Gas Mileage Drop 2008 HD

[hobby28]

I have a 2008 Silverado HD with a 6.0 56,000 miles. At the begining of the year I was pulling my race car and getting 12 mpg every trip. I am now getting 9 mpg on a regular basis and even running empty part of the time. I have noticed the exhaust pipe looks more black than it used to. If you rev the truck up it will puff some black smoke. I scanned the truck, it has no codes stored, the ect seems 15-20 cooler than the gauge in the dash, and the O2 sensors keeps fluctuating. What type of readings should I expect from the O2 sensors? I have changed the air filter and cleaned the MAF sensor. What do I need to look for.

[777stickman]

From your post my 1st inclination would be replace the ECT. If it's not sending the proper temp signal to the VCM it could be staying in the cold "enrichment" mode.

Try this site for OEM parts. Include your VIN with the query.

http://www.gmpartsdirect.com/

[j cAT]

Originally Posted by hobby28

I have a 2008 Silverado HD with a 6.0 56,000 miles. At the begining of the year I was pulling my race car and getting 12 mpg every trip. I am now getting 9 mpg on a regular basis and even running empty part of the time. I have noticed the exhaust pipe looks more black than it used to. If you rev the truck up it will puff some black smoke. I scanned the truck, it has no codes stored, the ect seems 15-20 cooler than the gauge in the dash, and the O2 sensors keeps fluctuating. What type of readings should I expect from the O2 sensors? I have changed the air filter and cleaned the MAF sensor. What do I need to look for.

check the fuel pressures as well. make sure they are in the correct range. check the regulator that it is not defective.

the ECT/fuel pressure issues may not throw any codes.

with frequent towing I would replace the plugs more often also. use ac delco irridiums.