P0440 Code out of nowhere

Daniel644

Original poster
Member
Feb 27, 2015
573
So I randomly decided to run a scan with my code reader, been living with a perpetual P0420 code for years, it went away when I bolted in a spare CAT I had laying around from another project (original CAT had been removed and a pipe welded in place before I bought the truck) but once I got that CAT welded in it came back, so my check engine light is always on, i'm planning to order a new CAT in this RockAuto order i'm putting together based on all of you guys's input to address that, but to my surprise I had 2 codes, one for the cat and a P0440 was also in there, I went ahead and cleared the codes to see if it comes back.

In the mean time I pulled both the solenoids (one below the PCM and the one at the back of the gas tank) and bench tested them to see if the solenoids where working, they both tested good in that sense. I doubt it's a Gas Cap issue, a few years back I was getting gas one night after work and the gas cap wouldn't screw back on (the ratcheting thing broke) so the gas cap is only a few years old and the rubber seal is in perfect condition, but I went ahead and reseated it after inspection, even then I'm paranoid about the gas cap triggering codes (happened on the drive home from buying my old firebird) so I always treat every gas cap like it's an old one and put them on with a good bit of force every time.

There have been maybe 2-3 times in the last several years where it had trouble with the pump clicking off too soon, but thats out of several dozen fill ups on the same pump and none in the last several months at least, so pretty sure that was a pump issue and not the truck. The only other input I can put out there is after a quick crank to move the truck on or off the ramps (so I could get underneath it) and shutdown I notice a fuel odor that appears to be coming from somewhere around the rear seat door on the drivers side, it is NOT noticeable behind the rear wheel but is noticeable in front of the rear wheel and fades after a few minutes.

What part would you guys try replacing first? Do you think I should still do the solenoids and if so are the cheaper brands OK to use or is this like the spark plugs where you should use the OEM part? I just put like $2,500 into this thing this month between tires, coil packs and the Brake System (Hit a chunk of semi truck tire on my trip to florida at the beginning of the month and it bent either the caliper or caliper mounting bracket and so i did the full PowerStop KC2062-36 cross drilled/slotted rotors and everything since I needed new front calipers and rotors) and so I need to start curtailing some of my spending on these "non-mission critical" parts if it's safe to.
 

Mektek

Member
May 2, 2017
656
FL
Something I just noticed on the pump clicking issue. It often happens to me, but yesterday I went to Bucees and did a fill up and not a single unjustified click off. They have the new hi tech pumps that slowly ramp up the fuel flow and I suspect this eliminates the problem.

The rear seat drivers side is where the purge solenoid is located so that's might have something to do with the problem. Ideally you could do a smoke test to track the leak - it could be a cracked line or o ring . If you want to save a buck go to a PYP and try a used part.
 

6716

Member
Jul 24, 2012
821
I chased a P0455 for a while, shotgunned some parts at it. Never did sort it out. Check engine light is always on. I check regularly to see if there is a code in addition to the P0455. I am convinced I will have that code as long as I have the truck.
 

Daniel644

Original poster
Member
Feb 27, 2015
573
OK, went ahead and replaced the 2 solenoids, while I was down there I got a better angle on the lighting and it looks like the dirt on the outside of the tank in the area around where the fuel filler line goes into the tank is damp, I think I might have the busted fuel filler on the tank issue I see other threads on. guess a trip to the hardware store is in my future.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Just be aware that if you replace the filler with straight brass fittings, you will have the same problem I had on my Avalanche where when it does click off, it will puke gas out the filler and destroy your charcoal canister filling it with gas. The overflow valve in the filler neck prevents overfilling the tank. I think Dorman has a proper filler replacement but is pricey. Or replace the tank. That's what I had to do.
 

Daniel644

Original poster
Member
Feb 27, 2015
573
Just be aware that if you replace the filler with straight brass fittings, you will have the same problem I had on my Avalanche where when it does click off, it will puke gas out the filler and destroy your charcoal canister filling it with gas. The overflow valve in the filler neck prevents overfilling the tank. I think Dorman has a proper filler replacement but is pricey. Or replace the tank. That's what I had to do.
What if I replaced the bottom rubber hose with this one https://www.amazon.com/gp/product/B07TB5QK37/?tag=gmtnation-20 it has a valve of some kind in it that people say fixes the puking gas issue. or I could do like the dude in the video you shared in this thread https://gmtnation.com/forums/thread...r-r-delphi-fuel-pump-quick-disconnects.20201/ where he epoxied the original check valve into the new fitting.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
That hose  should work. I found another video of the guys that used brass fittings. Those two together should work.


But it may not click off the pump early enough to prevent overfilling the tank and ruining the charcoal filter. Just a guess on my part.
 

