NEED HELP fuel smell—-I changed almost everything

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
2003 Trailblazer standard wheelbase. Changed: gas cap, purge & vent valves, fuel filler neck. The tank inlet check valve and evap can condition are unknown. The evap lines are all in good shape. The (top) inlet of gas tank is not cracked or compromised. I just cleared the p0440 code for literally the 7th time or so.

This is my DD. I can’t inspect it and get a sticker til I get the EVAP readiness.

Help! TIA
 

aaserv

Platinum Donor
Dec 1, 2019
332
baton rouge,la.
Lot of threads on this problem.
Use a factory gas cap? Some aftermarkets were known to not seal properly.
There were a lot of problems with the fill tube cracking right where it connects to the tank. This problem usually showed it self long before 18 years but worth looking at.
Canister is a problem seen more today with this much age on it. Charcoal becomes saturated and no longer vents properly. If we're just throwing parts this 1 would probably be next..
The fuel tank pressure sending unit also has a gasket where it mounts to the tank and is a known leaking spot..

From what I understand....Later models will throw a more specific code while we pre 2005 get the catch all 0440. Id look for signs of leaking around the tank and throw the charcoal canister at it if i found nothing obvious.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,859
Ottawa, ON
P0440 EVAP System No Flow During Purge
Possible Causes
Setting Conditions
Charcoal canister is loaded with fuel or moisture
Fuel filler cap is loose, cross-threaded, damaged or wrong part
Fuel tank, fuel filler neck or fuel sending unit 'O' ring is leaking
Fuel tank pressure sensor is damaged, disconnected or it failed
Fuel tank vapor line(s) is clogged, damaged or disconnected
Purge valve vapor line is clogged, damaged, or disconnected
Purge or vent solenoid power circuit is open (check the fuse)

The problem with breaking tank inlets was on 02/03 EXT and XL and was subject of a special extended warranty, which is no longer in effect. However, this problem could have migrated, to a lesser extent, to the SWB trucks but are now starting to manifest themselves due to this platform's age. IIRC, have heard of one other non-EXT that has had this problem. Definitely check the tank's condition.

One more part that could be swapped and not too costly is the tank pressure sensor. Unfortunately for this part, you need to drop the tank. Check the fuel pump's metal top and lines for any rust through while you're there.

Then, if still getting the code, I would try replacing the charcoal canister since it seems that it's not giving the flow the system is expecting. Since it's a little more costly, I would try this last. Also blow out the lines to ensure they're not plugged.

We do have a few threads on the subject if you want to read some more on it:

 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
Thanks for all the great replies guys! As soon as this tank of gas gets near empty I’m gonna drop the tank. I have a really strong feeling that it’s the supply and return metal lines to the fuel tank. I smell the gas by my driver and driver side rear door. While I’m in there I’ll also get the pressure sensor and have a charcoal canister handy.
 

Reprise

Lifetime VIP Donor
Jul 22, 2015
2,455
GM does sell pre-assembled / pre-formed replacement lines, if you find you need to replace them. But I think they're plastic (the 'metal' portions are mainly in the engine compartment, and the fittings on the pump assembly.

Fuel tank is on the D/S, as are the lines, so that would make sense as far as locating the smell.
If you find your charcoal canister is clogged, you can try running compressed air through it, if you don't want to make the spend for a new canister right away.
Also, make sure your Evap purge valve is functioning (it's in the engine compartment, in the intake manifold area. It'll have plastic tubing running to it, and GM usually has some green plastic surrounding the valve and / or the retaining clips.


To remove your fuel lines from the intake, you'll need a 3/8" line tool. Push the outer connection inward, once you've inserted the tool, to clear the flange on the inner pipe. You'll get it after some trial / error.

Make sure to relieve fuel pressure from the lines before disconnecting any of them by pulling the fuel pump relay in the underhood box, while the engine is running -- it'll shut down in 2 sec or so. Keep in mind that there will still be some residual fuel in the lines, as you uncouple the connections. Having a rag is handy. And if you're underneath the truck, definitely wear safety glasses when working around the lines.

The plastic sections in the underhood area that have connectors joining them -- you can release the connector by squeezing inward on the notched ends (and they'll spin freely so that you can locate those notches). Same at the fuel pump end (and the three connectors there are all different size / types, so you don't mix them up).
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
GM does sell pre-assembled / pre-formed replacement lines, if you find you need to replace them. But I think they're plastic (the 'metal' portions are mainly in the engine compartment, and the fittings on the pump assembly.

