poor mileage

[83cutlasssedan]

Hey everyone,

I have an 83 cutlass supreme with the 3.8L (non-computer controlled), and it has been giving me pretty crappy gas mileage. (I have been getting about 14mpg). I was wondering if anyone knew the type of mileage I should be getting and what I can try to fix this. I have tested for vacuum leaks, checked the timng, replaced the wires, rotor, distributor and plugs, and it hasn't gotten any better.

If you guys can think of anything else i can try please let me know.

Thanks in advance,

 

[78mali350]

nothin wrong with my camaro except high miles and it only gets 14mpg in the city and it;s a 3.4 so i think age did it to ya but i am not sure

 

[85t5mcss]

Well, if u did the tune-up and carb is adjusted properly, then I'd say the culprit is miles. The older they get and more miles on them the lessefficient they become. Compression is lost past the rings and valves and mileage drops along with it. MPG should be about 22MPG depending on rear gears and how u drive it. I'd do a quick compression check and tune the carb, see what happens, also change the air and fuel filters. If the car has been neglected and no regular maintenance then all these problems with wear and mileage happen even quicker. Try Sea-Foam or Lucas Fuel Cleaner also.

 

[83cutlasssedan]

thanks for the response

I was thinking it could just be that the car is getting old, but it does only have about 60000 original miles on it. I forgot to mention but I did replace the fuel filter, and the air filters, and the pcv valve are also new.

I'm not sure how to tune-up a carb though?

Also, I put the car back on the road last year after sitting for 2 years.

thanks,

 

[illregal82]

when i had a 3.8 in my regal i got horrible gas milelage i would have to damn new floor it just to get on the freeway it had 88000 on it . with the sbc 350 the gas milelage stayed about the same but way more power

 

[85t5mcss]

Old school mechanic can tune the carb. U can do it yourself, but lots can go wrong to make it worse. F/I is so much easier, but more $$$ and electronics.

 

[85 Cutlass Brougham]

Unfortunately, that's not horrible with city miles on that engine. I got about 14-15 MPG with mine when it had the 3.8 V6/TH200c/2.41 axle combo and 29 highway (!). It was a pizza delivery car back then. I now get about 14-16 city/22-24 highway with my 355/Th2004R/3.23 axle setup. The problem around town is that your car is geared for highway cruising and not acceleration. Therefore it takes much more throttle to get it going out of the hole than it would were it geared differently. It is also a underpowered engine for the application it is being put it. While it may have 190 Ft LBS of torque at 1800 RPM, it also has less horsepower than the 1995 Nissan Sentra beater I used to have that had a 1.6 liter engine in it (115hp Sentra, 110hp 3.8). My Cutlass took a yawn inspiring 21 seconds to hit 60 stock, the Sentra? 12 seconds ( Sentra was also 1,000 lbs lighter with better gearing). If you do an engine swap to something more suited to the vehicle rather than the EPA highway fuel economy numbers of the mid 80's, it could get better on all fronts. You could also look for the 3.23 geared axle from an 80's V6 g body that was set up for high altitude (GU4 option code on the trunk sticker, IIRC) and that may help you around town without spending alot of money.Just remember that it is important to match your gearing to the actual needs of the vehicle and the engine's powerband in order to maximize fuel economy, not just optimize it for one steady state speed.

 

[83cutlasssedan]

thanks for the info, I thought I might just be stuck with that mileage. It's too bad the engine runs so good still though, I can't bring myself to swapping it out for something bigger till I start having problems. I guess I will have to work on the suspension and exterior till then.

Thanks again

 

[85 Cutlass Brougham]

thanks for the info, I thought I might just be stuck with that mileage. It's too bad the engine runs so good still though, I can't bring myself to swapping it out for something bigger till I start having problems. I guess I will have to work on the suspension and exterior till then.

Thanks again

Yeah, mine still ran fine, even with 200k on it when I pulled it. I sold it to someone I knew for $200 installed and he drove it for a while before it died. I would wait on the suspension if you are going to swap. If it has a V6, the springs that are available aftermarket are all either V8 or turbo V6, both of which have more frontal weight than your 2 bbl V6, plus the turbo cars also had heavier transmissions with the TH200 4R as compared to your TH200C. I saw you said you have no computer. Did someone remove it? If so, did they swap to a regular carb and distributor or just remove the computer? It will run with the computer unplugged, but may get a little worse fuel mileage. I ran mine for a year with it unplugged because it was actually 6 seconds faster to 60 than with it plugged in. I timed it and it took 15 seconds unplugged and 21-22 seconds 0-60 with the computer!

 

[pontiacgp]

I'm running synthetic oil and the first time I used it it was real noticeable that the engine revs alot easier than with the conventional oil I was using. I can't tell you how much the fuel mileage improved from the oil tho cause I put an SP2 intake on at the same time..