Thank you guys for your replies.
I probably should have been a little more detailed with my application.
The LM324 has Vcc of 5V, the signal it gets from the sensor goes from 0-8V under it's normal operating range, and if it goes beyond either limit for unseen reasons, I want the LM324 to take in instead of the micro controller. This design works well. However the alternator seems to be transmitting AC noise into the lines which messes it up the RPM reading when the truck current consumption changes (I've tried two alternators).
My original prototype didn't have this issue, and was using a comparator. I used this quad op-amp to avoid needing multiple chips for space reasons.
I know I can rig something to work, but if/when I do, I'll be sending one to a couple buddies, and I want it to be as bullet proof as possible, so they don't accidentally fry something.
I'm just about to the point of just making a new PCB, as there are a couple other things I should change while I'm at it.
I appreciate the ideas guys. I'm going to omit some features on the new board. There was one buddy that wanted the extra features, hence the need for an Op-amp, well he can get an old board with a LM324 to LM319 adapter. lol
Thanks guys!