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Evap System Leak

I

Ian Christiansen

NAXJA Forum User
Location
Shelby Township, MI
I have codes 442 and 455 for a leak in the evaporative system. What should I be looking for? What does the evap system consist of? It's a 2001, 4.0, AW4, 231, with about 205,000 miles. It does have the 50 state emissions with the two pre-cats.
 
The P0455 code is for a gross evap leak. It's usually triggered by a leaky fuel cap. Try squirting a shot of WD-40
in the cap vent and rubbing a dab of grease around the
rubber seal. That might cure it, if not try a new cap.

It can also be caused by a cracked fuel filler hose. Check for
a gasoline odor around the hose, or a damp spot where
it's obviously leaking.

The 442 might disappear when the 455 is fixed. If not, you
might have an evap purge valve sticking or a break in an
evap hose.
 
I've been checking all the lines and haven't seen anything that stands out. The three rubber elbows that connect at the intake manifold look a little worn out and soft but nothing that would suggest gross leak. Would a vacuum leak cause any of this? I will check the fuel cap and filler hose too.
 
Also, does anyone know what the box is underneath near the rear axle that the three lines run into is? It has two lines that come from up front and another line that runs from the box to the fuel tank.
 
That box is probably your evap cannister where the fuel fumes are stored before being purged to the intake manifold. It might have the purge valve attached, or the valve might be nearer the engine. Any hose that's loose or cracked will trigger the codes you have.

The gross leak code is closely associated with the fuel cap or fuel filler tube though. When the ECM opens the purge valve, it wil check for vacuum in the tank, and if no vacuum it will set the P0455 code. So it's most likely to be a faulty fuel cap. Easy fix if that's indeed the problem.....
 
This may not be your problem, but on my 2001 I had evap codes when I was out of town. I took it to a mechanic said he replaced the rubber on the fuel lines below the drivers seat along the frame rail. I haven't had a problem since.
 
I checked all the lines and then checked them again with it running. Everything looks fine. I replaced the two rubber elbows at the intake manifold since they looked a little worn. I replaced the gas cap with a new one. I took the stamped steel cover off and checked the filler hoses and they look fine with no damp areas or fuel smell. The purge valve is up on the firewall on the passenger side and ticks. Its connected to the evap pump and small round plastic canister has one hose running into it from the pump. Anyway to troubleshoot those without just throwing parts at it? I'm gonna clear the codes and give it few days to see if the codes come back before I change anything else.
 
Dealerships troubleshoot these evap leaks using a smoke
machine that pumps smoke through the system. The smoke
will be visible at the leak site. I've heard of a home-made
smoke machine to test with, but don't know the particulars.

You've done the correct diagnosis IMO, without spending for
shop time at a dealer. It's worth waiting to see if the codes
come back, before changing anything else. The ECM does
evap testing after a number of drive cycles, but I don't know how many. The shop manuals say to drive the vehicle
for a day to confirm repairs, so if the codes don't return after several drive cycles, it should be fixed...
 
After clearing the codes on the 13th, and driving it everyday back and forth to work, I have a new code, 456. This one is evaporative system, small leak detected. So I changed the gas cap and replaced two rubber elbows at the intake that looked suspicious before I cleared codes 442 and 455. Anything else I should check before I take it somewhere to have the smoke test done?
 
My Mom's XJ has the same set-up as yours. The code was 0455. After I eliminated everything else (canister and hoses looked good), I replaced the leak detection pump, which turned out to be the problem.
 
Well, in truth, I ended up throwing parts at it....I replaced the solenoid first, because when my 2000 XJ with single cat threw the same code that was the problem. Did not fix it. I then replaced the vacuum lines in the evap system and still had the code 0455.

I was actually stumped because there are leak detection pump DTC's, but they were not showing up...but at some point I figured that the only two things I had not replaced were the leak detection pump and the charcoal canister. The pump was cheaper than the canister, so I rolled the dice and replaced the pump and it fixed it. (Plus there were no obvious leaks from the canister).
 
I had this problem on my 01 XJ... I followed the hard plastic lines from the pump back to the canister, inch by inch... as the lines go across the firewall to the driver side and down, the hard plastic line switches to a flexible rubber fuel line, and then switches back to a hard plastic line that runs along the lower drivers side of the jeep back to the canister. My leak was in the rubber section. I squeezed the rubber line firmly and it split right open it was so dried out and brittle. If I remember correctly there is more than one line. Then a few years later my jeep developed another leak in the rubber fittings at the end of the hard plastic line where it connects to the canister.
 
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