Just when it was time to have the Jag inspected, the check engine light came on with a P0456 code (small evap leak). Time to troubleshoot and figure out what is going on.

Basically, the EVAP system consists of the fuel tank along with the fuel cap, the charcoal canister, which in this car is right above the rear subframe, a solenoid vent valve attached to the canister that is normally open, evap hoses from the tank to the canister and from the canister to the purge valve (normally closed) and from there a hose to the engine. After doing quite a bit of research, I decided to start with the purge solenoid valve.

The purge solenoid valve is located under the left wheel well. The wheel well cover would need to be removed to access the valve. Once you have your sight on the valve you have to remove the two evap hoses (one going to the canister and one going to the engine), the electrical connector and one bolt that holds the unit to the frame. The valve is normally closed. You can try to blow through one of the hose fittings and you should not be able to blow any air through it. Similarly, you can try a handheld vacuum pump. If the purge valve holds vacuum, then the valve is most likely in good shape.

Last check for the valve - apply 12v across the two electrical stubs in the electrical connectors and you should here the solenoid click. When energized, you should be able to blow from one of the hose fittings and the air flow should be unrestricted.

This first test succeeded which bumped me out because that would have been the easiest fix, period. Now I have to figure out where the leak is.

Next step was to hook up the smoke machine. Since the purge valve was disconnected, I put one end of the smoke machine to the hose that goes back to the canister. Now, the vent solenoid on the canister valve is normally open. I verified this by observing smoke coming out of the canister.

Closing the canister vent solenoid can be typically be accomplished by a scan tool. I hooked up my Autel MaxiSys and it appeared that there was a function to test the evap system by closing the vent valve but that test kept failing. I ditched the scan tool and went manual mode. I traced the wiring to figure out which of the two leads on the vent valve was positive and hooked up a small 12v battery to energize it. Once I did that, I smoked the system and sure enough the vacuum on the smoke machine held at 0.020" which is the threshold for the P0456 code. I went to the gas cap to see if smoke was coming out but there was nothing. I actually removed the gas cap and no smoke was coming out period. I would have expected smoke or hissing but nothing which I do not yet have an explanation.

I then removed the rear seat to expose the fuel pump access caps but there was nothing remarkable - no smoke, no hiss. There are two evap hoses that are partially visible but again no evidence that they were leaking.

With the vehicle up in the lift, I tried to see if there was any evidence of smoke coming from the canister area. The canister view is heavily obstructed by the rear end but what I noticed was a almost imperceptible hissing sound accompanied by the aroma of fuel vapors. So, yes, there is a small leak and yes, it is unfortunately coming from the canister or one of the hoses that attach to it.

That sucks majorly because all the evidence suggests that the rear frame needs to be removed for further investigation. Sounds like a multi-weekend job and even though I can do it, its just a pain in the *** to have such a huge job just to replace the evap canister.

So no conclusion yet. Just a start to a new saga it looks like.


Purge valve under the left wheel well

Purge valve removed

Testing the purge valve

Smoke machine

Connecting smoke machine to the EVAP hose that goes back to the canister

Smoke out of the vent solenoid valve

Vent solenoid valve electrical connections to shut it off


Smoke and gauge falling to right about 0.020" - confirming P0456 to be a valid code

No smoke from the top of the fuel tank

 

It was time to get the car inspected again and besides that, I was tired looking at the check engine light in the dashboard. The code was the same P0456. I hooked up the smoke machine again and this time I was able to to hear an audible hiss from the top of the gas tank. Could not quite see any smoke but the hiss was good enough for me to investigate further.

I decided to drop the gas tank to investigate. You have to remove the exhaust and the drive shaft. Since the drive shaft was out, I will be doing the driveshaft u-joint replacement and both jurid replacements - this will be tracked in a separate thread.

I sealed the tank with plugs that I made (TPU 3D printing) and hooked the smoke machine directly to the tank. *PROBLEM IDENTIFIED*. It is a crack on the base of one of the evap lines on top of the tank exactly where I heard it. Not sure this thing is replaceable by itself but my first thought is to thoroughly clean the area and patch it with plastic epoxy.

If there are any better ideas out there let me know.


If I did not have a lift, I would simply not own this vehicle

Gas tank removed. Exhaust and drive shaft need to be removed. Not too bad

After sealing the tank and using a smoke machine, presto. The source of the leak.

 

I am confirming that I have repaired the tank by using epoxy material. Tank was cleaned on top, epoxy material mixed and slathered around the crack,
I used Marine Tex - extremely messy to mix up since it is like putty but boy when it is done it applies easy and hardens as a rock. I have tested the repair with the smoke machine and confirmed the whole system now is sealed.
The tank is back on the car and the code has not come back after several drive cycles. I/M readiness confirms EVAP test is successful.
Jag picture was taken 5 minutes ago. It is such a pretty car.