Hello folks, a while back I replaced my fuel tank with a Dorman tank from Summit which never came with a fuel cap. They insist the stock cap is supposed to fit but it doesn't (barely threads in before clicking, cap is nowhere near seated). In the meantime, I'm failing AZ emissions testing due to low fuel evap system pressure testing and I think the culprit is the crappy threading in the fuel neck and their test cap barely threading into the neck. Anyone know if there is a way to modify or fix the threading in the neck?

 

Without actually seeing it in person, could you use a large tubing cutter (for clean, square cuts, no chips) to swap the threaded section from your old tank and then use a piece of appropriately sized fuel hose and 2 SS hose clamps to hold it all together?

 

Are you positive it's the tank? Swapped my locking cap back to a stocker last year because the locking cap started binding in the filler neck. Was fine for 18 years, just started acting weird one day.

 

Its a dorman, that's the problem. Aftermarket is junk, but Dorman tops the list as aftermarket junk. Never ever lines up with their products. They should just stick to the simple things like grommets. When they started doing brake lines, harmonic balancers, power window motors... nothing EVER fits... its like they do it on purpose to get a good laugh in.

 

It does this with both the cap that came on my car originally (from 1991) as well as a brand new one I bought from the dealer. It's definitely the tank.

 

Unfortunately the tank was put in 5 years ago and I no longer have the original tank to swap the original threads / neck. This is the first time I've had to emissions test the car in Az and it passes everything except this pressure test.

 

Yes, I've had this issue with the factory tank and cap. Mostly in hot weather, which does match your location.

What I did to fix it was to take a flat file to the cap and trim down the peaks of the cap threads.

Then a large rat tail file to deepen the cap valley threads.

After a few minutes with the files the cap fit the tank perfectly. And has since then.

Note that the trimming wasn't much, so don't go crazy. Just file a little and check the fit. Once the cap works, it works.

RBob.

 

Thanks Bob, that's great advice for the long run. I'll give that a try. Unfortunately it won't do much for the problem of passing emissions. They have their own plastic caps at the testing station that need to thread into the filler neck to pressure test the fuel evap system. I think the reason I'm failing is because their caps aren't seating correctly in the neck either. I think it would probably be some sort of felony to sneak in to their station and file their caps lol.

 

This is both sad and funny, your conclusion is correct. But damn, on my OEM factory car, the factory cap and factory filler neck had issues when it was hot outside. It was so bad that the fuel filler door was held open by the factory cap that didn't seat.

On-the-other-hand, they (the inspection people) are using aftermarket parts. Which we know are crap....

So just maybe it is on them.

RBob.

P.S all third gen Camaro's and Firebird's are over 25 years old. Time for antique tags...

 

I wish AZ did that, they make every car after 1967 emissions test inside of Phoenix. Didn't have to worry about it before because I was out of the city, no such luck anymore though.

 

That's a good point on the station using aftermarket parts. Might have to just try a different station first before the money starts piling up at fixing such a stupid nit picky thing from an inspection.

 

I had the same exact problem. I would just buy a new cap, and it would last a year or two. And I'd have the same issue. My father took some sand paper (lightly) to the cap threads until it screwed down and fully seated. It's been many years using that same cap and still works fine.

 

As an update, looks like there are other issues with the Dorman tank in addition to the threads that are keeping me from passing. Current plan is to find an OEM tank and put that in.
Any good advice on places to find reconditioned OEM tanks? Also any recommendations on aftermarket sending units or are they just as junk as the aftermarket tanks are?

 

Might be difficult to find a junk OEM tank that isn't corroded inside. Ethanol gas, and age, sitting in a car that's bad enough to get scrapped... They make sealers to recondition old tanks, but not sure they'd be a good fit in a thirdgen. The plastic fuel reservoir might not react well, if the sealer is very thick I could see it blocking some of the passages.

 

So upon making a parts list and pricing it, it seems I've found justification to do my long awaited 4th gen tank swap instead, and even save some dough. I've started a new thread here for it - Please let me know if you have any experience with this, any help or sanity checking of my work is appreciated.

https://www.thirdgen.org/forums/tpi/...ml#post6209238

I guess the lesson of this particular thread is don't buy Dorman fuel tanks.

 

Dont buy any dorman.

 

I know this is an old thread, but I found it while doing a search on replacement fuel tanks and my experience may still be helpful. Based on research, I bought the Dorman tank. It fit perfectly.

