Well I have a 92 RS and all it has on it is a 3" Flowmaster cat-back system on it and I can only seem to get if I drive it like a Grandma.

I'm getting 15 in the city and 20-21 highway at 70-75. It seems like I should be getting some better gas mileage then this?

Also the car seems to smell like it's running a tad rich. How do I fix that and what bearing would that have on gas mileage?

 

hey, burning rich can have everything to do with bad gas mileage. if you havent already replace your O2 sensor

 

That does seem like a really low fuel mileage for that car. Definitely track down why it's running rich. Could be the O2 sensor, could be something else, but get that fixed and I'd almost guarantee you'll see a noticeable increase in your mileage.

 

Well just recently the o2 sensor was changed and also the cat to make it pass smog.

I just took a trip up north to see my girlfriend so I'm going to fill up and sere what kind of mileage I got. it was about 80 and I did bury the neddle but we'll see.

What could I do to make her stop running so rich? It knocks like a beeotch when I'm running 87 so should I bump up the timing? If so how much?

 

If it knocks now, retard the timing. Advancing it will only increase knock.

 

It shouldnt knock running 87 without any advance. My car just recently started doing this, so I am considering replacing the EGR valve to try and fix it (see my thread below).

Also, your EGR affects emissions and fuel milage pretty significantly I hear.

When I bought the car it got better than 30mpg on the highway. Now, that is probably less than 20, and **** milage around town. Also, it never used to knock but now it does. This all started in the late fall / early winter.

 

slow_90firebird

smoking man eh?

 

Well when my Dad bought the car the guy said only to use 91 since it knocked pretty bad. That was in 2003 with just under 75k miles on the car.

My dad has always ran 91 in it since the knocking is something neither of us like to hear and the car should run on 87 just fine but it knocks pretty bad.

So just this past October the car wouldn't pass smog and it didn't even when we first got it so the timing had to be played with. Now I had the timing set to I believe two degrees advanced. How do i retard the timing and to what should I? Will this affect power?

 

My 92 will get about 17-20 city and damn near 30hwy.

 

Nobody believes me around here when I tell them the mileage my '90 RS got with it's stock 305 TBI... 17-20 city was normal, and close to 30 highway was very consistent. Glad to see I'm not the only one with these results.

Even when I'd open her up and play a bit, I still got an average never below 14 city (lots of quick starts and pedal-to-the-medal driving).

Then again, the most people who think I'm full of it when I tell them my mileage are blue oval drivers...

 

Thrawn, my carburated 305 LG4, used to get that exact same gas mileage when i first got her. but now im lucky to see 15 in city, and i usually see 25 on highway.

Not sure whats goin on....

And im so with you on how no one believes the gas mileage (espcially when its people with 4 banger honda's that cant even get 20 city) lmao.

 

my 78 monza with a iron duke will get a easy 40mpg city with a th200, 2.73 rear gears, no emissions, weber carb and a full port match. Now my camaro is just about as stock as they come with only a 3000watt stereo system and a open air element. I have been helping a couple of my friends get better mileage and most of these fuel injected cars are programmed to use enough gas to make thier buddies in the middle east rich.

 

There are a bunch of things that will affect the fuel consumption. With the engine: plugs, cap, rotor, and spark plug wires can make a huge difference. Should use standard AC Delco or Autolite plugs (no fancy or plat's).

Make sure the injector o-rings are not leaking. EGR working correctly along with a good O2 sensor. CCP still in place? Stock air cleaner is better for mileage then an open element.

Then in the chassis, are the brakes dragging? u-joints shot causing excess bind, front end alignment? Missing the air dam?

Jack up and try rotating the front tires. Should turn easily. Can also do roll down tests to measure the actual vehicle drag.

RBob.

 

Is this statement due to the built in preheat?

DM

 

I'm kind of curious about the stock airbox vs. open breather as well. I've noticed first-hand I get better mileage/power on most of my vehicles with the factory "banjo" breather over an aftermarket open-faced.

I wonder if it has to do with air turbulence that's created in the closed type breather, or perhaps air temperature coming in through the "cool air duct" over the hot engine bay air?

 

[
Definitely the COOLER air.

quote=Thrawn;3744837]I'm kind of curious about the stock airbox vs. open breather as well. I've noticed first-hand I get better mileage/power on most of my vehicles with the factory "banjo" breather over an aftermarket open-faced.

I wonder if it has to do with air turbulence that's created in the closed type breather, or perhaps air temperature coming in through the "cool air duct" over the hot engine bay air?[/quote]

 

Hey Guys
Something that I have happen to me on older motors that effects power, mileage, and detonation. As the motor wears the timing chain streaches. At first it is like advancing the timing, motor will run it's best. Then as it ages it will make timing way off. I've come to notice it when you are setting the timing the timing mark will jump around on you. You'll set it then check it and it will be different like the distributor moved. Also they will start losing power really bad if streached out bad, they will idle and roll but will not get up to power. One last thing is to check the distributor for wear next.
Cheers

 

when my 86 t/a was stock with a 220k lg4 stock 700r4 and 2.73 gears i got 20-22 aorund town being easy on it. playing a lil it drop down to around 16-18 in town. no one belived me. now i built a 305 with cam lil headwork headers th350 trans with a 2800stall and running a tad rich im getting 17 in the city im happy with it. on my 86 though right before the motor went mileage kept getting worse and worse eventualy i averaged 15-17 in town. heck im getting 18 in the city in my 03 yukon xl (suburban) ive also seen where you get gas sometimes has an effect.