Replaced the gas cap..
Built a u tube smoke machine 12 volt powered driven by a 12v pump. Regulated it down. No smoke.
Paid a well respected repair station to find the leak I missed, no luck.
I can feel the solenoids clicking at the duty cycle purge solenoid and at the leak detection pump.
Should I be able to feel the pump whirring?
My tank is damaged on one end where the rollover valve should be. It looks to be covered in rtv and no vacuum line heading to the direction of the fuel sending unit.
How can I check the pump for operation?

 

I've been chasing an EVAP leak for over a year so I'm semi-qualified ... . The pump doesn't whir or anything, it is driven by vacuum and the PCM activates the solenoid on and turns it off when it reaches the end of the stroke and closes the switch in the pump. The pump frequency should get slower as the pressure rises and ultimately stop as it reaches a certain level. If the PCM has to continue to cycle the pump it looks at how fast it has to do that and determines the leak size from it.

Checking the pump is somewhat difficult as it's vacuum driven. There are some videos on youtube that use a vacuum source but that's not something everybody has at hand. You could try to disconnect the hose that goes towards the fuel tank (EVAP canister actually) and see if the pump tries to build pressure on that port. Problem is that the PCM is in control of the pump so it supposedly only runs the pump on cold starts between 40F and 86F coolant temp. Bi-directional scan tools can activate the pump but that doesn't work when the engine is running, and if the engine is off there is no vacuum. Catch 22.

Most DIY smoke machines (incl the cheap Amazon one I got) use mineral oil and while that smokes nicely it also condensates quickly while traveling through long hoses. You'll never see smoke around the tank even if that's where the problem is. Ask me how I know . I ended up disconnecting the vapor line from the tank at the charcoal canister and that worked better. Ultimately I also used a hose as a stethoscope and tracked the leak down to the fuel pump gasket. Some PO had replaced the pump but not the rubber gasket.

 

Thank you Der Truck for an excellent road map. Short, clean concise. This should be a sticky. As you mentioned some of the UTubers really break it down well.
, a really simple way to check your LDP for the cost of a balloon.
Wells always has excellent videos.

I guess on a morning cold start I can hook up a balloon to the outlet side of the of the LDP and see it inflate?

 

That should work, I have never tried that though. The tricky part is the many conditions that have to be met for the test to be run: Coolant temperature, fuel tank level, battery voltage during cranking (just learned that skipping through the Wells video). If you felt the solenoid in the LDP clicking you had the right conditions so give it a try.

 

Dertruck, can you provide some detail on how you were able to use a stethoscope (or even an improvised stethoscope) to pinpoint the fuel pump gasket as the source of the EVAP leak? I've been chasing a P0442 small EVAP leak for a few years, and suspect that the problem may be in the general area of the top of the fuel tank, but have not been able to find the leak after several inspections of the entire EVAP system and all components. Thanks.

 

I disconnected the line/hose coming from the fuel tank at the charcoal canister and instead connected a cheap Amazon smoke tester. The tester pushes low pressure air into the hose which then escapes through wherever the leak is. In theory you could see the smoke and voila ! Given the location and the somewhat weak smoke (as I wrote above it tends to condense further away from the source) I just used a piece of random hose (5/8" or something) which I stuck in my ear and moved the other end around above the fuel tank. The hissing obviously gets louder when the end of the hose is close to the leak.

Note that I basically just used the smoke tester as a low pressure air source. No need to get one of those, anything that can put out air at around 1PSI pressure will do the trick.

 

https://dodgeforum.com/forum/2nd-gen...tion-pump.html. see pic.

Can that rollover valve be removed?

I am told that I need otherwise a gas tank from a 2wd gasser, 35 gallons, long bed or short bed extended cab.

The frame spacing of cross members on 4wd looks different.

 

35 gallon tank only fits the long beds. To me knowledge the frame crossmembers are the same between a 2wd/4wd

 

I have a 34 gallon tank in my 98 Quad Cab, Short Bed.

 

I shoved the outlet hose of a HF 9.99 air pump (guaranteed to do 100 PSI, barely does 30) . into the hose leading from the charcoal canister. A loose fit that would not over pressurize the tank. Lots of leakage at that connection. . Crawled under the truck and could smell fumes.
There is a breeze today. Put my hand over the buggered rollover valve and could feel air leaking out. . At the same time I had a plastic shop glove over the leak detection pump. It didn't inflate. While running the engine.
I have felt the solenoids on the purge valve and LDP clicking.
As soon as the fuel level is lower I will drop the tank and pressurize it out of the truck. Eric O from the South Main Auto channel has taught me not to fire the parts cannon at once.
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