How can I confirm evap system is working correctly?

Bob.Gibson

TJ Enthusiast
Supporting Member
Joined
Sep 8, 2019
Messages
159
Location
New Zealand
When I purchased my 05 TJ it was fitted with an after market fuel cap that did not seal. It had no o'ring and I could see dust in the filler neck.
I would have expected an error code to have been generated but there was none.
I have now fitted the correct Mopar locking fuel cap.
How can I confirm this system is working correctly.
 
You sure someone didn't take the bulb of of your CEL ? Cause I would have expected a light also since in a way that would be like driving with no gas cap almost. :unsure:


Or did you have a CEL just no code for evap leak?
 
In a hurry one day, I forgot to put my gas cap back on after filling up. I only drove it about 10 miles to home and seen it then and reinstalled it. I didn’t get any CEL either. I pulled my code reader out and checked it and got nothing there are well.

I thought maybe I didn’t run it long enough like that or not enough on-off key cycles or something. 🤷‍♂️
 
Get an OBD reader and you can see two things.

1. If you have any Evap System codes
2. If the Evap system Readiness test is set to Complete or Incomplete.

If you have no codes and the system readiness is Complete, then the system is working
 
You sure someone didn't take the bulb of of your CEL ? Cause I would have expected a light also since in a way that would be like driving with no gas cap almost. :unsure:


Or did you have a CEL just no code for evap leak?
The CEL is working. I get seat belt and door warnings and h
Get an OBD reader and you can see two things.

1. If you have any Evap System codes
2. If the Evap system Readiness test is set to Complete or Incomplete.

If you have no codes and the system readiness is Complete, then the system is working
Definitely no engine codes.
I will check the Evap system Readiness later today and report back.

I have other Vehicles with Evap systems and on all of them when I remove the gas cap to refuel I get a sucking noise but when I remove the cap but on my TJ there is no sucking noise regardless of how low or hight the fuel level is.

Plugged in OBD scanner (Torque Pro)
No Error codes.

TEST RESULTS
TID $27 CID $71
$28$27
$2a$29
$2e$2b
$3d$2f
$3e
$5b
$5c
$71
$72
$73
$74
$75
$76
$77

All the above have a green tick in the box
I don't know what they all mean but am Googling it now
 
In a hurry one day, I forgot to put my gas cap back on after filling up. I only drove it about 10 miles to home and seen it then and reinstalled it. I didn’t get any CEL either. I pulled my code reader out and checked it and got nothing there are well.

I thought maybe I didn’t run it long enough like that or not enough on-off key cycles or something. 🤷‍♂️
The system only checks on cold start and the tank has to be somewhere between 3/4 and 1/4, I forget the exact numbers but your situation would have never done the test.
 
I had a look at my EVAP canister setup and it looks different to that shown in the 2005 TJ Service Manual I downloaded from here.
Specifically I have no DVLD pump. It doesn't look like it has been removed just never fitted.
Could this be because we have a different emission standard here in New Zealand and it is not required?

IMG-0292.JPG
 
The system only checks on cold start and the tank has to be somewhere between 3/4 and 1/4, I forget the exact numbers but your situation would have never done the test.

Good to know. Thanks. (y)
 
Hi dbbb1 can you please send me the information.

For those that aren't aware TJ manuals for every year are available in the TJ Resources form. You can just download the PDF and search for the terms you need
 
yes I do have a evap purge valve and solonoid

Well, I just noticed that the FSM does say : "LEAK DETECTION PUMP MONITOR (IF EQUIPPED)", and :
"When equipped with certain emissions packages, a
Leak Detection Pump (LDP) will be used as part of
the evaporative system for OBD II requirements.
Also refer to Leak Detection Pump."

Maybe in New Zealand at the time your Jeep was made there was not a requirement for the fuel system to self check for evaporative emissions leaks.

I have other Vehicles with Evap systems and on all of them when I remove the gas cap to refuel I get a sucking noise but when I remove the cap but on my TJ there is no sucking noise regardless of how low or hight the fuel level is.

I would not think that one would have any vacuum in the TJ's fuel system since when the vehicles is normally vented to the atmosphere VIA the charcoal canister when powered off.
In the picture you posed It looks like the black cylinder is the filter to the atmosphere, can you blow through the canister?