I'm trying to do some troubleshooting on my truck that I think might be COR related.

It looks like there are two COR designs. On 4Crawler's site there's a diagram for a design that looks like it works by grounding the fuel air flow meter pin - basically making the COR think that the engine is running and the switch in the AFM is closed. I think it's the 1985 design.

http://www.4crawler.com/4x4/CheapTri...s/FuelPump.gif

The other design, from the 1993 manual that's online, looks like it works by simply bypassing the relay completely.

http://personal.utulsa.edu/~nathan-b...38circuito.pdf

It would help to know which I'm dealing with. I guess the relay design hasn't changed, but how the test jumpering works changed. The first design uses the relay, it just gives it an always on signal. The second bypasses it totally. This makes a difference in figuring out what's going on here. I have a 1990 truck. Anyone know when they made the change?

 

The diagram shown in the 93 FSM is the same as the one shown in the 88 FSM(in that respect atleast). So around/before then.

 

Thanks, that answers it for me. I should have the bypass style jumper arrangement then.

 

I would assume it came about at the same time as the switch was made from the separate (driver's side) test jumper connector and the all-in-one diagnostics box.

Should be able to tell by inserting the jumper and turning the ignition on and off and listening for the CO relay clicking (or not) sound in the passenger side foot well. I know mine is a very distinctive sound.

 

Thanks. Mine has the separate diagnostics box drivers side of the fuse box. I'll try listening for the COR click.