Does anyone know what would cause the check engine light to come on and off after a tune up, it was never on before all i did was, fuel filter,spark plugs, wires, cap and rotor, oil change, (air filter and belt was done couple weeks ago) the truck runs a whole lot better now but just curious if maybe i set something off i didnt touch anything else so maybe someone here can shed some light on the subject thanks uys

 

Suggest your best move would be to read the codes to see what's up. Why guess, when you can know for sure what the computer doesn't like? Didn't catch the model year of your vehicle.

At any rate, if you have the OBD-II series computer (1994? - up), AutoZone or the like will read it for free.

If you have the older OBD-I computer (1987 - 1994?) - this thread will tell you how to read codes:
https://www.f150forum.com/showthread.php?t=10907

 

This may be a long shot --- i did a tune-up last week, and wound up breaking 2 vacuum lines (green & red/pink). Wouldn't have noticed it had i not looked closely. These two were plastic lines are very small, were weathered, old, and fragile. I've got the I6, and they were close to #6, directly above it, and next to the cab. Spliced a connection with a piece(s) of hose.

 

While i agree, you can/maybe-should check the codes... any code you get isn't going to decode and tell you, 'check vac line XYZ for break' or 'plug wire on #4 not secure'... Check for the obvious first.

OH, and might try resetting the PCM (disconnect the neg battery cable for about 10-15min)... relearning the computer to the new parts might help, but my GUESS is a vac line.

 

thanks guys btw its a 1994 ford 150 xlt

 

Your truck is the older OBD-I, not the OBD-II, those started in the 96 and newer models. Read the link, posted by the other member, about how to get codes from your truck. Those codes should tell you what the truck thinks is wrong and that should point you in the right direction to fix it.

Good luck!

 

Not to steal the thread but I got a 95 xlt. One of the responses said that 94 was the cut off of the OBD-I and another said that 96 was the start of OBD-II. I was wondering which one it is. Is 95 OBD-I or II? Thanks

 

1995 is the last year of OBDI, '96 and up is OBDII.

 

quick question if i broke a vaccum hose wouldnt i have lost power not gain it?

 

Not necessarily. Mine ran like Mike Vick at a PEDA convention with 2 broke lines.