Fuel tank is on the D/S, as are the lines, so that would make sense as far as locating the smell.
If you find your charcoal canister is clogged, you can try running compressed air through it, if you don't want to make the spend for a new canister right away.
Also, make sure your Evap purge valve is functioning (it's in the engine compartment, in the intake manifold area. It'll have plastic tubing running to it, and GM usually has some green plastic surrounding the valve and / or the retaining clips.


To remove your fuel lines from the intake, you'll need a 3/8" line tool. Push the outer connection inward, once you've inserted the tool, to clear the flange on the inner pipe. You'll get it after some trial / error.

Make sure to relieve fuel pressure from the lines before disconnecting any of them by pulling the fuel pump relay in the underhood box, while the engine is running -- it'll shut down in 2 sec or so. Keep in mind that there will still be some residual fuel in the lines, as you uncouple the connections. Having a rag is handy. And if you're underneath the truck, definitely wear safety glasses when working around the lines.

The plastic sections in the underhood area that have connectors joining them -- you can release the connector by squeezing inward on the notched ends (and they'll spin freely so that you can locate those notches). Same at the fuel pump end (and the three connectors there are all different size / types, so you don't mix them up).
Thanks so much for all the details! I will do all that 😎
So, I have changed the purge valve and vent valve, as well as the gas cap. I kept the old one, which was factory GM. I just installed a new filler neck, minus the lowest rubber hose that connects it to the tank inlet. My inlet wasn’t cracked or compromised. All the lines seem ok. I definitely will check out the metal lines on top of the fuel pump & charcoal canister. That’s next.
 

Matt

Guru
Dec 2, 2011
3,838
You didn't say you changed it, but along with the lines to the pump, check the top of the pump itself as they tend to rust out and cause the smell right where you said you can smell it.
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
You didn't say you changed it, but along with the lines to the pump, check the top of the pump itself as they tend to rust out and cause the smell right where you said you can smell it.
Yes, that’s the very lines I was referring to that I will check. Thank you, that makes a lot of sense as to the area the gas smell is strongest. I see that the metal lines are integrally part of the fuel pump, so I’m ordering up one today.
 
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Chickenhawk

Hobbyist
Dec 6, 2011
716
Best advice I can give you - having lived through exactly the same thing - is get new fuel lines, fuel pump and fuel tank lock ring in advance. It is highly likely the lines will break when you try to get them off the pump, and very likely the metal lines at the pump will be crushed. It will save you hours of work to just get a new pump and lines in advance because with the age of that truck, unless you live in the driest areas of Arizona, the lines will be almost welded to the connectors. With the 2003 model, there are two sizes of fuel tank, so make sure you get the lines appropriate to your size of tank. I also got a good fuel pump. (Bosch 67415).
 

gmcman

Guru
Dec 12, 2011
4,526
When mine started giving off a fuel odor like the OP's, the culprit was the curved metal fittings at the top of the fuel pump. The pump and plastic lines were fine, but the curved fittings were rusted through.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,859
Ottawa, ON
Ditto. Had that happen on the Saab but it was also very evident with fuel leaking.
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
Ok…so, I have my truck with my mechanic. He smoked the truck and only saw the smoke coming out from the vent valve at the gas tank. Nowhere else.
The brand new vent valve has no ground for some reason, so it’s always open and never closes.
No smoke from the lines on top of the fuel tank and the filler neck is brand new as well- just reiterating that.
Is there a good circuit diagram on this site or does someone have words of wisdom what we should check next?TIA
 
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gmcman

Guru
Dec 12, 2011
4,526
The only issue I see with a smoke test only, is the amount of pressure to the system. When the fuel system is energized, you're looking at 50 pounds of pressure. What doesn't escape with a smoke test, could escape with fuel under pressure.

If there was visible smoke escaping from the top of the tank, then I would think you would have a pretty nasty leak under pressure if it was fuel @50+ psi.
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
I hear you there, but I’ve only had a 0440 code. The smoke was coming from the (“normally open”) vent valve which is staying open, due to no ground signal at the valve. I do have a significant fuel vapor smell on the left side of the truck, and the gas station pump clicks off a lot when I’m filling up (tank near empty). But what could be causing no ground at the vent valve? Fuses all good.
 