Daniel644

Original poster
Member
Feb 27, 2015
573
Upon secondary inspection, i'm not sure thats the issue, I was just under there, cleaned off that area of the tank and tried to see if there was any play between the body of the tank and the neck and for the life of me I couldn't see any play. It's possible the apparent dampness I saw the other night could have been caused by the dew point at that time of night.

I went ahead and did a little "reinforcement" of the joint with some of that JB Weld Putty Epoxy around the neck after a light sanding with some 50 grit to give a little something to bite into, if there was a small vapor leak there that might seal it without having to do a bunch of work, I may go ahead and replace that lower hose that connects to the neck, but I really need to do a good wash the crud off everything to see what condition those hoses are in before I jump to that level.
 
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Daniel644

Original poster
Member
Feb 27, 2015
573
OK, somethings definitely wrong, so I replaced those 2 solenoids a week and a half ago and I just filled up the tank and got the WORST gas mileage ever, the only things that have changed since getting the BEST gas mileage ever is the new tires (same size as the last ones) and those 2 solenoids, this tank Averaged 12.7 MPG (my pre-replacing coil packs numbers where 13.8-14.5), sure I did a couple loops around the neighborhood testing out the 4WD but that wouldn't be enough to knock 10%+ off my MPG's. Note, I only drive the truck on the weekends, so only put like 60 miles on it since replacing the solenoids.

I'm certain it's in 2WD based on how it handles and I only drove a couple miles in 4WD and I could swear on the drive home yesterday (a 12 mile drive in 2WD) I could watch the fuel gauge move.

No check engine lights or anything so really just starting with what has changed since I got the best gas mileage ever.

Weather permitting i'm gonna go yank the new solenoids and test them out either tonight or in the next few days.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Check your charcoal canister. It may be full of fuel.
 

Daniel644

Original poster
Member
Feb 27, 2015
573
Haven't managed to get to the charcoal canister yet Need to get to a floor jack that is buried behind the mower and several other heavy objects, will try to get to that this weekend, or at least get the jack into a better position while the mower is out of the way to mow this weekend.

in the mean time I got a Vacuum/Pressure Pump and decided to do some testing, BOTH the new and old parts where "bench" tested, both performed the same way on each sets of solenoids.

on the Rear Solenoid (single fuel line at rear of gas tank part) Neither would hold a vacuum or hold pressure when Pump was connected to the port and no power was connected, both solenoids clicked when connected to 12 volt bench power supply, I need to get some alligator clips so I can test with power connected to see if it holds a vacuum as I just read (after doing the testing) that power has to be applied for this one to close.

On the engine side solenoid with pump connected to the port on the electrical connector side it would hold pressure but not hold a vacuum unless I put my finger over the other port then it would hold a vacuum but not pressure unless I put my finger over the other port. Again Bench tested both and solenoids clicked, I also just did a test where I pressurized it in the direction it would hold pressure then connected the 12 volt power and the air passed through the solenoid, so at least I know for sure the new purge valve is functioning properly, didn't read about how to test that one till after I reinstalled the old one, but I would expect the old one to be functioning fine since it pressurized the same way and the solenoid did click when benched, if the code comes back i'll pull it and test it properly.

For now reverted back to the original parts to see if the P0440 returns and if anything happens to fuel mileage.
 

Daniel644

Original poster
Member
Feb 27, 2015
573
OK, Further bench testing, pulled the Vent Solenoid back off the rear of the tank and connected it to my now upgraded 12 volt bench (added insulated alligator clips so I could keep the solenoid powered), when the solenoid is powered on the new solenoid will hold a small (about -5 PSI) vacuum, the factory solenoid will pump up to about -10 but lose it in a few seconds (note I can get to like -15 by simply putting my finger over the tip that I am using to fill the vent line hole so these vacuum values are rather low it would seam like) and cutting the power allows the solenoid to revert to the open position, so this seams to confirm the P0440 code would have been due to the vent solenoid, I have reinstalled the replacement part, Side note, both held pressure (upwards of 30 PSI) when the solenoid was closed and when pressurized the solenoid didn't open when power was cut, had to release the pressure to get the solenoid to drop back into the open position.

Still gotta get to the charcoal canister to check it out to see if there is any fuel build up in it that would explain the horrible gas mileage of that last tank, gonna try for that tomorrow.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
What brand were the replacement valves? Have you researched on how to test these valves? I'm not sure if the vent valve deals with a lot of pressure.
 

Daniel644

Original poster
Member
Feb 27, 2015
573
What brand were the replacement valves? Have you researched on how to test these valves? I'm not sure if the vent valve deals with a lot of pressure.
the brand was Standard Motor Products (they had the little heart symbol next to them on the rockauto listing so they seamed to be the popular brand for replacement) testing procedure I found only mentioned pulling a vacuum on them. So far the check engine light has not returned, including the 420 CAT code that i've been living with for years since using the replacement vent valve.
 
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