I have 305 tbi with 3000 miles on it. rebuilt the heads and block and tbi............... Have been driving her and notice my fuel economy is really bad best 14.5 worst 7 mpg. So far changed my map and o2 sensor no change. Hooked it up to my friends computer and was wondering about the block learn code ....... another mechanic suggested maybe something in the emission system is out of wack...... perhaps that might be causing the problem. As of right now I have to readjust my rockers....... but for the most part haven't been able to lock it down. I also notice a miss at low idle right now she's set a little low at 500 or so I have to raise her up to 600.................. I am running a hypertech switch, cooler fan switch and a 180 thermostat and a 3 core rad.

Any help or suggestions is greatly appreciated
Kenny

 

Running a 180* thermostat will increase power a bit, but also hurt fuel economy slightly; not nearly enough to account for 7 MPG, though. Could be a weak spark as well. Does the engine have power or is it JUST a gas hog right now?

 

Block learn tells you if the computer is adding or taking away fuel to keep it at14.7 to 1 air fuel ratio in the long term. the integrator is doing the same thing but in the short term. If everything is perfect they should be 129. If they go up they are adding fuel and visa versa. As for poor fuel economy it might be caused by leaking injectors, too high of fuel pressure, clogged air filter or reasons other than the engine like draging brakes, slipping transmisions, underinflated tires etc.

 

I may be way off but you might want to make sure you're catalytic converter isn't clogged up. Happened to me, no power and noticable gas mileage decrease.

 

Along with this, you would have severe performance loss too once it starts getting clogged real bad.

I'd say check the EGR system out, especially since you said you have a miss at idle.

 

the cat was new as of 6 months ago could it have clogged up that quick.............

Kenny

 

If the engine were running very rich, then yes.