Good octane news on my 97 Tbird !

[97tbird]

Some of you may have read my post on the topic about cars not needing Premium fuel a few days ago, where I stated that I have to use 93 oct in my 4.6L Bird to prevent pinging...even with FP, and after I had the MAF cleaned(once).

So...4 days ago, the Exxon station's 93 oct pump was broken, and I got 89oct..just a few gallons, and drove to work, almost wincing in anticipation, waiting to hear familiar "rattle", the typical pinging noise of the 4.6L; I didn't hear it, only the engine seemed a bit louder, and a very little bit erratic at idle, but no "rattle"/ping. On the way home, the idle had smoothed out, and the engine sounded almost 100% normal...
Still believing that the pinging was prevented by the little 93 oct I had before getting the 89 oct., I still didn't want to be/feel happy.

The next day, 93 was available, but I thought "what the heck, doesn't hurt to try again", and got half a tank of the 89 oct this time...no pinging, great acceleration!!!

it works with 89 oct.

I was so happy! now this is without FP even, and in 96F heat(which are good conditions for pinging)
I don't know what could've happened that the car doesn't ping under 89 oct anymore...Then I really TRIED to make it ping: turned a/c on full blast, and accelerated up a very steep hill, trying to keep it at 60-65 mph. STILL no ping!

Next time, I'm going to get a FULL tank of 89 oct and see what happens. With FP, and another careful MAF cleaning (which always gives me the creeps, although I did pretty good last time), perhaps I can keep the primo stuff out of the Bird!

Just wanted to let you guys know...will update any changes.

[ August 02, 2005, 07:34 PM: Message edited by: 97tbird ]

 

[JonS]

Try 87 next. You might be supprised that it works also. Just think of the $$ saved.

 

[97tbird]

Jons,

I don't know...a few yrs ago, even 89 made it ping..so I'm naturally scared to push my luck, but I might give it a try by putting a little of it first like i did with the 89.

what could've caused the improvement i wonder...I only used FP once or twice a long time ago(didn't go down on octane at that time...perhaps i should've tried it then, but i thought it was too early)

 

[JonS]

I've read that if you don't need high octane from the start, but use it, you will leave deposits and thus increasing your compression ratio, and from then on will need the higher octane gas to keep from pinging. You probably removed you deposits and lowered you compression ratio with the FP and can use lower octane again. That would be nice.

 

[97tbird]

Thanks, JonS.
yeah...I also hope I can go down to 87 of course, but 1st, I want to run a FULL tank of pure 87 oct and see if it's succesfull.

The car ran for the first 80k miles on regular. I only went to high octane after it began to ping with the 87 and 89 oct, so hopefully I didn't create any totally "unnecessary" deposits...

 

[mechtech]

Premium doesn't leave deposits.
We are not in the 1960s with leaded fuel, anymore.
Keep trying that 89, and see how it works. Right now, you are diluting the 93, and have slightly higher than 89.

 

[97tbird]

on my previous post it should be "..I want to run a FULL tank of pure 89 oct and see if it's succesfull..."

I typed 87 by mistake.