im going to college in sept, and with the milage im getting (200km per tank) i'm not going to be able to afford to drive my first true love. i really dont want to have to sell it, but i dont know what else i can try. ive done a complete tune up, top to bottom, and am still getting shitty mileage. at this point im desperate, and any ideas are appreciated.

 

What kind of driving are you doing?

For that matter, what *is* it? There's a big difference between, say, a stock S5 NA on the highway, and a heavily modded S4 TII in town racing from stoplight to stoplight.

Have you checked the ECU for codes? The S5 throws a check engine light, but the S4 will silently (for the most part) ignore a bad sensor and just use a default value. You have to go out of your way to check ECU codes on a S4.

For me, S4 NA, I can get about 300mi highway on 13.5gal. In town, when it's cold, I'm lucky to see 200mi on a tank.

-=Russ=-

 

my s5 na gets a lil over 250 mile. per tank, so like 15-16 mpg?

 

**** that's brutal, I was getting 22 in my TII.

Do a tune up, like quick.

 

Maybe your gas gauge is not working correctly anymore. How are you tracking the mpg?

 

safc...lean that **** out!!
with supporting mods of course...

 

Supporting mods with a SAFC on a N/A are the SAFC, he needs to do a FULL tune up, I would also check for seized brakes, and compression check.

 

He stated he did a complete tuneup.

I suppose asking what that involves would be helpful.

-=Russ=-

 

Holy hell, I never got much lower than 24mpg in my RX7's, city or highway. Though, at the track that ***** gone quick!

 

not without a wideband or a cheap A/F guage...

 

On an N/A you can probably get away without a wideband or A/F gauge tuning cruise.

 

i dont know about all of you .. but i get 400 km on a tank of fuel on the hwy .. and closer to 300 km inner city .. and inner city i usualy rev to 3 k or more ... mind u i drive a 88 base na but still i cant realy complain consiedering they way and what i drive i saw make it breath better .. exhaust and intake .. should help out alot ..

 

kinda figured...didnt want to get accused of misleading... you know how the critics are in here...

 

I read that he did a complete tune up to,don't know why I said that, well check for fuel leaks, dragging brakes, compression, and tire pressures. Hell maybe even a leaky injector.


My Idea of a full tune up is:
New plugs, wires, air, and fuel filters, new fluids in every part of the car, tire pressure set at 34ish, just replace everything that wears out.

 

You must drive pretty light footed...

I average around 17-20 combined and 22-24 highway, but mind you that highway is 80+ MPH for me.

but back up to the question at the start of this thread:
Either way 15-16 is not bad for a FC driven in the city. If the car really has had a full tune up (belts, all filters, all fluids, spark plugs, spark plug cables, timing checked, and O2 sensor) and you are still getting poor mileage, then try using a single ground spark plug (like a Iridium) and increasing the spark gap up .005 - .010. Might net you an extra mile per gallon.

 

if i drive keeping the rpm under 3500 i can get 230-250km/tank. as for the tune up, ive done air/fuel filters, plugs, wires o2sensor, fluids, the timing is fine, but belts are still to come. as for mods borla cat back exhaust. the injectors should be fine, installed new ones in sept. i will check the compression and i intend to get the car in the air next week to check for any gas leaks. thanks guys

 

Replace the O2 sensor. This can improve gas mileage in most cases.

 

I ran a search and came up with a long list of threads about power building and N/A-to-FI projects.

What is a SAFC (not in the FAQ)? I presume it leans out the engine burn (more air, less fuel), does this cost horse-power (I presume so), make the engine more lathargic, does it harm the engine or the apex seals? More info would be great.

 

I had really bad mileage in my gslse when the anti afterburn/air injectioin system wasn't hooked up. I'm sure this could apply to an FC also. The AF gauge was showing very rich durring cruise and light throttle. It also got bad milleage when the cat was clogged.

My best milleage in any RX was 30 plus (75MPH hwy) in an 85 12A car, with an FC coil running wasted spark, and a full exhaust with a high flow cat, and stock manifold.

 

OK, figured out what an SAFC is. Now, does this actually improve fuel economy on the N/A cars? How complicated is it to tune it have pre-based settings? Would I do more harm then good?

 

I got 17-19 combined. thats about average i guess..


Gil

 

Frequent short trips in which the car is never allowed to fully warm up are a killer on fuel economy. It is probably cheaper for you to drive the car than buy a new(er) one and get stuck with a new monthly or higher payment.

 

Depends, FC would be $58 more a month on gas then my Golf or a 240sx. (assuming I get 17mpg combined). I think I'm going end up with the FC though because I'm tired of fixing crap on my Golf (which I owe $4,000 on) and I just can't find a 240SX that I won't have to dump $1,500-2,500 into to make it presentible/drivable. End result is ~$600 more a year is still cheaper then either of the two cars, assuming I don' t have catstophic break downs.

 

Just a tip if get any kind of winter where you live then I wouldn’t think of an s13 240sx....they will rust out too easy. (They have thinner metal in the panels then other cars.) I've never seen a 240sx with out rust already started on it. But then again I live in Canada.

 

Actually, they improve fuel economy AND power when tuned correctly. NA FC's run quite rich from the factory. This wastes gas and hurts top end power. I've seen people dyno pretty substantial (for an NA, at least) gains with just a properly tuned SAFC.
As for my milage, its right about what Icemark said. With normal mixed driving its close to 20, mid 20's on the highway (personal record is 29), and 16-17 with spirited back-road runs. I do drive pretty conservatively in town, though. The key to good milage on these cars, once you have it properly running and in good tune, is to keep off the throttle in town. You'd be surprised how much fuel you waste by flooring it around town.