What are some things that can cause bad city mileage but not effect highway mileage?

My transmission always seems to do some funny things and make some odd clunks between 2nd and 3rd gear, but I wouldn't call it slipping. While taking it easy around town it does seem to "stop pulling" between 2nd and 3rd for a short time.

OTHER THAN THAT, anybody have any other ideas?

 

City mileage is a joke. It's impossible to use. Depending on where you drive, speed limit, amount of stop signs/lights, etc etc. It's so variable it's useless to even measure IMHO.
12MPG city is about what I would expect with a 350 in your 'sports car'.

 

You know what it is? It's having a V8.
Just feel lucky you get such great highway mileage...

 

*shrug* Just figured I should at least be able to pull high teens. But if you say so.....

 

Might get better mileage if you drive "easier"...but I dono how you're driving.

 

yep city sucks and highway is great, IF you cruise at about 75 and dont play around

if you, all the time around the city you know its going to be bad, i think 10-14 should be expected around town 25-30 on the interstate

 

A trans that is has any messed up gears beside over drive could cause this, or a broken one way clutch in the stator.
You said it "While taking it easy around town it does seem to "stop pulling" between 2nd and 3rd for a short time." Its called a 2-3 flair. One of two things is happening. Either the clutches for 2nd are turning off to soon, before the the clutches for 3rd can come on. Or the the clutchs for 3rd come on too slowly, so it seems to slide inbetween gears.

 

You can get much better gas mileage by not making any stops, including lights and street signs. the trade off may not be attractive.

 

Could be your rear gears are set more for milage then town driving. I swapped from 2.73 to 3.23 and noticed an around town improvement. Havent taken it on the hwy yet.

Also, "taking it easy" isnt always the answer for better mpg. Its driving in the efficency range of your setup(motor, trans, gears, aero dynamics). To learn this, you need to get a dash mounted vac gauge. Then start "playing". The faster you can go and pull the highest amount of suction is best.

We have so many hills where I live, because of gas people have started grandma driving around and requiring to pull "even" vac when you go up hills. It actually kills your mpg. What they need to do is speedlimit and learn to downshift going up hills and using the gears to help your mpg.

 

Stop the street racing that helps.

Kidding.

I totally agree that if your transmission is messed up some, your mileage will go down.

I am getting around 21 mpg doing combination driving, with a 305 with 150K on it, and it is carbureted and the carb. needs some work, and if I can get that, I would expect you should be able to get better than you are getting.

I agree with what most people said already. Only thing I can add is this. If you have a catalectic converter still, make sure its not restricting your exhaust flow. That can reduce mileage some.

 

Have you tried ajusting the TV cable? It may be out of adjustment and not letting overdrive engage. I have a fiero that needed it ajusted. Was not shifting into OD in town but was on the highway. Just a though

 

I would agree about checking the TV cable. It can cause all sorts of very strange behavior if it's not adjusted correctly.

As far as your mileage, with your gears and EFI, you should do better than that. My vote is the strange tranny behavior you were talking about. If you're looking to get better mileage, a manual tranny always helps. Like Sonix said, it's hard to determine what is "normal" city mileage because of all the variables. Are you dealing with a lot of stop and go, or just lower speed limits with the occasional stop and go?

 

I am in a similiar boat. Had my 91 with a 350 since birth. Saw 16 - 18 for city a while back (only 20 Highway). It has 150 K, new cats, fuel injectors, full tune up, IAC valve, EGR, Muffler. I am now getting 12 in city. I have moved so city driving is different, but also have different grade of fuel (lived in Cali before where only had 91 octane, now have 93 octane). My car passes smog great, so it should be burning effeciently. Trans was just rebuilt, and it is all stock. I drive easy for the most part, and let it shift into OD.

Could this be an issue of the oxygenation and ethanol they are adding to regular fuel? Are we essentially getting less gas in a tank? I know the ethanol piece lowers mileage. Maybe the oxygenation also lowers mileage? Both are added only to improve emissions/run more efficiently, but they both take up space in the gas tank.

 

I have carburetted 350 in an 89 IROC, and I end up with 17ish mpg on the highway, and about 13 in the city. Any idea why there is virtually no gap between these two numbers? I don't drive at crazy speeds, and I just can't figure out why it's so bad. I understand that the whole having a v8 eats the gas in the city, but what's the deal with highway mpg? my car does run sort of cool though, i think the thermostat is broken up. On the highway, the coolant temp is only aroun 140 degrees. Any ideas?

 

Hey at least you're half way there! But your city mileage is down a bit from what I've seen. I have a 5.7 and am getting around 15 city. Haven't checked hwy since a re-tune but was getting 13 city/18 hwy before.

Presuming you've got a decent running car (in good mechanical condition) and you drive conservatively, you can do better. There definatly is such a thing as performance WITH economy. Crappy mileage is not the price of performance in all cases. I'm shooting for high teens city and my car runs 8.60 1/8 mi. and I'm expecting sub 8.50's before I spray it. Maybe sub 8's then. I am programming my own chips so I can play with all the variables. Look at my sig for specs.

 

Good points. Vacuum is an indicator of how hard you are "driving" into the throttle. There are a lot of bad habits to break. I definatly don't baby this thing around, just ask my wife. I think she's gashed up my door handle with her fingernails! See above post.