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  #1  
Old 04-08-2007, 12:00 AM
G W G W is offline
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code o455

On my 97 E420 w/87k I am getting an error code of 0455 at various times and the low fuel light starts to flash when stopped for longer red light at idle. I understand from what I have read that this is most likely a leak in my closed fuel system. I have purchased and replaced the fuel cap but did not solve the problem. Are there other components that could be bad? If not, my plan is to make a gas cap, us a regulator and air supply to put 3 to 5 lbs of preasure in the system and soap the lines to check for leaks. Any other suggestions would be appreciated.

GW

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Old 04-08-2007, 12:49 AM
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P0455 :Major leak in purge system, hose in system not connected or, cap open/leaking.

Need to do a visual check of EVAP components.
Did you have the code cleared with a scan tool?

Do NOT apply 4 to 5 psi to the system, you will rupture a line fitting or worse distort the fuel tank....system uses about 1/2psi ( Half.) negative to self check.
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Last edited by dkveuro; 04-08-2007 at 01:13 PM.
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  #3  
Old 04-08-2007, 08:53 AM
G W G W is offline
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O455

Thanks for the response. ---- Yes, I have a code reader and am clearing the code a couple of times a week. ---- I have done the visual but have found nothing. ---- If the system works on negatve preasure there must be a sensor that monitors that. How often would it take a reading and where would this sensor be located? The low fuel light always comes on when warmed up and idling for more than a minute. The check engine can code occassionally at the same time or whenever.

Back to my orignal plan then, I should be able to preasure up to a pound or pound and a half without doing any damage?

GW
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  #4  
Old 04-08-2007, 11:17 AM
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The P0455 code is for a major leak. Does it interest you that you never have a minor leak?

In testing a fault code one must understand what is being faulted. The system does an evap test usually once a drive cycle (when conditions are right... tank between 1/4 - 3/4, below some altitude, rough road condition gone, etc.). To test the system the ME controller closes the vent valve, preventing the system from breathing through the charcoal cannister, thus sealing the system. It then pulses the purge valve allowing vacuum to pass into the tank where the tank pressure sensor (part of one of the tank senders) reads the value. The purge valve is pulsed till a pressure of about 25mb is arrived at or a time limit is reached. At the moment the pressure is reached the purge valve is closed and the system monitors how much vacuum is lost in 60 secs. It can't loose more than 5mb in 60 seconds.

So, if the pressure isn't reached by the time limit, the large leak code is registered. If the first step is completed and the leak down is greater than 5mb/min then a small leak code is registered.

As it turns out, a large leak is almost never a leak. The most common problem (after missing gas caps) is a purge valve that doesn't operate. This is because the first criteria of reaching a certain vacuum level can't occur if the purge valve doesn't pass the vacuum on. Other possibilities are a vent valve that is totally inoperative or a tank pressure sensor that doesn't register a change (a BS reading will give a circuit code).
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  #5  
Old 04-08-2007, 11:25 AM
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PS:

The pressure involved is really small. Twenty-five millibar is about 10inches of water. If you go here: http://www.onlineconversion.com/pressure.htm you can see that


25 millibar = 0.362594345 pound/square inch

Smoke machines designed to test evap systems with smoke are set to 1psi.

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