So, I got a brand new cat and replaced the O2 sensors, it's all done...but nothing changed. The mileage still sucks, I don't know what else could be doing it? My CEL isn't on, so it's not like the MAF is dead or something. I've replaced the spark plugs recently, the oil has been changed recently, the filter is fine, what can I do? I've been trying to improve my mileage forever and I'm just about ready to give up.

 

Your MAF could be contaminated. The CEL will not necessarily come on because the PCM does not have another sensor to accurately check the mass airflow against.

A couple of other things to consider could be high fuel pressure or brake drag.

Why did you replace the cat? Was it clogged?

Are your FE expectations realistic for your driving conditions?

 

i wanted to just replace the O2 sensors but they were seized in the cat, and nothingw ould get them out and since the cat is 10 years old everyone suggested trying it b/c it most likely is clogged as well. Should I clean or just get a new MAF sensor? How do I check high fuel pressure and brake drag?

I don't usually get heavy on the right foot when im driving, but i go the speed limit and i drive the truck like anyone else probably does, i give it gas and i let it go, i don't grandma it, but im not pedal-to-the-floor all the time.

 

You would need a special fuel pressure gauge to check it at the rail. Brake drag- jack it up and see if the wheels turn freely. There will probably be a small amount of rubbing but not that much.

I would try cleaning the MAF. There is a lot of discussion on the forums about the best way to do it. I would use something like electrical contact cleaner.

On a vehicle with no mechanical problems, the best things you can do for FE are easy and free:

• Lower your overall speeds;
• Shift below 2000 if you have a manual transmission;
• Drive with windows up
• Avoid short trips, especially in cold weather;
• Remove excess weight from the vehicle;
• Don't install oversized tires or lifts.