Mileage

You have dramatically changed the gear ratio with the oversized tires. There isn't much you can do easily to change that.

No, it wouldn't. The converter doesn't effect mileage.

Bigguy-I mostly deal with CJs--Headers may help improve your situation.A little!

But I would investigate your "CODES", Does the check engine light work. Is it on? Maybe you are running "Closed Loop" (the computer is not receiving real world data, from the sensors, and is Substituting it's own Pre-set values to keep the engine running. Running, not efficient!) EX. O2 sensor does not give computer "real data", till it's warmed up---computer substitutes EGBERT the NERD'S Data installed at the factory, until the O2 sensor comes online. This holds true for other sensors also.

Your rig has some age---REALLY Look hard for vacuum leaks, the flimsy rubber connectors are disintegrating now. I sometimes shove a piece of 1/2"-3/4" inch--several feet long, Heater Hose in my ear, and use the other end like a stethoscope to listen for faint hissing. Some vacuum lines are hard tubing, inside Wire Looms, if they break, it's hard to see or find the breaks. Sometimes you must carefully peel the splits open (wire loom) and look and tug on the lines.

I get about 18 MPG with my 6 cyl and 4 bbl Holley, on my '77 CJ 5 (Mr. Jeep)--a 21 Gallon tank was "a must", I was filling up every other day with 15 gallon on my long drives to work.

"Willy" gets about 11-12 MPG, 'course he has a 5.38:1 Gear Ratio, "Mr. Jeep" is 3.54:1

GOOD LUCK

PLEASE LET ME KNOW, YOUR JEEP IS DOING BETTER!

Pics are always a nice welcomed touch!

THE MEDIC

Forgot to mention you can get "CODED" at a popular parts store for FREE!

Return here with the code numbers, we will try to help you!

The Medic

The Catalytic Converter doesn't have a direct effect on fuel mileage but the leak in the exhaust can effect the 0/2 sensor which will effect mileage.

Take him to either store, "Zone" or "Advance"

Not real up to par, on these newer computer rigs.

The Crack may have affected a O2 sensor getting a real reading. But I do not know for sure. Maybe "Wrench Feller" Knows.

If it were not for maybe having a downstream O2 sensor. The Converter would be history in my neck of the woods. You probably could not remove yours due to the Computer would spit out all sorts of wrong info to the injectors. And they say it's unlawful, where they check this stuff!

Get him coded, come back and we will try to continue.

The Medic

CONFUSED? IS THE CHECK ENGINE LIGHT ON OR OFF NOW?

GOTTA KNOW FOR SURE IF THERE ARE CODES OR NOT!

TAKE HIM TO A DIFFERENT AUTO PARTS STORE FOR CODING!

YOUR RIG IS COMPUTER CONTROLLED--THE COMPUTER IS CONSTANTLY ADJUSTING STUFF AS TO WORK MORE EFFICIENTLY. WHEREAS MINE, "I" MUST BE THE COMPUTER DOING WHAT I CAN TO GET EFFICIENCY.

WHEN YOU LAST FOUND THE O2 PROBLEM AND FIXED IT, DID YOU HAVE THE CODE CLEARED?

I KNOW, I KNOW--IF IT GIVES THE SAME CODE, CAUSE YOU DID NOT CLEAR IT BEFORE, THEN WHAT. CLEAR IT, THEN DRIVE SOME MORE, IF IT POPS BACK ON. THEN CODE IT AGAIN. IT WILL NOT JUST RANDOMLY THROW YOU THE LAST CODE, IF IT COMES BACK ON---YOU STILL HAVE AN ISSUE, MAKING IT DO THAT!

SOME PLACES WILL NOT CLEAR YOUR CODE---BUT IF THEY SHOW YOU HOW, AND TURN THEIR HEAD. YOU CAN DO IT. JUST GOTTA TALK RIGHT!

MINE IS A CARBURETOR, I HAD BEEN TRYING TO JET IT CORRECTLY FOR FUEL EFFICIENCY."READING THE SPARK PLUGS".I COULD SEE "TOO RICH" AND SEE "TOO LEAN". BUT IN BETWEEN WAS NEARLY IMPOSSIBLE "FOR ME"

I FOUND A SITE DISCUSSING, USING A O2 SENSOR TO SEE WHAT THE ACTUAL "BURN" WAS OR THE AIR/ FUEL RATIO

I INSTALLED A PRIMITIVE "ONE WIRE" O2 SENSOR JUST AFTER MY HEADERS, AND STARTED USING A VOLTMETER SET ON MILLIVOLTS TO MONITOR IT. MY JEEP NEVER HAD A O2 SENSOR. NO COMPUTER!

THIS TOO WAS HARD TO USE, AS THE VOLTMETER FLUCTUATED EVERYWHERE (NOW I'M BETTER AT READING IT!) BUT AT THE TIME, I DECIDED TO GO TO THE NEXT LEVEL.

I INSTALLED A AIR/ FUEL RATIO GAUGE, SEVERAL OUT THERE.I GOT A MIDDLE OF THE BUNCH TYPE (IT WORKS WELL) IT HAS A BUNCH OF LIGHTS ON IT.3 COLORS PROGRESSING. RED=LEAN, YELLOW=STOICH OR CORRECT RANGE, GREEN=RICH. SORTA SAYING THIS SO YOU WILL GET THE IDEA!

I WAS ABLE TO SELECT THE BEST JETS FOR MY CARB---I LOVE IT!

THE GAUGE REALLY WAS MEANT TO HOOK ONTO A COMPUTER CAR LIKE YOURS, THE INSTRUCTIONS SHOW HOW TO HOOK INTO THE SENDER WIRE (YOU PROBABLY HAVE A HEATED O2, WITH 3 OR SO WIRES) MINE WAS JUST ONE, AND CONTROLLED NOTHING EXCEPT MY GAUGE. YOUR'S CAN BE TAPPED INTO WHILE CONTROLLING THE COMPUTER TOO.

THIS MIGHT TELL YOU WHETHER YOUR BURN IS CORRECT.14.7:1 AIR/ FUEL IS "PERFECT" RUNNING CLOSE IS REALLY ALL A COMPUTER CAN DO, A CARB IS IMPOSSIBLE, BUT YOU CAN GET IT CLOSER THAN OUT OF THE BOX

Wrenchtech MAY BE ABLE TO HELP YOU FIND THE SENDER WIRE OUT OF THE BUNDLE!

HERE'S SOME OF MY PICS

THE MEDIC