Gas caps...

I got a locking gas cap that requires you to unlock it with the key from Quadratec a while back and went and got the Jeep inspected (Texas) and the gas cap failed the pressurize test. I put the original gas cap on to get it to pass the inspection. I was wondering if the gas cap I got from Quadratec was defective or was the inspection guy crazy. Would there be any harm in putting the quadratec gas cap on?

You might get a CEL with code suggesting you have a small vacuum leak in your fuel system....

A defect is possible.

As I recall, only OBD-II will "throw" a code with a fuel cap pressure failure (it's supposed to not allow vapour emissions through it - that's what they're checking for when they take it off and check it out,) which is only applicable for 1996-up XJ. OBD-I did not, as I recall, have a code for that. (It would have been something like "Evaporative Emissions Control Fault" or somesuch.)

Simple solution? You've had a cap on there that you know passes test, right? Put your locking cap back on, and only put the other cap back on when you go in for test. Swap them back once you get home from emissions test. It's much the same thing I do with my EGR valve (it's disconnected except when I go in for test - engine actually runs cleaner without it anyhow - according to their machinery!)

I thought it would throw a CEL, but I wasn't sure since it was OBD-II.

Having the locking quadratec cap on will not affect anything such as MPG, performance or anything?

Crusher16 said:

I thought it would throw a CEL, but I wasn't sure since it was OBD-II.

Having the locking quadratec cap on will not affect anything such as MPG, performance or anything?

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It should not. It doesn't have anything really to do with engine management (directly) - just evapourative emissions. In a properly-working evapourative emissions control system, the fuel vapours from the fuel tank will be routed to (and stored in) the charcoal cannister underhood, and thence into the intake stream for combustion. Typically, the charcoal cannister only accumulates fuel vapours when the engine is not running (when the engine is running, the fuel volume decreases at about the rate the fuel vapours increase anyhow, so it evens out.) I can't swear to how the system keeps tabs on it, but I'm fairly sure there's a pressure sensor somewhere that monitors it (I still need to take a general course in OBD-II one of these days.)

However, even having no fuel cap should not affect fuel delivery - which is what would have an effect on power, fuel economy, fuel efficiency, and the like. The only "real" effect you would have on fuel economy from having no cap at all would be the slight but measurable loss of fuel from evapouration out the filler neck. Almost - but not quite - negligible.

But, OBD-II would throw a fit if it thought the fuel cap was too badly out of whack. I don't recall offhand if it's a "hard" (CEL/MIL) code or a "soft" (no CEL/MIL) code or not - but you can check the code chart in the tech section of my website - since I compiled it from FSMs anyhow.

It should throw a code for a "small leak detected in the evaporative system". If you want to know the specific code, drive home from the gas station with the cap sitting in your cup holder and see if the light doesn't come on. I see this code alot on newer vehicles after people fill up and don't tighten the cap down all the way (atleast 3 clicks is a good rule of thumb).

If the cap is in fact bad, and you're still in the market for a locking gas cap, the one I use I bought from Autozone back a couple of years ago when gas prices first shot up and gasoline thefts shot up with them. Cost me about $11 or so if I remember correctly, and I havent had a single problem out of it. I actually like it better than the one I got for the KJ from Napa....and mine was cheaper

And 5-90, if i'm not mistaken, it is a Hard Code when it comes to bad gas caps. Every time i've seen one fail, it's thrown the light on.

99XJSPORT06 said:

And 5-90, if i'm not mistaken, it is a Hard Code when it comes to bad gas caps. Every time i've seen one fail, it's thrown the light on.

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Entirely possible - I just don't remember. Too many whacks to the head, O knight who until recently said "Ni.":laugh3:

(Damn - knew I forgot something... - Ed.)

Ok, thanks guys.

I run a locking Stant cap. Passed emissions this past Feb. Guy hooked up tester to gas cap and it passed.

Not sure why yours wouldn't? Same concept right?

Although I did get the non pre-release cap....Stant offers two caps.

The pressrue release cap only releases pressure when you unlock it before untwisting though....shouldn't affect anything when locked and such.

I edn up buying a new gas cap every year, actually every other time I go to Montana I haven't figured out if I'm leaving them @ gas stations or if people are ripping them off. I bought the locking one this time so we shall see.

WaXJ_Skier said:

I edn up buying a new gas cap every year, actually every other time I go to Montana I haven't figured out if I'm leaving them @ gas stations or if people are ripping them off. I bought the locking one this time so we shall see.

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Next time you roll through Missoula I'll give them ALL back

I've not been a fan of locking ones, if someone is out to steal your gas I'd rather have them siphon it than punch a hole myself..

RichP said:

I've not been a fan of locking ones, if someone is out to steal your gas I'd rather have them siphon it than punch a hole myself..

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That's more or less my thinking too.

On the other hand, I can't help but wonder if the OEM gas tank skid has any benefit against the "ice pick" crowd...

Rob Mayercik said:

That's more or less my thinking too.

On the other hand, I can't help but wonder if the OEM gas tank skid has any benefit against the "ice pick" crowd...

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Yea, it does, it will channel the gas to one location if they punch more holes in it so it drains faster....

5-90 said:

O knight who until recently said "Ni.":laugh3:

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:yelclap:

RichP said:

I've not been a fan of locking ones, if someone is out to steal your gas I'd rather have them siphon it than punch a hole myself..

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What if they are out to only steal your cap or contaminate your gasoline without you knowing?

Locking cap has added benefits.

Blaine B. said:

What if they are out to only steal your cap or contaminate your gasoline without you knowing?

Locking cap has added benefits.

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I've always tried to not piss people off myself so they don't generally go after me but as for random people, nothing you can do.

For the "what it's worth" file, my XJ spent about 5 hours(!) on it's drivers' side 2 nights ago, as I had rolled on a hill and the guy behind me had no winch (me either). My locking gas cap is a Stant brand, but I don't know if it is for the OBDII stuff or not. The cap actually allowed NO fuel to drain for the entirity of the roll/recovery. Kudos to Stant for a good product! I am not sure if the OEM cap would have held or not. Full tank at 25 gals. (did the vent mod- can now run for almost 500 miles, instead of 400!!).

An extra 5 gallons?

Next time that you have the fuel pump assy. out, reach in and re-route the vent line up towards the top of the tank. I had to use a piece of hose with an elbow molded in to get up to the top of the tank.You want about 3/4" between the top of the line, and the tank.