I changed to the 746 injectors, fixed cracked manifold, put on a new manifold gasket back in early November and had no drop in mpg. I was getting 15mpg since January 2016. That's when I started driving it.

I drove with no cat, muffler, or tail pipe for a few weeks until mid November. No drop.

I had a shop weld on a new cat, old muffler (still good), and a new tail pipe. This was in the first couple days of January.

I still hadn't noticed a drop however the last times I put gas in I've only got 12.5-13 mpg. This would be in February.
My gas hand doesn't work exactly correct either so I've always done it by miles and it's worked.

So I don't know why my mileage would just drop 2-3 mpg. I will say I do have a couple pin hole exhaust leaks the shop missed when welding. One is right in front of cat and one is right in front of muffler. Two little spot welds will fix this. I don't think that would cause a drop because I drove it for 10 months with no cat, muffler, TP. I wonder why this drop happened?

Cane, (and all), The three wire Zirconia O2 sensor in a Renix Jeep is a variable resistor. The ECU feeds 5 volts, and how much the O2 grounds that is what the puter uses to trim the mix after the MAP roughs it in. An O2 failing "open", (like mine did), will just let the ECU use default pulse width settings for the injectors. Another scenario...what if that 5 volt feed is grounded? By the O2 or elsewhere... I don't know what the ECU would make of that. Point is, just unplugging it and seeing what happens is not necessarily a bad idea. Granted it would more likely be the wire grounding, but easy enough to rule out the O2 it's self by unplugging it.

This thread was somewhat sabotaged by a moron, but right on top is a link to EcoMikes O2 testing info > https://www.cherokeeforum.com/f2/ren...ce-rms-133153/