P0456 small evap leak issue

[Kaptainkid1]

I have the old P0456 CEL.
2002 Jeep TJ 170k miles.
So here are the things I fixed and double checked.
New Mopar Gas cap.
Dropped the gas tank and checked all the rubber lines and tank pressure. No leaks.
Smoked likes from the evap canister in engine bay to gas tank no leaks.
Evap Canister sealed and no leaks.

Here is where I think I have a problem but can't figure how to test it.
I think it's the VLDP pump is broken or maybe the electric line to the pump maybe the issue. I found a youtube video on how to test a LDP pump and my pump and back up pump is working according to this YouTube DIY.


Once the LDP pump is plug in to the TJ, I'm not getting any pressure in the LDP pump line out but when I bench test it and trigger the pump manually it blows up the balloon.
So here is the issue I tested the female line from the engine bay and with a voltmeter I'm getting 13.5 volt from the leads. We have 3 leads in the plug and two leads trigger 13.5 volt but no pulsating. I'm guessing it should pulse base on the youtube on how to bench test.
Doesn't anyone know for sure if these electric leads should just send constant volts to the VLDP Pump when the engine is running?

 

[Kaptainkid1]

Here is the bench test.

 

[CharlesHS]

You are getting 13.5V when you test the connector, but under load the voltage may drop below what is needed to drive the pump.
Trace the wiring and look for other connectors or grounds to see if there are loose or oxidized wiring connections or grounds.

 

[williambmac]

you should have a constant b+ at terminal 2. Terminal 3 is the ground which is controlled thru the pcm
So unless you have a DRB III or an aftermarket Scanner that allows control of the evap system, you aren't going be able to test the system correctly.

You can circuit test terminals 3 and 4 from the LDP to the PCM, You want less than 5 ohms resistance end to end.
If you don't have high resistance in these circuits, I would be willing to bet that you have either a bad purge solenoid or a LDP is faulty.


Look at page 8w-30-15 in the 2002 service manual in the resource section. Thats your wiring diagram.

You can also read page 25-18 in the emmisions section, description and operation of the LDP

I do this shit all day long for GM. 94% of the time a P0456 is a purge solenoid.

 

[LukesfirstJeep]

Slight thread hijack.

Anybody know how to remove the pump on a 2005 TJ, where it's mounted inside the passenger rear fender well? I can see 3 fasteners that hold on a cover plate, the electrical and hose connections, but don't see how to pump is removed.

 

[Kaptainkid1]

you should have a constant b+ at terminal 2. Terminal 3 is the ground which is controlled thru the pcm
So unless you have a DRB III or an aftermarket Scanner that allows control of the evap system, you aren't going be able to test the system correctly.

You can circuit test terminals 3 and 4 from the LDP to the PCM, You want less than 5 ohms resistance end to end.
If you don't have high resistance in these circuits, I would be willing to bet that you have either a bad purge solenoid or a LDP is faulty.


Look at page 8w-30-15 in the 2002 service manual in the resource section. Thats your wiring diagram.

You can also read page 25-18 in the emmisions section, description and operation of the LDP

I do this shit all day long for GM. 94% of the time a P0456 is a purge solenoid.

"If you don't have high resistance in these circuits, I would be willing to bet that you have either a bad purge solenoid or a LDP is faulty."

I bench tested the Purge solenoid as well and that's working.
I can't imagine having a new LPD pump being broken. So will check the the wiring next and maybe by a 3 rd Set of new parts LDP and Purge valve.
Thanks for the input.

 

[williambmac]

"If you don't have high resistance in these circuits, I would be willing to bet that you have either a bad purge solenoid or a LDP is faulty."

I bench tested the Purge solenoid as well and that's working.
I can't imagine having a new back LPD pump being broken. So will check the the wiring next and maybe by a 3 rd Set of new parts LDP and Purge valve.
Thanks for the input.

So you are saying that you have already replaced the purge solenoid and LDP

 

[Kaptainkid1]

So you are saying that you have already replaced the purge solenoid and LDP

I bench tested the Purge valve too. But only bought a LDP pump.
I was thinking just replacing both with new parts a 3rd time for LDP and just a replacement for the Purge valve 1st time.
At this point I'm just throwing parts at it and seeing if it fix it.

 

[williambmac]

I bench tested the Purge valve too. But only bought a LDP pump.
I was thinking just replacing both with new parts a 3rd time for LDP and just a replacement for the Purge valve 1st time.
At this point I'm just throwing parts at it and seeing if it fix it.

I wouldn't replace the LDP again. If you replaced it already and the code came back, it's not your problem.

I would replace the purge and go from there. Just because it's fine on a bench test doesn't mean it doesn't have an intermittent issue with sticking partially open.

I replace a ton of them on GM vehicles.

If you clear out the code, how soon does it come back?

In order to properly smoke test the system with a tester, you need to be able to seal the evap system with a proper scan tool.

A small evap leak is just that..... a small leak that can be very hard to detect.

I would also consider inspecting and replacing any rubber lines in the system, especially up around the LDP and Purge.

 

[Kaptainkid1]

I wouldn't replace the LDP again. If you replaced it already and the code came back, it's not your problem.

I would replace the purge and go from there. Just because it's fine on a bench test doesn't mean it doesn't have an intermittent issue with sticking partially open.

I replace a ton of them on GM vehicles.

If you clear out the code, how soon does it come back?

In order to properly smoke test the system with a tester, you need to be able to seal the evap system with a proper scan tool.

A small evap leak is just that..... a small leak that can be very hard to detect.

I would also consider inspecting and replacing any rubber lines in the system, especially up around the LDP and Purge.

When testing purge valve I always carb clean the valve and them spray WD40 to lube the sliding pin. The same process is done to the LDP pump as well. I want make sure these units are clean and working properly before putting them back. Also when I disconnect the LDP pump and run the engine for 10 mins I do pull a CEL and I get P1495.
Once everything is hooked up. My Jeep pulls a P0456 code after 30-60 miles drive.
I've been chasing this P0456 code for months now.
When smoke testing the evap system I start from LDP line to the charcoal canister and then directly to line back to the gas tank. I had the gas cap off and made sure I was sending smoke through system until smoke was coming out of the gas cap. Closed the gas cap held pressure for about 5-10 mins. I triple checked all the rubber line and nothing was leaking from there. I even dropped the tank and checked all the plastic fitting that normally break and has caused other TJ owners P0456 codes. Those parts on my rig we're good and visual inspection on every line and rubber fitting at this point.
I stumped the LDP pump doesn't pump pressure back into the charcoal canister when the engine is running.
You know when the evap system is working properly is when you go to gas station and open the gas cap and pressure vapor are escaping. I don't get that indicator any more and I suspect my evap isn't holding pressure or the LDP isn't pressuring system or purge is stuck open. One thing I noticed the purge is ticking when the engine is running . Should the purge be ticking when the Jeep is running?

 

[06TJ35's]

About to start my journey with this dreaded small evap leak.