The CHTS for my stock 73 2.0 died on Sunday. Luck would have it that it happened in the street just outside my house, so it was a relatively easy push back into the garage. Checked the resistance of the sensor and determined that it's completely failed open.

After much research, I find now that the 73 2.0 was unique (thanks to Anders page) and that the 017 CHTS is a unicorn as well.

So, what are the options and/or work arounds for the CTHS on a 73 2.0 without replacing bug chunks of the FI system?

Robert

Did 914 rubber make up some new ones. I would call them and check.

they are all basically the same, so the 022906041a would be suffice funny that Porsche has superseded many 1.7 2.0 fuel injection parts to the same part number

If you replace it with 022906041a, do you end up leaving the resistor inline to maintain the 'proper' behavior with the 73 ECU?

No

(copied from Anders site)

If you have a 1973 2.0L and you want to keep the original setup, make absolutely certain that you have the correct combination of components. The 0 280 130 017 head temperature sensor's cold (70 deg F.) resistance is about 1200 ohms, compared to 2300 ohms for the 0 280 130 003 and 0 280 130 012 sensors. Use of the ...017 sensor with the 039 906 021 ECU (1974 model) will result in a lean mixture during warm up, causing low idle and/or backfiring on over-run. Use of the ...012 or ...003 sensor with the 022 906 021 E ECU (1973 model), with or without the ballast resistor, will result in a rich warm-up mixture. Take the extra time and determine exactly which head temperature sensor is installed in your car and make sure it matches the setup.

The CHT sensor from 914Rubber is the same as the 012 and not correct for the 73 2.0 and using it will make your mixture too rich. since it is already 2300 ohms instead of the 1200 ohms of the original one on the 73 2.0. and adding another 270 ohm resistor will add to that problem.

however that rich mixture will only happen until the CHT heats up and the resistance goes to near 0 ohms, or in the case of the 73 2.0 +270 with the added ballast resistor.

what may work, (and this is what I did on my 73 2.0 system with the 012 cht) is to add another resistor in parallel. I used a 2500 ohm. When cold this cuts the total resistance down to around 1200, same as the original. and when it warms up and the CHT resistance goes to around 0, the extra parallel resistor had no effect any longer. Now if in your case the ECU does need to see the extra 270 Ohms of the original ballast resistor you could put it in series with the CHT and still run the 2500 ohm in parallel. this would give you 243 ohms hot which is close enough.

you can play around with this calculator >

https://www.allaboutcircuits.com/tools/para...nce-calculator/


YEMV.

This is the wiring setup I used.

Click to view attachment

and with a vari -pot added to tune

Click to view attachment

on the car

Click to view attachment

in the above picture the black wire is from the CHT and the bump in the red wire near the coil is the added resistor going parallel to ground.