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      04-04-2022, 12:56 PM   #1
JesterZ
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06 M Coupe no power

Hello Everyone. Went out to the M Coupe to start it this morning. Fired right up but then about 1 second after ignition I heard a pop and lost all power. So sudden the tach is still sitting at 1k rpm. No power at all. Nothing. Drove it twice yesterday, battery is new and fully charged. New alternator a year ago. New belts a year ago. Can anyone advise on location of a main fuse / capacitor that might have blown? I wrench on cars including this one - never experienced something like this. And think the pop is a strong clue for someone who knows more than I do. Thanks
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      04-04-2022, 01:14 PM   #2
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Quote:
Originally Posted by JesterZ View Post
Hello Everyone. Went out to the M Coupe to start it this morning. Fired right up but then about 1 second after ignition I heard a pop and lost all power. So sudden the tach is still sitting at 1k rpm. No power at all. Nothing. Drove it twice yesterday, battery is new and fully charged. New alternator a year ago. New belts a year ago. Can anyone advise on location of a main fuse / capacitor that might have blown? I wrench on cars including this one - never experienced something like this. And think the pop is a strong clue for someone who knows more than I do. Thanks
Check the BST by the battery.

https://www.zpost.com/forums/showthread.php?t=1482602
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      04-04-2022, 04:10 PM   #3
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@Steeler, Thanks!! This is exactly what I was looking for. Will check when I get home tonight and report back, but based on perusal of that thread I think this is likely the culprit.
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      04-04-2022, 08:31 PM   #4
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Agree that it's the BST… you can temporarily push the power cable back into the BST to move it around under its own power… if you are luck that it makes good enough contact.
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      04-06-2022, 08:55 AM   #5
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Followup question for Steeler, ClearanceDiver and the group: I haven’t been able to get to the car yet due to a super busy schedule but agree it’s almost certain it’s BST based on the symptoms. What do folks think about permanent bypass vs repair / replace? I’m handy and considering putting a replacement B+ cable with BST back in the car, but don’t love the idea that it could randomly pop again in future. What have others done?
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      04-06-2022, 10:33 AM   #6
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Quote:
Originally Posted by JesterZ View Post
Followup question for Steeler, ClearanceDiver and the group: I haven’t been able to get to the car yet due to a super busy schedule but agree it’s almost certain it’s BST based on the symptoms. What do folks think about permanent bypass vs repair / replace? I’m handy and considering putting a replacement B+ cable with BST back in the car, but don’t love the idea that it could randomly pop again in future. What have others done?
Clearancediver can likely answer better than I can.
My personal opinion is that BMW put that system in for good reason.
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      04-09-2022, 07:51 PM   #7
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Thanks Steeler, Just one vote to put it back the way it was (with the BST functional) is good enough for me.
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      04-09-2022, 07:56 PM   #8
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Well Everyone, I finally got around to checking the Z4M Coupe battery compartment tonight. I went out, hit the unlock on the fob just to see if power had magically returned before doing anything to the car - nope. I then manually opened the rear hatch, no light. I then removed the battery cover, and tried moving the B+ cable to confirm whether the BST had blown - but there was no in/out movement of the cable. Suddenly the trunk interior light came on. Voila! Power returned. Just lock that. Car started right up, with just a bit of hesitation after initial ignition (does it when it’s cold). Anyone know how on earth I could have lost all power and then it came back? And with symptom of a pop sound that ended up not being the BST? Or is it possible BST blew but I just managed to shove that cable around enough for a connection?
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      04-10-2022, 06:57 AM   #9
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"Or is it possible BST blew but I just managed to shove that cable around enough for a connection?"

This sounds the most likely, something funky is going on so you might want to remove the positive clamp from the battery and examine it more closely. Take it apart, clean all the contact surfaces, try and see if there is any movement in the bst connection.
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      04-10-2022, 08:46 AM   #10
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Quote:
Originally Posted by JesterZ View Post
Well Everyone, I finally got around to checking the Z4M Coupe battery compartment tonight. I went out, hit the unlock on the fob just to see if power had magically returned before doing anything to the car - nope. I then manually opened the rear hatch, no light. I then removed the battery cover, and tried moving the B+ cable to confirm whether the BST had blown - but there was no in/out movement of the cable. Suddenly the trunk interior light came on. Voila! Power returned. Just lock that. Car started right up, with just a bit of hesitation after initial ignition (does it when it’s cold). Anyone know how on earth I could have lost all power and then it came back? And with symptom of a pop sound that ended up not being the BST? Or is it possible BST blew but I just managed to shove that cable around enough for a connection?
Quote:
Originally Posted by grannyknot View Post
"Or is it possible BST blew but I just managed to shove that cable around enough for a connection?"

