If this fits my 300SD 1981, I would like to have one. How do I pay?


tyl604@aol.com
Adrain Taylor

I think I will buy one too. How do we pay?

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Here are some answers to some questions that have come up several times:

1) This is not a kit of parts. Most people will not be able to handle the soldering of the small SMT parts. For this reason it comes assembled and tested, with user instructions.

2) Paypal is preferred. Alternate arrangements can be made, just PM if needed. My paypal ID is rlm_0513@earthlink.net (that's with an underscore between 'm' and '0')

Thanks,

__________________
Bob
'82 300D Petrol B-G Metallic

For those wondering about the 84 and 85 models and the tach amp, my 300 CDT (production date 01/84 - must've been one of the first one off the line that year) there is NO tach amp under the cover on the assembly mounted inside the DS fender. If you remove the cover and look at the sockets, the #3 socket (they are numbered) doesn't have the metal female pin in it.

On this style the tach gets its signal from a different sensor mounted at the BACK of the engine in the bellhousing of the transmission - just behind and below the bottom of the oil filter assembly. The sensor is held in place by an allen-head screw and it takes a 5mm allen key to remove it.

My sensor is bad and needs to be replaced. You can test it by unplugging the 2-wire cable connector at the center of the hood opening just in front of the cowl. If you follow the wire from the sensor up to the connector it is easy to find.

With the car off, connect an Ohm meter to the two make pins of the cable connector. It should measure 1.9k Ohms +/- .2k ohms (that is 1900 Ohms +/- 200 ohms). If that measures OK, then start the car and use a volt meter to measure the voltage across those same tow pins. At normal idle speed of 750-800 RPMs it shoud measure ~4V +/- .1V.

If EITHER of these measurements is outside these value ranges, it needs to be replaced. Mine measured 2024 ohms (in spec) but only a few millivolts at idle.

A lot of folks are experiencing frustration when debugging their tach systems because of the "lack of feedback" that the system is able to give. Is it the amp or the sensor? Is it the sensor or the gauge?

I've taken one of the tach amps, and made it into a diagnostic tool by adding an LED and modifying the software a little bit (see photo).

To use the tool, plug it it into the tach amp socket. Turn the key to the glow position. The led will flash for 20 seconds. If your gauge works, it will indicate a constant 1200 RPM during this 20 second period. Once the LED stops flashing, start the car. If the amp is getting pulses from the sensor, it will flash, once per pulse. The speed of the flash will go up and down with engine speed.

So-

No flashes at glow = no power to amp
No flashes at idle = possible bad sensor / bad cable
Flashes at idle, but stops flashing at higher RPM = weak sensor input or sensor too far from pin
Flashes at glow and idle, but no needle movement at gauge = bad gauge or wiring

Tool is available for loan.

Attached Thumbnails

 

__________________
Bob
'82 300D Petrol B-G Metallic

I'll take one... can I mail you a check?

__________________
1992 300D 2.5T 249k - Parked with a bad transmission
1981 300SD 142k - Daily driver

The above is from this thread...the next quote is from this thread (post 22)

I measured mine and I get a reading (I think around 80 ohms) between 7 and 9, which should be correct, and which does your new amp use? Because I think I want one!

__________________
1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

You need to first be sure that your car is equipped with a tach amp at all. There was a switch sometime in 1984/1985 to a different scheme that deleted the tach amp and used the EGR computer instead. This may not have been true for your car, as I don't have any experience with euros.

PM me your email address, and I'll forward installation instructions with photos. It talks about how to tell if you have an amp or not.

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Bob
'82 300D Petrol B-G Metallic

I didn't have a tach amp originally, I didn't have a tachometer originally. I do have the little receptacle for the amp. I got a tach from another diesel and installed it. I got an amp, ran a wire from pin 3 to the tach and gave the tach +12v. I've got +12v at pin 6 and GND at pin 2 (they were already in the receptacle) and the three crank sensor pins, 7, 8, & 9. But I don't know if the crank sensor pins are the same for the cars with and without tach amps...I would assume that the pinout of the receptacle would be the same, but that;s me assuming As far as I can tell, the tach should be working...I don't know if its a bad gauge or bad amp or if the pins for the crank sensor aren't giving the amp the input that it requires...does the amp output AC mA? I've tried to measure with the car running, but never had a good ground other than the cigarette lighter, so the numbers were bouncy. I guess I should check the amp more thoroughly before deciding its defective...but I have no way to test the gauge.

__________________
1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now

You need to borrow the diagnostic tool.

The amp outputs a pulse train. One 3ms, 5V pulse per engine revolution. To properly see it, you need an oscilloscope. A DVM will only give you a coarse indication that SOME signal is present - not necessarily the proper signal.

The diagnostic tool sends a signal to the gauge (even before you start the engine) so you can see if the gauge and wiring are working.

Try to eliminate potential problem areas one at a time.....

__________________
Bob
'82 300D Petrol B-G Metallic

I don't have the right kind of tach setup to benefit from this, but I am very impressed with your finished project.
I hope you will tackle the early style cruise amp next......

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Here is my latest bizzare issue....I replaced the tach sensor pickup (boy was that fun , and yes, the old one was destroyed, frayed wire! ) and now I get a needle that "slightly" lifts off the peg at idle, and rises to maybe 1500rpm when the engine is at like 3000+....it moves smoothly, its just reading like 50% lower than it should be.... The tach amp is good, I tried two different working ones that work fine on our 300D....with the same "weak needle" result on mine.

So I have gone from dead tach to smooth but inaccurate tach. Why o why is it so hard to fix these!?

Any ideas why its reading low like that? I just don't get it. Maybe I will need to borrow that diagnostic tool also....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Could the pickup have too much gap with the pin that it reads.......

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Thats what I am currently looking into, it does look like it could be closer....I am going to try and get it as close to the pin as possible.

(I am out in the garage typing this.... ) Now thats live-forum-ing!


On a cool note, I figured out that the 1 and 1/4" deep socket (27mm) works on my crank pulley bolt to rotate the engine! How awesome! I can't believe I've had it that long and never realized it was the right size for the crank pulley! Its because I usually only think in/use metric....never occurred to me that it was roughly 27mm....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Can you put me in line for borrowing the diagnostic tool?
For some reason, I thought the amp output was in amps, and increased as the engine speed increased...could just be something I made up.

Is it a 6 point? 1 1/4" is just shy of 32mm...careful, don't want to round THAT bolt.

__________________
1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now