Hey everyone I'm having some issues with my 03 Tj 4.0. keeps throwing a code for the leak detection pump pressure switch. I have emissions here in ct and my test date is right around the corner. So far I have checked over most of the Evap lines and also changed the LDP . Haven't found any noticeable leaks or issues jeep run like a top no issues at all other then this code. I'm banging my head on the wall here trying to diagnose the cause. I was hoping for some help for all my fellow jeepers. Thanks in advance
Locking gas caps, even when new, are notorious for leaking air through the key slot that trips the evap leak detector. Are you running an aftermarket locking cap? If so, I'd try a standard non-locking Mopar gas cap.
When our friends in California started with OBDII and the rest of the states followed one of the items addressed was Hydrocarbon emissions due to fuel evaporating. Not all emissions come out of the tail pipe. The law requires that a 0.020" leak in the entire fuel system be detected. That's about the size of a normal straight pin! This could be anywhere from the purge solenoid under the hood to the gas cap. They are very hard to detect!
There are smoke machines that inject smoke into the evap system to detect leaks but I doubt if you want to buy one of those.
Next best tool is your nose. In an area with no wind use your sniffer. You might want to use a hose in the nostril (and no, I'm not kidding, I've done it!) to find the leak. You may have a problem convincing the local PD that is what you are doing. "Really officer, I have this tube sticking out of my nose to find a vapor leak! Really!" And gas fumes are hard on the little grey cells so not too much!
According to Chrysler, Evap leaks are the #1 reason for repeat repairs.
I think you are right. Personally I really dislike LDP's. The Natural Vacuum Leak Detection that replaced it is much better. The 1494 has more to do with wiring than leakage.
According to the factory service info the P1494 can be cause by:
"low vacuum supply" to the LDP
"LDP switch sense circuit shorted to ground"
"LDP switch sense circuit open"
"Wiring harness intermittent"
"Powertrain Control Module"
"When monitored: Immediately after a cold start, with battery/ambient air temp between 40 degrees and 90 degrees and coolant temp within 10 degrees of battery/ambient."
"Set Condition: The state of the switch does not change when the solenoid is energized"
Past history would indicate most likely point of failure is the actual LDP.
Could you borrow one from your buddies? Swap and see if his fails and your's passes? Remember the engine has to be cold to test it.
To hack ldp I would replace the line to to tank with one or possibly 2 y connected together small sealed bellows like used as vacuum actuators for some climate control air doors
The small sealed bellows will act like a much larger sealed air resivour that has flexible rubber lines but no leaks. The system cannot be very picky if it is ok with air volumes varying from a nearly empty to a nearly full tank
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