2003 QC 3.9 4x4

OK. I have changed the following:

Cap and Rotor
Plugs
Plug wires
IAC Valve
TPS
Map Sensor

I am still only getting around 12 mpg. I have an evap p0455 code which I know is prolly due to a cracked line somewhere. Should not be affecting MPG. What would be my next thing to look at? O2 sensors maybe?

Will be cleaning throttle body this weekend. I know it is pretty dirty.

 

Vacuum leak could still be it somewhat all those vacuum lines run the emissions system properly. A new O2 could help with the MPG yes; I know my truck runs much better after I replaced my top O2 I now get better power/performance.

Have you run a few bottles of Chevron Techron Fuel System Cleaner yet it will take about three bottles to feel anything and Chevron Techron Fuel System Cleaner is considered the best.

Another suggestion is try Gunk engine flush it did a great job of restoring some power to my engine I think it freed up a piston ring but be careful if not sure of how much sludge is in your engine start slow with MMO magic marvel oil add to your oil and it will slowly clean out the sludge it works great use for two oil changes to slowly clean out the sludge then use the Gunk engine flush for a final flash flush.

Caution the Gunk engine flush can damage an engine if it has heavy sludge buildup using it can cause way to much sludge to come loose at one time and clog up your engine oil passages and starve your engine of oil and burn up your engine.

 

All very good suggestions. From my understanding the O2 sensors can be cleaned. Is this correct? I am not getting any codes for the O2 sensors which leads me to believe they are dirty. I have ran some Seafoam through the gas but only once.

I will be finding that pesky hose that is causing the evap code this weekend so will take some time to look over all the vacuum lines. I cannot hear any whistling that indicates a vaccumm leak but who knows.

 

I looked into cleaning my O2 sensors it doesn’t work from my understanding best to just replace them they are under severe heat they don’t get dirty just worn out.

I never saw any codes but I can say that replacing my O2 made a difference in power and smoother running engine.

 

How is your exhaust system the cat and muffler these can cause poor performance if your system is still bolt on you could replace them yourself if welded you need a shop to replace those for you.

A performance muffler can net you a few more HP same a high flow Cat a few more HP plus get a shop to do performance tailpipe bending for you that helps a little.

Know this though most performance mufflers are noisier than a stock muffler sometimes way louder.

 

Cleaned my O2 sensors, made no real difference, changed them out and it helped the MPG a little.

 

I saw someone had cleaned the O2 sensors on another thread but your prolly right. They will become burnt and how would you clean that? lol. I just recently had the exhaust replaced from the CAT back. So you would start with the O2 sensor before the CAT then?