I have a 86 GXL, only mod is open exhaust and it is my dd. I have a afc and a afr gauge installed. Now for the problem. I was driving yesterday and getting off the highway at about 3000rpms, my afc started boucing around from 1000 - 9000 in the rpm range but the engine speed was constant. about 10 secs later the tach in the dash started bouncing around but the engine speed was still constant. The tach was jumping from 0 - 5000. I put it in neutral and coasted for about 10 more secs the the dash lights started flickering and died. So, far I swapped batteries, I changed the main 80 amp fuse in the engine bay and I also swapped ecu's. Checked the connections at the afc and checked nearly all fuses under the dash on the drivers side. The same problem persist. The only thing that I though was out of the ordinary when I swap ecu's after running the car for a good while they where both pretty hot. Extremely hot. I dont know if that was from engine heat or if something is causing them to fry with too much voltage or what not. Im wondering if anyone has dealt with this problem or have any idea what it could be. The only other issue I had that day was I nearly ran out of gas like 2 hours before that incident. I really hope we can get this solve, its my only way to work tomorrow... Thanks in advance.

 

Check all ground connections.

 

just looked and all grounds are connected fine. Going out for a second check and more troubleshooting.

 

All connections are fine, I could not find any problems at all. Everything seems to be connected. Im gonna give it a drive and see if I can give you guys more info.

 

Examine the emissions harness for shorts and major damage. Check the CAS wiring to make sure the connections are solid and undamaged.

Don't just "check" grounds. Remove them, clean them up, and reinstall. Make sure to deal with the ground on the top of the engine as it is the ECU ground.

http://www.aaroncake.net/rx-7/grounding.htm

 

I drove it for about a good hour and no problems at all. I will take your advice and look into that Aaron Thanks

 

I just drove it again and it started right back up, also I just noticed the speedometer is of now. Its reading 15 miles over for some reason. I took a look at the cas harness and it looks like it has been tampered with before, but everything is connected and looks good. I'm gonna try cleaning it a bit and see what happens. Is it possible just to replace that sensor or do you have to replace the whole cas?

 

I think manage driving it to work tomorrow. The problem is not present anymore, but i need to find the cause. Any suggestions on what could have thrown the speedometer off and how to reset it back? I didn't think the speedometer was tied in with the ecu. As for the grounds, all are good but i cant really check the one under the uim. I can physically see it and feel that its connected, but i cant see the condition of it. If you guys can think of anything else im all ears!

 

could it be bad solder joints or the likes?