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Quick update - tested it out last night, put in 5 gallons, transferred it to the main. All went through smooth. Burned some of the fuel, added 10 more gallons, then transferred it. All went well and it filled the main. Started the vehicle this morning and had CEL and TRAC OFF illuminated. Pulled the codes and got P0441 and P0455. These imply something is wrong with the EVAP (charcoal canister) system. I checked and everything looks good from a hose connection perspective, so I'm wondering if it's an issue with the gas cap. I pulled it, tightened it down and cleared the codes. I'm all ears for anyone else that may have experienced these issues. Let's hope it doesn't return!
Both these codes indicate a probable leak in the evaporative emissions control plumbing for the fuel tank. The codes are likely due to a failure of the evap system autotest, which runs some number of hours after the engine was last run and fuel tank temperature has stabilized (typically in the middle of the night.)

There is a Toyota Repair Manual Supplement (EG-048-04) that covers the operation of the evap system, and provides troubleshooting help. This is based on the use of Toyota diagnostic tools, but if you can rig a manometer or Magnehelic gage capable of measuring inches-of-water-column pressure levels, you can probably follow the fault tree.

Below is one of the illustrations from this Supplement showing system pressure at various times, relative to solenoid states, and where a P0455 "gross leak" might be detected when there is a vacuum leak of ambient air into the evap system.

Here is the link to the complete document:
https://www.autocodes.com/uploads/toyota/EG048-04.pdf
 

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I cleared the code and it hasn't come back yet. I believe the issue was a loose gas cap. I also found that the instructions and parts provided with my kit were different then what was provided with @rx100 kit. Mine came with the wrong size barb, hose, and directions for where I should connect the two rollover valves (OEM and LRA). These ended up being installed on opposing sides of the fill neck. I'm going to monitor this and potentially change these out (thankfully I can do this without pulling the tank). More to follow.
 

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I cleared the code and it hasn't come back yet. I believe the issue was a loose gas cap. I also found that the instructions and parts provided with my kit were different then what was provided with @rx100 kit. Mine came with the wrong size barb, hose, and directions for where I should connect the two rollover valves (OEM and LRA). These ended up being installed on opposing sides of the fill neck. I'm going to monitor this and potentially change these out (thankfully I can do this without pulling the tank). More to follow.
Spoke too soon, CEL came back this afternoon (figures it would right after I said it was gone). Obviously I'm going to swap the hoses, but wondering if it's something else. Ordered a smoke test machine for EVAP systems and will use it to inject smoke in the lines and see if I can find a leak somewhere. Always something, always something... :cry:
 

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It will be interesting to see what your smoke test reveals.

My plan has been to pressure test everything before installation, due to this (the fuel tank, and the filler pipe assembly, mainly).

A pinhole in one of the welds somewhere would be very hard to see, but should show up quickly by a pressure test. I hope that your trouble is easily solved without having to remove/reinstall anything big.


N
 

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It will be interesting to see what your smoke test reveals.

My plan has been to pressure test everything before installation, due to this (the fuel tank, and the filler pipe assembly, mainly).

A pinhole in one of the welds somewhere would be very hard to see, but should show up quickly by a pressure test. I hope that your trouble is easily solved without having to remove/reinstall anything big.

N
I really hope it's nothing crazy like that. I'd be so upset if I had to pull the tank for a pinhole in the welds. I'm really hoping it's just a hose fitting somewhere easy.

You ever used a smoke test machine before? I'm assuming I just pour the smoke into the fill tubes on the tank and see where it escapes from? I've seen videos online of them using an evap port under the hood, but not sure that applies in this scenario since I'm assuming it's coming from a hose connected to one of the tanks...
 

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As N356 suggested, I'd start with a pressure test, applying a slight positive pressure to the system and then spraying every hose connection or other potential leakpoint with a spray bottle filled with detergent/water solution, or kid's bubble solution (or home-brew equivalent) for longer lasting bubbles.

Since the bubbles from any leakpoint will have a "life" of at least a minute, a small leak may be easier to find than a tiny, transient whisp of smoke from a smoke machine.
 

