I know this doesn't fit with the pattern of "more power, more speed", but I'm looking for better mileage. I have a nice 1988 GTA with the 350 TPI engine. I use it as a commuter car and put 70 miles a day on it, 60 of which is highway. I'm getting about 16 MPG currently. Is there anything I can do to improve that? Cutting back on the power is not a bid deal to me - I set the cruise at 65 and just enjoy the ride. Does anybody make such a thing as an "economy chip"?

-Farren

 

16mpg is kind of crappy for highway miles. I assume you have a 700r4 and that it IS shifting into overdrive?

What rear gears do you have?

Have you replaced your o2 sensor recently? A malfunctioning o2 sensor will give you incredibly bad gas mileage

When is the last time you've done a tune up?

How many miles on the motor?

 

All good questions but my answers are vague:

Yep, it's the 700R4 and it is shifting into O/D. Showing just over 2000 RPM at 65 MPH.

I have no idea what the gear ratio is in the rear end. I wish I did. I didn't get any paperwork with the car and can't find the RPO codes anywhere.

I O2 sensor was replaced last week and I'm not sure they did it right because the "check engine" light is back on. Perhaps getting that cleared up will solve the problem.

No idea on the tune up question. Hasn't had one in the month that I've owned it. I'll mention that when it goes back in for the O2 issue.

Mileage on the engine is the tricky question. The title shows 135,000, but the odometer shows 35,000. I have no idea if a previous owner assumed the extra "1" wasn't showing on the odometer or if it really isn't showing and should be. I wish I had a way to know for sure how many miles are on it!


So, when gently driven, what should I be getting for mileage? I'd be tickled to get it into the 20's.

-Farren

 

The first thing to do is get the SES light cleared up, and a good tune-up. As far as the rear gears go, judging by your speed and rpm listed I'd say you have the 3.27's, which are the same ones I have, and were the standard gears in an 88 GTA. In my car I'll get about 20-22 MPG on pure highway driving, and about 18-20 on a city/highway mix.

------------------
Scott
88 GTA L98
14.389 @ 95.2 mph, 2.001 60'
In search of the elusive 1.9 60 foot time.

 

I've never got much better than 18 MPG in the city with my 350. I do 25+ MPG on the highway.

Your 16 MPG mixed highway/city sounds pretty poor though. Definitely get the SES light problem fixed..

You might have a leaking injector (or injectors) which are causing the engine to run rich.. That would trip the O2 sensor for sure.

Even if you have to go to a proper shop to get it fixed, do it. If you can save 3-5 MPG, the gas savings will probably offset the repair costs in the long run.



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1990 GTA L98/4L60

 

Try putting some 2.73 gears in there..

 

I have a 350 in my iroc, and i use to get like...14/15 in the city and about 16 on highway... and this may sound stupid but i installed the Performance Resource chip and can now get about 22 on the highway and around 19 in the city (depending on how i drive it, hehe) from what i understand...and have heard from other people the chip lowers the injector pulse rate or something like that... other than that i used to be pretty close to your MPG's

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89 IROC-Z 350 TPI

-Flowmaster Cat-back

-MSD 8.5mm Wires

-K&N AirFilters

-Ported Plenum

-Performance Resource Chip

Comeing:

-MSD GM Replacement Coil, and 6A or 6AL amp.

-Gutted Airboxes

-Edelbrock TES Headers

 

I heard that lower engine temperatures help atomize fuel better, so...What I did was installed a 160* thermostat and made sure my air deflector was bringing air into the radiator. You can also set your fan to go on when you turn your car on, which will keep your temp below 160 with the new stat.

I used to get 15 mpg on average, just by doing this cheap mod, I average 20 mpg now.

-Erik W. '86 Firebird 2.8L MPFI

 

Can't agree with niu2001's post. Lowering the coolant temp increases power because it increases the air density charge to the cylinders. It has the opposite effect on atomization (vaporization) of the fuel and economy.

I get 19-21 mpg, the lower when I've gone to the strip, the latter when I haven't. I agree with the earlier posts about the SES light and tuneup, including clean air filter. The gears won't make that much difference (at least not enough to offset the cost for a couple of years). Synthetic lubricants front to back will help economy.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 3.08 open, cat-back from '90 305HO, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress.
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.