Evap leak issues
#11
this is my understanding of this system. maybe i got it wrong. please correct me if so.
if the flow meter zeros...which it did...there is no leak. further smoke testing is not required. there should be no vac or pressure build up on these builds as the evap vent is always open. the system is only sealed during leak testing. pressure and vac can only occur due to a clogged or faulty evap vent path. I've seen tanks collapse bend sideways and hit the driveshaft due to clogged vent paths...yeah fuel pumps can suck hard.
if the flow meter zeros...which it did...there is no leak. further smoke testing is not required. there should be no vac or pressure build up on these builds as the evap vent is always open. the system is only sealed during leak testing. pressure and vac can only occur due to a clogged or faulty evap vent path. I've seen tanks collapse bend sideways and hit the driveshaft due to clogged vent paths...yeah fuel pumps can suck hard.
#12
this is my understanding of this system. maybe i got it wrong. please correct me if so.
if the flow meter zeros...which it did...there is no leak. further smoke testing is not required. there should be no vac or pressure build up on these builds as the evap vent is always open. the system is only sealed during leak testing. pressure and vac can only occur due to a clogged or faulty evap vent path. I've seen tanks collapse bend sideways and hit the driveshaft due to clogged vent paths...yeah fuel pumps can suck hard.
if the flow meter zeros...which it did...there is no leak. further smoke testing is not required. there should be no vac or pressure build up on these builds as the evap vent is always open. the system is only sealed during leak testing. pressure and vac can only occur due to a clogged or faulty evap vent path. I've seen tanks collapse bend sideways and hit the driveshaft due to clogged vent paths...yeah fuel pumps can suck hard.
Last edited by shades67; November 9th, 2020 at 1:29 PM.
#13
CF Veteran
this is my understanding of this system. maybe i got it wrong. please correct me if so.
if the flow meter zeros...which it did...there is no leak. further smoke testing is not required. there should be no vac or pressure build up on these builds as the evap vent is always open. the system is only sealed during leak testing. pressure and vac can only occur due to a clogged or faulty evap vent path. I've seen tanks collapse bend sideways and hit the driveshaft due to clogged vent paths...yeah fuel pumps can suck hard.
if the flow meter zeros...which it did...there is no leak. further smoke testing is not required. there should be no vac or pressure build up on these builds as the evap vent is always open. the system is only sealed during leak testing. pressure and vac can only occur due to a clogged or faulty evap vent path. I've seen tanks collapse bend sideways and hit the driveshaft due to clogged vent paths...yeah fuel pumps can suck hard.
In this case, we don’t know for sure what the freeze frame data for the code was, nor do we know if the OP’s mechanic attempted to run the smoke test under the same conditions. It could be as simple as the ambient temperature causing the gas & tank to expand, during which time the leak is present; but the smoke testing isn’t done until the next morning, and by then, everything has cooled off and the leak is temporarily sealed again.
According to the OP, the gas cap message has been coming on for 2 years - I can understand why it would be easy to look at other things since the vent valve fixed it the first time, but gas caps are as prone to failure as any other component. They are a lot cheaper than a vent or purge valve and given that both have been replaced, in addition to the fuel pump, is it beyond reason to suspect it has failed as well?
I’ve also seen gas tanks collapse due to clogged EVAP systems. The most common failure we see is the vent valves getting clogged with dirt (many of our customers live on gravel) and failing to work at all. Usually by the time we get to them, dirt has gotten into and/or through the canisters. Every time we replace a valve we relocate the fresh air filter to the engine bay, because GM’s recommendation to position it above the transmission wouldn’t keep them from getting plugged.
#14
Have you (or your mechanic) checked or replaced the gas cap? It’s an easy thing to overlook and assume it couldn’t be the problem, but oftentimes the seal can dry out and not seal properly, even if you tighten it until it clicks.
There’s also a 2 way valve inside the cap that’s supposed to release excess pressure or vacuum as needed. It’s possible the vacuum side of the valve failed which is why it’s passing a smoke test (system under pressure) but keeps setting the check cap message while driving (system under vacuum).
There’s also a 2 way valve inside the cap that’s supposed to release excess pressure or vacuum as needed. It’s possible the vacuum side of the valve failed which is why it’s passing a smoke test (system under pressure) but keeps setting the check cap message while driving (system under vacuum).
#15
According to the OP, the gas cap message has been coming on for 2 years - I can understand why it would be easy to look at other things since the vent valve fixed it the first time, but gas caps are as prone to failure as any other component. They are a lot cheaper than a vent or purge valve and given that both have been replaced, in addition to the fuel pump, is it beyond reason to suspect it has failed as well?
#16
CF Veteran
I've owned the truck for a little over 2 years. The P0455 code came up shortly after purchase. A new vent solenoid fixed it. The fuel cap message started coming up about 2 months ago. I've replaced the cap, purge valve, and vent solenoid. After the first leak test found a leak at the top of the tank, I replaced the fuel pump due to a pin hole from rust and all of the tests I've listed have been done since then. The fuel cap message problem still persists.
If your mechanic didn’t perform the smoke testing under the same conditions which the code set (engine speed and temp and intake air temp are the primary factors), that’s when the test needs to be done. Temperature is going to have a significant influence because the cause of the leak could be affected by temperature.
Keep in mind that new components does not mean good components. Failures happen with new components for a variety of reasons - do not assume the parts you’ve replaced are good just because they’re new.
Thread
Thread Starter
Forum
Replies
Last Post
mccabe3549
Silverado & Fullsize Pick-ups
10
January 17th, 2018 8:00 AM
Steinwayflyer
Tahoe & Suburban DIY and Useful Threads
3
October 24th, 2011 4:47 PM