I have an idea for a good Troubleshooter tip unless it is already used.
It dawned on me the other day, that we have done a lot of fuel filler necks on GM products for P0440 General Evap Problem & P0455 Evap Large Leaks and possible P0442 small leaks.
98 Olds Intrigue:
1998 INTRIGUE Fuel filler neck 2 002.jpg
The first one I did several years ago kicked my a$$, until I smoked the evap system from the gas cap surface on the filler neck forward. That is when I found the fuel filler neck leaking.
There is a check valve in the fuel tank that blocks pressurized smoke from getting to the filler neck. A normal smoke test from the purge hose will not reveal this problem. The normal conclusion is that there is no leak.
The PCM knows that there is a leak because it uses vacuum to find Evap leaks and vacuum actually pulls the check valve away from it's seat whereas pressurized smoke tends to isolate the filler neck leak by holding the check valve closed.
Another effect of smoking the evap system with pressure is it tends to seal the vent valve solenoid tightly and it cannot release when commanded due to pressure holding it closed after the initial bi-directional command to close it for smoke testing. This can cause a false alarm causing some to believe the vent valve is defective. The Vent valve then opens and closes normally when pressure is released.
This is a huge problem in the "rust belt" where salt causes filler neck corrosion around a plastic "no spark" filler hole. Eventually, the plastic loses its bond with the metal filler neck causing a small, to large evap leak.
1998 INTRIGUE Fuel filler neck 001.jpg
I have seen this on GM vehicles from the late 1990's to the early 2000's (with more on the way, I suspect) such as Grand Ams, Malibus, Grand Prixs and Impalas
Some filler necks are already obsoleted by GM but aftermarket replacements are available through Dorman and Spectra, but the last Dorman one we did was a poor fit though... It literally forced me to stretch the filler hose to it's limit.
Thanks, Bob
It dawned on me the other day, that we have done a lot of fuel filler necks on GM products for P0440 General Evap Problem & P0455 Evap Large Leaks and possible P0442 small leaks.
98 Olds Intrigue:
1998 INTRIGUE Fuel filler neck 2 002.jpg
The first one I did several years ago kicked my a$$, until I smoked the evap system from the gas cap surface on the filler neck forward. That is when I found the fuel filler neck leaking.
There is a check valve in the fuel tank that blocks pressurized smoke from getting to the filler neck. A normal smoke test from the purge hose will not reveal this problem. The normal conclusion is that there is no leak.
The PCM knows that there is a leak because it uses vacuum to find Evap leaks and vacuum actually pulls the check valve away from it's seat whereas pressurized smoke tends to isolate the filler neck leak by holding the check valve closed.
Another effect of smoking the evap system with pressure is it tends to seal the vent valve solenoid tightly and it cannot release when commanded due to pressure holding it closed after the initial bi-directional command to close it for smoke testing. This can cause a false alarm causing some to believe the vent valve is defective. The Vent valve then opens and closes normally when pressure is released.
This is a huge problem in the "rust belt" where salt causes filler neck corrosion around a plastic "no spark" filler hole. Eventually, the plastic loses its bond with the metal filler neck causing a small, to large evap leak.
1998 INTRIGUE Fuel filler neck 001.jpg
I have seen this on GM vehicles from the late 1990's to the early 2000's (with more on the way, I suspect) such as Grand Ams, Malibus, Grand Prixs and Impalas
Some filler necks are already obsoleted by GM but aftermarket replacements are available through Dorman and Spectra, but the last Dorman one we did was a poor fit though... It literally forced me to stretch the filler hose to it's limit.
Thanks, Bob
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