I added a variable resistor in series with my temperature sensor to the Fuel Injection Computer. Set it up for about 300 ohms.

The car is running great and solved the hesitation problem that I was trying to fix. Smoother idle, seems like more power and better gas milage.

By adding the resistance I trick the computer into thinking that the engine is cooler and it must enrich the mixture. I have 180,000 mile on the car so there may be air leaks and I am getting closer to the original mixture.

Any comment or similiar experience?

Walt 1988 Audi 90 5 cylinder CIS-E II FI system

 

Re: That's clever!

 

Well done! Could you please provide more details? I would love to perform it myself.

Curtis
'88 90q

 

I have an identical '88 and have had idle problems after it warms up. Maybe your fix will help mine too. Which temp. sending unit is for the computer? I know of the one that goes to the Auto-check gizmo and gauge with the brown connector. Is that the one, or is there another one?

 

Hi, nice job, could you e-mail me details on performing this...I have a 1988 90 also. Thanks.

DMarks@kc.rr.com

 

The coolant temperature sensor consists of two NTC resistors within one housing. One resistor provides information on engine coolant temperature to the ignition control unit. The second resistor provides the same information to the fuel injection control unit.

The singals from these sensors are used to provide corrections to the fuel mixture and ignition timing based on engine temperature.

Both resistors in the temperature sensor have the same resistance values. The sensor is located in the cylinder head coolant outlet flange (on top)

Remove the two point connector and measure with an ohmmeter as follows

point 2 to ground value below
point 1 to ground same value below
resistance to ground = coolant temperature
20,000 ohms = -22 F
10,000 ohms = -4 F
5,000 ohms = 32 F
2,000 ohms = 68 F
1,000 ohms = 104 F
500 ohms = 140 F
300 ohms = 176 F
175 ohms = 212 F
100 ohms = 247 F

I added a variable resistor to point 2 (that's the point on the temperature sensor)
The wire color is black/red
It connects to point 3 (that's the point on the FI control unit)

The FI control unit is under the dash near the rear of the glove compartment, remove the lower cover panel, two screws just below glove compartment, slide cover off, tilt white clip that held the cover on, this allows access to the FI control unit.

I added the variable resistor near the FI control unit so that I could adjust it from inside the car. However it is probably easier to add it under the hood near the sensor.

I adusted the resistor based on the sound of the engine and ended up with about 260 ohms. That makes a 212 F coolant read like 150 F to the computer.

Well it worked for me.

Good luck and post anything you find out.

 

any idea whether this would work for an 87 5kq?

 

hello i have an 88 90 sedan with the 5 cylinder inside the temp sensor all 3 of my wires came out of the connecting socket that goes in the sensor its a brown 3 prong could you tell me what wires go where it would be very helpful because my ride wont start ...help....