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As N356 suggested, I'd start with a pressure test, applying a slight positive pressure to the system and then spraying every hose connection or other potential leakpoint with a spray bottle filled with detergent/water solution, or kid's bubble solution (or home-brew equivalent) for longer lasting bubbles.

Since the bubbles from any leakpoint will have a "life" of at least a minute, a small leak may be easier to find than a tiny, transient whisp of smoke from a smoke machine.
Ok, but if I may ask, can you give detailed instructions on the pressure test? Building a Manomemter as you suggested previously is way beyond my level of knowledge/expertise. Laymans terms, please!
 

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Is the CEL coming on when driving or at stop sign, etc? Test conditions may require you to mimic load conditions to set DTC when the system detects the leak. This can be difficult if the car was driving at the detection point.
 

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Is the CEL coming on when driving or at stop sign, etc? Test conditions may require you to mimic load conditions to set DTC when the system detects the leak. This can be difficult if the car was driving at the detection point.
No, does not come on when driving, only after the vehicle has sat for several hours (the vehicle runs an evap check and that's what is triggering the CEL, as there's a leak somewhere in the system).
 

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You could make your own pressure tester by sacrificing a fuel filler cap: drill and install a Schrader valve, with a pressure gauge, or use a trusted air supply with a gauge, and pump it up to whatever the test pressure is (sorry don't recall of the top of my head but its in the shop manual in the EVAP section). Going to be something small, like 5psi or something like it.

Then apply the bubble test like FJ Test described in post #206 and search for the leak.

If you can't find the leak, leave it pressurized for a few hours and confirm if it looses pressure (disconnect the battery so the system doesn't do its own leak check during this).

If that doesn't show anything amiss, then check the lines to the charcoal canister (as some are pressurized at different times depending on its own leak check).

Hopefully it will be something simple like a hose joint.

Norm
 

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You could make your own pressure tester by sacrificing a fuel filler cap: drill and install a Schrader valve, with a pressure gauge, or use a trusted air supply with a gauge, and pump it up to whatever the test pressure is (sorry don't recall of the top of my head but its in the shop manual in the EVAP section). Going to be something small, like 5psi or something like it.

Then apply the bubble test like FJ Test described in post #206 and search for the leak.

If you can't find the leak, leave it pressurized for a few hours and confirm if it looses pressure (disconnect the battery so the system doesn't do its own leak check during this).

If that doesn't show anything amiss, then check the lines to the charcoal canister (as some are pressurized at different times depending on its own leak check).

Hopefully it will be something simple like a hose joint.

Norm
Thanks Norm! I'll order up a new fuel filler cap and give this a shot. I'll check for the exact PSI (unless someone here knows it off hand).

When I came out this morning I didn't get a CEL, so it's very intermittent.
 

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Thanks Norm! I'll order up a new fuel filler cap and give this a shot. I'll check for the exact PSI (unless someone here knows it off hand).

When I came out this morning I didn't get a CEL, so it's very intermittent.
I think you'll find that the CEL is being triggered when the vehicle fails its daily EVAP system test. This test is automatically performed every day when certain conditions are met. This typically occurs every night (or early AM) when the vehicle has been shut off for 5 or more hours. The threshold for failure may vary depending on ambient temperature, volume of fuel in the main and aux tank, etc., etc. See the link below for specific troubleshooting info for evap system failures.

5 PSI is WAY too much pressure for this test. For example, determine the area (in square inches) of the largest side of the tank and multiply by 5, and you'll see how much force you'll be exerting on the tank welds with 5 PSI internal pressure. I don't know the dimensions of your tank, but assume for a moment that the largest side is 18" X 24", or 432 square inches. Multiply by 5 PSI, and you'll see the resulting force is 2160 lbs. This risks bulging the tank or fracturing a weld.

That's why I suggested pressurizing the tank to a few tens of inches of water column, and using a manometer to read these low pressure values. 1 PSI = about 28" of water column, and I'd recommend using LESS than 1/2 PSI.

