I've got about 500 miles on my 3VZ_E since I first started it up.

First tank of gas, I averaged, 13.4mpg
Second tank fo gas, I averages 12.8
I am on my third tank. But it's nto looking any better. I have run about 100 miles, and I am at less than half a tank.

I have been running mid grade.
The engine is timed perfectly (10btdc)
I put in brand new OEM spark plugs. Aftermarket wires.
The intake is kind of messed up.
The upper intake hose that connects to the throttle body doesn't seal properly (half of the rubber collar is gone, and I fixed it with *gasp* duct tape, but I am doing an ISR mod, which is why I havne't fixed that).

I know I should expect bad gas milage for a little while. But I Wasn't expecting it to be THIS Bad.

Also, I am running Valvoline dino based 10w30 in the crank case right now. WIll be going to Valvoline dino based 5w30 when I do the 500 mile oil change.

The truck will get amsoil synthetic after the first 5,000 miles, and I get my oil leak dealt with.

Anyhow, I don't have any CEL's and my O2 sensor checks out fine when I meter it.

Any clues?

 

The leaking intake will DEFINITELY cause problems. I'd suspect that is where most of your mileage issues are caused.

Dop you have auto or manual tranny? Autos SUCK for fuel economy.

Have you replaced the O2 sensor lately? I replace mine with 205k miles on it even though no CEL and my mileage increased significantly.

I also had a SIGNIFICANT vacuum leak around AC Idle Up valve. Use an UNLIT propane torch while the engine is idling to check for vacuum leaks. They are very common on older engines. Did you replace all the vacuum lines during your rebuild? (pretty engine, BTW)

 

that intake leak is really gonna give you some issues, does the engine run rough at all...i remember when i was working on my truck i tried to start the truck with the intake off, to not avail just a lot of stalling, then reattatched it but didnt clamp it, and it ran super rough, then clamped it and everything was fine and dandy.

also if your motor is brand new, or just rebuilt, its in its break in period where your gonna get lower gas mileage, poorer performance. give it a 1000 miles seee what happens, then go searching

vacuum leak is a def a big possibility!

 

I to just had my 3.0 redone. New Valve job, Timing Belt, Water pump, All new hoses, Wires, Plugs, Etc. My gass mileage also not good. Is it true that it needs time to break in ? Also I here a very slight tapping, but it seems to be getting better with mileage. I now have about 200 miles on it.

 

Mine's a 5 speed.

I replaced all of the vacuum lines with Mr Gasket Silicone hoses. I also replaced the EGR and PAIR vacuum tubes (everything from the intake, to the valves) with new OEM tubes (EEK!). I would have done all of the intake tubes with new OEM, but I have been planning on doing the ISR mod, so I didn't replace those. Currently, I am working on the ISR but can't find an exhaust shop who will do the bends for me.

The truck runs smooth as silk (MUCH better than it did, as it had a rod knock).

It ticks like crazy, but I think it's the injectors (had them rebuilt by Witch Hunter Performance) which I am told is pretty normal.

 

I would double check for a vacuum leak. It's possible something didn't get hooked up properly, also; these things have 10 miles of vacuum tubing!

My first suspicion is that bad intake tube.