Few problems with an 03 tahoe z71

[silky]

Hey guys/gals.

I am having a few problems with my tahoe and I need an emissions test so I need to take care of it.

1) CEL has been on for about 1 month. It comes on, I clear it, it comes back, I clear it and it comes back again. It comes back as different codes

The original 3 codes were Lean bank 1, Lean bank 2, and Random Misfire. The next time it was just Lean bank 1, Lean bank 2. The newest code is p0455, or Gross leak in te evap system...(lean bank 1, lean bank 2 is gone)...

Now, the truck has started to run funny since the cel came on. The gas mileage is down maybe a few % (based on how fast I fill and the avg/economy readout. Sometimes on cold starts tht truck vibrates. It's not a massive vibration but you can feel it. The plugs and wires are new so I figured the problem was a vacuum leak. I sprayed carb cleaner around the intake manifold and vacuum lines and what not and nothing changed. I did notice that the hose that goes from the MAS to that plastic thing that goes into the intake has no clamp where it meets that plastic thing....is this normal? I have some live stream feeds I would like your opinion on...

this is all at idle....

o2 sensors:

Bank 1 s1 = -2.5 to 0 % stft, and .075 to ~.800 volts

Bank 1 s2 = NA stft (weird?), and volts are pegged at .075 (cycles on when on the throttle, pegged at idle)

Bank 2 s1 = 5.4 to 2.3 % stft, and .08 to ~.800 volts

Bank 2 s2 = NA stft (weird again?), and volts pegged at .0730 (cycles on when on the throttle, pegged at idle)

MAP= 10.3 in/hg. Isn't this low? I know my stealth is getting about 19 at idle.

MAF= .658 lb/min

TPs= 10.9%


thanks guys, and any info would be appreciated.

John

[bwood]

Check all the plastic line coming from and to the EVAP canister. I should be mounted up above the rear axle with a plastic tube from the gas tank that collects pressure/vapors from the tank and then there is a tube that goes all the way back up the front of the engine. Remove the plastic Vortec cover from the engine and look for a little green service cap. This is the service port for the EVAP system. Just under that port is a solenoid that opens and closed to allow the vapors from the system to be burned off through the intake. A cracked or broken line, a solenoid hung open or a damaged/missing component could cause a lean condition. I can remember discussion about a vent valve or check valve that can get rocks/debris in it and cause EVAP system issues. Unfortunately I can't find the posts about it.

[bwood]

Originally Posted by silky

Bank 1 s2 = NA stft (weird?), and volts are pegged at .075 (cycles on when on the throttle, pegged at idle)

Bank 2 s2 = NA stft (weird again?), and volts pegged at .0730 (cycles on when on the throttle, pegged at idle)

I do not have any experience reading live data, but I wonder if this has to do with the actual lean issue? Or if the truck is ignoring them due to the existing CEL? Just guesses. Also give you gas cap a check, it also is part of the EVAP system.

[silky]

thanks, will take a look at it now!

[LEEVON]

my wife's 02 tahoe was throwing p0171 and p0174 (lean banks 1 and 2) as well as the p0455. It idled really rough on a cold day until it would warm up and smelled rich. Pretty much what you're describing?

I suspected the intake manifold gaskets but could not find the leak. After research (google "p0171 tahoe") searching fsc.com, gmfullsize.com, etc... I took a chance and replaced them with the new GM "green" gaskets. This is a common problem with these and seems to surface around 100K miles, ours was at 90K. It was about a $175 job after the gaskets, fluids, replacing belts, and such. Not too difficult of a job, maybe 4 hours on a saturday with interruptions. It runs great now w/ no codes.