and I have checked
the fuse in the relay per your instructions (an "American" 10 amp fuse
by the way) and it is fine. I checked it with an ohm meter just to be sure.
I've also removed the pickup in the bellhousing (again, driver's side,
rear of engine behind the oil filter) and cleaned it.
Still no tach. Is there anything else I can check?
Thanks in advance for any thoughts!
RSC
Karl
Disconnect it. Get a multi-meter and set it on AC volts. Connect it to the plug end that has the
wires going towards the drivers side. Start the engine. The sensor is a AC generator. Read the
voltage at idle. It should be around 4V AC. Increasing engine speed should increase volts.
Zero volts?
Either a bad rpm sensor or a bad flywheel.
A flywheel from MB is 'order from Germany' and over $400!!!
And yes, they do go bad. I just replaced one 2 weeks ago for this exact problem.
"Robert S. Carroll" <rcarr...@insightbb.com> wrote in message
news:WIWdnevB_ON6PYzY...@insightbb.com...
Robert S. Carroll
> Go to the 2 pin plug on the middle of the firewall, above the valve cover.
> Disconnect it. Get a multi-meter and set it on AC volts. Connect it to the plug end that has the
> wires going towards the drivers side. Start the engine. The sensor is a AC generator. Read the
> voltage at idle. It should be around 4V AC. Increasing engine speed should increase volts.
> Zero volts?
> Either a bad rpm sensor or a bad flywheel.
> A flywheel from MB is 'order from Germany' and over $400!!!
> And yes, they do go bad. I just replaced one 2 weeks ago for this exact problem.
>
>
> "Robert S. Carroll" <rcarr...@insightbb.com> wrote in message
> news:WIWdnevB_ON6PYzY...@insightbb.com...
>
I'll check it as soon as I get home.
Thanks!
Robert S. Carroll
> Go to the 2 pin plug on the middle of the firewall, above the valve cover.
> Disconnect it. Get a multi-meter and set it on AC volts. Connect it to the plug end that has the
> wires going towards the drivers side. Start the engine. The sensor is a AC generator. Read the
> voltage at idle. It should be around 4V AC. Increasing engine speed should increase volts.
> Zero volts?
> Either a bad rpm sensor or a bad flywheel.
> A flywheel from MB is 'order from Germany' and over $400!!!
> And yes, they do go bad. I just replaced one 2 weeks ago for this exact problem.
>
>
> "Robert S. Carroll" <rcarr...@insightbb.com> wrote in message
> news:WIWdnevB_ON6PYzY...@insightbb.com...
>
I disconnected the plug and hooked my multi-meter up to the two
connections on the plug going to the driver's side. I set the
multi-meter to AC volts and started the car. At idle, the meter reads
about 4.5 volts. As I give the engine throttle with the linkage the
voltage increases at a pretty constant rate. I did not rev the engine
too high, but the voltage increased to 10-11 volts. It would appear that
it is working.
Again, I checked the fuse in the relay behind the kick panel on the
passenger's side and it is OK also.
Thoughts or ideas?
Thanks for the help. I've been tinkering with this for quite a while and
picking up ideas where I can and so far your help has been the most
accurate and valuable!
RSC
Roger Shoaf
"Karl" <auf...@prodigy.net> wrote in message
news:32nQg.6850$Ij....@newssvr14.news.prodigy.com...
> Zero volts?
> Either a bad rpm sensor or a bad flywheel.
> A flywheel from MB is 'order from Germany' and over $400!!!
> And yes, they do go bad. I just replaced one 2 weeks ago for this exact
problem.
Shucks before I would spend $400 for a flywheel I would replace the magnet
stuck it the flywheel. Sounds like that would be a quickie job for a
machine shop.
--
Roger Shoaf
About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.