I have a 94 F150 5.0 4x4 which I tuned-up yesterday. The spark plugs & spark plug wires are all connected properly. The only time the check engine will come on is after 5 minutes of driving. The truck is running great and has no other issues. Has anyone ever experience this before? Please help!!!

I've scanned it and it comes back negative. No codes show up.

 

How many miles on the o2 sensor? over 60K, replace for MPG reasons, even if it is functional, It's switching speed has slowed & accuracy dulled. Error code scans will tell you what's wrong for sure. Sounds sensor related, as the CEL waits till closed loop function begins!

 

X2....sounds like an O2 sensor...read the code it will tell you want it is.

 

No codes are popping up.

 

"no active codes" actually means you got #11 or #111 when error code scans are performed! No codes at all means operator error or no ECU communication. If you have a check engine light, you should have code/s.

 

To God be the glory! I discovered what the problem was. After double checking all the plug & wires... I noticed that I accidentally broke the vacuum line. I've should of paid close attention to the coffee can looking reservoir. Thanks a bunch fellas.

 

gotta love Folgers, the smell of oil & tranny fluid dripping from your elbows to start a morning off right!!That's why Ford used an old coffee can ya know?