Last edited:

budwich

Guru
Jun 16, 2013
1,720
kanata
I hear you there, but I’ve only had a 0440 code. The smoke was coming from the (“normally open”) vent valve which is staying open, due to no ground signal at the valve. I do have a significant fuel vapor smell on the left side of the truck, and the gas station pump clicks off a lot when I’m filling up (tank near empty). But what could be causing no ground at the vent valve? Fuses all good.
Not sure I understand what you are saying. The vent valve is normally open so there won't be any ground towards it. IF the PCM wants to close the vent, then the ground is placed to activate the valve close... but it has to be commanded. So then are you saying, it can never be commanded closed in your situation?
 
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mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
IF the PCM wants to close the vent, then the ground is placed to activate the valve close... but it has to be commanded. So then are you saying, it can never be commanded closed in your situation?
Yes sir, this is exactly what’s happening and what I meant. It’s never closing.
 
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budwich

Guru
Jun 16, 2013
1,720
kanata
ok... but the person who did the smoke test, should have commanded it to close via a tech2 or equivalent. IF that action was not successful, then the focus can be place on the vent valve itself (which you indicate was changed) or the wiring which can be readily checked with a meter. IF one can not "instruct" the closure then the system can also not instruct the closure during the test which then results in the code being set.

Your description of the mechanic's smoke test leads one to believe there is nothing wrong with the vent valve and its operation. IF he did a smoke test and DID NOT use a tech2 (or equivalent) to activate the vent closed, then the smoke will come out of there BECAUSE the vent is normally open. Hence, the result is expected. As suggested by others, you need to ensure that the vent valve is operational via the system using a tech2 or equivalent to command its operation to close. Until you do this, you will be chasing your code for a long time as the system is then unable to be checked further as it is trying to detect a vacuum which will never happen with an open vent valve. The mechanic should have done this "simple test" as part of his testing.

OF course, there are other follow up tests for the rest of the evap system to determine which area is a potential contributing factor in the code.... for instance, commanding the purge valve open at a certain time during testing, etc.
 
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JerryIrons

Active Member
Dec 20, 2011
420
I smelled fuel for quite a while from bad fuel lines. Eventually the leak got bad enough to drip gas on the driveway, once that happened it was pretty easy to figure out. Backing up in the driveway from a cold start was when I could smell it, and mistakenly thought it was "normal" from the system running a rich fuel mixture at cold start. (because I never saw a leak at first)
 
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Mektek

Hobbyist
May 2, 2017
580
FL
If you are from the rust belt, then the metal parts on the top of the tank are prone to rusting out. My TB has never seen salt, so when I pulled the fuel pump, everything was rust free and in good shape.
 
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mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
I have a guy that can do the Tech2/command. My guy already had done a bunch of testing, each valve was tested OK off the truck (as stated, they are brand new). He also saw (by key on/off, running/engine off, meter testing) that there was always no ground present on the white (grounding circuit) wire. Unless there’s something suspect in the engine bay, the harness is intact, no damage, etc.
I’m gonna have the command test performed to see what happens. So far, when I picked the truck up (Wednesday late evening) the CEL was off. Thursday the truck wasn’t used. On Friday, the CEL went on, then went off that same day. It hasn’t come on again since. It’s just after Noon now here and I’ll use the truck today again.
 

budwich

Guru
Jun 16, 2013
1,720
kanata
the evap test stuff does not run all the time. Certain conditions have to be met before it executes by the system. The ground will not be put on the vent until a evap test is required by the system (at that point in the test).... so you won't see a ground until you manually command it or are in the middle of a system evap test.
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
the evap test stuff does not run all the time. Certain conditions have to be met before it executes by the system. The ground will not be put on the vent until a evap test is required by the system (at that point in the test).... so you won't see a ground until you manually command it or are in the middle of a system evap test.
Alrighty. Of course, the CEL is back on. I’m hopefully gonna get it checked out further this week. An aside- I found out that smoke was coming out past my new gas cap, too. I’ll check it also with the original cap, which eyeballs OK…and also return the new cap for a different one.
Thanks for the help so far!
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
the evap test stuff does not run all the time. Certain conditions have to be met before it executes by the system. The ground will not be put on the vent until a evap test is required by the system (at that point in the test).... so you won't see a ground until you manually command it or are in the middle of a system evap test.
Hey man, I’m trying to get the guy to look at this truck of mine, but it’s taking forever. I want to buy a reasonably-priced command computer to do the manual EVAP switching myself. Which one would you or anyone recommend?
 

