Is it a late 99 with the coil on plug setup? If so, put an earlier head on it. Thee exhaust ports are tiny on mid 99 and up...emissions.

My 99 has a built up motor using a 95 head, 00 intake, 62mm tb, .030 bore, srt4 injectors k&n intake, comp cam, 258 crank and rods, 242 tcase with ax15. I average 18 city in winter, 22 or a bit higher highest. Summer sees about 2mpg increase. My mpg is with using cruise as much as possible. I can get as low as 13mpg with it if I'm beating on it

After owning 6 of them, I lack the patience required to own another. Most of mine got around 13

I love my renix, have had 2 of them, and prefer them over any other year except 96.

'88 with 33s, 4cyl, no muffler, got about 9mpg. Ha ha

No SES light, but I did replace both O2 sensors. Went from 14 to 18 mpg. Engine all stock, 235 75 tires.

which o2 sensors did you buy? looking to do the same.

Bosch, both of them. Make sure the exhaust is warmed up when you go to remove them.

Don't want to jack the thread or anything but I have a 96 with 189k miles and about 20k ago I would say it was getting considerably higher gas mileage then what I am seeing now. It's down to about 14.5 mpg in the city if not a little worse sometimes. Summer isn't making much of a difference. My check engine light has gone of a couple times autozone said it's one of the o2 sensors and the last time it was changed was about 100k. Always used synthetic oil since it was bought at 40k. What should I try besides changing o2 sensor? Already cleaned the TB...Thinking about getting the neon injectors from the junkyard as well...
Thanks,
Lee

Uh... Change the oxygen sensors.

X2

Are thrush glass packs offset and fit in, what is the part number? I got a rusty muffler. It could be fun to try, though I'd have to be light on the throttle driving through my own neighborhood. I got a rusty muffler.

I have a 2001/ 130k/ auto with CAI (OK, performance air intake, not cold air), changed all the fluids, new O2 sensors upstream (Cali emmissions), spacer, cleaned the AIT, 235's. Got 16.4 last tank knocking around town. Most recent tank on the road was 18.4 (winter). Bad but up from the 14.6 I first got before I changed all the fluids.

Hahah I get about 10 city with 31's on 4.5" and a rack.

Both or just the one that is making the check engine light come on?

I like doing things in pairs, if it's $, just change the one indicated by the code.

I get somewhere between 12 and 15 mpg with 35 inch xterrains and stock gears.