Ignition Circuit Monitoring Temp Sensor 89-95
928.606.155.02

The sensors are mounted at the cylinders 4 and 8 on '89 and '90 models, and at cylinders 3 and 7 on the '91- models.

Mounting the sensor srequires Molykote HTP paste (white) and torque should be 10Nm.
New sealing rings should be used, nr 013.812.6 refer to manual pages 28-75 to 29-78

Checking the voltage for proper operation:
1. start the engine and bring it to proper operation temperature
2. pivot the limp-mode relay and move it a bit up, not removing it, to get access to the pins.
3. set voltmeter to 10mv range and connect leadt to e2 and 1e
4. measure voltage at idling 2000 rpm. Voltage difference must remain withing range of -2,5 mv to +2,5mv. If the measurement exceeds range, loosen one sensor an d rotate, fasten and test again. If still out of range, do same on other sensor. If still out of range replace sensors.

This is not really a limp mode, but a design to prevent the car from catching fire. Driving the car in this limp mode will make it ruin badly, and it is known to cause serious vibrations that make the torque tube snap. Really.

IMR -> Green LED = Driver side problems, Red LED = Passengerside problems.

They're the sensors for the Ignition Monitoring System.

They screw into ports on the underside of the exhaust ports on the heads - there is a port under each cylinder's exhaust port on the heads. On non-cat S4's, they actually have a hollow bolt in every single cylinders's outlet to pump air into each exhaust port. However, on 89-95 cars which originally had a catalytic converter from factory, they are all blocked off with a threaded plug, except one cylinder on each bank which has the sensors in them to detect lower exhaust temperatures from a failed ignition bank (due to failed coil, ignition amplifier, etc.) and prevent a fire in the cats.

On an 89, they were originally installed on cylinders 4 and 8 (the rear -most on each side), but per a bulletin from Porsche, they were moved to cylinders 7 and 3 in 1990. I'd reinstall them in cylinders 3 and 7, and then sort out the rest of the system (clear plastic relay attached by the LH ECU).

You can see one of the blocked off exhaust ports in your photos..
 

Hilton

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