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Discussion starter · #21 · (Edited)
Thanks N_Rob.

I'm getting some confusing info, maybe my meter isn't fast enough to keep up.

SCENARIO #1: When using ISTA : Terminal 50E reads 11.8 V when pressing start and terminal 50L reads 53 Amps

SCENARIO #2: However, when I read the battery Voltage at the starter solenoid connection voltage seems to drop to zero. Also not reading any current draw off the battery.

Measure at starter : 12+ volts, drops to 0
Measure at the jump location of B+, 12+ volts, drops to 11.85V

Does this mean anything or does ISTA Terminal 50E and 50L tell me all I need to know?


The ISTA test procedures says to read at battery and if SCENARIO #2 occurs, replace the CAS module as shown below.................


HERE IS SCENARIO #2 ISTA Test below

Step 1
Rectangle Font Screenshot Parallel Number


Step 2
Rectangle Font Screenshot Parallel Software


Step 3

Rectangle Font Parallel Number Screenshot



This is I'm measuring for SCENARIO #2

Output device Camera accessory Cameras & optics Audio equipment Gadget
 
Still waiting on removing the plenums and measuring the B+ wires on the starter itself as mentioned before.

Anyhow, mmm back to your waste time method "kidding", repeat the test above, in the second picture choose YES, let see how the result outcomes.
 
Discussion starter · #23 · (Edited)
Still waiting on removing the plenums and measuring the B+ wires on the starter itself as mentioned before.

Anyhow, mmm back to your waste time method "kidding", repeat the test above, in the second picture choose YES, let see how the result outcomes.
Plenums off, measuring here: Voltage drops to 0.6V when start is pushed. This is between this point (blue) and ground.
If I measure from this point (blue arrow) to the battery jump connection (the positive side of where you charge the battery), it measures 0 volts and when I push the start button it measures 11volts. (my battery is a little run down from testing)
Which one should I be measuring?

I'm not finding loose battery cables.

Output device Camera accessory Cameras & optics Audio equipment Gadget



WHEN MEASURING BETWEEN THIS POINT and Ground, voltage only drops to 11.85. BTW - how do you remove that little black bolt cover that is shaped like a nut/bolt. It is 17mm in size, and covers the battery cable connection where the arrow points?


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Discussion starter · #25 ·
How about the braided wire down below in the picture when you push the start button what does it read before and after you push the button?
I forget now, car is not where I live, so I can't run out there and get it real quick. How should I be taking these measurements?

#1 or # 2 (or both) ?


Handwriting Vertebrate Drawing Circle Font
 
You've already found the issue. The solenoid top cable should not drop to zero when starter is enabled. Remove that cable and clean the terminal and tighten that nut again. Do the same on the other end of the wire, which from memory is the black plastic nut where you measured 11.85V. That black plastic nut is really a nut. Use a wrench and get it off.

If memory is wrong then that cable goes to the alternator itself but I don't think that's right...
 
Discussion starter · #27 ·
You've already found the issue. The solenoid top cable should not drop to zero when starter is enabled. Remove that cable and clean the terminal and tighten that nut again. Do the same on the other end of the wire, which from memory is the black plastic nut where you measured 11.85V. That black plastic nut is really a nut. Use a wrench and get it off.

If memory is wrong then that cable goes to the alternator itself but I don't think that's right...
Thank you, everything looks very clean, no corrosion, but I will do that. Even the braided wire is shiny copper. And thanks for the black nut answer! Its on there pretty tight, didn't want to break anything.

What should be the reference for measuring these voltages? Should it be between solenoid top cable and ground?
 
Discussion starter · #29 ·
Measure the top B+ in the picture to chassis, you should read 12V at all time (battery voltage).
Put the meter on the braided wire and to chassis and measure then push the start up button and measure.
Ok, will measure braided wire. I think what is happening, is when I push the start button, I hear a plunger or something move. When it moves, voltage drops to zero. So something must be short circuiting to ground at that point?? What would that be? And why does voltage not drop to zero at other points along that same circuit?

