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Re: 86 4kcsq trunk lock

The 4k lock system runs on vacuum. There are a few possible problems with your

1) the pump has died, this would cause a failure in the entire power locking
system, so I don't think you have that problem (from you post),
2) the trunk lock vacuum valve has blown a seal and will not keep pressure
enough to open the lock
3) the lock rod that connects the vacuum valve to the lock itself has come
4) there is a leak in the hose that is going to the rear lock vacuum valve

So to test all this out try:

for 1) if the other locks open when you switch the drivers door and you hear
the pump run, then the pump is still good,
for 2) have a friend flip the key in the drivers door while you stand at the
rear and listen carefully by the trunk lock (you will look funny... but hey).
If you hear the sound of leaking air then a blown valve may be you problem
for 3) when your friend flips the lock (ala number 2) and you hear the rod
clink or you hear the vacuum valve engage but nothing happens then the rod may
have come loose
for 4) you can pull the rear seat bottom cushion by pulling up hard in the
center of the front part of the seat. They have a friend flip the drivers lock
and listen for any leaks on the miriad of little vacuum tubes you will find
under the seat. If you hear a leak then tape it and see if that fixes the
issue, then replace the hose.

If you find the rod or the vacuum valve are to blame I would try to ask the
local Audi shop or dealer what they can do to get into the trunk so you can
fix the problem. I do not know of a good way and the Bentley doesn't say. Good
luck and send a post if you learn something new.

James Carolan
86 4kcsq with a leaky trunk valve now sealed with epoxy BTD"some of that"