Spark plug fouling

[twobjshelbys]

Regarding O2 sensor location:

The entire system is based on averaging. If the engine, 8-stack adjustments and fuel injectors are properly balanced then sampling one cylinder is the same as sampling 8 (for a two O2 system) or one side for a one O2 sensor config...

My car had bungs in two locations: On one cylinder header and downstream past the point where the 4 individuals join but before the muffler itself. It is difficult to get the ideal position for this location. Ideally the O2 sensor is vertical but you can't do that. Mine was mounted on the passenger side at about 10-oclock.

I moved the sensor from one location to the other and there was a difference... My tuner expert said the difference was that at low idle speeds air does in fact find its way back into the muffler to the O2 sensor and "fool" it. My solution was to raise the idle speed to about 0200/1000 (depending on which direction you're looking), ie, just off horizontal, and pointed inward towards the chassis. For this reason it is important that if you use a tailpipe sensor at a shop that you get the sensor inserted far enough but not so far as to get it in one of the feeders. Regretfully, I don't have any photos of the O2 sensor installation.

This exercise taught me a lot more about DFI systems than I really wanted to know!

This is a tedious process that took me nearly a year to sort out. I'm an engineer so tried much of it myself using test drives where I could get the RPMs up. I would data log, do a run, adjust a table and try again. The Accel system is not self-learning so all tables had to be complete. Eventually I concluded the only way to really do it was on a dyno.