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tdewald52
09-08-2010, 07:39 PM
Before I take the MM back to my local parts store to have the "EVAP" flag ("...probably just your gas cap...") reset for the 3rd time, does anyone have any ideas on why a perfectly good-running MM would do this when the trunk is slammed shut? I've now witnessed it twice while dropping the kids off at school---they get out, I pop the trunk so the oldest can retrieve his football gear, he slams the trunk (not horribly---he wants the car, at some point), and the light comes on. Rubber seal on the cap looks good and it seems to shut tight, mechanically.

Any good info. is always appreciated.

:help:

Troy
04 Merc Marauder (bone stock)
115K miles
TWINSCRW
09-08-2010, 08:11 PM
There is a charcoal canister mounted on the underside of the trunk floor that has a solenoid attached to it... it may be leaking. I had the same problem with a CVPI and it would trip the light every 1000 miles or so. It is not easy to detect where a leak is in the EVAP system but that would be what I would check after replacing the gas cap.
JBeezy
09-08-2010, 08:12 PM
Funny! My car had the same code pop up just the other day. Cleared it and now it's back. It only does it when I take long highway rides. Hmm!!!
RF Overlord
09-08-2010, 08:51 PM
^^^what TWINSCREW said^^^

What code are you getting, and is it the same each time?

There is an actual "gas cap" light in the instrument panel, so if that's not illuminating then it prolly isn't the gas cap. You can try pulling down the evap tray under the trunk and verifying that you don't have a loose or cracked hose, but if visual inspection reveals nothing obvious, then a smoke test is the logical next step.
tdewald52
09-09-2010, 05:21 PM
Thanks for the ideas---I'll pull the exact code tomorrow and advise

Troy:bows:
tdewald52
09-10-2010, 03:52 PM
Alright, the code is P0456. I went ahead, had them reset the 'puter and bought a new fuel cap. We'll see what happens next...
tdewald52
09-14-2010, 05:56 PM
Well, the light came on again this morning, new fuel cap and all....right after he slammed the trunk. Dropping the canister/solenoid module as I type. Is this just a throw away part? Is it possible to service this unit like I did the EATC solenoids?
By-the-way, from the look of the hoses under there, I wouldn't be suprised if it was indeed a hose. Has anyone had to replace these hoses yet?

Thanks
JBeezy
09-20-2010, 08:58 AM
Did you ever get this fixed? I'm about to start looking into this as soon as I get these heads put the on Mustange.
tdewald52
09-20-2010, 06:01 PM
Not yet---it's not affecting the fuel mileage or performance. Guess I need to do some research on this "smoke test"...
tdewald52
09-20-2010, 07:21 PM
Out of curiosity, can someone tell me where the "fuel tank pressure" sensor is located?
TWINSCRW
09-20-2010, 09:33 PM
Well, the light came on again this morning, new fuel cap and all....right after he slammed the trunk. Dropping the canister/solenoid module as I type. Is this just a throw away part? Is it possible to service this unit like I did the EATC solenoids?
By-the-way, from the look of the hoses under there, I wouldn't be suprised if it was indeed a hose. Has anyone had to replace these hoses yet?

Thanks
I got a used canister with the solenoid and hoses off of a grand marquis and swapped it all out it was no big deal to change. In my case the abuse the car sustained as a police vehicle was obvious and fairly easy to diagnose. I do not remember the exact code (might have been p0442)
The code that was mentioned,P0456 Evaporative Emission System Leak Detected (very small leak)
Could be a leaky o-ring or even a dry-rotted hose
TWINSCRW
09-20-2010, 09:45 PM
Also if anyone is interested I have the full list of diagnostic codes.... it is too long to post (I tried LOL). the list is in the 90,000 character range. But I would be happy to email it to anyone or if a moderator would like to post it up in a sticky just let me know and I will send it over.
Zim Hosein
09-23-2010, 07:11 PM
Also if anyone is interested I have the full list of diagnostic codes.... it is too long to post (I tried LOL). the list is in the 90,000 character range. But I would be happy to email it to anyone or if a moderator would like to post it up in a sticky just let me know and I will send it over.

What format do you have the list saved as electronically TWINSCRW?