Eric04

Platinum Donor
Dec 3, 2014
367
West Michigan
Short answer: no. Having done a good bit of searching for bidirectional scanners, I can say there are no cheap options if you want one that actually performs as advertised. There's too much cash wrapped up in licensing agreements and the knockoffs are largely suspect.

Fuel odor causes on this platform, as noted, are rarely anything other than corroded fuel neck or corroded elbows atop the fuel pump.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,859
Ottawa, ON
Command level scanners, a clone Tech 2 is in the range of $300. There's also the GM-MDI that's cheaper however does require a computer to use it. I think that's about as cheap as you can get.

Then I remembered that there is the Thinkdiag that is almost as powerful as the Tech 2. This one is $110 with a $10 coupon. One of the things it doesn't do is passthrough for module programming.


 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
Short answer: no. Having done a good bit of searching for bidirectional scanners, I can say there are no cheap options if you want one that actually performs as advertised. There's too much cash wrapped up in licensing agreements and the knockoffs are largely suspect.

Fuel odor causes on this platform, as noted, are rarely anything other than corroded fuel neck or corroded elbows atop the fuel pump.
I get it about the mfr licensing and such. I DID suspect the metal elbows atop the pump, but I feel the (new) vent valve condition of never closing is causing my fuel odor and CEL.
It’s weird that I never got a p0449 code. I feel that the bidirectional test will show no ground signal from the PCM. My buddy had to manually ground the white wire (pin C17 at the PCM) to get the vent valve to close.
At any rate, I got in with a shop that has the equipment, so it will be looked at this weekend.
Thanks for the help, guys! I’ll let you know what happens.
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
Update: this truck is fun, and I say that sarcastically.

I took it to a shop with the bidirectional scanner, a Snap-On one. Mega bucks and with GM 2021 software. A real shop.

PCM is good. Smok again. My new filler neck was defective, was replaced by them. New gas cap. I returned the two defective parts. Tank pressure sensor was shot, so it was also replaced. Emissions inspection done, all good.

I take the car home Thursday eve, perfect. Car sat the next day. Saturday, I back out the driveway, go forward about 200 feet- CEL comes BACK on.

I use my best scanner, p0440 code AGAIN. 🤬
 
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mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
Update: after flip-flopping whether to replace this truck or not, I’m gonna hold onto it. I DO have a valid inspection now, until August 31, 2022. It’s a dependable truck which rides great. I have complete I/M readiness, although the CEL comes back on after so many drive cycles.

PCM is working properly. The only old thing left is the fuel pump. I still have a significant fuel smell, so I’m inferring that the FP metal lines are rotted and “holey” 😆

I’m thinking after I replace it, the issue will finally be solved! Q: one of my tank strap bolts is stripped in the broken and spinning frame clip. Best source for a replacement piece?

Thanks guys!
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,859
Ottawa, ON
Probably a fastener supply house or an auto parts store that carry Dorman's Help! stuff. Another way would be to weld a long fully threaded bolt in the hole where the J-nut goes and use it as a stud. I recently did this on my Avy.

PXL_20210504_192939572_resized8011580142792562795.jpg
 

mudpaws672

Registered Member
Original poster
Mar 17, 2021
25
Long Island, NY
Probably a fastener supply house or an auto parts store that carry Dorman's Help! stuff. Another way would be to weld a long fully threaded bolt in the hole where the J-nut goes and use it as a stud. I recently did this on my Avy.

View attachment 101887
Nice. I figured Dorman’s Help! stuff. I’ll check them out. Also, thanks for the stud idea!
 
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Chickenhawk

Hobbyist
Dec 6, 2011
716
I had my pump replaced last year because of the fuel smell from rotted lines. I bought all new lines, new fuel pump and a new lock ring in anticipation, and I was correct. It is hard (if not impossible) to replace old lines without destroying the lines on the pump. I also had to get a new tank strap, plus the fuel line I bought was not the correct one. For me, the 2004 had two different lines, depending on where the filter is located.

Good news is that the smell has been gone for months, and my mileage is back up to where it was when new. I now get 600KM on a tank, with mostly highway driving, which is very good.
 

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