Gas cap/P0442 small evap leak/mod/repair

[fdryer]

My car suffered the dreaded gas cap leak on its 3rd or 4th year, '06-'07. With a relatively good gas cap I tried spraying silicone on the gasket and it solved the error code. Fast forward to last week (11/23/15) and the error code came back (same cap now 12yrs old). Examined the cap and gasket and smeared some motor oil on the gasket and waited a few days for the reset. No reset so I pulled the cap off the retainer to examine it. The plastic filler neck is fine, undamaged. I had disassembled the cap years ago so I did it again and this time removed the U-shaped sealing ring. It was intact and not cracked or suffered dry rot (silicone preserved it) so it didn't appear to be the issue. Reassembled everything and the error was reset only to reappear...................

What I did find was the cap seems to not use the seal as I had imagined as the cap seems to bottom hard with plastic to plastic coupling with the rubber seal just sitting inside the filler neck(?). I decided to experiment before breaking down and buying a replacement cap as I could not see anything broken. Since GM gas caps use a vacuum and pressure seal, the internal mechanism appeared to be fine, leaving the rubber seal in question.

My experiment? Finding an O-ring thick enough and sized appropriately enough to fit around the U-shaped channel in the seal. I disassembled the cap by removing the central core by pressing it to one side as I forced the retaining tabs to release, one tab at a time until the entire central core came off. Removing the rubber seal for inspection revealed no cracks so its reusable. Rummaging around my garage I decided to use a thin O-ring for faucets. It was sized way too small in diameter and had to be stretched over the rubber seal after replacing it back onto the plastic core. The core holds the rubber seal as I stretched the O-ring around to fit into the channel. Popped the core back onto the cap and put the cap back into its retainer and on the filler neck. I tried a few drives but being impatient I reset the error code and it hasn't come back. This was a few days ago and I suspect the O-ring provides a way to seal against the plastic fuel filler neck better.

I have no dimensions for the O-ring and have a home made O-ring made for another experiment if this one fails. My guess is if the rubber seal is intact and not cracked, silicone treatment and an O-ring may be the cheap repair solution for anyone willing to experiment. I did this to answer another question that may have been answered with this O-ring mod; the steel fuel filler tube has rusted and peeling metal. I wondered if this tube has deteriorated to the point of pinhole leaks (generating the error code) requiring replacement. If necessary, I can either replace the tube or try epoxy paint to seal it. With the error code gone, I think the fuel filler tube is fine for now as the gas cap mod seems to keep the error code away.

I didn't try searching for replacement U-shaped seals as I would imagine there may be several types of GM gas caps and auto stores may not bother stocking these seals. I may be mistaken if anyone is willing to find out for their gas cap problem and if a single one size fits all rubber seal is available.

[billysvue]

THe previous service announcement brought to you buy Delta FAucet.

" See what DElta can do".

I'll have to find my plumbing box and try this.

[billysvue]

I dug around in my plumbing box but came up with squat. Trip to HOme Cheepo looked grimm ,as I couldn't find any O-ring remotely close in I.D. to fit the O.D. of the gas cap where the Ugroove rubber gasket is located. All displayed were too small and I didn't want to overstretch one to make it fit.

I did find a 'bath shoe gasket", marketed under PartsmasterPro trademark (p/n 58481).

It's a flat gasket ,3/32" thick x 2-5/8" O.D. x 1-11/16" I.D.,,, perfect size, almost as if
PartsmasterPro and GM were talking to each other

http://www.homedepot.com/p/Partsmast...8481/203197297

I reset the CEL, with a batt cables disconnect( and shorted together), followed by ignition relearn.

Light is out, but for how long???

We'll see if it stops the dust from migrating into the filler neck- like I've seen it after dusty road trips into AZ.

Cost for the gasket is $2.27..

Note: due to the thickness of this gasket and the fact that it fits down against the existing U-groove gasket, it'll be difficult to press down far enough to get the tabs pst the locking flanges in the filler neck. Persist and ye shall succeed.

I did this to an aftermarket Stant locking cap.

[billysvue]

Originally Posted by billysvue

I did find a 'bath shoe gasket", marketed under PartsmasterPro trademark (p/n 58481).

It's a flat gasket ,3/32" thick x 2-5/8" O.D. x 1-11/16" I.D.,,, perfect size, almost as if PartsmasterPro and GM were talking to each other
http://www.homedepot.com/p/Partsmast...8481/203197297
I reset the CEL, with a batt cables disconnect( and shorted together), followed by ignition relearn. ..
Cost for the gasket is $2.27..

Note: due to the thickness of this gasket and the fact that it fits down against the existing U-groove gasket, it'll be difficult to press down far enough to get the tabs pst the locking flanges in the filler neck. Persist and ye shall succeed.

I did this to an aftermarket Stant locking cap.

To clarify: I removed nothing from the existing cap- only slid the new gasket over the center of the cap. It rests down against the existing U-groove gasket- which only purpose once the bath gasket is installed , is to backup the new gasket tight to the filler neck opening.

I suppose I could have removed the stock gasket to make more room for the Home Cheepo variety, but I didn't.

[billysvue]

BTT- this is working for me. So far....
....

http://www.homedepot.com/p/Partsmast...8481/203197297

[billysvue]

... closing in on 300 miles- no CEL

[billysvue]

650 miles and all is well

[billysvue]

2000 miles later- no idiot light

[fdryer]

An update with a different outcome from my initial post about P0442; the recurring error code was followed with a sudden loss of fuel pressure from a recent trip. This lead to replacing the fuel pump a month before NYS inspection. After pump replacement (92k miles) another error code appeared, P0455. I found my gas cap loose, possibly from pump replacement. I reset the error code and ran errands. No error codes returned. My car needed state inspection before the end of the month (February), let about a week go by to see if codes would reappear. None so I called the repair shop that did the pump replacement and asked for an appointment. Since the shop knew about the error codes, they asked me to bring my car in. Passed NYS inspection last week.

I can only guess a combination of things occurred that ended with fuel pump failure and at least one error code (P0455) associated with pump failure.loose gas cap. P0455 and P0442 never returned. When my car broke down, it was in NJ and parked overnight before arranging for a tow (insurance coverage) to a reliable repair shop. I chose to have a repair shop perform pump replacement at reasonable cost. It would have been more expensive if I was forced to have a local repair shop in NJ replace the pump so I used my insurance tow service bring my car to someone I've used over the years.

[PJank]

Had code p0442 come up right before state test due. Thanx to finding this sight was not only pointed into the right direction but also the solution. Found an O ring at ACE hardware for $2 that fit perfectly and passed my states test, Thanx