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legozombie

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I tried doing some research and didn't find anything relevant so here is a new thread. There is a question at the end, I am just trying to give as much back story as I can. Without further adieu...

So last week I was changing out the fuel sender on my stock 350 sbc QJet-M4M3 1983 K20 p/u and was under the truck for about a week moving the bed by myself and lowering the tank and whatnot. As I was putting everything back, I was testing my electronic fuel pump to make sure that fuel was leaving the tank due to a botched first attempt, I think from a kinked hose right after the sender. Right next to the fuel pump (located at the turn when the lines turn to go to the engine bay from the back of the cab), I noticed that someone spliced a rubber section of hose into the metal lines. I noticed the line was super cracked so I decided to replace it. This line (important for later) came from the vent port of my 3-port sender to the vent port of the EVAP/charcoal can (6 port can). Once everything was in place, I decided to test drive it to go fill up on gas since I only had like 5 gallons. I live a couple of miles from a gas station in a very hilly area. On my way there I tried shifting into the 3rd gear (4-speed M/T) and I noticed a lack of power. I shifted back down thinking I was low on gas hoping to limp to the gas station. However, on an uphill, I could tell my truck was about to die so I pulled over and called AAA for gas under the assumption it was a lack of fuel problem. I was like a block away from the gas station. To keep the story concise, I filled my tank halfway and I still couldn't get my truck to start. Eventually, somehow, my truck started on a super low idle and would die as soon as I pressed the gas pedal. The only real difference between before and after was that cracked line I replaced so I cut it and sure enough my truck started up strong and didn't have any issues at all and I made it back home (and a trip to the hardware store for bricks and lumber since then)

Since there was a rotten hose there before I think that may be the reason my truck stalled once in highway traffic. I may have kicked the fuse tap that connected the fuel pump on that occasion but I can't tell for certain. There was another time I left my truck idling in front of friends house for about 20 minutes and my truck just died when I tried taking off which I have no clue why but it eventually turned on. I'm thinking that the cracked hose closed enough to kill the engine.

So the problem this last stall was that air wasn't getting into the tank and there was a vacuum since the vent line was blocked somewhere after the line I replaced to the engine bay. I don't mind keeping my charcoal canister and I definitely don't want a line straight to my sender/tank exposed under my truck. I just checked the line and I'm pretty sure air is passing through the hoses unobstructed. I shot compressed air through all 5 ports (one of them shot charcoal beads out, whoops) and none of them seemed to have any obstruction. I haven't pulled any vacuum on any port yet.

I found some old stock and am thinking of throwing money at it since it's probably the original. How can I check that my EVAP can is working correctly?

Thank you
 
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legozombie

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No bites yet from this crowd but in my research I found this image. It may be useful to someone out there.I don't know if it's exactly for GM but it seems exactly what I have for my 5/6 port. I just hate not knowing what's going on in the black box and I don't want to cut my hard-to-find canister open.
You must be registered for see images attach
 

legozombie

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I am going to throw money at a new canister and a new PCV valve. I have part number 17061005BT so it's probably original and needs to get replaced anyways. I see that my PCV valve is covered in oil so I am going to replace that as well as all the vapor/vacuum hoses I touch. Here is my hose routing
 

fast 99

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Possible reason for no response is OP is too long. Need to be more succinct. Occasionally a poster drags on with unnecessary diagnostic details. If we need more information to fill in the blanks someone will ask for it.
 

legozombie

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Fair enough. I'm also using this forum as a truck diary/library lol.

TL;DR Engine stalled and eventually started rough idling. I cut the vent hose between the evap can and gas tank and it started up. Please help me fix
 

DoubleDingo

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@legozombie I have learned the hard way in not getting replies to questions over the years, especially when you're stuck and are looking for answers, leaving you to just search and find it somewhere. I always thought that adding the details would yield better replies, not very few, or sometimes zero replies. I have recently started shortening my inquiries and have been getting more feedback.

If you're using the forum to document your progress, start a thread just for your rig in the appropriate sub-forum, and ask away on everything else in the appropriate forums, and then you search that a later date if need be.
 

legozombie

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@DoubleDingo Yeah I'm picking up what you're putting down. This post was ultimately meant to be a question to the community with some back story, as you mentioned. I'll just keep it concise next time. Thanks
 

Ricko1966

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If you think the tanks not venting due to cannister problem,run the truck with no gas cap. Problem gone? You have a vent problem. Follow the vent line to the front pull the line at the front,leave it open,did the problem come back. The problem is from that point to the tank. Problem still gone? Verify all routing to the cannister. All good? Replace the cannister. If you need to run temporary with no cannister put a fuel filter on the line at the front to keep dirt and bugs out of the vent line. I've been trying not to post much to avoid personal attacks. I wanted to answer this on day 1.
 
