Cylinder Head Temp Sensor Options

[young55961]

I think I may be missing the Cylinder Head Temperature (CHT) sensor on my 1975 Porsche 914 2.0L engine.

The sensor shown in Picture 1 is the Intake Air Temperature sensor, correct?



I can't find the Cylinder Head Temperature sensor anywhere on the engine.

In Picture 2, is that the correct mounting location for the CHT sensor?



If anyone has a picture showing the CHT sensor installed in the cylinder head, I would really appreciate it. It would help me identify the correct location.

Thanks for your help!

[JamesM]

Picture 1 you have there is of "Temp Sensor 1" it is a thermo switch that activates the 5th injector "cold start injector" while cranking if it is cold enough.

As for your CHT "Temp Sensor II" for those heads you have there the enlarged tin screw hole by the #3 cylinder looks like where you will have to install it as they do not appear to be drilled in the standard 914 d-jet location.

Also those are not 914 2.0 heads you have there.

Is this a bus motor/heads?

[young55961]

Picture 1 you have there is of "Temp Sensor 1" it is a thermo switch that activates the 5th injector "cold start injector" while cranking if it is cold enough.

As for your CHT "Temp Sensor II" for those heads you have there the enlarged tin screw hole by the #3 cylinder looks like where you will have to install it as they do not appear to be drilled in the standard 914 d-jet location.

Also those are not 914 2.0 heads you have there.

Is this a bus motor/heads?

It is not the original heads. The PO converted it to carb. I am try to bring back to Fuel injection.

[JamesM]

It is not the original heads. The PO converted it to carb. I am try to bring back to Fuel injection.

They did more than convert it to carb, that isnt a 914 2.0 motor.

The head temp sensor location will work however, you will not be able to fit 2.0 intake runners to those heads without modifying one or the other.

I assume since this was done by a PO it has the proper cooling tin for the 1.7/1.8 spark plug location? Or did they modify the stock 2.0 engine tin?

I ask because with all this you are facing somewhat of an uphill battle getting a stock 914 2.0 d-jet system to work with it. A task that even with all stock parts can be monumental for some.

Being a speed-density type of injection system, without modifications the stock d-jet systems only work with a stock motor, change the displacement, cam, or flow characteristics of the heads and they no longer run correctly unless you modify them.

Carbs are the old school solution people used to take in a case like this to make the car run again. When they state the put carbs on because they couldnt get the fuel injection to work, the problem probably wasnt the fuel injection, but rather the engine they were trying to put it on.

Have you torn this engine down to know exactly what is in it?

[frank_c]

If anyone has a picture showing the CHT sensor installed in the cylinder head, I would really appreciate it.

As @JamesM mentioned, the heads in the photo that you posted are not 914 2.0 heads. For reference, the photo below shows a 2.0 head with the FI Cylinder Head Temp sensor location circled. Also notice that the spark plugs mount at much more horizontal angle, and that there are only three studs for the intake runner (instead of four).

[JeffBowlsby]

What being referred to here as temp sensor 1, is the thermoswitch, not TS1, although its function as a switched ground for the cold start valve is correct.

TS1 is in the air plenum, sensing the intake air temperature.

[JamesM]

What being referred to here as temp sensor 1, is the thermoswitch, not TS1, although its function as a switched ground for the cold start valve is correct.

TS1 is in the air plenum, sensing the intake air temperature.

Yup, misspoke on the Bosch naming there

Per the PET its "temperature switch" per the Bosch manual its "Thermo-time switch"

Bottom line though, its a temperature regulated switch to ground a circuit that only receives power while cranking and has no impact on the engine otherwise.