hey all, my check engine light will not work in my 87 F150 I6 EFI and ive run all tests to determine the fault to be my 60 pin processor according to the Chiltons EEc diagnostic book. the truck runs perfectly but the light wil not come on and it will not send data to my otc 4000 enhanced scan tool (or anything else for that matter). i have continuity to the socket which is new and the bulb is new. i even plugged it into the turn signal to insure that it works... i think it would be rather stupid to buy a processor to solve a light not coming on... any help is appreciated

 

What does not make sense to me is why the truck runs perfectly if the PCM is at fault. It may be just that one particular function of the PCM isn't working. It's possible for part of an IC or PCB to fail. I would do some more checking - maybe some of the connector pins in the socket are corroded or you have a short somewhere?

 

whats strange is that the book states that if there is power to the socket, and the bulb works, then the processor is to be replaced. seems pretty asinine to me so ive been digging through wires and checking grounds... hoping to find a more adequate answer then part replacement...i wish i had a breakout box

 

If you turn the key from off, to on (but not start) the light will either light, or light for a short while and turn off.

Then you know the light is working. Maybe the fuse is blown, or the wiring is bad, or the socket is corroded.

Assuming it does light at that point, there are instances where the truck "runs perfect" and the EEC is not working correctly - i.e. it feels right because it's stuck in open loop.

 

I though somebody once said that the CEL was not implemented on the 1987 F-150.

 

are you sure the light bulb isnt burned out or been removed prior to you owning this rig

 

bulb is good(brand new) socket is good (brand new) both were tested in the turn signal socket to verify that they did work correctly

 

how do you have the bulb wired in?

 

I've yet to see an 87 with a working check engine light. The circuit is there on the printed circuit on the back of the gauge cluster, but there is no wire between the computer harness and the dash (or a pin in the dash harness for that matter). You can verify this by pulling the cluster, tracing the circuit to where the harness plugs in and then look to see if there is a wire in the harness. I bet there isn't. The thing about it that I don't understand is that the code reader won't work either. Maybe try it with an analog voltmeter (positive to battery, negative to STO, turn key on and see if you get 12V to test the output from the computer). Then if there is 12V with the key on, turn it off and try to run the diagnostic check again.