poor fuel economy after header install

93 K1500 5.7L 4X4
I HAVE INSTALLED HEDMAN HEADERS WITH COLLECTOR BACK DUAL EXHAUST. MY MPG WENT FROM BAD (12-15) TO TERRIBLE (7-8) WITH THE TAILGATE OFF. I BELIEVE I SHOULD HAVE HAD AN INCREASE NOT A DRAMATIC DECREASE. IT RUNS BETTER BUT EXHAUST SMELLS VERY RICH.
I WELDED IN A NEW O2 SENSOR AND RUN ONLY THRUSH MUFFLERS. I CHECKED THE TIMING AND SET IT TO 1 DEGREE ADVANCE.

CAN THE FUEL MIXTURE BE ADJUSTED THROUGH THE COMPUTER?
-DEALERSHIP WONT EVEN HOOK UP TO MY TRUCK BECAUSE NO CAT

WHERE COULD I FIND SOMETHING CAPABLE OF ADJUSTING MIXTURE SHORT OF REPLACING ENTIRE INTAKE SYSTEM?

IS THERE ANYTHING I'M NOT THINKING OF?

ANY SUGGESTIONS ARE GREATLY APPRECIATED.

THANKS
-12 ga :banghead:

Test have shown that removing your tailgate does NOT inprove MPG or decrease any wind drag. That is why tailgate nets arent popular anymore.

Seems as though you lost back pressure. Your engines computer is sensitive to back pressure loss.

And I see you have no CAT. That is a no no. I must terminate this discussion now.

what do you mean by welded in an O2 sensor?? did you weld in a boss and thread it in or did you actually weld the sensor?? if you welded the sensor it's destroyed. do you have a 1 wire sensor? if you do try using a 3-wire heated sensor it might be too far downstream to get hot enough.

TERMINATE THIS :biggrin2:

*MAYBE IN ILLINOIS THEY DONT SALT THE ROAD BUT THEY DO HERE AND WHEN THE CAT DEVELOPES A WHOLE IM NOT ABOUT TO SPEND MY HARD EARNED MONEY ON A NEW ONE*

ANYWAYS I WELDED IN A BUNG AND SCREWED THE SENSOR IN.
ALSO IT IS ONLY ABOUT 6" FURTHER DOWN THE LINE THAN THE STOCK LOCATION BUT I CERTAINLY COULD TRY THE THREE WIRE SENSOR.

AS ALWAYS ANY SUGGESTIONS ARE APPRECIATED
-12 ga

i just did an install on a 93 1\2 ton 350 dropped in hedders and a flomaster exaust kit. we had the same problem it turned out there was a pluged injecter and a bad wire. as far as the cat goes it made no diff with or without. ps the massively rich exaust almost made you pass out once we swapped in the injecter it ran much better k5 out

I put on headman headers on my 81 cj5 with a 350.

When I put on CATS - they were removed before I bought the jeep my MPH per gallon went up a few miles.

I agree with the other back pressure has allot to do with it.

What is weird when I put on the air pump my mileage went up more and my exhaust note got louder and sounded allot better.

I feel like I got better low to mid power. That is what I need for off-roading so I really do not understand why people remove emissions stuff.

Hell the EGR keeps the engine cooler. I got proof of that.

After about 2 hours on the trails I am getting 245 with the EGR and headers I am hitting 220.