My Truck over the course of a week went from 14-16mpg to 12 and then to about 9-10 where it has been staying. I have also noticed about a 1/3 power loss too.

I am currently in the process of replacing the plenum, I was jsut cleaning the intake gasket seats when the sun decided to go down and should have everything back together tomorrow. there was so much oil puddled in there it was pretty obvious my plenum was blown. My intake gaskets were toast also. Looks like the truck had been overheated a bit by the previous owner. I am half tempted to take the intake to a machinist and make sure the intake is flat before reinstalling.

I also replaced the IAC, the temp sensor and cleaned out teh throtte body etc real good.

Any other suggestion as to what I could do to make my power return? While i had it open i also replaced the cap and rotor with a new Accel kit and Bosch 8mm wires. I put new iridium plugs in a bit ago but never finished the tune up.

thanks

 

Possible clogged cat , did u do tune up while its easy to get to the cap and rotor ?

 

Although you cannot finish it tonight, I would suggest replace timing set using a double roller chain, and possibly water pump if you are not sure how old it is. Preventative is better that OH Shucks!

 

+1....

 

If you had that much oil inside the intake, without a doubt the O2 sensors are covered with carbon causing the PCM to dump fuel and probably need to be replaced. Also as mentioned before, the cat has probably been partially clogged by all the burning oil.

Bad O2 senor readings plus partially clogged cat = very poor mpg and loss of power.

 

I have a brand new 3" high flow cat and a custom y-pipe. and o2 sensors jsut got replaced. they fouled up pretty bad a week or so ago, thats what tuned me into a possible plenum problem. Sounds like I got everything then. cool

 

I see you're in Utah. They may have already switched over to the winter blend gas in your area which in itself will cause a 1-2 mpg loss combined with a blown belly pan gasket will definitely account for the major part of the mpg and power loss. What % ethanol is in the gas in your area?

 

It could be the iridium plugs too, I've heard bad things about those on this site but have no personal experience

 

You've sparked my curiosity, what's the Winter Blend gas in Utah?

 

During the winter months the gas companies mix an antifreeze with the gas to help eliminate gas line freeze up. Taking that into consideration plus the colder intake air causing the PCM to increase the fuel and ethanol now being added in bigger percentages, from my experience I'll lose 2-2.5 mpg during the winter months. Just the nature of the beast.