fuel knock?

[shortontime]

Took my 7.3 in for a checkup, specifically the injectors and gps. Diagnostics showed nothing from #8 cyl. They put in a new injector, and went over the gps. Replaced GP's on that side since they had it apart for the injector. No I have a terribly loub knock. At idle, acceleration, but when it's slowing down and the engine is braking so to speak, no knock. Mechanic says it's "fuel knock" Is this bad? Could it be a bad injector? The knock was not there before, and I do see a very noticeable improvement in power with 8 cyl's, but the knock is super annoying.

What's your thoughts?

Also, 12MPG, w/ contractors cap? Very little hwy driving, but still, 12? What about straight piping the exhaust and chippin it and adding a high flow intake? It's got K&N now, but that's not exactly high flow is it?

Thanks guys!

[jesilvas]

Possibly a bad injector.

[shortontime]

Thanks for the big welcome! I've been reading a lot on this forum and I can't believe the knowledge in this place. I wish I knew half of what some of you know.

I've been thinking of selling this truck, but I just put $1300 into it and my total is now only about 11,000. It's strong, but with the fuel economy and the potential issues it may have, I wondered if I'd be better off with a new F150. At least the wife would drive a new truck, not this one though.

Thanks again for the response and the big welcome!

[jesilvas]

The #8 has always been a pain on these. Because of the way the fuel and HPO system rails were setup in the heads, the #8 was right after the #6, so it didn't always get all the fuel/oil it wanted and needed. To solve this, they put in a "long lead" injector. It has a different code than all other 7. It's possible they put in the wrong one or you just got a bad out of the box stick.