Octane levels

[Joe Fast]

Question... I have two 1999's one with the SOHC and the other without. The regular engine runs fine on regular gas; however, I find that the SOHC, which has very low miles (6,500) only runs well with 92 octane or better. Anyone have similar issues with their motors?


Joe

 

[Rockey]

Octane is simply a numerical rating of a fuels resistance to detonation. It will NOT burn faster, slower, hotter, colder than a fuel with a different octane rating, all else being equal.

Its possible that the 92 octane fuel that you used had additives in it that affected performance. Did you always buy from the same place?

With that being said, the only way octane would affect performance is if you vehicle was detonating and the engine management had the ability to retard the timing because of this. Some vehicles actually advance the timing until they sense detonation then back the timing off X degrees. I don't think the 99 X had the ability to advance/retard timing based on detonation detection.

 

[jgilbs]

i know the SOHCs are the only excplorer engines with a knock sensor, so maybe it does have that ability.

 

[Rockey]

i know the SOHCs are the only excplorer engines with a knock sensor, so maybe it does have that ability.

If it has a knock sensor then thats probably the reason for the difference in power. I really didnt think any X had a knock sensor. Why does the SOHC have one? What is the compression ratio of that motor?

 

[aldive]

My SOHC runs great on 87 with the stock computer program as well as the custom 87 program as well as running great on 93 with the custom 93 octane program ( Apten Flasher ).

 

[cfkane]

The fuel formulation can have an impact on octane requirements. For example a 10% ethanol blend can interfere with the additive action on a straight hydrocarbon blend. Consequently different additives are required to keep the engine clean. The best technology in use today consists of polyetheramine in a 200 ppm dosage for a clean engine. Depending upon the fuel used and the additives in it you could very well have significant deposits at 6,500 miles.

A simple test that will clean up the engine would be to add a can of BG products 44K or Chevron Techron to a full tank of fuel and run the tank until near empty. The will give you a dose of about 2000ppm which is sufficient to clean any deposits. Be careful not to run the high levels to frequently as PEA will change the oil viscosity and overuse will lead to lubrication issues.

 

[pmcmaster]

Not sure on your 1999 but my 97 4.0L sohc is fitted with a knock sensor (RH side cylinder head by intake manifold) This sensors 'knocking/pinging' and signals PCM to retard ignition. Although mine is an 'export' model I believe theres no difference to 'home' models and mine runs quite happily on 93 octane (unleaded).

 

[caldi55]

I have a 97 SOHC, it has a power pak instead of a distributor. If not to advance/retart ignition what other purpose would it serve?

I do notice that i get better mpg when i run 89 as opposed to 87

 

[Oversquare]

cfkane - now we're talkin! I'm interested in what you have to say! Please PM me any resources that you have regarding your information.

-Brad