87 Turbo knock sensor issue

cre · 02-18-2010, 10:55 PM

The MKIII doesn't have OBD-1, it's diagnostic system predates the California state specifications known as OBD-1 and is much more primitive... there is a serial out within the ECU, but it is not something available even to general service techs; it's pretty much just used for diagnosing the ECU itself.

Your problem is VERY common and is usually solved by replacing the knock sensor wiring. I'll find you a link to a writeup on the rewire and post back.

cre · 02-18-2010, 11:07 PM

http://www.supras.com/06/techcenter/display.php?QID=69

supraman7 · 02-19-2010, 04:19 PM

Thanks for the heads up about the ECU differences.
Other people have also suggested that it’s probably a wiring problem. So I borrowed a friends special ohm meter that gives me exceptionally detailed readouts and does more than a regular meter. It has indicated there is a normal reading in my knock sensor wires. I also heard that some cars had a slightly lower than normal reading in the wires creating a problem. This is not true in my car.
I still may replace the knock sensor wires if I can’t find any other way to fix this. Thanks for the link it will help me.

cre · 02-19-2010, 06:21 PM

People are suggesting it from experience. Define "normal" readings... What are you measuring? Resistance? Voltage drop? Capacitance? The knock signal is a VERY fine signal which is VERY susceptible to interference unless you've put an oscilloscope to it testing isn't going to prove much.

Good luck with it; Let us know what else turns up.

supraman7 · 03-05-2010, 07:44 PM

You were right, replacing the high frequency knock sensor wires solved the problem. I’m impressed with this forum. Thanks again for the advice.

02-18-2010, 10:55 PM	#1
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	The MKIII doesn't have OBD-1, it's diagnostic system predates the California state specifications known as OBD-1 and is much more primitive... there is a serial out within the ECU, but it is not something available even to general service techs; it's pretty much just used for diagnosing the ECU itself. Your problem is VERY common and is usually solved by replacing the knock sensor wiring. I'll find you a link to a writeup on the rewire and post back. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

02-18-2010, 11:07 PM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	http://www.supras.com/06/techcenter/display.php?QID=69 __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

02-19-2010, 04:19 PM	#3
supraman7 Stock Join Date: Feb 2010 Location: Santa Monica, California, USA Posts: 4	Thanks Thanks for the heads up about the ECU differences. Other people have also suggested that it’s probably a wiring problem. So I borrowed a friends special ohm meter that gives me exceptionally detailed readouts and does more than a regular meter. It has indicated there is a normal reading in my knock sensor wires. I also heard that some cars had a slightly lower than normal reading in the wires creating a problem. This is not true in my car. I still may replace the knock sensor wires if I can’t find any other way to fix this. Thanks for the link it will help me.

02-19-2010, 06:21 PM	#4
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	People are suggesting it from experience. Define "normal" readings... What are you measuring? Resistance? Voltage drop? Capacitance? The knock signal is a VERY fine signal which is VERY susceptible to interference unless you've put an oscilloscope to it testing isn't going to prove much. Good luck with it; Let us know what else turns up. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

03-05-2010, 07:44 PM	#5
supraman7 Stock Join Date: Feb 2010 Location: Santa Monica, California, USA Posts: 4	It worked! You were right, replacing the high frequency knock sensor wires solved the problem. I’m impressed with this forum. Thanks again for the advice.

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