Hello Everyone,

I am experiencing very poor highway gas mileage. However city driving seems great.

I am running a LT-1, engine, tranny and rear-end all from the same car. It is from a '95 Z-28 with 3:23 gears. It is an automatic.

A few notes.
I do not have a catalytic converter installed and the air pump is not hooked up.
That is not really by choice, because I do want to pass emissions. However, it was easier to leave the cat out for now and I am missing one hose for the air pump.

I assume the tranny is working properly. I think 4th gear is actually the electronic overdrive? Is that correct.

Thanks Again,
Gus

 

How does the motor run overall? Smooth-rough? You may not be getting enough air-flow in to the motor. I had a '95 Formula with essentially your same set-up except for I added a Trans-go shift kit which didn't effect the gearing but I had excellent high-way mileage. Yes, 4th gear is OD by the way. Do you have all 4 gears? Try starting from a dead stop and accelerate modestly up to about 70mph and count how many times it shifts to make sure you are getting into 4th.

 

Sounds like you should use autotap or LT1 edit to see what's going on. I suspect it may be running in speed density mode.

 

what do you consider bad gas mileage? I'm getting around 16-19 around town, and usually average around 25 on the highway. I also have no cat or air injection. or EGR for that matter. In fact I have no emissions equipment what so ever on the engine. like wm_sorg suggested, sounds like it could be Speed Density mode.

 

I have not hooked up the odometer so I am estimating 12miles per gallon highway.

From the wiring diagrams the ALDL connector appears to have 2 important wires. The others are postive reference/power or grounds. Any experience with wiring in an ALDL connector?

I have a scan tool if I can get a read out connector.

Thanks Again,
Gus

 

Only a few important wires for the ALDL.

The ALDL signal wire, a diagnostic wire and a ground.

For programming I only needed to hook up the aldl wire and the ground.