Regarding the gas cap-- The factory cap definitely will not fit, but you don’t need to rethread the filler neck. I had a new OEM equivalent for an ‘85 Camaro, Stant 10822 and it wouldn’t go more than about one turn. I contacted the Dorman tech line by chat. They advised me that they used a Carquest / Stant 10834 cap for their testing. That cap fits a large number of newer GM and other vehicles. If you look up a 2010 Camaro V8, this should be the cap. It seems to seal well and no MIL lights. It would seem to me that if you have an emission test, the technician should use that 2010 Camaro application for his adapter.

 

There is no pressure monitor or anything on our cars that would trigger a code. You can drive around with a rag stuffed in there if you wanted, or no cap at all. Not that I am endorsing it

 

Right: but in many jurisdictions, part of the emissions testing protocol is, they look in "book" and pick "cap" that "book" says goes with "car", install it, pressurize the tank, and if it doesn't hold, FAIL.

When I lived in CA I saw, lived with, and endured it first-hand. Yeah it sux, but w/e, it's just part of life. It's like racing: the track is the same for everybody. At some level ya just gotta learn to suck it up buttercup and deal.

It's not always a question of "tank" is "crap"; might just as well be, "test cap" is crap. It hardly matters; troubleshooting the individual parts is not the need here; passing the test, IS.

Might be possible to temporarily install something (toilet tank-to-bowl seal or similar object comes to mind) with gorilla snot on the tank, so that whenever they put crappy "test" "cap" on, it seals unconditionally. Whatever it is, it only has to last long enough for "test" to succeed.

 

Well, it's unfortunate that the state regulators are unreasonable, but the start of this thread suggested that the tank filler neck is defective. The correct answer is that the filler neck is not defective. Dorman designed it to use a more recent design cap. If you buy that cap, it will seal. Even though the car may not have an OBD pressure sensor on the EVAP system (I haven't had a reason to go look yet), I can can tell you that the cap fits properly. It easily spins down to the seat and the seal visually seals on the filler neck. There is no gas smell. I will leave it to you to negotiate with your local emission regulators, but for those of us who don't need to pass emissions tests and want to use a Dorman tank, just go buy a 10834 rather than trying to modify the tank.

 

Either way, Good information to have. Did Dorman say why they used a newer cap instead of the "correct" cap?

 

No, I couldn't get a "why" from Dorman. The tech support person looked up what he called the "verification testing" data from when they tested the design. He indicated that was the cap that they used for prove out testing. He didn't seem to have design information. With all the information on this thread, I was a little skeptical, so I took the tank with me to the parts store. They let me take the cap out to my truck to test fit it before I bought it.
Incidentally, there are many other comments about replacement tanks and fit, especially around filler necks. I was concerned about that. But, this tank actually has better filler neck alignment than the factory tank. I did try to duplicate the thickness of the factory tape on the mounting surfaces using a soft pvc based roofing tape cut to width. It took 4 layers to match the original. My thought was that if the alignment was off a little, I could adjust the number of layers to bias the mounting-- for example, add a layer on a front corner and opposite rear corner. Given where the tank contacts sheet metal of the car underbody, it wouldn't take much angular change to move the filler neck a considerable distance. Fortunately, that wasn't required, once it dropped into place, it was good.
Now if I could just get the fuel gauge to work. I rolled the tank a couple of times to test the sender with an ohmmeter before installation to be sure it wasn't hung up, but now it just reads empty with 5 gallons in the tank (the old sender read full all the time, so I know the gauge works.). Maybe I can shake it loose with some slosh...

 

Seems I heard somewhere before that 'the simplest explanation that fits all the facts is most likely to be the right one.'

 

Exactly correct. GM didn't start an on board EVAP leak test until enhanced OBDII around '97-'98, earlier in CA. I don't know what AZ is doing for emissions testing. It seems strange to me that they would test a vehicle beyond the OEM and Fed standards for that model year, but who knows. I guess I'm glad I live in Oregon and better yet in a no DEQ county. I diag and repair emissions systems for customers all day long. Lots and lots of GM products but EVAP faults only on '97+.

My IROC I design, build and maintain for best performance and reliability. Little concern for emissions standards. I mean, fumes out the tail pipe we try to avoid but no tail pipe sniffers out my way.