I have 2 problems I am looking for advisement.

My first issue is that my overall engine performance sucks lately were I am only getting roughly 8-9 mpg fuel economy and normally get 14-15. Also associated with this is the fact that I seem to have an overall performance loss, particularly going up hill where I feel like I want to get out and push to get up. Also cruising at a steady speed I will notice that my rpm's will surge up and down about 4 or 5 times, at which point I curse a few times and it gets going again.

I also have a P0455 error which is gross leak or no flow. I have inspected all the hoses and made sure they are all connected, and replaced all of the smaller 5/16" hoses. I need to try and determine which component I should look at as being faulty in that system but am not sure where to go first. I will add that I also replaced my gas cap with a new OEM cap and when I open the cap for a fill up, I don't hear the pressure release/swishing sound that would normally be made.

Since these problems have started I have replaced plugs, wires, distributor cap and rotor, air filter, pcv valve, cat and muffler. All were due anyway, at 225,00km.

 

check the plenum

 

I climbed up and had a look down and I don't really see any significant sign of oil, there is just a thin film of moisture inside. I have never had to add a single drop of extra oil beyond keeping it changed every 5,000 km. Would the vacuum test confirm conclusively, I see conflicting opinions in other threads?

 

run the vacuum test on a fully warmed engine. See what it says.

Also may want to pull the throttle body, and look around in the plenum with a dentists mirror, or similar..... there does appear to be a bit of oil in there, but, that may just be from the PCV system.

 

I replaced my exhaust on Saturday with a new Walker Direct Fit and I must have hit or pulled on the EVAP lines in the process. I started my truck this morning and had the same code P0455 and after doing a quick search on here and found the problem. I crawled under the passenger side and felt the canister. I had a hose that was slightly loose. I pushed that puppy back on and code is gone.

 

I'll recheck those hoses in case I missed one earlier. They are all on.
---I dropped the canisters below the passenger side and there was a hose clamped on with hose clamps, that connected the two canisters together. Although they did not appear damaged at first, I blew on the intake hose and sure enough the air was just pouring out around those clamps. I removed the hose and cut the ends off the hose and clamped it back down, and now I don't have any air escaping.

As for the plenum test, I had my garage do the test as per the instructions and I do not have a blown plenum gasket.

 

After two weeks it appears my evap system error p0455 is solved as my cel has not generated that code. Sadly however, the light is back on and I checked code and am getting transmission code P1740. It makes sense now that this code is on why I am experiencing a surging of rpms at highway speeds of 80-90 km/hr, especially if the torque converter is not staying locked up. Could this also be causing me to come up nearly 60-80km short on a full fuel tank?