Evap Leak Code P0442

[Jeepoftheseus]

Hey everyone,

My 98 Wrangler TJ is throwing a p0442 small evap leak code. I bought a smoke machine so that I could skip the guess work, but I noticed the evap service valve has a warning that it should only be pressurized to 1 psi maximum. It looks like my craigslist smoke leak detector outputs a fixed 19-23 psi and cant be adjusted. Do I have any options here?

 

[macleanflood]

Bypass the valve or deliberately induce a leak to reduce pressure.

I'll bet if you disconnect that valve and tap it it'll be full of charcoal.

Mine was on my 97. New Standard Motor Products valve and a VC120 canister and no more issues for me.

-Mac

 

[Jeepoftheseus]

Bypass the valve or deliberately induce a leak to reduce pressure.

I'll bet if you disconnect that valve and tap it it'll be full of charcoal.

Mine was on my 97. New Standard Motor Products valve and a VC120 canister and no more issues for me.

-Mac

This is helpful, unfortunately I didn't detect any charcoal in the area around the service valve. I went ahead and ordered a new smoke leak detector that should work as intended. I bet I can sell the other one as fast as I bought it on craigslist.

 

[AaronPaul]

Bypass the valve or deliberately induce a leak to reduce pressure.

I'll bet if you disconnect that valve and tap it it'll be full of charcoal.

Mine was on my 97. New Standard Motor Products valve and a VC120 canister and no more issues for me.

-Mac

If you introduce a leak (like disconnecting a hose), you’ll reduce pressure but also lose control over where the smoke flows.
The leak will allow too much smoke to escape before it pressurizes the system properly, making it harder to pinpoint small leaks like the P0442.

Let the smoke machine run into a separate chamber (like a sealed bottle). Allow the smoke to slowly enter the EVAP system without direct pressure.
This is less precise but prevents over-pressurization.

Just my 2 cents though.

 

[Jeepoftheseus]

If you introduce a leak (like disconnecting a hose), you’ll reduce pressure but also lose control over where the smoke flows.
The leak will allow too much smoke to escape before it pressurizes the system properly, making it harder to pinpoint small leaks like the P0442.

Let the smoke machine run into a separate chamber (like a sealed bottle). Allow the smoke to slowly enter the EVAP system without direct pressure.
This is less precise but prevents over-pressurization.

Just my 2 cents though.

This is really helpful. I went ahead and bought the proper smoke machine anyways. It arrives tomorrow. I've drawn up a complete diagram of the evap system, too, so I'll understand everywhere to look. If everything goes well I'm going to do a write-up for the forum so that I can keep paying forward all the great help i've gotten from the forum.

 

[AaronPaul]

This is really helpful. I went ahead and bought the proper smoke machine anyways. It arrives tomorrow. I've drawn up a complete diagram of the evap system, too, so I'll understand everywhere to look. If everything goes well I'm going to do a write-up for the forum so that I can keep paying forward all the great help i've gotten from the forum.

AWESOME! I am sure lots of people would appreciate your help and a diagram. I hope you find the fix soon. Let me know

 

[macleanflood]

You'll find a complete drawing and service procedure in the factory service manuals available for download under the resources section.

-Mac

 

[NashvilleTJ]

This is really helpful. I went ahead and bought the proper smoke machine anyways. It arrives tomorrow. I've drawn up a complete diagram of the evap system, too, so I'll understand everywhere to look. If everything goes well I'm going to do a write-up for the forum so that I can keep paying forward all the great help i've gotten from the forum.

The most likely cause for the small evap leak is a faulty / worn gas cap. Be sure to look there as well during your smoke test. If the cap is original, it’s likely a good idea to replace it anyway.

 

[Jeepoftheseus]

Update!

I seem to have fixed the problem.

I knew the issue probably wasn't the gas cap, because a new one didn't solve the problem. I went ahead an d bought a smoke leak machine and got a couple buddies together with flashlights and laser pointers. We hooked the machine up to the service port and began searching the evap system for the leak. No smoke. No smoke anywhere. We even tried bypassing the service port and couldn't find anything. I pulled the canister purge valve and blew hard. A little bit of air escaped, which made me think I might need a new one. We gave up and put it back together. We turned the jeep on so that I could feel the leak detection pump with my hand for any movement and listen carefully to the purge valve. However after listening and feeling for a few minutes we discovered the check engine light was now off.

Disconnecting the canister purge valve, blowing through it, and reconnecting it seems to have solved the problem... for now. If the check engine light comes on I think Ill buy a new purge valve. What does everyone think?

 

[Jeepoftheseus]

You'll find a complete drawing and service procedure in the factory service manuals available for download under the resources section.

-Mac

I some how missed this, I think I looked at the parts manual and thought I was looking at the service manual lol