Check Engine Light Woes

[Omboc]

I recently purchased a 1992 4runner and have had problems with the check engine light ever since. It's an automatic, and V6.

Whenever I exceed speeds of approximately 40-50 miles per hour, the check engine light comes on, and there is a large drop in the mileage I recieve. Driving around town, the engine never comes on. What are some possible causes/solutions?

 

[Jeff4runner]

Little late post, but you may have to get it scanned. I know the dreaded scanning is a fortune, but there are places that do it cheap/free. For instance, check local schools if they have an auto class, or just call around to any repair shop. Odds are, they will have an OBD 1 scanner, and can scan it if you give them buisness.

As for causes, it could be anything. RPM sensor, any other engine sensor, transmission output speed sensor, etc. However, due to the fact that it comes on under higher load/faster speed, it might be one of the A/F ratio sensors going wacky, or getting abnormal flow readings. Again, this needs to be scanned. If you want to test that, find out what rpm youre at going 50mph, then downshift to 2nd gear or something, and go the same rpm in that gear (like 25-30 mph). If that triggers the light, then you narrowed it down to something in the fuel system.