Early 2000’s Jeep 4.7L EVAP codes (large/small)

[1 SX]

Hi everyone, I have a client who just bought a 2000 ish (I believe 2001) jeep grand Cherokee limited 4.7 L V8 with the automatic quadra all-wheel-drive. It has about 114,000 miles.

It was sitting for about a year parked on the previous owners lawn. I already replaced brake lines, transmission lines, coolant lines, installed a new battery, the very basics to get it running again and moving. The body has no rot, but under it has a lot of surface rust from sitting on a moist soaked surface for a year, on top of being driven in the Northeast winters for sometime (this is the reason why I had to replace all these other lines)
But I am pretty sure the evap codes are the main reason why the previous owner stop driving this jeep.

The client is using the vehicle every single day, but the jeep keeps throwing a check engine light for EVAP codes, both small and large. I have reset the check engine light about five times and it always comes on around 54-63 miles. The other code is for oxygen sensor high-voltage I already replace that and that is fixed..

To try to fix this issue with the evap codes, I either replaced or verified: the lines coming from the gas tank to the charcoal canister under the hood, those lines have already been replaced probably within the past two years no cracks or anything in that line, I even blew into that line and the gas tank held pressure until I released

Replace the gas cap
Replaced the electronic purge solenoid valve next to the charcoal canister
Verified all the rubber lines are intact and whole
The only thing I did not address or replace, is the leak detection pump system under the left front headlight.
The PVC hoses and vacuum hoses are also all intact.
I even cleaned every accessible ground in the engine compartment thinking its a ground issue, but the OBD computer reads 13.9 V at idle.

Anyone have any tricks, tips, or insight on how to get this to pass inspection as in New York when you register a vehicle you only have 10 days to get it inspected, so the client is going every 10 days to different shops to have the Jeep fail to get another 10 day temporary inspection at 21$ every time.

Thanks!!

 

[Trav]

Is this a plastic or metal tank? Did you smoke test it?

 

[1 SX]

I can’t remember what the tank is made out of as there is a skid plate coverin it, but it is California emissions with four oxygen sensors.

Is this a plastic or metal tank? Did you smoke test it?

I did not smoke test it, but that will be in the very near future I feel like. How would I go about getting a smoke machine or something like that to test the evap lines?

 

[eljefino]

Fill the gas tank and keep it filled. Many cars only run the EVAP test between 1/4 and 3/4 tank, and you can pass with one I/M incomplete for 01+, and two incomplete for 96-00. Since you hit the wall at 54 miles, top it off every 40.

 

[Capt W]

In early 2015 had recurring P0455 and P0456 on my 2005 Caravan; inspected everything as best as I could. My wife rented a smoke machine from Party City for about 10 bucks. Plumbed that into the system and after about 20-30 minutes discovered a small leak at the fuel pump mounting flange on top of the tank. There was even a slight bit of oily weepage from the O-ring seal (but I never thought to look there). Replaced entire fuel pump since I was in there...codes cleared and never came back in the ensuing 100K-plus miles.

 

[Timmastertech]

The LDP system is beautiful but can be a challenge sometimes. The LDP is vacuum operated so there is a vacuum line to the LDP solenoid on top of the pump. There are 3 wires going to the LDP, one is power, one is pulled to ground by the PCM to energize the LDP solenoid and the third is the LDP switch. When the PCM wants to run an evap leak test, the PCM sends a duty cycled ground to the LDP solenoid which applies vacuum to the LDP diaphragm lifting the diphragm, closing the LDP switch and stroking the pump. As pressure builds in the evap system the pressure will hold the diaphragm up keeping the LDP switch closed at which point the PCM stops energizing the LDP solenoid and counts to see how long it takes for the LDP switch to open back up. If the switch stays closed for a predermined amount of time that varies based off of fuel level, engine run time/temp and ambient temp, the system is judged to be leak free. If it does not the system is judged to have a leak and based on how long the switch took to open the PCM judges large or small leak.

To diagnose effectively, a scan tool with the ability to run the LDP forced monitor test is a must. The questions that need to be answered are whether or not their is vacuum to the LDP solenoid, is the PCM energizing the LDP solenoid and is vacuum flowing to the pump chamber. Is the pump stroking (you can hear it go thwack thwack thwack when it pumps) and is the switch changing state. If the pump is functional (not a crazy high failure rate) then a leak needs to be found. I usually start by capping off the large hose from the LDP to the tank and running the monitor test to see if it passes. If it passes that verifies the pump. If not then I need to check vacuum and electrical signals to the pump. If it passes with the pump isolated from the rest of the system then I know I have a leak to find and I would use a smoke machine to pressurize the system through the tank line with the LDP disconnected.