I've noticed a slight engine knock sound at low rpm, just after shifting, as I start to press the accelerator. This only happens after the engine is warmed up. Truck is a 4.6L V8, 5 spd. This isn't due to pre-mature shifting, since I can wind it up a bit and it will still knock during initial throttle. The knock is very slight, only noticable when the window is open.

Have been running 87 octane since day one. Tried 93 octane and don't notice any knock. Why would the octane increase help? I thought these engines would adjust across a range of octane levels. Possible the anti-knock sensor is defective? Or, is my computer just trying to run very lean? Have not tried the computer reset. Any suggestions are appreciated!

 

See the post below pinging 97 f150 4.6, you may find the answers you seek. Or it maybe you're just getting crappy gas. The only time my engine has pinged is hauling my trailer loaded and a bunch of firewood in the bed 100* weather on a 10% grade up walker pass.

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'97 F150 4.6L XL WHITE,FLEETSIDE R/C L/B, LEER SHELL W/FISHING POLE RACK, BED MAT,LIMMITED SLIP,245/75/16 DESERT DOGS ON POLISHED ALUM, WHEELS.
AIRAID, 3" CAT BACK OUT THE SIDE w/MAGNAFLOW MUFFER

 

Thanks Whiteflight, I'll take a look at the MAF. Also, I'll try a different gas station for the next tank of 87. Truck only has 11K miles, so I was kinda surprised/annoyed to hear this. It's pretty quiet, but there is some predetonation it seems. Most people probably wouldn't have noticed it, but us truck fanatics can really tell our vehicles pulse.

 

BAZ,

I have a similar situation with my 99 F-150, 4.6, automatic. When I slow almost to a stop, and then accelerate (e.g., turning a corner, etc...) I hear a rattling or dieseling sound for just a second or two. This only occurs when the engine is hot. I have always used Brand Name 87 octane, but filled up with 89 yesterday. So far I haven't heard anything. I will keep you posted.

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1999 F150 4X2 SuperCab, 4.6 (Romeo). TuTone White/Gold, Bedliner, Prime Designs Bug Deflector, Ventvisors. No cracks, no Engine Mods, no Problems.

 

BConehed, haven't heard a knock with this tank of 93. Thing is, as others on this board pointed out, the higher octane should be unnecessary and is masking the problem. I'd much rather find out that cleaning the MAF or some other thing fixes the problem. I have probably babied the truck a little too much and might take it out on the highway for a good thrashing and see if that clears anything up. Most of my driving is short runs around town. I'll post any updates and appreciate any more suggestions, TIA.

 

Yea Baz, If you baby it too much and just drive around town you may have some carbon build-up on the heads. You gotta open it up once in a while, I beleive you said yours was a stick. Get on the highway go through the gears wind it up to about 4000 rpm and cruise in 4th awhile you'll blow all that carbon out the tail pipe. I have been using 87 octane since i bought the truck in '96, I put 89 in when I head out on a camping trip cause I'm usually loaded down and going up grades. I read a post the other day and the guy said he got anothe 40-50 miles per tank using 93 octane. I guess you have to run several tanks before this happens as the computer has to learn to compensate or you could reset the computer by dissconnecting the battery. I figured it out the other day even paying more for premium, if I got 2 mpg more I would save about $200 per year that would almost pay for a superchip. keep on truckin'