A manometer is nothing more than a small-diameter clear plastic or glass tube, vertically-oriented. The unit of measurement "inches of water column" is the pressure exerted by the weight of a column of water in a vertical tube.

You have made a manometer when you drink liquid through a straw, applying negative pressure at the top of the tube to draw the liquid up into the straw. In our case, we want to apply positive pressure to one leg of a "U" shaped tube, and see how high (in inches) we force the water up into the opposite side of the tube.

Making a U-tube manometer like this takes 5 minutes and costs $5, maybe $0 if you have some materials laying around. Take a 4'-5' length of 1/4" or 3/8" diameter clear vinyl tubing, form it into a narrow "U" shape, and tape it to a piece of cardboard or thin plywood. Install a plastic barb fitting in one leg so you can connect another piece of flexible tubing to your test port in your fuel filler cap. Add some food coloring to a cup of water, and fill the "U" about 1/4 full with water. Also tape a yardstick between the legs of the "U" so you can measure the difference in height between the top of the water column in the two legs.

Place a "T" fitting in the line between the manometer and the fuel filler cap, and use a bicycle pump to SLOWLY pressurize the system to somewhere around 18" of water column, then start spraying your leak detection solution on all joints and connections.

(For more info on manometers, see: schoolphysics ::Welcome::)


For specific info on diagnosing Toyota's evap system with integral vacuum-pump, see: https://www.motor.com/wp-content/uploads/2016/02/6_EvapSystem_0216.pdf
 

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I think you'll find that the CEL is being triggered when the vehicle fails its daily EVAP system test. This test is automatically performed every day when certain conditions are met. This typically occurs every night (or early AM) when the vehicle has been shut off for 5 or more hours. The threshold for failure may vary depending on ambient temperature, volume of fuel in the main and aux tank, etc., etc. See the link below for specific troubleshooting info for evap system failures.

5 PSI is WAY too much pressure for this test. For example, determine the area (in square inches) of the largest side of the tank and multiply by 5, and you'll see how much force you'll be exerting on the tank welds with 5 PSI internal pressure. I don't know the dimensions of your tank, but assume for a moment that the largest side is 18" X 24", or 432 square inches. Multiply by 5 PSI, and you'll see the resulting force is 2160 lbs. This risks bulging the tank or fracturing a weld.

That's why I suggested pressurizing the tank to a few tens of inches of water column, and using a manometer to read these low pressure values. 1 PSI = about 28" of water column, and I'd recommend using LESS than 1/2 PSI.

A manometer is nothing more than a small-diameter clear plastic or glass tube, vertically-oriented. The unit of measurement "inches of water column" is the pressure exerted by the weight of a column of water in a vertical tube.

You have made a manometer when you drink liquid through a straw, applying negative pressure at the top of the tube to draw the liquid up into the straw. In our case, we want to apply positive pressure to one leg of a "U" shaped tube, and see how high (in inches) we force the water up into the opposite side of the tube.

Making a U-tube manometer like this takes 5 minutes and costs $5, maybe $0 if you have some materials laying around. Take a 4'-5' length of 1/4" or 3/8" diameter clear vinyl tubing, form it into a narrow "U" shape, and tape it to a piece of cardboard or thin plywood. Install a plastic barb fitting in one leg so you can connect another piece of flexible tubing to your test port in your fuel filler cap. Add some food coloring to a cup of water, and fill the "U" about 1/4 full with water. Also tape a yardstick between the legs of the "U" so you can measure the difference in height between the top of the water column in the two legs.

Place a "T" fitting in the line between the manometer and the fuel filler cap, and use a bicycle pump to SLOWLY pressurize the system to somewhere around 18" of water column, then start spraying your leak detection solution on all joints and connections.

(For more info on manometers, see: schoolphysics ::Welcome::)

For specific info on diagnosing Toyota's evap system with integral vacuum-pump, see: https://www.motor.com/wp-content/uploads/2016/02/6_EvapSystem_0216.pdf
Awesome, thank you so much for the explanation! The good thing is I haven't seen the CEL come back since yesterday afternoon. I drove to work this morning and drove home just a little while ago and it's still clear, so not sure what's going on since it's so intermittent. The code did come back yesterday afternoon, but that was also after I showed someone at work how to fill gas between the two tanks, so I had to remove and replace the cap. Hoping it's the cap causing the issue.

