Rednroll

Hi I currently have a P0456 code (small evap leak). I was going to start throwing parts at it to try to fix the problem but it seems the best way to go about this would be to perform a smoke test to track down where the actual leak is occurring. Ok, so I did some research and get the concept of how to perform a smoke test. I will obviously need some type of smoke machine.

The thing I'm unsure of is where should I connect the smoke machine to perform the tests? My best guess as of now would be to disconnect the purge control value under the hood and blow smoke into those 2 hose connections which connect to the Purge valve.

Anyone perform an EVAP smoke test and can provide some advise?
So far I've been searching on how to perform the test, watching multiple Youtube videos, reading multiple forum posts and am coming up empty. Everyone says to "perform a smoke test" on the Evap system to find a small leak but nobody shows how it is actually done on a JK.

Purge Control Valve.

Rednroll

Also, while I was inspecting my vacuum lines around the purge control valve, I noticed the rubber hose connected between the air box and the valve cover was disconnected. Could this be the problem? I'm unsure if that hose is part of the EVAP vacuum system.

LC Boyer

That is probably for crankcase vent. Hook it up, see if that fixes your problem

Rednroll

Yes, it is the crankcase vent. Was just curious if this could be the problem or not, of course I'll be reconnecting it.

karls10jk

I was ready to break down and pay for it to be done but I kept running into people who had issues with the plastic on top of the tank being the issue. I thought there's no way that was my issue, I threw parts at it, and....it was my issue. I could only see the issue when I dropped the tank. There are some hoses that run from the filler neck, along the filler neck tube, and down to the tank. I tightened them against the tube because I thought it was sensible. Well, it ended up cracking the hairline fracture even more and caused a more consistent issue.

Follow the other folks- drop your tank and inspect the smaller line that goes into the top of the tank. That white plastic nipple likely has a crack in it. To make it easier to inspect without causing more damage, I cut the tube halfway along and just put a vacuum line splice in there. I ended up having to drill on that nipple, epoxy in a new fitting, then connecting it to the hose. Don't get the line super tight, that only causes more problems.

resharp001

I really hate this code. I get it from time to time, clear it, and it stays gone for a good bit of time only to randomly pop back up weeks down the road.

Karl - your advice is not really motivating me to investigate ugh.

karls10jk

I got the code for a year, maybe closer to 18 months before I broke down and started getting into the gas tank. All of the work to get to the tank is the worst. Drilling the plastic nipple and using the epoxy to reinforce it isn't bad, not even terribly time consuming aside from ensuring the epoxy is completely cured before you start moving things.

Rednroll

I'm going to try and avoid dropping the gas tank for now. I was going to start by replacing the evap vapor leak detection pump and o-ring since that seems simple and common but then started to consider doing a smoke test may be in my best interest. If smoke test pointed me towards the gas tank, then it would be time for the dropping gas tank mess.

Odd enough, I reconnected the crank case/valve cover vent hose, cleared the CEL and so far the CEL hasn't come back on after driving to work and going out to lunch. Last time I cleared the CEL, the light came back on during my drive to work. The hose was disconnected at the airbox side. Likely disconnected by shop that changes my oil and forgot to reconnect after checking the air filter. Just wondering if that makes sense if the valve cover vent hose being disconnected could cause the P0456 code. Gas tank is currently half full.

Still would like to understand how to best perform a smoke test on this system.

I can get a decent smoke machine for $80-$100. Shops charge about $100 to perform the test and inspection. Makes sense to just buy the tool and DIY.

Rednroll

This guy performs a smoke test on a TJ where it looks like he's doing the test at what looks to be the purge control valve. So that's why I'm thinking those hose connections may be where to do this test on a JK as well, but am unsure.

resharp001

Interesting video. Pretty convenient for him everything to look at was literally right there in one spot!