Whats up Ryan,

10 mpg huh?? My heads/cam motor gets well over 10mpg and I beat the living crap out of it. I think you know from experience that I drive my car hard, and it still does better than yours. I think you need to swap cams and maybe check out your muffler bearings and see if they are stuck. Well, good luck.

Brian

 

if i drive 80% highway i get 14 mpg
if i drive 100% street i get about 11.9

(i would be really happy w/ 26) lol

i just thought that was normal, even my friends AMG benz push 493 hp gets better mileage then me

and im stock w/ 275...

would optispark cause lower mileage?

i know ur cat can clog quickly if the fuel isnt all burned, and if ur O2's are bad the cat will go quickly after,

so i gotta probably replace both, but im gonna hit the opti first will i see any gas mileage improvemnts?

 

the same guy with the amg, also has a camaro z28, he hit a guy on the free way not to long ago, and scrached his hood up, but he gets about 10 aswell, hes not concerned cause hes got alittle money in the bank but i care, i want a few more then 180 mile to a tank.

but if i gotta go on a long drive, there are stretches where 150 miles is not an uncommon break between gas stations

longest ive seen is 162 miles... wow for the cars sake i hope it makes it...

but i guess my gas cap is leaking too im gonna go check that out at pep boys.

 

Interesting. This doesn't seem to be year specific. A little more data on mine.
97 SS, M6, vert., so it's a little heavy, with only about 65,000 on it. Runs OK, with mid 14's in the quarter, in the mid 90 mph range. All driving is city, never gets into 6th. I drive hard but seldom rev. past 4,500rpm.
The dealers responce after service: "Reflash PCM, no codes stored, road tested 8 miles, all scan data within spec. no codes set or abnormal conditions found at this time". This included checking all four 02's.
Out side of getting 11.16 now 13mpg the car runs great. I added a bottle of injector cleaner and as expected there was no change.
I think I'll wait on changing the CAT's until I do the 95-96 header/single CAT convertion.
So.....your guess is as good as mine.

 

think reflashing the PCM could help any?? how much did it cost to do it??

 

I also have the crappy milage problem (about 9mpg, seems to have dropped to 8mpg with the 383). I have done the following since I started noticing it, and it's still there.

(Note I didn't do these because of the problem, so don't freak out).

Intake Leak
Removed Catalytic Converter
Plugs x 2
Wires x 2
Coil x 2 (one went south)
Fuel Filter
PCV valves
Evap Canister
Hoses/Pipes to the Evap Canister control switch (black box on pass side of intake)
Opti replacement (old one physically cracked)
O2 Replacement
New Motor (aka every gasket replaced)
New fuel Injectors
New Fuel Pump
PCM Reflashes galore (LT1 Edit)

None of the above have helped in any way (but the Evap Can helped me pass emmisions).

What's left to check:
EGR (no codes so... <shrug>)
Check Valves in Vaccum lines
???

 

Shouldn't be any more than $70 for both of them, from Jason Cromer. Do a search on here for his email/phone number.

As for bad MPG, cleaning my EGR valve helped improve mine. Don't know how much yet because I did in the middle of a tank of gas.

I also didn't notice the coil in some of your guys' lists. That and its wire should be checked/replaced too if you've done the other ignition stuff. And then there's the opti-spark, which I didn't see... a failing distributor can make poor combustion which will make MPG take a dive.