Need instruction: smoke test for 2004 4.0 evap system

rjaym · Oct 18, 2024

code 0442 ( small leak ) took to a shop for smoke test (160$) they found a crack in a plastic line at evap pump - that line assembly is no longer available- so I made an effort to repair it. After repair I cleared the CEL and test drove - 0442 popped up !

I decided to buy a smoke machine as it’s about the same price as a test - I just don’t know the procedure for smoke testing the evap system. I assume someone here is a tech and can either make a simple video or post a written instruction from a professional service manual. My rig has a Schrader valve in the engine compartment for tapping into the evap system ( or that’s what I see as the connection point.) I’m curious if any points in the system needs to be sealed off / plugged. To pressurize the system ( albeit very low pressure) the smoke machine I bought has a built in compressor. Searching the forum seems this is a common problem and will likely become more common with age. A detailed write up / video that pertains to the 4.0 / 2.5 tj would be a great addition to the how to . - if I can get the details I’d be happy to make video / write up - rjm

TheBoogieman · Oct 19, 2024

Thread 'Evap system leak'

Mar 22, 2019

Jumping in here-- we've got a 2004 TJ that keeps throwing EVAP codes. Smoke tested it at an offroad specialty shop multiple times, and nothing — no leaks found. Gas cap is clean and testing fine.

Any ideas?

macleanflood · Oct 19, 2024

Basically unplug a vacuum line from the intake...I like the one that goes to the tube on top of the engine from the filter box to the throttle body.

Plug in the smoke machine. Make sure it's fuel of juice... usually mineral oil. Heat it up and turn it on. Make sure your getting smoke before you plug it into the aforementioned hose.

-Mac

C.J. Roberts · Oct 19, 2024

rjaym said:
My rig has a Schrader valve in the engine compartment for tapping into the evap system

My mechanic and I chased evap leaks for two and a half years before he was finally able to find the leak. It was that Schrader valve. He removed it, replaced it with a plain rubber hose, and no problems for 7 years.

Spike Strip · Oct 20, 2024

Around 11.30 in

rjaym · Oct 20, 2024

Thanks spike strip! That will be my primary process. I’m imagining that the to check the entire system it’s a trouble tree type process I.e. if no smoke then -> …… etc. really wish we had access to an emissions test manual for the tj

rjaym · Oct 20, 2024

This video is very detailed and informative on how the generic Chrysler evap system works.

Spike Strip · Oct 20, 2024

On an early Land Cruiser I stuck the smoke hose into the Gas tank fill tube and plugged the opening with a rag. Pressurized to about 10 psi on the compressor, and found leaks that way. Of course that won't tell you if the gas cap is the culprit.

Good luck

Buckz6319 · Oct 21, 2024

I made a evap smoke machine many years ago and it worked perfectly.
I may still have a video of it on my YouTube page

rjaym · Oct 24, 2024

I bought a smoke machine off amazon and found the leak and hopefully repaired it. The set up and test was/is pretty straight forward and doing the fix myself certainly saved me $$ -including the cost the machine. Fixing something yourself along with knowing you saved a few Simoleans is always satisfying. Here are a few pics and notes of what I did.
1) because I already knew the general location of the leak -(see original post) ( near the evap pump passenger rear wheel well) I removed the tire and pulled back the inner fender plastic to allow access to the evap pump.
2) I removed the schrader valve from the test port engine compartment driver side - IMPORTANT!! -THIS VALVE IS LEFT HAND THREAD!! - started the smoke machine and put the tapered hose adapter in the schrader valve hole. The machine has an adjustable pressure regulator - I ran it a minimum pressure (about .5 psi. -a whisper.
3) checking the evap pump location at rear smoke is readily coming out from the hose CONNECTION TUBE on the manifold looking piece. - The connection tube was cracked at its base -basically the manifold was cracked. YEESH!! This item seems to be unobtainium - no long available -it looks like it is made/sold as a complete hose assembly - but again obsolete.
4) I used some plastic epoxy and patched the crack - not leaking after second test - time will tell... I am now on a search for a replacement evap hose assembly
any help there is appreciated.
If anyone would like to borrow the smoke machine I'm happy to loan it out.