1974 2.0 Temp Sending Unit

[LLOYD&WILSON]

Have been working on a project car for some time now. Was actually my grandfathers vehicle. I have the motor complete however whenever I plug in the Temp Sending Unit the car will lean out to the point of dying. Have replaced unit twice to see if faulty defect. Any thought from the wiser.


-Thanks
Kyle

[TheCabinetmaker]

the temperature sendor is a silicon device that increases resistance as the temperature goes down (opposite of a resistive device)

the temp sendor serves for cold engine conditions and will signal the brain (ecu) that the engine is cold and thus the brain will deliver a richer mixture.

if the sendor is disconnected, the resistance is infinte, an that replicates a cold motor. thus when you have the sendor removed, expect the engine to run very rich, whish is fine for cold engine starts until she warms up, onced warmed up the reistance will fall, and the mixture will lean out to normal operating value

typically a cold sendor will read 1000 or 2000 ohms when cold, andwhen fully warm the resistance drops to 100 ohms or less.

get an ohm meter and test the sendor only run this test with the sendors wire to the ecu disconnected. besure to vigurisly wiggle the sendors wire, as these devices often fail from the wire being broken (ie high resistance) or fail becuase the wires insulation has failed, near the sendor and the wire shorts to the sendors body giving very low resistance. some times becuase of vibrations, the problem is intermittant.


also check the condition of the the wire that connects to the sendor for any break in the insulation or wire.

also note that orignal type sendors are getting hard to find for some 914 models, it could be you have an incorrect sendor type, which could screw things up

if the car runs with out the sendor attached, see if the wire that is un=attached is shorting to ground or not. if it is not shorting to ground, then it is infinte reistance, which would give a rich mixture, if the that wire is then shorted to ground, the resistance will degrese towards zero, and the mixture will should really lean out. if the engine is fully warm, she may run somewhat with it shorted, with a cold motor if she is leaned out she may die. a cold motor needs to run richer to keep than a warm one )think of the cold school chokes on carbed motors, they make the mixture richer when cold, this tempeatue sendor basically provides the "choke" function on the D-Jet cars

good luck

are your replacement sendors new or used? and what part numbers are on them, where did you get them?

[Dave at Pelican Parts]

Sounds like the mixture is very lean, and unplugging the CHT compensates enough to let the car run.

How's the fuel pressure? I know of a car that would idle only without the pump running (just on gravity priming) because the CHT was unplugged.

--DD

[Garold Spire]

my 914 starts easily cold but shuts off and wont start when warmed up. Cranks ok and the fuel pressure is 29 psi. just wont start. my cylinder head temp sensor is on the driver side because the heads were switched when the valves were redone. otherwise everything is as it should be. Any suggestions?

[Garold Spire]

I shorted the cylinder head temperature lead and it wont start. I isolated the cht lead and it wont start. I reconnected it and it starts and runs but dies after a minute or so. and the fuel pressure is fine at 29 psi all the time. Need some suggestions.

[Dave at Pelican Parts]

How's the fuel pressure when it dies? There could be trash in the fuel tank that plugs the inlet after a bit.

--DD