I think your gas tach must have been bad. If you try to plug a gas tach into a diesel 124 the needle will be buried above the red line at idle. BTDT

This is because the gas and diesel engines get their signal from completely different means.

Gas uses the ignition coil trigger from the distributor, so 3 pulses per revolution (assuming a 6 cyl).

Diesel uses the ring gear via a Hall sensor with 144 pulses per rev.

The ring gear signal goes to the EDS module which does rely on the OVP working. The car will run without the OVP, but you'll have poor idle control, and also the ABS won't work, as the ABS computer also uses this protected voltage source.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Where did you mention this was a gas conversion? How did a gas tach get in your car, and how did it work before the manual trans was there with a diesel motor?

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thanks for following up. Great you got it going. The diesel tach operates on a hall sensor. The gas probably works off the ignition coil. I bet the gas wants to see a higher voltage than the diesel tach.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

anybody know of a source for a wiring diagram for my 1992 200
td? The AC quit working and we cannot find the wiring piece by piece.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.