I have an 81 rx7 that i just had to replace the ECU in because of a annoying buzzing sound, but after i replaced it i had the "Exhaust overheat" light come on, it comes on when i start the car, not just after its been running. I found the sensor on the passenger side under the carpet and unplugged it but the warning light did not turn off. I plan on replacing the sensor (if i ever find one). but I can not figure out why the light has not turned off. Is it possible its an old code from the original car the ECU is out of? if so how do i reset the ECU. Any advice is helpful.

 

The ECU in first gens do not store codes. The schematic can be found here: http://www.foxed.ca/rx7manual/manual...ingDiagram.pdf. A lot of the sensors you can just ground the plug to get it to ignore it.

Then schematic you want is on page 12 of this PDF. It's plug B-13 and can be found by taking the drivers side bin out.

 

Most of the sensors on the older cars are set up "open=active" so that a sensor failure (which almost always results in an open circuit) will trip the light. as KCREPU says, generally you have to ground them to bypass them.

 

i actually already have that PDF printed out in a booklet form, had to use it back when i had an electrical fire, very handy. but do you know where i can find a new sensor? I don't really like the mentality of if its broke, take it out and forget about it. would much rather know if something is going bad then just wait until there's a catastrophic failure that could have been prevented.

 

Really dumb question here, have you checked the fuse? Way back when I was a teen my buddy had this happen to his car and he ripped out everything from a parts car and swapped them out with no luck until he was under the dash and asked me for a fuse and it automagically fixed it. If I remember correctly it was a small glass fuse in a seperate holder from the rest under the dash and looked like an add on but was on both his FB's

 

the only glass fuse that matches that description would be the ECU fuse. And I already tested the fuse and its good.

 

Have you tried grounding the wiring side plug to see if the light/buzzer stop? Testing is the first step. If this stops the light/buzzer then you have confirmed that the ECU and wiring are good.

 

i already fixed the buzzer (different thread) that was a bad ECU now this light has come on and i just need to figure out why it came on.

 

Looking at the schematic I referenced earlier this this thread, the light gets it ground from the sensor. Please do the recommended testing.

Here is something that has really helped me. I was an Electronic Technician in the Navy and we had this really easy process to help solve electrical problems. It's called the "Six Step Troubleshooting". Here is a link to the process http://letu.edu/opencms/opencms/_Aca...ng_-_small.pdf

1. Symptom recognition
2. Symptom elaboration
3. Listing of probable faulty functions
4. Localizing the faulty function
5. Localizing trouble to the circuit
6. Failure analysis

 

Here is the testing procedure from the 1985 Factory Service manual. This is will still work for your years car. Page 4A-31. http://www.foxed.ca/rx7manual/manual...ssions_12A.pdf

 

Took long enough but finally found the problem, I had a broken wire in the harness leading to the heat hazard sensor. Just spliced in a new wire and the light sent out. THANK GOD