87 Turbo knock sensor issue

supraman7 · 02-18-2010, 09:58 PM

I have a 1987 Toyota Supra Turbo (MKIII), the check engine light dashboard lamp has been lighting up approx 15 to 60 seconds after the motor is started. The light will come on sooner rather than later, if I put a load on the motor.
The following are the checks I’ve done and their results:
I put a load on the motor while listening for sounds and found no detectable knock or ping coming from the motor. There is, however, an exhaust leak where the exhaust pipe meets the turbo, but I don’t believe that would cause the sensor to activate.
This model has an OBD 1 computer. When I did the diagnostic code check, the trouble code read out was #52, which indicates it’s a front side knock sensor. I removed the computer and both knock sensors from a friend’s 1987 Supra Turbo and tested them on my car. They had the same part numbers as the parts from my car. When in my car they functioned the same as my parts and presented the same check engine trouble light and knock sensor code number. This would indicate that my car’s parts are functioning well and that the sensor connectors are not bad.
I checked the communication lines by back probing from the sensor to the computer, they checked out OK. Also, I tested my computer and sensor with an ohm meter, I got the right input and received the right output values.
I’m perplexed. Is there anyone who has knowledge of this type of OBD 1 computer knock sensor problem or any other OBD 1 issue? If so, please let me know how it was resolved. Thanks.

02-18-2010, 09:58 PM	#1
supraman7 Stock Join Date: Feb 2010 Location: Santa Monica, California, USA Posts: 4	87 Turbo knock sensor issue I have a 1987 Toyota Supra Turbo (MKIII), the check engine light dashboard lamp has been lighting up approx 15 to 60 seconds after the motor is started. The light will come on sooner rather than later, if I put a load on the motor. The following are the checks I’ve done and their results: I put a load on the motor while listening for sounds and found no detectable knock or ping coming from the motor. There is, however, an exhaust leak where the exhaust pipe meets the turbo, but I don’t believe that would cause the sensor to activate. This model has an OBD 1 computer. When I did the diagnostic code check, the trouble code read out was #52, which indicates it’s a front side knock sensor. I removed the computer and both knock sensors from a friend’s 1987 Supra Turbo and tested them on my car. They had the same part numbers as the parts from my car. When in my car they functioned the same as my parts and presented the same check engine trouble light and knock sensor code number. This would indicate that my car’s parts are functioning well and that the sensor connectors are not bad. I checked the communication lines by back probing from the sensor to the computer, they checked out OK. Also, I tested my computer and sensor with an ohm meter, I got the right input and received the right output values. I’m perplexed. Is there anyone who has knowledge of this type of OBD 1 computer knock sensor problem or any other OBD 1 issue? If so, please let me know how it was resolved. Thanks.