Any Chevy Truck Techs?

[Pro300x24LD]

Check engine light comes on my 5.3 99 z71. 'bout a 1/8 tank of gas in the truck, stop by auto value, they run code, something about emissions something or other, guy says, tighten gas cap, we'll reset light.

Light goes off, gas cap is tightened, fuel light comes on, go get fuel.

Run truck down to 1/8 tank again, check engine light comes on, stop by another part store, runs code, emissions crap, tighten gas cap, we'll turn the light off.

Light goes off, gas cap is tight, fuel light comes on, go get fuel.

Driving to work this morning, hit 1/8 of tank, light comes back?


So I go to autozone on way home from work, guy runs code, same code, emissions/evap.

Tells me smog pump or possibly smog sensor in gas tank?

Says dealer only part, wallet at home, cold out, take his word for it and go home. Going to call around tomorrow and see, but shoudl I just stay above 1/4 tank in gas and forget about it for now?

[lokinutz]

Sounds dumb, but I'd try a new gas cap.

[1BadAction]

what code? whats the number? "some code" could be one of about TEN for a screwy evap system, all of them will damn near pinpoint what the problem is.

[David - WI]

As someone else suggested, I would first replace the gas cap and see if it fixes the problem (my '00 Silverado had a bad cap)... then check for vacuum leaks in the evap lines... then check for loose or damaged wiring... then try replacing the solenoid valves last.

There's an evap canister purge solenoid valve right behind & above the throttle body... on the intake manifold.

There's also a vent solenoid valve mounted on a bracket near the fuel tank.

I would check both of those for loose hoses and/or wiring.

The computer is supposed to open both valves to empty the evap cannister if a bunch of conditions are met (engine running, warmed up, etc.)

The system tries to self-diagnose itself by opening the purge valve but leaving the vent closed when the engine is started cold... and checks to see if it can draw a vacuum on the fuel tank.

If the gas cap leaks... the system won't be able to hold a vacuum on the fuel tank and the diagnostic will fail. But, any leak in the vacuum lines or a bad purge or vent solenoid valve would probably cause the same problem.

[Pro300x24LD]

I have been keeping ti above 1/4 tank and haven't had a problem since. It will come up sooner or later, at that point I will get the exact code. David, you have echoed the thoughts of a friend of mine who works at GM and is an engineer on the truck platform, he told me to get him the code # next time and that it will basically tell us exactly what the problem is.

Thanks guys

[AnthonySS]

Same problem on a 1997 Jimmy with 4.3...apparently the computer will do self test a various fuel levels and if it fails the test 3 consecutive times it will come on...if it passes it will stay off...I think the code is 146...yes it is a fuel vapour thing and I have been told its nothing to spend money over on the Jimmy ...it's just annoying but like you...mine will come on most times at about 3/4 Tank and then shut off some days and then sometimes at about 1/8 tank...Yes make sure the cap is tight casue I have made mine shut off after re-opening and re-tighten cap....

Merry Christmas