My 91 supra gets 10-12mpg...HELP

[suprajjang]

I have a 91 supra turbo and I can't seem to find whats causing this car to get around 12mpg. The only mods on the car are BIC ddp, Blitz nur spec exhaust, apex power intake, and hks ssq bov. Now in trying to fix this problem i have installed a brand new o2 sensor from toyota, new oem fuel pump, and changed the fuel filter. I also checked my stock IC pipes for any cracks or holes and i did not find any. Also the car runs very rich because it backfires often and there is a big puff of black smoke after i floor it. I drive the car easy in the city always shifting around 2000-2500 but I need your guys help on solving this problem.

Thanks

 

[aye mate]

How do you know thats the correct MPG you are getting? Are you doing it by mileage you drive and dividing it by 18.5(fuel tank capacity)? Unless you are actually running the car out of gas when doing this I would think its not very accurate. Also, someone said that the Supra won't run a tank dry, that when you run out of gas there is still about 2 gallons in the tank.

Another possibility, fuel level gauge might be off. Try cleaning the sender in the tank.

 

[NDBoost]

what i do is i fill the tank from E light to Full then take the mileage i went on the previous tank and divide the two. That gets your MPG, been accurate for me. I usually get 10-16mpg

 

[cwapface]

???????!?!?!?

you calculate gas mileage by taking the number of miles you have driven and dividing by the number of gallons it took to fill your tank back up to full. Not sure why you would use 18.5 anywhere in that equation or blame mileage on the fuel level sender ????????

You said it yourself that your car runs way too rich. You have stock ecu and injectors, right? Get a good boost gauge if you don't already have one and see if you can detect a tiny boost leak just by watching what it does. Other things to try are installing new injector seals ($30 and 2 hours) or grab your multimeter and doublecheck continuity from the o2 sensor to the ECU. Wiring harnesses have a way of hiding the real cause of problems...

 

[aye mate]

???????!?!?!?

you calculate gas mileage by taking the number of miles you have driven and dividing by the number of gallons it took to fill your tank back up to full. Not sure why you would use 18.5 anywhere in that equation or blame mileage on the fuel level sender ????????

Good point, I get my gas out of a farm pump and I have to crank the handle by hand, needless to say, it doesn't have a meter to tell you how many gallons have been put in. I haven't used a normal pump in years. Just wasn't thinking...
And the fuel level sender thing, I was saying that maybe the fuel level sender was malfunctioning and he was thinking he's getting worse mileage than he really is. Maybe if it was getting a bad connection and dropping faster than the level was.

 

[suprajjang]

well when the needle gets below E i go and refill. I then take the mileage driven and divide by the amount of gas that i filled. I then repeat that and its always 10-12 mpg. I still have the stock ecu and injectors and when i rebuilt the motor couple months ago i had the injector seals replaced.

 

[Nick M]

Sounds more like long term fuel trim is way rich. Easy on the loud pedal. Pull DTC's and see what you come up with.

 

[Boss302]

it couldn't be a throttle position sensor could it? the car isn't sluggish or anything like that?

 

[GrimJack]

I know exactly where the problem is. Look down and slightly to the right. See that foot down there? It's made of lead.

 

[jdub]

I know exactly where the problem is. Look down and slightly to the right. See that foot down there? It's made of lead.

LOL :joshers:

Suprajjang are you throwing any codes?
I've got the same aftermarket parts (except for the downpipe) + a lot more...getting 20-22 MPG around town.

 

[tkvtec]

I know exactly where the problem is. Look down and slightly to the right. See that foot down there? It's made of lead.

Agreed. When I drive superconservative, I can squeak out maybe 20mpg, but that is keeping the car from leaving vacuum period. If I boost at all, that drops immediately and I have averaged 15.6-16.8 mpg. If I am running full boost all the time (only 10psi currently), forget it. That immediately drops. I drove 120 miles this weekend. Cruising on the highway most of the way at a steady speed, not under boost. I only really hit it hard mayabe a dozen times covering at most 25 miles under full boost and I got about 14.5 mpg.

 

[lagged]

even with 550s and a lexus afm i get reasonable gas milage. i have an NA lsd and i drive like a maniac about 280 miles a week, usually filling up about 10 gallons at a time, usually a little more. thats 28mpg at the most right there. pretty darn good

its probably more like 21-23mpg but i am happy with that.

 

[Red Dragon]

I get around 12-15 and proud of it. Of course the car is only a weekend car, I boost the hell out of it when driving, as its always "for pleasure" and I don't care if gas gets to $10 a gallon I wouldn't care (now for my DD thats another story)

Of course this doen't help you, except to confirm that these gas suck some serious MF'ing gas at wot with mods.

 

[suprajjang]

i always shift around 2000-2500 so dont think its my lead foot:icon_bigg

also the car is not sluggish at all. if i do floor it the car pulls strong to redline. The car is not throwing any codes so im clueless on what it is.

 

[lagged]

do a tune up including new o2 sensor. if that dosnt help it, do a compression test.

 

[suprajjang]

already has a new o2 sensor from toyota and did compression couple weeks ago

cylinder 1-165
cylinder 2-168
cylinder 3-164
cylinder 4-166
cylinder 5-165
cylinder 6-164

 

[tissimo]

keep the boost no higher then 5 in hg.. will help gasmilage..

same mods minus bov i got 20 mpg mixed driving (highway, city, hauling ass)

make sure breaks aren't sticking.. my slider pins stuck a little on my car, cause uneven pad wear and im sure killed milage

 

[born2drv]

i'm getting horrible mileage now, i also have a boost and vacuum leak.... i think the vacuum leak is causing my car to run very poorly. i'm getting it all taken care of very soon.

 

[suprajjang]

Ok just went through this tank of gas. i put in 13.5 gallons and drove 170 miles before the needle went right under the E line:nono:

 

[IHI-RHC7]

Hmm, sounds like a huge boost leak to me...