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Old 04-03-2009, 10:13 PM   #1
yeehawbob
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Default How to Diagnose EVAP system leak???

I see that many have posted this question before but with NO replies!!!
Is this such a difficult thing that no one knows about it????
I am sure everyone has gone thru this issue by now, unless you have been replacing your vacume hoses every fre thousand miles.

Anyone with any information??
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Old 04-03-2009, 11:00 PM   #2
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The evap system prevents the fuel fumes from venting into the atmosphere by containing them within the system where they accumulate in the vehicles charcoal canister which is then purged upon vehicle startup. The only way to check the system for leaks is with a "smoke machine" which forces smoke through the lines. Unfortunately this requires removal of mutiple parts as the lines are routed through various panels throughout the car. Of course this "smoke machine" is expensive as it's obviously a specialty tool being that it will not ignite the fuel fumes. Even with this tool, tracking down an evap leak is rather tricky. There could be multiple leaks due to the system's parts being roughly the same age and condition. 9 out of 10 times, an evap leak is caused by either a faulty gas cap or a cracked plastic vent tube on the filler neck. The evap code will also be triggered if you remove the gas cap with the vehicle running. IIWY, I'd start by replacing the gas cap and then clearing the code. If the code comes back(usually after about 100 miles), then I'd look into replacing the filler neck vent tube. You could find the part numbers on realoem.com. Good luck, please follow up and report back to us with your findings.

Also, just a hunch, but not certain, check your secondary air pump. I'm not sure if this would trigger an evap code, but our secondary air pumps are known to separate and allow air to leak when the pump is running. The secondary air pump is part of the vehicle's purge system in that it pumps clean air into the exhaust for the first 30 seconds or so after startup to compensate for the rich condition caused by the purging of the charcoal canister. The secondary air pump is connected to the factory air box via a black rubber hose. It looks like a thick black pancake which is composed of multiple plastic plates held together by 6 aluminum rivets. The rivets tend to break, allowing the plates to separate and air to leak out. If yours is broken, I have a spare, otherwise you could simply drill the rivets out, disassemble and clean the pump and then rebuild it using machine screws and lock nuts instead of rivets. Hope that helps.
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Old 04-09-2009, 07:37 PM   #3
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Wow! I could not have asked for a better answer.
The car is at the shop and yesterday we hooked up the tech II tool but it did not put out any codes for the EVAP system.
I have replaced the gas cap and had it checked for vacume leak but both the new and old gas cap comes out okay.
My indi did perform a smoke test on it in Jan but that came out negative as well.

Here is what I found out yesterday.
The car compu is looking for a signal from an AUTO Tranny ABS module while my car is Manual.
The car was in shop last fall for repairs and the mechanic (crook) may have replaced my module.
Also my brake light switch is faulty according to the Tech II and I plan to replace it very soon.
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Old 05-19-2009, 10:26 PM   #4
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So The final virdict still remains as after all the fixes and resetting the codes, it is still giving out the EVAP leak code with a tech II tool.
I have not checked the secondary air pump, but will do that today.
I did take a visual look at the filler neck vent tube but could not see any thing unusual there but that does not mean it is not bad. The new filler neck is expensive so i was thinking of checking everything else before I shell out $200-300.
Any one has a diagram of teh evap system?
I checked realoem but I cannot seem to get a good view there.

TIA
Bob
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Old 05-28-2009, 10:45 PM   #5
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Okay the secondary Air pump is fine.
The Filler neck vent tube is fine.

The only thing remaining is the Vacume hose that goes under the intake manifold.
I really do not want to take the manifold apart but looks like I will have to.

I welcome suggestions of that project and if someone has a good writeup on how to do it then it will be awesome.
TIA
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