1995 F-150, 4.9 six, 5 speed, 2WD, stock tire size, 2.73:1 rear axle, 165K miles, computer shows no codes, odometer checks perfect with mile markers.

Recently bought this truck. First tank of mostly highway driving gave 19.2 mpg with 8 degrees advance. Increased timing to 14 degrees advanced and next tank was 20.6 mpg with similar driving. BUT.... now it knocks some when I take off from rest. With 8 degrees it never knocked at all.

Should I retard the timing to eliminate this knock or is it ok?

 

I don't think any knock at all is ok. I would change it to 12 degrees and give that a try.

 

Retard the timing. You won't see any immediate effects but allowing it to knock over a long period of time will cause major damage. Try backing it off to 10* and see how it does.

 

Personally I would retard the timing so it doesn't knock. What I think it happening now is you are having detonation which is causing the knock. If it does this long enough you can start to burn holes through your piston crowns. One thing you could try is using a high octane gas, the higher octane makes the gas harder to ignite, so you won't have any detonation. But, personally I would just retard the timing so it doesn't knock.

 

Detonation is great for a diesel but bad for a gas engine retard that timing or things will start to break

 

or just run 89 octane (midgrade) as opposed to 87..it wont cost more than $2 more a tank....and if you yield better mpg's than its worth it and will pay for itself...

 

He can run premium. But if it still knocks if wont help him. Knocking is the air/fuel mix exploding while the engine is still trying to compress it. It causes the parts of the top of the piston to melt and be blown off.

If you hear any knock immediately left off the gas so that it stops. Then retard your timing, test drive, if it still knocks, then retard more.

 

yes..i realize that...but if a higher octane fuel will prevent the knock then run as much timing as you can....the benefits are more power and efficiency...also maybe run colder plugs and a smaller gap...that will reduce chances of knock...

 

I retarded the spark advance back from 14 degrees to 12 degrees. If it still knocks I'll go to 10 or the original 8. This truck gets such great gas mileage I don't want to ruin it. Thanks to all who gave advice.

 

Back in the day, a little knock just as you floor it and ceasing as the motor builds RPM was the shade tree mechanics way of telling the motor was optimally timed and advanced as far as it could be.

 

Try a higher octane gas to see if it makes a difference.

 

add a water /alcohol injection system to it, and boost your mileage way up up to 50%
Do It Yourself Water Alcohol Methanol Injection | Parts List

http://www.motherearthnews.com/Green...on-System.aspx

http://www.popularhotrodding.com/eng...all/index.html

a simple mist water injection unit can be make cheap and to come on just after idle, with the mister in the top of the air cleaner top/lid,

http://www.wam-a-bam.com/UltraMist.html

 

reps to you Chellie !