I Have A 95 Lt1 6 Speed.. I Blew M The Original Engine. So I Had To Replace It With Lt1 From A 97 Auto Tranny. The Engine Was Swapt But I Didnt Change The Computer It Still Has The One From The 95. The Problem I Have Is That Im Only Geting About 150 Miles To The Full Tank. My Friend Has A 97 Lt1 Trans And He Is Getting About 300 But His Is Automatic. My Question.. Coul It Be Cause I Need To Replace The Computer For A 97 Lt1???

 

I Have A 95 Lt1 6 Speed.. I Blew MY The Original Engine. So I Had To Replace It With Lt1 From A 97 Auto Tranny. The Engine Was Swapt But I Didnt Change The Computer It Still Has The One From The 95. The Problem I Have Is That Im Only Geting About 150 Miles To The Full Tank. My Friend Has A 97 Lt1 Trans AM And He Is Getting About 300 But His Is Automatic. My Question.. CoulD It Be Cause I Need To Replace The Computer For A 97 Lt1???

 

Did you swap the engine and transmission or just the engine?

 

i swap just the engine.

 

How far did the old engine go on a tank??

 

Did you swap out the knock sensor for a OBD-II version? The '96/97 LT1's have a different knock sensor resistance.

If not, I'll wager that's a big part of it.

 

Bad gas mileage can occur for various reasons. I wasn't even aware you could succesfully do a M6 to Auto swap without having made changes in the stock PCM. You may want to consult a tuner about this. Unless I am reading your post wrong, and you are saying the motor is out of the A4, but you remained an M6.

If thats the case, then there should be no difference. There are some things that can help improve your mileage though.

-getting the PCM tuned anyway to your specific mods
-checking and replacing any ignition related items (plugs, wire, coil, ect.)
-changing the stock thermostat for a 160 degree one
-bypassing the TB coolant
-adding an LT4 knock module
-adding simple bolt ons that lessen restriction such as CAI, or exhaust
-change the oil every 3,000-5,000 miles, and or keeping up on any regular maintenance items

 

It wouldn't hurt to get the PCM reprogrammed with the correct program and then go from there.

 

It should run fine with your 95 PCM, but you do need to swap the knock sensor from your 95 into the 97 block. You should be getting a DTC 43 code for the mismatch between the 100Kohm 97 knock sensor and the 4.5Kohm sensor your 95 PCM is expecting to see. As a result, you would get almost constant knock retard, and that would reduce fuel mileage.

Did both the 95 and the 97 have stock 24# injectors?

Poor fuel mileage can also result from :

-exhaust leaks before the O2 sensors
-misfires
-faulty/contaminated O2 sensors
-faulty fuel pressure regulator
-leaking fuel injectors

Helpful hint.... turn off the "caps lock". That's why your post looks sort of goofy with the first letter of every word capitalized.

 

I know what your problem is... You should replace your right foot with a lighter model

 

PLEASE do not post the same question on multiple forums. I just moved the one you posted on "General F-Body Tech...." and now I find this one. Merging.......