I spoke with Cruiser Brothers and they suggested I replace the gas cap first, then perform the smoke test if the code comes back again. Looks like I have several options at my disposal, so we'll see what happens. More to follow!
 

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Awesome, thank you so much for the explanation! The good thing is I haven't seen the CEL come back since yesterday afternoon. I drove to work this morning and drove home just a little while ago and it's still clear, so not sure what's going on since it's so intermittent. The code did come back yesterday afternoon, but that was also after I showed someone at work how to fill gas between the two tanks, so I had to remove and replace the cap. Hoping it's the cap causing the issue.

I spoke with Cruiser Brothers and they suggested I replace the gas cap first, then perform the smoke test if the code comes back again. Looks like I have several options at my disposal, so we'll see what happens. More to follow!
If there are multiple connections where rubber hose is clamped onto a metal pipe or fitting, verify that each clamp is tight, and give it another day or two for the rubber to fully conform to any irregularities in the fittings. Ideally the fits and finishes on everything should create a vacuum-tight seal from the very beginning, but sometimes they don't. It doesn't take much of a leak to create the very small pressure differentials the self-test system is trying to detect.

I don't think your gas cap is the problem, you never had any evap system failure codes prior to the tank install, correct? Same cap?
 

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@DucRider a couple of quick items to check:

1) The connector for the over-flow tube on the main tank. (blue twist collar in the picture below) There's an o-ring inside this connector that was easy to dislodge and required lube to reinsert the tube from the filler neck. Any chance this connector isn't seated properly?

2) As FJTest said, the gas cap hasn't changed, but your filler neck has. The rim of my new filler neck, the edge that seals with the cap, had a very rough finish when I got it, almost like a splatter paint finish. I used a Dremel to smooth it out before I finished the install so not sure if it would have been a problem, but if yours is the same maybe it is preventing the cap from sealing properly?
 

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I don't think your gas cap is the problem, you never had any evap system failure codes prior to the tank install, correct? Same cap?
No, but as CRay says below, the filler neck changed and that could be part of the problem.

@DucRider a couple of quick items to check:

1) The connector for the over-flow tube on the main tank. (blue twist collar in the picture below) There's an o-ring inside this connector that was easy to dislodge and required lube to reinsert the tube from the filler neck. Any chance this connector isn't seated properly?

2) As FJTest said, the gas cap hasn't changed, but your filler neck has. The rim of my new filler neck, the edge that seals with the cap, had a very rough finish when I got it, almost like a splatter paint finish. I used a Dremel to smooth it out before I finished the install so not sure if it would have been a problem, but if yours is the same maybe it is preventing the cap from sealing properly?
I'll check the part that connects to the blue twist collar. I don't recall seeing an o-ring come out when I removed the OEM fill neck.

Interesting feedback on having to dremel the edge of the LRA neck smooth. I'll double check that tomorrow (don't want to mess with it now as I want to see if a code pops up again). The two times I've had the code have been after removing the cap, so trying to leave it and see what happens since I haven't seen an error thrown in ~36 hours.
 

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Went out this morning at 9:30 and no CEL still. That’s ~48 hours without the light, and I’ve been driving it in between that time period. I had the new gas cap so decided to swap it out now. This way if the error comes back I’ll know it’s something else. Here’s some photos of the fill neck and the difference between the gas caps.
 

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Found my leak! CEL never came back, but went to gas up at Costco last night and noticed some gas on the ground when filling the main tank. Apparently the rubber hose between the new fill neck and the section of main tank that I cut off wasn't 100% sealed and was letting some fuel out. Got that fixed today and tested the system out. No issues now. Can't wait to get a full fill on the aux tank now! Thanks to everyone for their inputs on ways to test it. Guess I can return the smoke machine :D
 
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