Couple E34/M50 Problems - Need some hep

[bbg]

Hi Gang:

I'm having a few problems with my '95 525iA (~87k mi), and I need a bit of help nailing down the diagnoses.

#1

I'm hearing an occasional "thumping" sound from the engine bay every 5-10 seconds or so. With the a/c off the sound is the same intensity and frequency regardless of engine speed, gear (P,N, or D), or road speed. Once the a/c is activated, then the growling/chattering begins.

The dealer has tentatively diagnosed this as (a) worn-out belt tensioner bearing(s).

* Does this sound right? I've not dug out my Bentley manual yet, but is there just one tensioner pulley to replace? I want to make sure that I don't over order parts. The serpentine belt is original and needs replacement too, so while I've got the front end torn apart I plan to attack this as well.

* I've wondered if this could be the compressor clutch going south ($$$). Is there anyway to separate the diagnosis of a failing comp clutch from a failing tensioner bearing?

#2

Ignition/starting problem

(i) For the past 4-5 months, I have occasionally had trouble removing the key from the ignition. It seems like the ignition has a deathgrip on key. Once I finally get the key out, the "car" still thinks the key is in the ignition. For example, I still get the chime & dashboard warning upon opening the door; and the steering wheel will not lock. When I try to re-insert the key it is very difficult to both insert and turn, but once in it works OK. I have finally learned to NOT immediately remove the key when the increased resistance is detected. Instead I push it back in, turn it to the ON position, then back to OFF and it pulls out normally. [Whew, that's a long paragraph].

(ii) Now for the last 2-3 weeks, when I turn the key _quickly_ through ON to the START position there is a brief (<<1 sec) cat strangling / grinding noise and then it sounds like the starter spins down (if that's even possible). The engine, of course, does not start. If I turn the key back to OFF, and then to start, the engine starts normally. This happens 90+% of the time. However, if while turning the key I pause in the ON position for about 3-5 seconds before attempting a start, this problem only happens about 10-20% of the time.

* My first thoughts are that this almost seems like stopping in the ON position allows a [weakening] capacitor in the starter circuitry to fully charge -- whereas quickly moving from OFF to START doesn't always allow this to happen.
* Does this sound like I need a new starter, or is there some other component suspected?
* I wonder if (i) & (ii) are somehow related? If not, is (i) just a sticky/dirty switch?
* I feel like I may be running on borrowed time with this problem. I hope that I can diagnose & repair before the dealer has to...

Thanks for all your help!

[Reidal]

I'm no expert but for #1 if the noise upon starting the a/c is always there and it goes up and down with engine rev’s and stops/reverts to the other noise when the a/c cycles off (wind up the temp setting to fake the a/c into it's off cycle) then clutch or actual compressor would be my pick. It maybe a combo of both with the clutch making the compressor tick over but with lots of slippage so the noise frequency doesn't change much.

For #2, as far as I know, and based on experience with other locks, it sound like the Ign switch lock barrel and /or key may be worn causing the mechanism to not fully complete it's mechanical switching.

Alternatively, there may be a spring in the barrel which manages the position of the lock pins which is/has failed.

Either way, you may find your self stuck one day so it may be a good idea to have a locksmith have a look at it soon because while you should be able to get one out on call out when it finally locks up completely, it will cost you less to take it to them now.

[Bellicose Right Winger]

There are two tensioner bearings, one for the AC belt, and one for the alternator, PS, & waterpump. You can test the bearing on the AC clutch by removing the belt, give the pulley a spin and check for roughness and play in bearing. My tensioners w/120k make noise also.

I know this violates conventional wisdom but I've only had good success using WD40 in balky ignition locks. WD40 is a poor lubricant but its a great solvent and does an outstanding job of removing old lubricants and anything else the previous owner may have put in the lock. If you go this route, use it sparingly, and you've been warned.

I've had similar intermittent noises in my '93 525iM w/Marelli starter. This slowly deteriorated into an intermittent no start. I discovered a loose 12/13 mm nut on the solenoid, the nut closest to the starter. This connection carries all the current the starter draws so it need to be clean and tight. There was evidence of arcing on the washer under the nut. Unfortunately I didn't find it until I removed intake, in order to remove the starter and began to disassemble starter. You can reach this connection without removing starter, but disconnect your battery first. The other 12/13mm nut is connected to battery and is hot all the time.

Paul Shovestul