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Old 02-07-2006, 04:33 AM
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Join Date: Nov 2005
Posts: 7
Any ideas to open locked fuel filler flap?

I have a 86 300e with a lot of issues lately.

Am in the process of trouble shooting some major electrical issues - hoping that a new OVP will do the trick for most of it.

However my central locking system quit working! I need to fuel up! I cannot get into the trunk by way of a key in order to get at the actuator.

Anybody have any ideas? I'm kind of new at this!


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Old 02-07-2006, 06:11 AM
tvpierce's Avatar
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Join Date: Feb 2002
Location: Portland, ME
Posts: 612
Why can't you get into the trunk?

Regardless, look under the DIY section (blue tab at the top of the page). There is a section on installing keyless entry. It will give you a good look at the vacuum actuated auto lock system on these cars. This is a good place to start.

Good luck.

Jeff Pierce
Jeff Pierce

Current Vehicles:
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Old 02-07-2006, 10:59 AM
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Join Date: Nov 2005
Posts: 7
the key I have has never worked on the trunk lock itself. It fits, but won't unlock the trunk. The only way in is through the central locking system.

I originally got this car as a daily driver.

The week I decided that I'd start updating this car and invest in it's future it started making a lot of demands! In two months I've had more go wrong with this car than in the 2.5 years that I've owned it.

Thanks for the idea, I'll take a look at that - not sure what to do with it but will figure it out. I researched the DIY section for 3 hours last night/ this morning and didn't find anything specific.

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Old 02-07-2006, 11:35 AM
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Join Date: Dec 1999
Location: Utrecht, the Netherlands
Posts: 405
If you can access one of the vacuum lines it may be possible to apply vacuum to the line and open the trunk/fuel filler flap. With my 1975 280 is was able to open the doors that way from the trunk when I left the key in the car and my cat locked the doors.
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Old 02-07-2006, 12:10 PM
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Location: San Francisco, CA
Posts: 3,097

It is most likely that the trunk lock is original, so go to your local dealer and order a master key using the car's VIN number.

Does the rest of the door lock/unlock system work?

Is the vacuum pump under the rear seat (right side) working when you lock/unlock with a key in the door?

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Old 02-07-2006, 03:33 PM
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Join Date: Jun 1999
Location: Albuquerque, NM USA
Posts: 1,946
If you take your VIN and your personal ID to a Mercedes dealer, the dealer will know the proper key to fit your trunk.

This assumes, of course it hasn't been changed since the car was produced.

Since your ignition key won't work trunk, something's changed, but it's more likely the ignition switch was changed.
Kent Christensen
'07 GL320CDI, '06 SLK350
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Old 02-07-2006, 04:12 PM
Posts: n/a
I would expect that by pulling out the rear seat acessing the vac pump, you could find a way to apply vacuum with an alternative vac source and open everything up.

Good luck,
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Old 02-08-2006, 02:04 AM
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Join Date: Nov 2005
Posts: 7


Thanks for the suggestions - was pretty late last night when I posted. Was working on another problem when I realized the problems with the central lock. Didn't think about finding another vac source.

I pulled out the seat and found that the foam housing for the pump was soaked. from a rain leak - assuming from the trunk. The electrical connections didn't look too wet. when I unplugged and plugged in power I could hear some clicking. The vac hose came off easily. once I disconnected the hose and reconnected. the lock actuators were manipulated by hand much easier. When I manually manipulated the locks and/or did so with a key, I heard no reaction with the pump. Don't have the tools to check leaks in the vac system.

By that time it was after 2am - So I gave up on it for another day. Thinking a little more clearly now - applying some vacuum should do the trick. Will have to try that. The key I have is the original - just think the lock needs replacing.

Thanks for the help!
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Old 02-08-2006, 02:22 AM
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Join Date: Aug 2005
Location: Palmdale/Ventura, CA
Posts: 813
I used a small tire pump and applied pressure to the the main yellow line
coming from under the rear seat leading into the interior. This unlocked
all my locks. Conveniently, there was a rubber fitting right there allowing
the main line to be separated.
And... like the others said, go to the dealer and order a VIN based key.
Probably solve your trunk problem.
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Old 02-08-2006, 09:31 AM
Posts: n/a
If the pump is not coming on it is not a vacuum problem, it is a bad pump or an electrical problem.

Good luck,

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