I bought a 98 F150 just awhile back as a yard truck. 4.6 V8, Automatic transmission 4X4.
Truck was running great. Then started it in the morning ran for 5 seconds then dead. Will turn over but no start. Checked the fuse and there all good Relays are also working. Did a spark test on passenger side coil no spark. did same on the driver side and the vehicle decides to start. I leave in run for 30 min and it dies. No engine light. re start it and it is running rough and still no Engine light. Plug in my code reader
and the computer is not communicating at all whit the scanner. Check the scanner and its working fine on my Expedition. Back to truck restart it still running rough plug in scanner but its not able to communicate with the computer.
Rpm tach on dash has totally gone crazy. Any buddy out there have the problem? Thanks in advance for any help.

 

It sounds like you have a bad battery. I would get the battery load tested.

 

Have you checked ALL the fuses? The cig lighter fuse also protects the OBD2 port.

 

ya glc, I checked that fuse when it would not read.

 

I'd start checking all PCM-related wiring. You may have a bad ground somewhere.