just a general tech post. i was driving a used car that had a CEL. when taken to get the code read, it turned out to be a misfire on cylinder #1.

the moron owner has been using 87 octane when the manual calls for 91 octane. could this be causing the misfire? or is something else to blame?

i know misfires can be caused from lack of spark, poor compression, or a lean fuel mix. can running lower octane create a lower A/F ratio???

 

Here's the scoop...

Cars designed to be running 91 oct. are tuned for that octane. By tuned I mean timing settings and A/F ratios. Usually 91oct. means the ecu set's it's timing to advance more with 91 oct. The manufactures build in measures that would adjust to correct this, Some are not as good at it.

Now by running 87oct with that timing advance would definately cause ping's and or missfire's.

It really just matters if the ECU can cope with it. Some can some can't.