spot_55

I have been looking for a few hours for a thread i seen awhile back on fuel mileage on swapped cars. I can't seem to find it through the search tool can some one help me? I am getting really LOUSY fuel mileage(less than 12 mpg) and trying to figure out why. I have a 05 L59 5.3 and a 4l60 in a 71 chevelle with a 2.73 rear gear and a 255/60 tire. normal driving , No spirited driving, cruising 60 mph at 1500 rpm. very lil town driving.

nomoneyz

iTrader: (15)

Do you have a high stall.

spot_55

I don't have a stall my setup is all stock.

gofastwclass

iTrader: (2)

I remember the thread you are referring to but I don't know where it went.

I would say you have something really wrong and I can't imagine a stall killing that much MPG unless it was huge. For comparison: I get around 16 city and better on the highway in the Thunderbird (2000 5.3 / 4L60E / 3.23 gears / 3620lbs) which includes some closed course WOT runs on every tank. The car has a "muffler shop" merge to the single factory 2.25" V6 exhaust and picks up hot air from under the hood because I'm too lazy (and busy beating on it) to install the dual exhaust pipes i bought for it and fabricate a new cold air inlet. Maybe this weekend between other projects...

spot_55

I run 2000 trans am manifolds and cats, 2 and a 1/2 inch dual exhaust through some cheap turbo mufflers. has less than 300 miles on the o2 sensors,has new air filter, new fuel filter/regulator (using the corvette FPR) ,all plug wires check good (checked Ohm resistance).

t72ss402

iTrader: (10)

Did you have it tuned? After taking off all the stuff you dont need for your swap you need to have it deleted from the computer also.

Tim

Bo185

How are you calculating MPG based of speedo odometer or GPS? You speedo maybe off. Giving you the wrong MPG.

fast400

iTrader: (1)

spot 55,
I've got a L59 in my 69 firebird. I can tell you I've been tuning mine a bit, and I still can't get past 16mpg....my driving is at 90mph and lots of kickdowns. One of the first things I've noticed is that the ethanol calculation occurs not by ethanol content in the fuel but rather o2 sensor readings and change in fuel level reading. Do you have HP tuner?

sweetk30

stupid question ?

but did you happen to hook up the brake switch for the tourqe convt lockup kick out function ?

easy way to verify its working is go drive at highway speed and be in overdrive. then just lightly push brake at same time as gas still pressed.

should be a few hund rpm jump up if its working.

this would make for a lower fuel milage if not working also.

and as kind of said ethonal mix these days drop's fuel mileage on all vehicles over stright gas. takes 2x the ethonal to make same power as gas. so fuel mileage will go down. so look for the lowest % of mix on the pump.

spot_55

I had all the stuff deleted from the PCM that no longer pertained to my swap.

I used my GPS to calculate my mileage.

My TCC wire is hooked and working properly.

I do not have HPTUNERS yet .


I did however find a small fuel leak.(seeping fuel around a fitting) I think that may be the issue. I think over a hundred miles a leak that small may leaked a few gallons of fuel at 60 psi. I hope that is the issue. Power Tour is around the corner and with that kind of mileage it will not be happening for me.

sweetk30

are you using the gps figured miles per gal ?

or the miles drivin ?

i would rather take miles drivin on said gal per you put in. the old school method for real world info.

i dont trust the info lots of this new crap gives us . way to many variables in the info thay dont ask you for to get a specific # .

garys 68

iTrader: (1)

I've got an L59, T10 4 speed, 2.73 rear. I'm getting a little better than 16 city but over 20 hiway. I'm wondering if you're over geared for a heavy car. You might try driving around without the OD on if the 4L60 locks up in 3rd.
If that does better, you can swap out the rear to 3.08+.
A 5000lb Yukon gets about 16mpg with 0.70 OD trans and 3.42 or 3.73 rear end.
https://ls1tech.com/forums/conversio...-chevelle.html
https://ls1tech.com/forums/conversio...u-getting.html

gofastwclass

iTrader: (2)

Good point about being over / under geared. I wondered about that but honestly never look to see what RPM I'm turning in my auto because it's not typically on the highway for long trips.

For me the non-sponsor (before I knew about this site) tuner that shall remain nameless who did my original tune (to remove VATS) made some conflicting changes to my PCM. In short, the car ran but not even at the potential of the stock setup. Before tuning the PCM we talked about getting the car on the dyno at his facility after I built it and I assume the changes I discovered after buying HP Tuners were to be quickly undone to impress me by showing some "easy" power gains on the dyno in an attempt to wet my appetite for buying speed parts through them.

I'm not saying that is your problem or even implying there is a magic bullet, I'm just saying it could be a combination of things. Like the famous Sherlock Holmes quote “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”

jagwrjack

I have a 2002 Ls1 in a 93 Rx7 with a 6 spd. and 3:90 gears. I'm getting
25 mpg. The engine has H/C, longtubes and a mail order tune by 'Wait for me'.
Car weighs less than 2900 lbs.

Bo185

How is the fuel mileage actually calculated? Buy the GPS? Or my taking miles driven by the amount of gas you add to refill the tank???

spot_55

The Mileage is being calculated by miles driven versus gallons put in. I have driven this same route everyday for the last 8 years so I know how many miles it is. But just to be sure I drove 2 of my other Vehicals that route and compared the odometers and both were within a tenth of one another.

I really don't think my gearing would affect it that much considering that the yukons had 3.43 to 3.73 gears with what measures out to be pretty close to a 31 and a half/ 32 inch tall tire and at 60 mph rpms are in the 1600 range.
And with my 2.73 gears and 26 inch tall tires at 60 mph I am turning around 1550 rpm. The car seems to have plenty of power its not ******* or lugging in any way.

I did find a small fuel leak and I am hoping that is where my mileage went, I will be getting fuel in it tonight on my way to work and will see if it improves.

spot_55

Ok guys I believe the tiny fuel leak I had was the issue. I filled up last nite at a lil over 17 MPG versus 11.8. I found the leak 30 or so miles into this tank of fuel so I will see how it improves.