12 mpg, running rich?
Thread Starter
Teching In
Joined: Apr 2016
Posts: 23
Likes: 0
From: Chicago suburbs
12 mpg, running rich? My swap is a 5.3 aluminum block, with t56 in a 3000 lb car. I have a psi conversion harness, and computer. I have been shaking the car down, mostly cruising. I will occasionally do some wot pulls, but not enough to really ruin the fuel economy. I have driven less than 100 miles, and already had to put 7 gallons in the tank. It seems like 12-14 mpg is pretty bad for a swap like this. It also seems like it is down on power.
Anything I can check before I call psi? should I take it to have a tune done? what can I test?
Anything I can check before I call psi? should I take it to have a tune done? what can I test?
Poor milage First, is it going into closed loop? What is your rear gears? What are your short and long term fuel trims? If you do not have a scanner that will give you this info just use your smart phone, download the Torque Pro App ($4.95) and get a Bluetooth adapter for the ALDL. This will give you a ton of info to help track down your problem.
If everything chexks out, I would drive it more. 100 miles really isnt enough to figure gas mileage unless you know for certain that the tank was completely full at the start and then completely filled it again.
Thread Starter
Teching In
Joined: Apr 2016
Posts: 23
Likes: 0
From: Chicago suburbs
How do I find out if it is going into closed loop? I have 3.31 rear gear, and I do use the torque app. I will check the fuel trims when I get home. I did fill the tank as soon as the car was ready to drive, since the car was on empty, and the fuel was pretty old.
closed loop shows up on the o2 sensor signal wire, you can watch it fluctuate from 0.002volts to 1.00x volts, never ending flipping back and forth like that when in closed loop. you will see it sit on 1volt when at WOT and should go to 0 and stay there during a high rpm deceleration (fuel cut).
3000lbs with that engine should give you around 28mpg highway cruise minimum. I can do 32mph with 2800lbs and a 9.3:1 LSx finely tuned (15.2:1~ cruise open loop)
Plugs should all look clean, white with a tiny bit of tan, almost new for at least 10,000 miles of driving. Use a quality plugs and filters (oil and AIR FILTER very important). Make sure you use as much gap as possible (better/complete burn with a larger gap).
Lots of things affect fuel economy, I have become an expert at achieving mileage. Here is a short list that can alter economy in no particular order
injector phasing(spraying through overlap), alignment, tire pressure/compound, rolling resistance in general, brake drag (push the car, does it push easy?), overdrive/lockup (in your case, gearing and cruise RPM should be fine), ignition timing (should be 35-40* btdc during cruise for most engines on 93 octane), a/f ratio (closed loop is fine for novices but slight greater economy, 2-5% can be achieved with open loop finite tuning), I am forgetting some things (its on the forum in my other old posts if you dig it up, related threads)
3000lbs with that engine should give you around 28mpg highway cruise minimum. I can do 32mph with 2800lbs and a 9.3:1 LSx finely tuned (15.2:1~ cruise open loop)
Plugs should all look clean, white with a tiny bit of tan, almost new for at least 10,000 miles of driving. Use a quality plugs and filters (oil and AIR FILTER very important). Make sure you use as much gap as possible (better/complete burn with a larger gap).
Lots of things affect fuel economy, I have become an expert at achieving mileage. Here is a short list that can alter economy in no particular order
injector phasing(spraying through overlap), alignment, tire pressure/compound, rolling resistance in general, brake drag (push the car, does it push easy?), overdrive/lockup (in your case, gearing and cruise RPM should be fine), ignition timing (should be 35-40* btdc during cruise for most engines on 93 octane), a/f ratio (closed loop is fine for novices but slight greater economy, 2-5% can be achieved with open loop finite tuning), I am forgetting some things (its on the forum in my other old posts if you dig it up, related threads)
