How to tell if you have bad check valve

**evola4** · 05-26-2008 12:55 PM

How do you know if you have a bad check valve, I've looked at all my check valves that I could see and they all look ok, no cracks or anything of that sort. Is there another way to tell. Same question goes for the gas cap as well. How would I know if I have a bad one.

**dirtybrd** · 05-26-2008 01:03 PM

You can blow thru one way but not the other, it's good.

**jrau13** · 05-26-2008 01:14 PM

Do a boost leak test and that should tell you as well. Gas cap, not sure.

**Dirty** · 05-26-2008 01:23 PM

If you have a bad gas cap you should throw a cel.

**evola4** · 05-26-2008 01:24 PM

cool thanks

**A4TL** · 05-26-2008 04:18 PM

the thermoset plastic will be crumbling away. this in turn gets stuck in say your N80 valve which then costs you a new check valve and n80 valve.

I've got USP plastics $1.66 check valves all over my engine. works great.

when i pulled the check valve off before the N80 purge valve you could see the end of the nipple facing the valve had a small chunk missing. of course i could never get it out of the n80 valve :(

**AudiA4Turbo22** · 05-26-2008 04:21 PM

sorry for the thread jack, but how would u know ur n80 is bad??

**BOPOH** · 05-26-2008 04:34 PM

Originally Posted by A4TL

I've got USP plastics $1.66 check valves all over my engine. works great.

sorry to jack thread but where did you find that?

**HIERLEVELZ** · 05-26-2008 07:04 PM

Originally Posted by A4TL

the thermoset plastic will be crumbling away. this in turn gets stuck in say your N80 valve which then costs you a new check valve and n80 valve.

I've got USP plastics $1.66 check valves all over my engine. works great.

when i pulled the check valve off before the N80 purge valve you could see the end of the nipple facing the valve had a small chunk missing. of course i could never get it out of the n80 valve :(

Which of the following is the appropriate size?

http://www.usplastic.com/catalog/pro...uct%5Fid=15641

**A4TL** · 05-26-2008 08:03 PM

well there are actually a few different sizes :) and at lease one is a multi-function valve which would require two check valves .

I just bought a handful of them because they come in handy.

n80 is easy to check..

i used a 9.6 to 12V power supply with the bare wire (cut the end off) .

when there is no power you can not blow/suck anything through the. tight seal.

then you apply the power (don't worry about neg/positive you'll get it right). and it shold flow smoothly in both directions.

there's even a screwdriver to adjust it but i strongly suggest you don't do that unless you know what you are doing.

feel free to clean it. i tried everything on the planet but mine was jammed open a little and no matter what it was leaking air with no power; thus evap leak , mushy brakes, poor mpg, hard starts,etc.

there's a big pump in the back of the car that creates alot of vacuum. if you have the desire, replace the N80 with a straw (cut it down) and you'll see misfires galore and a sputtering engine. There's enough vacuum coming from the back of the car to stall the motor if the n80 malfunctioned and flowed 100%.

the n80 goes down the wheel well then back the rear of the car where this vacuum pump is located.

automatic cars have another pump of course in the engine bay. i assumed it was for brake assist or something like that.