My dads truck knocks and pings if he runs anything other than 89 in it. The truck only has 70,000 miles on it. He would like to save the money on fuel if anyone has any I deas please let me know.

 

I have had the same problem with a few cars and have learned of various possible causes.
As engines accumulate miles, the combustion chamber gets coated by carbon deposits, which effectively increase (slightly) the cylinders compression ratio. As you probably already know , engines with higher compression require higher octane fuel to run properly.
Carbon also affects the engine by getting hot and becoming a non controlled ignition source, and it is usually when you accelerate that the high rate of combustion cycles cause some piece of carbon to get really hot -red hot- and this causes ignition timing issues also known as pinging.

Improper ignition wire routing in the 5.0 engine can cause ignition timing issues if the spark manages to jump from one wire to another due to worn cables or electromagnetic induction.
I have also seen this problem being caused by sparkplugs of the wrong temperature range.

Solutions are fairly simple. You can clean the carbon of your combustion chambers by several chemical means (fuel additives and cleaners like seafoam)or by spraying a light mist of water with a spraybottle into the intake with the engine running. the water turning violently into vapor in the ignition chamber most of the time manages to dislodge stubborn carbon deposits. Be very clear I sad a LIGHT MIST, dont go spraying your intake with a garden hose or you will hydrolock your engine and pinging will be the least of your problems.
You can back your timing down a little.
You can change your ignition wires and veryfy they are routed properly.
You can change your sparkplugs for a colder model or simply another brand.

Hope this helps.

 

FGS is right, the only reason your truck would need a higher octane fuel is because the compression ratio is not normal. Higher octane fuels resist premature ignition, thus these 89 or 91 octane fuel is used in performance engines with higher compression. You should look into the carbon deposit issue first. It is the easiest fix. Just do an engine flush the next time you change oil.

 

One other related issue just popped into my head. You mentioned that the truck only has 70K miles. You did not mention the model year of the truck so I dont know if it is fuel injected or carburated.
If it is fuel injected, I find rather strange that with only that mileage the truck is developing carbon deposits to the extent of causing pinging issues.
Fuel injected engines are very efficient in their use of gasoline, so I would think that there has to be some reason for the unusual carbon accumulation.
Maybe it is running rich (many reasons for that alone, leaky injectors, bad fuel pressure regulator, computer never goes to closed loop, and many more) maybe it is running too cool.
Now if it is carburated, you probably are just in need to adjust the carb.
Let us know.

 

one word: s e a f o a m

 

Sorry guys the truck is a 92, F-150 4x4

 

Just a little note before my dad bought the truck it sat for almost 10 years in storage. He bought it in 04 and it had 36,000 miles on it. The truck was part of an estate that was not setteld for that lenghth of time. Hope that will help you guys a little more. Thanks for all the help so far

 

Yea so it is EFI. So yea run down to your local shop and get a can of sea foam (2.19 here) and put it through the break booster and then turn the truck off and let her sit for a few min then fire her up and wait till the smoke stops then see if its any better. Since it has been sitting and such make sure that your plug wires arent cracked and such just wait till night time fire up the truck and look at the engine in the dark look for arcs and such.

 

So how do I use this sea foam again.

 

Take the can of it and then take your break booster vaccum line from the break boost and put the tube in the can well it wont fit just put on hard and the vaccum will take care of it not leaking. Then do about 3/4 (I always do the whole can) and then turn the truck off and let sit for about 2-4 minutes fire her up and watch the smoke and the neighbors yell and wait for the smoke to stop and you are a carbon free or well GREATLY reduced on it.

 

Thanks Alot I just wasn't sure about the brake booster you were talking about. I will try it on saturday and let you know how it works.

Thanks Again
Nick