(I have video recording of plunger sound if that helps)
 
Check the braided wire to see how the starter internal circuit function. Seems the starter is internally shorted or stuck, have you tried to whack it?. Or a weak battery, have you tried different battery or jump it with another car?.
If the 12V B+ voltage drop when you initiate starting, try to remove that cable from the starter path and see if the voltage drops. You can isolate the starter by removing the 17mm plastic nut either the forward or the rear ones to check the voltage drop, just cover the B+ cable terminal when you remove and not to touch the chassis or it will spark.
 
Discussion starter · #31 ·
I've tried a few whacks, but haven't moved cable housing out of the way yet to give it a really good whack. So far, the whack has been on the top of the starter. I put a pipe on the starter, then whacked pipe with hammer. Wonder if turning the engine might help as well?

Also, yes, put my 545 battery into the M6 and still no crank - same results.

It looks to me that the 12V B+ on starter travels directly from starter to the jump location (left side shock tower). If I remove one of the 17mm plastic nuts, it will remove power from 12V B+ at starter. Did I overlook something?
 
In the engine bay picture at front of the engine main wiring loom plastic cover the front connectors are removed, Did you just removed them?. Is there any other wirings removed?.
Wonder if turning the engine might help as well?
Not sure if it will help stuck the starter, for the starter to turn with transmission in gear the "plunger" must be extended as you mentioned earlier
OR
Prepare to turn crankshaft with 32mm socket at front, extend the plunger and crank the engine with a ratchet or a long bar to see if it is stuck (to do this safely you need to disconnect the battery B+ cable form the starter path by removing the 17mm nut, isolate the cable going to the starter, or the engine will turn and might start when the starter got unstuck).
It looks to me that the 12V B+ on starter travels directly from starter to the jump location (left side shock tower). If I remove one of the 17mm plastic nuts, it will remove power from 12V B+ at starter. Did I overlook something?
I already explained this in post#.3. The battery/charging cable comes all the way from the battery to the jump point and then spliced to the front 17mm nut and spliced to the starter and to the alternator.
 
I think you can extend the plunger with just applying 12V to the starter connector (I think) without pressing the start button to rotate the crankshaft, still remove the B+ cable from the starter path.
 
Makes no sense to check for a short - voltage at the engine terminal is not tanking. A short would not only tank voltage at the starter but set wires on fire as well. Voltage at the solenoid tanks cause the starter is sucking current but wiring is unable to provide power.
 
Discussion starter · #35 ·
Mystery solved guys! Thanks for all your help!! Turns out a loose bolt at the rear of the battery feed that runs thru the wire housing under the plenum. The bolt that holds the starter branch of B+ was loose inside the housing (platti - yes, it was me that removed some of those connectors, I had started taking the wiring apart last night so I could look thru all of it).

The measurements taken at the starter before finding this were:

Starter B+ = 0V when start button pushed, 12.2 V when not pushed
Starter braided wire below = 0.65 V when start button pushed, 0 V when not pushed.

The cable must have been just loose enough to not allow current to flow

The old girl even fired up for about 5 seconds before her computers realized all the connectors were off. She is wanting to go somewhere. Oh how I missed the sweet sound of her S85 !!

Thanks Guys!!
 
It is not uncommon for that connection to get loose, I am sure this case is the second one , that was the next to check but you were late on measuring the braided wire which will confirm the current isn't flowing and that take the starter from the equation temporary since it is not supplied with B+ enough juice under load demand, just like weak or dead battery, but you confirmed battery is not the issue.
And why does voltage not drop to zero at other points along that same circuit?
The solenoid isolates the high current from attacking the startup circuit.
 
Discussion starter · #37 ·
It is not uncommon for that connection to get loose, I am sure this case is the second one , that was the next to check but you were late on measuring the braided wire which will confirm the current isn't flowing and that take the starter from the equation temporary since it is not supplied with B+ enough juice under load demand, just like weak or dead battery, but you confirmed battery is not the issue.

The solenoid isolates the high current from attacking the startup circuit.
In hindsight, mean measuring the voltage upstream of the starter, it wasn't interrupted by the break in the circuit, which is why it didn't go to zero - that was a big clue. I'm blaming the loose bolt on the guys who replaced the starter (if they did, and I see evidence they did). I've put about 2500 miles on the car since I bought it. It should not have come loose that fast.

Thanks again for the help! No fun having a perfectly good working machine stop working and not knowing how much work you may have ahead. My garage is built for planned downtime, not unplanned downtime!
 
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