Gross evaporative system leak on 4.0?

Pzilly

Pzilly

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Supporting Member
Joined
Jan 24, 2019
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42
Location
Pittsburgh PA and often Denver Co
Hey gang,
Are these things picky on fuel caps? Found two spares under the seat, ask my uncle who bought this new and he said about once a year the CE came on and a new fuel cap and code clear would make it good for about a year, please keep in mind my 04 LJ only has 79k miles on it so a year for him was not that many miles. Reason I wonder about this is I am also getting codes for "minor evaporative system leak" and also " gross evaporative system leak" some times one, sometimes the other, sometimes the light goes away forms few days. I can post the OBD codes later, right now I actually have some down time in the hotel. Being this is not my DD having a hard time keeping track of what's setting it off so looking for ideas.

Thanks
 
Yes, they are picky on fuel caps. In fact, I've heard that most people haven't had much success with anything other than OE Mopar fuel caps.

If it's not the fuel cap however, the best thing to do is buy a smoke tester tool (or take it to a shop that has one) and perform a smoke test on the evap system. That will pinpoint where the leak is coming from, as they can be very, very difficult to track down.
 
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On my 2001 4.0L there is a 90 degree rubber elbow at the front of the evaporative cannister that WILL dry rot and crack which will give you a gross evap leak. Last time mine went bad (last year) I simply took it off and wrapped it with gorilla tape and have been trouble free since! Just something else to look at if not the gas cap or cracked line?
 
you can have a smoke check done, they put smoke into the tank via a special cap, then see where the smoke comes out.
 
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