What am I doing Wrong?

[cjohnson0914]

HI! Im new here and I have a 2007 Tahoe LTZ 2wd and since the first month having it, Its been problems. Just changed the EVAP Canister And now I'm having a misfire code pop up. The Tahoe gets about 7 MPG and that's on a good day. The whole thing shakes when going about 65 on highway not a smooth ride. It runs at about 2000 RPMS on open highway. Is that normal for this type of SUV to run at such a high RPM or do I need to replace something? HELP!!!!

 

[NathanJax]

mine runs 2000rpms or so at 75mph. Sounds like you need to take it to a PROFESSIONAL mechanic and let him diagnose it for you. We can guess, but at the end of the day, it's a $20,000 vehicle and with the issues you're having, need a professional opinion and fix.

 

[ccapehartusarmyINF.(ret)]

okay why did you change the evap canister what pointed you do that
iive been going thru evap emmissions problems recently so ive become quite saavy
2000rpms is the cruizing rpm roughly for my my tahoe at 70 to80 mph
how does it idle
an actual misfire can cause the vehicle to shake but you would also notice a loss in power or your tires need balancing a few of the weights may have fallen off and thrown the balancing off
first thing is pull the plug from the missfiring cylinder and make sure your getting spark
if thats good move on to the injector

 

[cjohnson0914]

Thanks for the quick reply's. The tires was balanced a few weeks ago I thought that would fix it also but nothing. I changed the EVAP because of the P0455 Code. It turned the engine light off for only 2 days. It is showing a misfire on cylinder 3 (P0303). It seems every time I get the light off it pops back on with a new code. I have took it to the local Chevy shop here and they didn't know what could be causing the gas mileage to be so low.

 

[Clean07Burb]

7 miles per gallon at best??

 

[AZSCTACO]

Clogged cat. converters???

 

[992dr]

P0455 Code = check your gas cap, inspect and if necessary replace with a new one.
Remove your negative cable to the battery for 15 minutes and the code will clear.
Hopefully, that will resolve that.

I believe #3 is a DOD cylinder. If you are throwing codes for a miss in that cylinder and it does not go away, it may be time for new lifters or a DOD delete install.

 

[aflumb]

i suggest you find a different dealer. but also get the code history from them. you may have more than just one. there is no reason it should pop a different code every couple days. you need a really good scan tool to get the rest of the codes that are in the history of the computer. also the dealer should ride/drive with you with the scan tool hooked up, so they can see the parameters at the speed your talking about. i hope this makes since.

but if the same cyl is popping the mis-fire code, i would do the following just to check some items:

-change spark plug to another cyl--- drive and see if the code moves (if not then)
-change coil pack to different cyl (see if code move)
-change plug wire to different cyl.

if it moves to where you changed part then its the part you moved

but DOD seems to be the most common problem

i would try the part swapping first as it could save you alot of time and money being able to do it yourself since its really not that hard..

GL!!!

 

[cjohnson0914]

The cat. Converters have been check and are clean. Yes that is the best I've seen it get is 7 mpg. I will move a few things around to see if that helps. I hope it don't keep this up. It may find itself at the car lot for sale pretty soon if it does. As far as the rough ride I haven't got that figured out either. It's like riding on a washboard nonstop.