HELP! Evap emissions leak (nightmare)

Hello All!

Any help would be much appreciated in helping me resolving this issue! I've read and searched countless forums with no resolve. I have a 2001 Jeep Cherokee Limited. I don't drive it often. About 2 months ago I had the small emissions leak engine light code come on. I replaced the gas cap with a Jeep cap and reset the light. Came back on after a few cold starts. Now it has gone to a medium evap leak engine light code. I've had the system smoke tested, it came back with no leaks found. I have inspected all lines and rubber connections, and don't see any issues. The technician who did the smoke test said that since no smoke leaks were found it could be the leak detection pump or evap purge valve.

So here is where I'll add a little more info to see if it helps solve my issue before I go spending $200 on a LDP that isn't confirmed as the issue.

I understand that the fuel system is pressurized and tested for leaks by the LDP only when the vehicle is on a cold start, under around 90 degrees outside, and with under 85% full. Coincidentally, or not, I have noticed that when starting the vehicle under these same conditions I notice a very strong fuel smell coming from around my fuel filler cap, which is also the same area the fuel tank vent valve is. Also, if I open my fuel cap at that same moment it is smelling of gas it lets out a lot of pressure. Outward pressure, not inward, which I find odd since I read the LDP should only pressurize the tank by about .25 psi?

So here is my question. Is it possible that the LDP is broken and over pressurizing my fuel tank causing the fuel filler cap to vent or the fuel tank vent to open?

Is it possible the fuel tank pressure sensor is broken and causing the LDP to run longer than it should?

What else could be causing this fuel smell in that area that would not have been noticed during a smoke test?

Or am I crazy or stupid to think about all these possibilities and should just replace the LDP? :eeks1:

If you suspect a faulty fuel tank pressure sensor, I'd see if your guy with the smoke machine can find some specs on acceptable fuel tank pressures that he can read with a scan tool or a pinpoint test that can determine excessive fuel tank pressure. Might not be able to, but just a thought.

Have you pulled the tank? checked for bad hoses, gasket at fuel pump? Cracked ring at fuel pump assembly? I believe the regulator is on top of the fuel pump assembly............could be that...........

I haven't dropped the tank yet. Wouldn't the smoke test find a leak if it was coming from one of those areas? Its a medium size leak now, at least the engine code is saying.

I fixed my sis-in-law's '00 with small evap leak a month ago. Her culprit was a rusty metal hard line that went from the cannister by the left rear tire underbody to the gas tank. I replaced it with a plastic hard line that advance sells for $6/3'. Those rubber elbows on the cannister are also prone to deteriorating.

I doubt that the LDP pump is bad, since it seems to be doing a test as told to by the PCM, and does not generate a high P.S.I. I doubt that the evap purge valve is bad since the PCM is constantly pulsing it once you get to closed loop operation and a bad one can cause its own DTC code.
Since the leak started out small and has progressed to medium, it sounds like a leak to me, that wasn't found with smoke test. Wouldn't be the first time. My Jeep had to be tested 3 times before the dealer found it, luckily under warranty. Since you are smelling fuel near the tank, I would suspect the leak to be near that end of the vehicle, near the EVAP canister or fuel pump.

Don't put too much into the size of the leak. Chrysler leak detection is a joke, I've 3/4in hoses broken in half and only small leak codes set. I would have it smoked again, as sometimes they are extremely hard to find. You could still have a bad purge valve that works electronically but not mechanically. And if the LDP has failed, it will assume a leak since the criteria to run the test is never met.

You need to run a smoke test with a machine that tests for how large the leak can be. We have the Bosch system, cost about $2,400. Most shops have the cheaper $500-$600 systems that wont reveal a leak even when there is one. I would take the Jeep to a reputable shop (independent) and I guarantee they will find your problem. Stop chasing your tail.

So my Cherokee is a 2001 with 71k miles. It doesn't have any rusted anything under it. So that's out of the equation. Its always been an Arizona car and garaged so all the rubber is in good shape (inspected it all anyways to confirm). Today when I cold started it I went under the hood and could feel the LDP pumping/clicking away. Then after a few minutes it stopped and the purge valve began ticking away. I really do trust the technician that did the smoke test. He kept it for two days looking for a leak. However, I'm sure it was a cheap smoke machine. Is there any possible chance that the jeep gas cap I purchased is faulty right from the start?

Hamis001 said:

Its always been an Arizona car and garaged so all the rubber is in good shape (inspected it all anyways to confirm).

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Hot climates are the worst for rubber components. Arizona, Southern California, Parts of Texas and Nevada ALWAYS have rubber deterioration problems (whether it be door seals, rubber hoses or evap stuff). Your mechanic sounds like he knows what he is doing. Sounds like the EVAP stuff is working (making noise when its supposed too). I would start with another leak test, this time with a machine that can pick up the smallest leaks through a mano-slack-tube, most smoke machines are visual and aren't effective at finding leaks unless you tear everything out of the car. I have worked in this industry long enough and chased MANY evap leaks that other shops couldn't find. I promise you will find a leak if it is tested properly.

Oh, and welcome to the Forum! Pics of your rig?

I pursued the small leak code on my 2001 a few years back. What I found was that Jeep used single wall rubber tubing to join sections of the gray plastic tubing that is the evap emissions piping from the pump under the hood to the canister near the tank.
I found two junctions, one fairly near the firewall in the engine compartment.

Single wall rubber had dried up and was cracking. Replaced with double wall fuel tubing. On my 2nd 2001 I found cracks beginning but not yet leaking. Replaced that tubing with double wall fuel hose as well.

Check this or just change the rubber tubing portions before doing anything more complex.

My 2001 has had the problem twice. Both times it has been a deteriorated rubber or connector.
Not having a smoke machine I use an air brush pressure regulator, set to about 3-psi, to pressurize the system.
A spray bottle, filler with soapy water, is used to pin point leaks. You can usually hear the area of the leak, assuming you are in a quiet place.

In mine, I ran by a mechanic with a smoke machine. It was the rubber joint where it exits the engine compartment and starts running along the frame rail. Dry rot. It could be anywhere, but I would look at that one first. This repair was done years ago. The system is very sensitive to codes. We had our first "cold night" of the year last week. I did some work earlier this year involving those lines and I got a P0456 again. Sigh. I'm guessing it's where I spiced broken lines together with vinyl tubing because it's what I had. Probably head down and get some proper vacuum hose, but I'm not sure that will fix it. The vinyl tube was a very snug fit.

And remember, just because you hear them working, doesn't mean it's mechanically working.