My '88 F-150 302 has 232,000 miles. Runs great in almost all conditions. I've noticed recently that under load (pulling ~4,000 pounds) going up slight hills at highway speed, I can hear a knocking noise. It's like a fuel/ignition knock. If I vary the throttle slightly (let up a little) it will reduce or stop the noise.
Any ideas on this one? I have read that over-advanced timing can cause detonation. I'd like to check the timing, is there a reference someone where I can find the specs and how it needs to be set?

 

Yes, the instructions are on the VECI label under the hood.

 

Wow, that makes it easy. I thought there was just worthless information on those tags and didn't read them

It says to disconnect the in-line spout connector... never heard of that. Where is it?

I'm going to round up a timing light and see if I can get this done soon. I pulled the distributor a good while back to replace a sensor and didn't go through this procedure to time it, so I'm sure it's off.

 

The SpOut plug is a grey plug that is right by the distributor, you unplug it, time it, then plug it back in.
This pic has in ain black for some reason, everyone I've ever seen is grey.

 

While you're at it, read ALL the other stickers & labels at least once so you'll know what you've been missing. Personally, I photograph them so that when they degrade, I don't lose the info.

 

I would see them flying around the car wash all the time when folks would wash their engine bay. The high pressure would blow them right off but ironically they were mostly GM stickers. Must be using the gov't glue.

 

Sometimes this problem is as simple as carbon buildup. I've fixed this issue before by simply using a whole can of throttle body cleaner on an engine. Have it running, spray and rev, spray and rev... until the can is gone. And if it doesn't fix it, your only out about $5.