This sounds the most likely, something funky is going on so you might want to remove the positive clamp from the battery and examine it more closely. Take it apart, clean all the contact surfaces, try and see if there is any movement in the bst connection.
Agree 100% with GK.
Pull the positive cable and see what happened inside the BST.
The bang you heard was an arc flash.
Caused typically by inconsistent connection between contact points.

Might be as simple as cleaning. Kinda like filing the contact points on an old points distributor. ....Oh the joys.
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      04-10-2022, 09:28 AM   #11
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Quote:
Originally Posted by Steeler View Post
Might be as simple as cleaning. Kinda like filing the contact points on an old points distributor. ....Oh the joys.
Using a matchbook cover to set the gap! (Remember matchbooks?)
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      04-10-2022, 10:45 AM   #12
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Originally Posted by wdb View Post
Using a matchbook cover to set the gap! (Remember matchbooks?)
Luckily me dad was a tool and die maker so had all the gear.

The Lucas 25d in my S1 Europa needed gapping pretty much monthly, or after each rain day
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      04-10-2022, 11:42 AM   #13
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Quote:
Originally Posted by Steeler View Post
Luckily me dad was a tool and die maker so had all the gear.

The Lucas 25d in my S1 Europa needed gapping pretty much monthly, or after each rain day
LOL...I know wdb is more than a little familiar and certainly remembers the Lucas 25d...I still use this "modified" one...(the Lucas 3 position switch photo added for "clarity").
Back on BST topic...Should like to add that the neg (-) bat cable should be first disconnected before cleaning the pos (+) clamp/terminal to minimize chance of arcing/welding.
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      04-11-2022, 12:15 PM   #14
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Thanks Everyone for the replies. Burnishing points brings back fond memories of my used ‘77 MGB (first car) and that Legendary Lucas Electrical :-) Will check the battery connections thoroughly and report back.
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      04-11-2022, 05:39 PM   #15
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I'm sorry but the '77 B had electronic ignition -- which, if you can imagine, was worse than points! The factory electronics failed constantly and cost an eye.
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      04-12-2022, 10:54 AM   #16
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There is actually a small charge that "blows" and separates the cable from the battery terminal connection. This is supposed to happen in a bad collision to eliminate the possibility of gas tank contents igniting from electrical "sparks" etc….. there is a separate small wire (SRS system) that joins the BST at the BAT/battery cable that initiates the charge.

That is why wiggling/pushing the battery cable back into the battery terminal can reestablish (sp?) the connection/power.

Get INPA/INSTAD software to read the codes that have been generated.

As part of your "repair" I would disconnect and clean the connectors under drivers /passenger seats with electrical cleaner.. clear codes if you didn't do this with the battery disconnected. SRS wiring passes through both those connectors. Also clean the afore mentioned cable connector that is located some 12-24" back from where it connects to the BST. That connection can get dirty and cause a fault due to increased resistance in the wire. I eventually cut this connector out and replaced it when it faulted once to many times and I couldn't clean/get within the correct resistance value. Both mentioned software programs allow you to test and read the actual resistance of the wire.

Apparently you can get and splice in used BST end of cable…. but they are/have been difficult to obtain according to posts on this issue over the past number of years. Given that the battery is located over the gas tank in the Z…. I'm in agreement with the BMW engineers decision to have the car built with a BST installed.

Have fun….
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      04-16-2022, 02:45 PM   #17
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Regarding ‘77 MGB - I bought it for a song because the distributor had been stolen and the lady who owned it couldn’t prove it to ran without issue. We must have put an earlier model distributor in it because it most certainly had points.

Regarding the M Coupe - Found issue! The pop was an arc. Smaller cable secured via 13mm nut was loose. Should have followed RCA golden rule - what was last changed. I had brought it out of winter storage and put batter back in. Must not have tightened down properly. Anyhow - problem solved!!
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