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Discussion Starter #1
Hello everybody I'm new to the Forum I I am a technician by trade but haven't really worked on much old stuff I have a 1988 Toyota Supra that I recently acquired ran and drove really really good for a while I let sit for a couple days and now I can't get it to start I've pulled the check engine light codes I got code 12 I have replace the distributor and checked for broken wires reset the computer but still get code 12 for the CPS.

im wondering what else I should check before putting a ecu in it and if I do need to put a ecu in the car do I need to match up any numbers? Etc
I'm so used to having to get everything reflashed/reprogrammed I have a feeling I'm overcomplicating this

And before someone says it i have used the search engines I just may not be using the right key words
 

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I've mostly read that topic if I missed something in it im no sure what, but I've also read a lot of posts my have missed something
 

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Also I may not have stated this but I have no spark. But unless I am overthinking it again. Wouldn't the OBD1 code 12 turn off spark because the ecu has no idea what rpms are
 

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Sounds like it could be ECU based on your troubleshooting. ECU going bad randomly is a problem these cars suffer from. Follow the TSRM
 

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you can remove cps and spark plugs to test by hand. unplug fuel pump. spin cps and trace signal with an oscilloscope to ecu, igt at ignitor, spark plug. cps goes out much more often than ecu. the manual also lists simple voltmeter tests for the ecu. if those are all ok i would be even more doubtful of ecu failure.
 

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you can remove cps and spark plugs to test by hand. unplug fuel pump. spin cps and trace signal with an oscilloscope to ecu, igt at ignitor, spark plug. cps goes out much more often than ecu. the manual also lists simple voltmeter tests for the ecu. if those are all ok i would be even more doubtful of ecu failure.
Thanks for the info what manual are you using this is the first I've heard about some of these tests
now I just need to see if the scan tool at work has an oscilloscope feature i haven't used one of those since I was in college
 

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the scope isn't necessary, i just like visual confirmation, and a usb pc based scope from hantek is $80. if you think about it, the code is generated by a working ecu, so only a small section of the ecu could be bad to generate code 12. if that was bad, it would most likely be from a fault in the CPS circuit. the more likely fault source is the 30 year old wiring running through a 300 deg engine bay, or the cps with plastic cover bolted to a hot aluminum head and probably not gap checked in decades.
 

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Now, I'm no expert here or anything, but if I had a dollar for every time a Supra owner had a CPS issue, I could probably afford to finish my Supra. ;)

OP, please do update us when you sort out what the issue ended up being. Always good to have resolution!
 

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Thank you for the info ill let people know what fixes it
I was trying to point you in the specific direction of testing the CPS, every time one of these cars turns over but doesn’t crank everyone screams CPS, so take it with a grain of salt but your code appears to point to ECU(they go bad) or CPS (they go bad).
 
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