1986 F250HD XLT Lariat 4wd 351HO c6 trans. emissions light came on the other day I am puzzled by this. truck is non-catalyst and all the useless smog stuff was deleted by a previous owner except evap and egr systems. there has been no change to drivability or gas mileage just the dash light stays on. for first 5 weeks I've been driving the truck the light was not on. brake booster and master cylinder are both shot so there is probably a vacuum problem. all other systems are operating as they should. Any ideas?

 

This has got to be a good start point anyway........https://www.ford-trucks.com/forums/1...ons-light.html

 

okay thanks. gonna find and disconnect it in couple of hours. most likely the culprit as I have just surpassed 120K on this truck. If that doesn't do it i'll check egr and evap components and remove the bulb from the dash.

 

The same thing happened to my 1986 with 4.9L engine. The light came on at ~190K miles and all emissions equipment had been deleted @ ~120K. I removed the bulb.

 

don't you love the early to mid 80s thought patterns. put emissions equipment on a truck that was designed as a non-catalyst vehicle = no useful function. gonna pick up an aftermarket non-egr intake manifold and get rid of the egr as well.

 

the computer has an internal timer that triggers the light, (at least on Rangers)
I forget where but there is a reset button somewhere..........

 

I found this at the top of the page ["stickies"]: https://www.ford-trucks.com/forums/1...ons-light.html