Just picked up an '86 GXL the other day, and it seems that I put in $10 of gas (~3.8 gallons) and after 45-50 miles its almost down on E again! This has been twice now. What could possibly be wrong? Running super rich somehow? My modified 12a gets 20-22 mpg, I thought this would at least get 20. Thanks for ANY tips/help. Btw.. how low does the gauge have to get before its actually EMPTY?

Matt

 

Have you done a tune up yet?


You're getting 13-14mpg, its not unheard of in FC's. You can certainly do better, i get around 19-21.

 

This is mostly highway miles btw... yes new plugs, wires, the whole works. Could it be the fuel filter or injectors? Car has a newer engine (60k miles) so everything should be working correctly.

 

send in your injectors to be cleaned,balanced and bluprinted. that can eff up ur gas mileage big time

 

IMO:
thats something you should never find out.... the crap that floats on top of the gas is not good for the motor.

i act like 1/4 tank is "E"... running out of gas is silly.

 

FC's are known to run rich, but damn avg of 8mpg drop, thats pushing it, get ur injectors cleaned. also mess with your air/fuel ratio screw thing (next to the vacuum sensor) and see if it needs adjusting.

 

And you probably need a new O2 sensor also. That's what the ECU uses to "trim" the fuel for highway cruise. If it's out of wack, it can lead to bad gas mileage.

 

Thanks for the tips.. I wouldn't mind messing with the A/F screw, but I don't want to make it any worse, and i'll definetly get the oxygen sensor replaced.

 

yeah old cars need a full tune up. more than just plugs. Its also possible that the age of the emissios controls are killing you.

 

i get somewhere between 50-60miles to a quarter tank off 10-12$....but i have bigger injectors and its a 88 GXL 2+2.... i get like 200 to 220 to a full tank....disgusting.... lol

 

Why do you have larger injectors on an N/A? We run pig rich from the factory. That's pretty silly, unless you have some fuel way to control it.

 

Mileage is well covered in the FAQ. There are links to several mileage related topics which are full of info.

 

my 87 large street port TII conversion gets about 80 miles to 3/4 tank, wtf? I think I need to do some serious tuning to squeeze out every mpg. plus maybe my driving habits are killing gas mileage too, keep it out of boost as often as possible and refrain from wasting gas by boosting past ricey *** hondas who rev at you

 

I drove 340 miles on one tank driving my '88 SE home from where I bought it.

Edit: and have never gotten mileage close to that since

 

I at one point got about 27mpg in my n/a, that was good stuff, freeway trip though, even rodding it around town i got 17. When i turboed that block all hell broke loose and so did my wallet

 

on my 90 gxl (bone stock) I get 26 mpg nearly always with my tires being at 28 lb (bumpy detroit roads), all hwy, at 70 mph, 400 miles a week.

we have a lots of threads of mpg problems and "possible solutions" but noone every posts followups and spell out exactly what worked for them.

 

for a while i only got 120 miles to the FULL tank!!! then i replaced the shitty o2 sensor, and bam, literaly twice the mileage...... . besides they're cheap, i got mine for $45, bosch, direct replacement.
and with todays gas prices, i need all the mileage i can get. it takes $50+ to fill my tank .

 

wow. 26 is very impressive. On hwy driving i get 20 and sometimes, depending on the weather and temp, it may drop to 17 or 18 around town. I should prolly have my injectors cleaned and maybe put in a new fuel filter. It couldn't hurt right. One thing i did notice is that for extended periods, drafting really works. Find a fast SUV or a 18wheel rig and get within a few carlengths behind it and set your cruise. You could be saving 3 or so more miles to the gallon.

BTW, what is the size of our fuel tanks?

 

Closing yet another mileage topic...We've been over this 10,000 times, people.