Ongoing Gas Cap Problems

[01rubyrora]

Hi everybody, I believe this is my first post, so I'll try to do my best to keep it short while providing as much detail as possible. I drive a 2nd Gen 4.0 and love it, but since I purchased the vehicle, I have had problems with the gas cap. First, the check gas cap light came on. Okay, that is normal, I thought to myself. Just replace the cap, no big deal. I picked up an ACDelco cap from some auto parts store (can't remember which one at the moment), and after clearing the engine code and a couple dozen miles, the check gas cap returned, along with a check engine light. Okay, maybe a bad cap I thought. So, I picked up a different cap. This is where things got interesting. It fit INCREDIBLY tightly. As in, I had to put my weight into pushing the thing on every time I filled the tank. And don't get me started about pulling it off. Well, that fixed the gas cap and engine light for a while. Then, one glorious day, the gas cap got stuck to the filler neck. And I mean S-T-U-C-K. It was a huge debacle, but I ended up driving to Belle Tire where they pretty much just snapped it off with pliers since that was all that would work. Re-installed the factory cap since it was all I had left, and obviously the DIC message and engine light came back on. Well, I just replaced the gas cap with a NEW OEM cap from RockAuto, as well as a new vent purge solenoid, which I hope will keep the check engine light at bay. I'll have to wait a couple weeks to tell for sure, but here is my current dilemma, along with a few questions: The brand-new cap is still difficult to put on (not quite as difficult as the one that got stuck, but it is still unpleasant), still difficult to screw to a click once it is on, and isn't friendly to pull off. Do I have a warped filler neck? If so, does it HAVE to be replaced? If I have to replace it, what is the most cost-effective way to do that? I'm a novice at auto repair, but I can do some basic things (brake pads/rotors and rear shocks are my biggest accomplishments on my 'Rora). Thanks for the help!!!

[sall]

Is it rusty? I know a lot of 2G guys have had issues with the cap. It seems taking a scratchpad or fine sandpaper across the top of the filler neck solved the issues, but your seems to be more related to threads or both.

[01rubyrora]

There is/was some rust, and I have attempted to sand it, as well as take a wire brush to the outer edge (with the neck stuffed with a rag to prevent anything from falling in). I am unsure now whether I have to look at the inside as opposed to the outside of the neck. It is definitely a lot better than it was, but the step that I haven't done, the resealing using silicon or whatever else it may be, probably wont help to solve the whole "can't easily get the cap on" nonsense. I am truly puzzled. Could it be the plastic bits in the filler neck that warped? just grasping at straws here, it's what I do best.

[Paulaurora]

yes same here its most of the time its the rust and i have new cap and i still have to screw in the cap back like 10 times before it seals and then no check engine light if i just screw regular way 2 3 turns when gas tank half full i get check light. but i didnt had chance to send the rust out. After i got new cap it was good for few weeks so i guess maybe rust strips off the plastic or something and it leaks air.

[tigger]

Aug 22, 2017 12:08:21 GMT -6 01rubyrora said:

Could it be the plastic bits in the filler neck that warped? just grasping at straws here, it's what I do best.

Possibly/Probably. Thinking the "tight" cap was incorrect cap, and prying it off didn't help.

Mine goes on and clicks in a 1/4 turn with very little downward pressure to seat the tabs in the channel, comes off in a 1/4 turn with no downward pressure... It's original to the car, but I've always kept it conditioned.

You could try a thin application of white lithium grease on the rubber cap seal and locking tabs, as well as in the channels inside and entire outside of the filler neck. May help...

[01rubyrora]

Thanks, Tigger, I'll give that a shot! and yeah, I wish I knew why that tight cap wasn't correct, it was verified as a factory fit. Who knows, I guess I'll just get ACDelco for everything in the future to avoid that problem...

[awehlage]

You need to take a small sanding block with 100 grit and spin the block until all the rust is gone. Make sure you put a damp towel in the gas fill tube so no debris gets into your tank. After everything is clean and you see bare metal on the lip where the cap sits take some rust fix and spray it on the lip. Let it dry and you could then coat it with whatever color paint you want. I chose satin black because I already had some and then cleared it. No P0442 code since then!

[Dominic]

Everyone is spot on. I just got through with this also, I took some 80 grit sandpaper and sanded down where the cap makes contact and around and then used brake cleaner cleaned the entire inside of the gas compartment, I also noticed a small hole just below the fuel spout and cleared it. a new GM original acdelco gas cap from rockauto and it I dont have this issue anymore.

[01rubyrora]

Months after having no problems with the chack gas cap light and continuous conditioning have yielded yet another check gas cap light and P0442 engine code (which is different from the P0440 code I was getting before). Might have to get a smog check done... Is that the best way to go about this?

[AuroraGirlFromMars]

Wouldn't be a bad idea. I know there are 35 dollar and up scan tools that can tell you if that specific emissions system passes a check. For example, my Catalytic converter system and SMOG don't pass, because they both have issues. 1 of my smog diverter valves are bad, some of the lines are bad, and the pump is in unknown condition. My catalytic converter is full of crud and is inefficient. My EVAP is also bad, and it could be the gas cap or a purge solenoid.

[jh]

Hello - first of all, how do you clear the error code when you get a new gas cap? (I got one due to the same message your car displayed, but I don't know how to clear the code so I don't know if that solved it or not).

I also have the PO440 EVAP System Malfunction. The solution from the AutoZoe scan is 'Replace EVAP PUrge Solenoid Vacuum Hose'. Thoughts from those who have been there - is it the hose, or the unit? 2001 V8 (inherited recently).

Thx!

[Paulaurora]

The gas cap code will go away if there is no more issue at that end or you need to use the scanner tool to remove the code. for po440 means not enough vacuum . you can watch this video to get idea how system works and it will show u all the codes www.youtube.com/watch?v=Dfj-F_pTj5M. mostly its po443 is bad purge solenoid but you can see location of it in this link and check all the tubes but po440 did came up for me few times when it was as simple as bad gas cap . aurorah.proboards.com/thread/27084 .. i would clear all the codes first and if check gas cap wont comeback. but if po440 will comaback i would check deeper but most likely it will go away if gas cap no longer at fault .