justinss

I was getting gas one day in my 89 gxl and suddenly the check engine light came on. I drove about 3 miles from the gas station to my house so I could check the codes. The car ran fine on the drive home (but I didnt get on it with the check engine light on. I never took it over 3000rpm). I checked the codes, and it gave me code 9 for the water thermosensor.

First I tried disconnecting the battery for 5 mins. to clear the codes. I started it (it wasn't hard to start, and it wasn't flooded). After the idle came down, I took it around the block a few times. The check engine light didn't come on until it was fully warmed up. I reset the codes again, and then started it and got the same results. It can go all the way to the redline without any problems before the light comes on. After the light comes on, it will hesitate starting at about 4000 rpm.

I don't think the sensor could be bad, since everything works fine until the car has fully heated up, and only then will the check engine light come on. My guess would be that there may be a ground problem with the ECU? I am not sure though, and want to get some opinions before I try to fix it. Thanks.

deadRX7Conv

Make sure that it is plugged in fully and that there is no corrosion on the connection.
You still need to test the thermosensor. Don't jump to any conclusions until the thermosensor is tested good.
Download the FSM and read the Fuel/emissions chapter.

justinss

Well, I took the alternator off to have easier access to the plug. The plug to the thermosensor wasn't loose, but I pushed it in anyway to be sure. I put the alternator back on and started the car. I ran it for about 30 minutes, and the light never came on. So I guess it was a pretty simple fix after all. When I started the car, it reved to a little over 4k instead of the usual 3200. Is this because the ECU had to relearn something or did I mess something up?