Preignition?

'98, 4L and no engine changes except a few more holes in the air box.
Runs fine, no ping on hills or with a load, but just idling, it sounds like a diesel or there's marbles in the cylinders. I wanted to check the resistance in the oxygen sensors but how the heck do you get the connecter off. It looks like its crimped on. The plugs are Bosch platinums. I use regular gas, but not the same brand all the time. That's all I can think of.
Walt

Walt,

You have a build up in your cylinders this causes your compression ratio to go up. The simple solution is to run a higher octane gasoline.

I am sure there are some products you can run through your engine. I'd try some techron to see if it helps but think you may find yourself having to use higher octane gasoline. I recall posts a few years ago on here about your problem. Your engine does not have a knock sensor or else the engine computer could retard your timing and prevent the preignition.

Martin

I'll try a tankfull of the expensive stuff and I was told about a top engine cleaner and will look for that next.