I do not disagree it could be the fuel. I do disagree that it is the grade of fuel that is the problem. I have been running 87 octane in it for years and didn't have a problem. I still suspect either another vacuum leak that I am having an extreme degree of difficulty finding, the fuel management system, the ignition system, or some related sensor relaying info to the computer.

 

First , I agree with your statement. What I'm suspicious of regarding the fuel is, did you get a load of water or other junk with one of the fill-ups, not the grade of fuel. Your vehicle should have a knock sensor that should cut back some, but not all detonation/preignition if that is what it is. Over advanced ignition timing will cause it to ping also..,,,,,,,,,,hanky

 

Actually I do not believe my vehicle is equipped with a knock sensor. It is a 94 so it is pre OBD2. As far as possible causes for pre-ignition the 2 most common are not enough fuel/ to much air or timing is advanced to far. There is no adjustment for timing because it is a waste spark system, there is no distributor.

 

What is the operating temp of the vehicle? Why did you need to replace the radiator fan? I' m beginning to wonder if there is a temperature condition involved . It is possible that something changed after the trailer towing episode. Did the vehicle possibly overheat at any time? Lets check the temp /cooling system for any unseen problems.,,,,,,,,,,,,hanky

 

I replaced the radiator fan because I noticed several cracks forming and decided the fan was cheaper than replacing half the front end. The vehicle has never overheated. I replaced all the fluids primarily due to age. When I went through the vehicle it was in preparation to give it to my little sister, so I didn't want there to be anything wrong with it. also Yesterday I dove back under the hood to try to find the problem. I sprayed brake clean all over everything in an attempt to get the idle to fluctuate to indicate a vacuum leak, nothing. I then removed the air filter and looked at the MAF sensor, nothing. I accidentally left the MAF sensor unplugged and went for a drive, detonation was non existent. As soon as I plugged it back in the detonation was back. Is there anyone in the northern VA area with a smoke machine?