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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
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Experience:  Have owned a repair shop for 25 yrs.
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Chevrolet Avalanche 1500 I have a 2004 Avalanche 5.3 motor

Customer Question

I have a 2004 Avalanche 5.3 motor that I am installing in another vehicle. Motor is up and running but throwing codes P0453 and P0446 for fuel tank pressure and vent valve. I checked the fuel cap and realized the fuel tank pressure was in fact high. (got a puff when I opened the cap) Decided to check for vacuum on the system from the solenoid purge valve thinking I may have a kink in a hose or something. I found that I was not pulling any vacuum on the solenoid purge valve on top of the intake. Replaced purge valve and no change. I am getting 12V to the purge valve but it is not opening. It seems to me that the purge valve should be opening with either no voltage or with 12V but neither the new or old valve is working that way. Am I missing something here, where else should i look for the error codes I am getting?
Submitted: 3 years ago.
Category: Chevy
Expert:  Bill replied 3 years ago.

Welcome to Just Answer.com. I'm here to help you and your 100% satisfaction is my goal. Please Accept if you are satisfied.

Hello,

Both of those codes lead towards excessing vacuum in the tank and are usually caused by a stuck open purge valve although you say you already replaced that. Normally there will be little or no vacuum at the purge valve when disconnecting the hose that leads to the tank. With the electrical connector disconnected the solenoid should be closed and no vacuum. With it connected there may be a slight bit of vacuum depending on temp and engine load, etc. The solenoid is pulse width controlled by the pcm and if commanded on at idle at all... will only be in the 10% range.

What I would suggest is reading the fuel tank pressure sensor reading with a scan tool with the fuel cap off and seeing if there it is reading a vacuum. We may have an issue with the fuel tank pressure sensor itself which is on top of the tank in the fuel tank meter assembly. Do you have access to a fully functional scan tool that can command the solenoids off and on?

Bill

Customer: replied 3 years ago.

I have a scan tool that can read the codes but I am not sure if it can command the solenoids off and on. My guess would be no. It is a cheap scanner, Toptek 180 model. Just to clarify there is no vacuum with the electrical connection disconnected on the purge valve and no vacuum with it connected.

 

When I opened the fuel cap yesterday, I noticed a puff of pressure so I am guessing the fuel tank pressure is in fact high. Haven't taken a second look at this since I was assuming the solenoid was stuck closed and I was not getting any vacuum on the system.

Expert:  Bill replied 3 years ago.
It's difficult to determine if you had a "puff of pressure" or a puff of vacuum. Again, the pcm only turns the purge valve on a small amount under normal circumstances. We may have an issue with the fuel tank pressure sensor, a restriction in the vent or a shorted or damaged wiring harness. Initially we need to read the fuel tank pressure sensor data and see what it's reading.
Customer: replied 3 years ago.
Just went thru my scan tool and it doesn't seem to be able to read the actual tuel tank pressure from the pcm. Also just started up the vehicle and let it run for a few minutes, opened the fuel cap while it was running and I am sure that there was pressure there. I had my face right down by the cap and could feel the puff when I popped the cap. Any suggestions for me or do I need to get a real scan tool and start over?
Expert:  Bill replied 3 years ago.

It would be the correct way to diagnose it (with a scan tool). You may try visually inspecting the vent solenoid for a restriction. I've seen them restricted with anything from dust to insect nests.

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Customer: replied 3 years ago.
The vent solenoid and vapor can are both new. Is it possible that i could have plumbed it in wrong? There are 3 ports on top of the vent canister, I connected the one labeled purge up to the intake solenoid purge valve. The small one next to it to the fuel tank, and the large port up to the vent valve. Can you verify for me that i did it correctly?
Expert:  Bill replied 3 years ago.

I couldn't tell without seeing it.

The best pictures I could find are below. There are a couple different setups...

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Customer: replied 3 years ago.

Ok, in the top picture moving from top to bottom, vent valve, purge valve, fuel tank. correct? If so I will have to get a better scan tool and checdk lines for pluggage.

thanks

Expert:  Bill replied 3 years ago.

I can't quite recall without seeing it however the top picture should show it pretty well

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Customer: replied 3 years ago.
Ok thanks for the help. Can i contact you in the future if I get a proper scan tool and can read the actual tank pressure?
Expert:  Bill replied 3 years ago.

absolutely...

I'll be away for a while doing Valentines day duty. :)

Customer: replied 3 years ago.

It will not be today and probably not for a week or so.

thanks, how do i get back to you in the future so i don't have to start over. i am new to this site.

 

Expert:  Bill replied 3 years ago.
just reply here

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