I bought a 1990 f-150 with the 5.0 efi motor. Ran fine when i got it three days ago. Going down the road i lost power and it started knocking. I checked the vacuum it is steady at 18inches. Compression is 100 - 115psi in all cylinders. When cold the motor doesn't knock until given gas. After it warms up the knocking gets louder. I'm lost please help

Thanks, Eric

Scan for error codes.

I tried that and not pulling up any error codes engine light never comes on either. I am in the process of getting the motor out i'm going to tear it apart hopefully I can see whats going on. Thanks for the reply

Eric

If your CEL light doesn't come on temporaraly at start up, the bulb is out or PCM prob.

It does come on at start up i took it to ford dealer they ran the test said no errors were found.

I think i'm going to just put all new cam bearings and rods it the motor and what ever else it needs when i tear it apart. Any ideas on what else i need to change while i have the motor apart.

Looking at the compression and knocking I would get it bored and install new pistons and rings while it is apart. Also do a valve job while apart. Sometimes lifters make noise but not a knock. For the amount of work to install new bearings I would do a rebuild.

Looking at the compression and knocking I would get it bored and install new pistons and rings while it is apart. Also do a valve job while apart. Sometimes lifters make noise but not a knock. For the amount of work to install new bearings I would do a rebuild.
Ditto An engine is only as strong as it's weakest link. My 87' 5L tests +- 2 psi of 180/ cylinder. Only 78k, the last 25k running synthetic w/ a stablizer added to insure upper end lube filming for start ups. Switching to Synth. after break-in will insure the most return on your investment!