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Discussion Starter · #1 ·
I've found multiple posts about this issue but never a resolution.
-I replaced nearly all the hoses/lines related to my evaporator system (many were soft and deteriorated)
-the purge solenoid
-the vent valve purge valve (which was bad)
I've confirmed my vent hose is not plugged. Everything has been replaced except the evaporator canister itself. The tank has so much vacuum pulled on it, while driving with a fuel pressure gauge on the windshield, it will lose pressure immediately (within about a mile or so) until the car cuts off...OR, as the pressure is dropping, you can get out, loosen the cap, hear a lot of air sucking into the tank and the fuel pressure gauge will shoot back to normal...if you drive with the gas cap loose, it never loses fuel pressure. No codes.
As a side note, either this issue or driving with the cap loose seems to have worsens fuel mileage.

Thanks for any ideas or input guys.

Thanks, G
 

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Have you replaced the fuel return line, or checked it for obstruction?
How about the entire fuel delivery module in the tank, or even just a new vented cap?
 
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Need to track down where the vacuum stops. Disconnect the line from the tank to the evap canister at the canister and see if it's pulling a vacuum as the car runs. If it is, test the other side of the canister, and go from there until you find the problem.

Another possibility: maybe there's an electrical short somewhere in the system and the evap solenoid is staying open all the time, which may be causing the excessive vacuum?
 

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Discussion Starter · #4 ·
Have you replaced the fuel return line, or checked it for obstruction?
How about the entire fuel delivery module in the tank, or even just a new vented cap?
Thanks much fort your response and input. I have only checked the vent line...it had not occurred to me that anything to do with the fuel return line could cause this. I have replaced the fuel hangar assembly...in fact, at first, replaced it...and the car started blowing fuses...the vacuum on the tank was pulling a higher amp load on the new replacement fuel pump and causing the fuel pump fuse to blow. That's when I discovered the vacuum issue. I reinstalled the old pump which was a obviously a better pump...as the car will shut down...but the higher amp draw on the pump, although not good for it, never caused the fuse to blow.
Fuel pressure on gauge is good as long as cap isn't screwed on.
As far as the cap, I was thinking vented caps only vented out when there was pressure...do they vent inwards too? I'd feel like a real idiot if it was just the cap causing this.

Thanks, G
 

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Discussion Starter · #5 ·
Need to track down where the vacuum stops. Disconnect the line from the tank to the evap canister at the canister and see if it's pulling a vacuum as the car runs. If it is, test the other side of the canister, and go from there until you find the problem.

Another possibility: maybe there's an electrical short somewhere in the system and the evap solenoid is staying open all the time, which may be causing the excessive vacuum?
 

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Discussion Starter · #6 ·
Thanks for the response and suggestions...tracing that vacuum would be a good idea I can do. I'm in the middle of redoing the floorpan layout in my hobby shop...a few more hours of work and I can get our Airstream rolled back and out of my lift bay, get the wagon on the lift where I can access the evaporator lines again and trace down the vacuum. Now I assumed that since I have constant vac from the purge solenoid and that I have vacuum on the tank when I remove the gas cap, that it is nonstop vac all the way back.
As far as the electrical short...that's pretty much I thought it had to be as I confirmed there is vacuum pulling ALL the time from the purge solenoid line going down to the evap....so I figured maybe it was a bad ECM since it demands/controls the purge solenoid via the ground as the hot is constant. I was hoping to secure another ECM, which I assume would have to be reprogrammed for my PASSKEY then try it. I could risk sending my ECM out to be rebuilt and ask them to confirm that function at the same time. Is that plausible for them to do?
 

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Thanks much fort your response and input. I have only checked the vent line...it had not occurred to me that anything to do with the fuel return line could cause this. I have replaced the fuel hangar assembly...in fact, at first, replaced it...and the car started blowing fuses...the vacuum on the tank was pulling a higher amp load on the new replacement fuel pump and causing the fuel pump fuse to blow. That's when I discovered the vacuum issue. I reinstalled the old pump which was a obviously a better pump...as the car will shut down...but the higher amp draw on the pump, although not good for it, never caused the fuse to blow.
Fuel pressure on gauge is good as long as cap isn't screwed on.
As far as the cap, I was thinking vented caps only vented out when there was pressure...do they vent inwards too? I'd feel like a real idiot if it was just the cap causing this.

Thanks, G
No, they only vent inwards. All emissions from the gas tank are supposed to go through the evap canister. That's a good idea, to replace the gas cap.
 

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No, they only vent inwards. All emissions from the gas tank are supposed to go through the evap canister. That's a good idea, to replace the gas cap.
Yes, the cap. Loss of fuel pressure with cap on but okay with cap loose--sounds like the present one is not admitting air like it should.
 

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Woodmaster--curious, any update?
 

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OP:............ "Everything has been replaced except the evaporator canister itself. ".......

Unless I missed it up there somewhere, did you deal with the tank as you intended in the thread you started about the issue?
 
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