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75gmck25

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My canister is an old 2 port that connects to a dedicated port on the ‘75 Quadrajet. However, since I’m no longer using that carburetor, I just left the end of the hose to the carburetor open, and it works fine. I also pulled vacuum on it to verify the tank vent line is open, so it does serve as a tank vent.

My point is that as long as the vent lets air into the tank, and prevents a vacuum, figuring out how the canister works is a follow-on task.
 

Grit dog

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@DoubleDingo Yeah I'm picking up what you're putting down. This post was ultimately meant to be a question to the community with some back story, as you mentioned. I'll just keep it concise next time. Thanks
That’s not a problem. You weren’t too long winded. The internet doesn’t always answer your questions immediately.
But @Ricko1966 did. If it’s a vent problem, no gas cap will diagnose that issue. Which you may have already diagnosed by cutting the vent line again.
Another question? Why the electric fuel pump? Out of necessity, bad cam lobe or ? I run an e pump on the 86 because the enigne has no provisions for a fuel pump, but otherwise carb and mechanical pump are preferable imo, short of having a high$ fuel system that is set up right. JMO
 

Grit dog

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If you think the tanks not venting due to cannister problem,run the truck with no gas cap. Problem gone? You have a vent problem. Follow the vent line to the front pull the line at the front,leave it open,did the problem come back. The problem is from that point to the tank. Problem still gone? Verify all routing to the cannister. All good? Replace the cannister. If you need to run temporary with no cannister put a fuel filter on the line at the front to keep dirt and bugs out of the vent line. I've been trying not to post much to avoid personal attacks. I wanted to answer this on day 1.
Don’t worry about crazy dude. You have a lot of good intel to share here.
 

Radiohead

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I've been trying not to post much to avoid personal attacks. I wanted to answer this on day 1.
Who tf is doing that? I've never felt anything you wrote of a technical nature to be incorrect or lacking. If anything, you've helped fill in where I've forgotten stuff. The occasional spelling errors, meh. Doesn't affect your accuracy.
 

Ricko1966

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Who tf is doing that? I've never felt anything you wrote of a technical nature to be incorrect or lacking. If anything, you've helped fill in where I've forgotten stuff. The occasional spelling errors, meh. Doesn't affect your accuracy.
I've been attacked big, 3 times, recently. Over nothing, most of its been taken down. But makes you feel like just staying out of things. Oh yea, spelling,punctuation,heck even content. It's not until the second or third time I'm reading something that I realize,crap I need some punctuation Damm you spelled that like a 3rd grader,jeez,you left out a whole sentence,that doesn't even make sense.
 
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Radiohead

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Even with the rare disagreements I have with posters from time to time, none of those disagreements were fueled by squares. It's only the stuff related to that P word where problems have happened.

You keep doing you Rick, I support your writings on here and appreciate your knowledge base. Lames gotta lame. Keep it up man.

Back to the question of the thread, I wonder if a little testing won't suss this issue out, like maybe a collapsed/plugged steel lines for the fuel/evap control system. Or maybe now the original canister is bad due to having its charcoal shot out of a hose.

Oh, tech tip of the day. When testing things like this, don't feel regret like @legozombie feels and use as little air pressure as possible to make your tests. Full shop air applied incorrectly can add to your parts bill, removing your beer budget in one fell poof.

Ever got your fingers bit blowing out a caliper piston seal? ;)
 

legend57

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@legozombie Have you been able to test out Ricko1966's tests? I'm currently in the process of installing the fuel system on my 1976 K20 and am curious what you find. I spent most of last week trying to understand how the evap system works. I fully agree it sounds like a vent problem.
What I'm not 100% clear on is the evap system is for capturing fuel vapor from the tank. When the fuel is being consumed while driving, a vacuum is generated and air needs to be able to flow into the tank to equalize the pressure. I'm not clear how the evap system would allow this. If it doesn't then a vented cap is necessary. Or, perhaps the vent line that goes to the air cleaner allows a backflow of air into the tank. (?)

 

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