Need some Tach Tech help with gauge and MPG meter
 

Hi Guys,

Working on a 83 944 and the MPG gauge is not working. I have checked with a scope, both pulses are present at pin 1 from the DME fuel injection signal, black/yellow wire, and the speedometer hall sensor is working producing a good pulse at the HG terminal, so I know the signals are there, but the gauge isn't reading anything, pinned to the right.

I put the meter on the workbench and put in a pulse signal from a sig gen and still didn't get anything. I checked the gen signal by putting it into the tach input, pin 6, got the tach to read 1K to 6K RPM just fine.

So I need some help at the circuit board level of this tach/MPG o'meter thing. Anyone have schematics of the tach/MPG circuit, or been successful in board level repair of the tach/ECO meter?

Any help, would be greatly appreciated. Thanks!!

Cheers

I would be surprised if anyone has a schematic, but did you look for cold solder joints, this is known to be a common problem in the DME's.

Thanks for the reply. I have it apart, but haven't pulled the needles off yet or the face, not sure of the safest way to remove them. I was going to tackle that next, and yes, cold solder joints seem to abound in Porsche products. :rolleyes:

Guess I will just dive in and get the face off and reflow all the joints.

Appreciate the input.

Cheers

Well I managed to remove the needles and then the face and re-flowed all solder joints on the board and tried it again, still no go. Put it all back together and put it in the car and no go as well. Putting the dash all back together for now, may find a replacement one day but for now will get back to restoration of all the other things. :)

Thanks all.

Cheers