[hi rpm]

E92 335xi has intermittent slow crank, twice in a week it's stopped briefly before cranking more.

Checking voltages I have (typical values)

Multimeter:
12.05 after sitting overnight, at engine bay terminals.
13.25-13.6 engine running, at terminals.
14.5 engine running, between alternator positive cable connection and alternator body.
12.4 right after shutting car off at engine bay terminals.

Cheap lighter socket voltmeter:
12.05 off after sitting.
12.4 off after running.
12.8-13.35 engine running; driving, various acc's on/off.
Dips lower when cranking, saw 9.xx once.

Sometimes it fires right up reading 12.05 volts.

Battery about 3 years old, the largest diehard gold.

2 years ago, replaced driver side ground strap with a battery cable and spliced a new end section of the positive starter-alternator cable that crosses over the engine. (Both corroded.) Started great for 2 years after.
I noticed that postive cable gets too hot to hold before the engine is warm, so my guess is there's an issue with it.

Ideas/advice welcome.

P.S. Is there a good way to connect a jumper from the alternator positive to the positive terminal, in parallel with the battery-starter-alternator cable?

[fastboatster]

might be your starter going out. had something very similar, had to use my jump pack a couple of times and then finally, after a short while, it wouldn't crank at all. how many miles does your car have? yes, also check the resistance of that positive cable.

[hi rpm]

Originally Posted by fastboatster

might be your starter going out. had something very similar, had to use my jump pack a couple of times and then finally, after a short while, it wouldn't crank at all. how many miles does your car have? yes, also check the resistance of that positive cable.

82k mi. Can the resistance of that cable be measured on car? Assume it's supposed to be the least resistance path between alternator and pos terminal...Should it be close to 0 ohms?

[fastboatster]

Originally Posted by hi rpm

82k mi. Can the resistance of that cable be measured on car? Assume it's supposed to be the least resistance path between alternator and pos terminal...Should it be close to 0 ohms?

probably slightly larger but probably on the order of a few ohms, but I don't know that. probably would be good to measure that resistance with battery disconnected. My starter quit at 133kmiles (2009 328i), your mileage may vary, though. I am just spitballing here, some people with ISTA installed might post in this thread later with more systematic way to troubleshoot your problem, I tend to shoot the parts cannon too much

[wrevilo]

HPFP can cause starting issues also. I had cold start long cranks, which was one of the ways that helped diagnose that I needed to replace mine.

[hi rpm]

Originally Posted by wrevilo

HPFP can cause starting issues also. I had cold start long cranks, which was one of the ways that helped diagnose that I needed to replace mine.

I've been wrong before but I can't imagine that would actually cause the starter to stop cranking, which has happened twice here.

[gbalthrop]

Originally Posted by hi rpm

E92 335xi has intermittent slow crank, twice in a week it's stopped briefly before cranking more.
Checking voltages ...typical values)
12.05 after sitting overnight, at engine bay terminals.
13.25-13.6 engine running, at terminals.
14.5 engine running, between alternator positive cable connection and alternator body.
12.4 right after shutting car off at engine bay terminals.
Cheap lighter socket voltmeter:
12.05 off after sitting.
12.4 off after running.
12.8-13.35 engine running; driving, various acc's on/off.
Dips lower when cranking, saw 9.xx once.
[Those Voltage values, & reported intermittent slow crank, suggest an issue in the Alternator B+ wire (LARGE Red wire between Alternator & Jumpstart Terminal). ALL voltages are LOW except 14.5V at Alternator. Your battery is NOT being properly charged when engine running. Voltage drop of 2.0V to 2.5V is NORMAL during starter cranking.]
... 2 years ago, replaced driver side ground strap with a battery cable and spliced a new end section of the positive starter-alternator cable that crosses over the engine. (Both corroded.) Started great for 2 years after.
I noticed that postive cable gets too hot to hold before the engine is warm, so my guess is there's an issue with it.
P.S. Is there a good way to connect a jumper from the alternator positive to the positive terminal, in parallel with the battery-starter-alternator cable? [YES, VERY Carefully ]

It appears that you have correctly Identified the wiring fault, namely the Large B+ Cable that runs between the Alternator & Jumpstart Terminal. Here is RealOEM.com diagram:
https://www.realoem.com/bmw/enUS/sho...diagId=12_1339

Cable Heat, as well as voltage readings, suggest that. I presume the REASON you spliced/crimped NEW End Section onto that cable before was similar crank/charge issue? There have been other reported cases of that cable coming completely loose from End Crimp Connector, or breaking at that connector.

While that B+ Cable is the most likely suspect, ANY loose or corroded wiring or connectors can cause your symptoms, from:
1) Battery to Jumpstart Terminal, including Transfer Point at front of battery;
2) B+ Cable from Jumpstart Terminal to Starter;
3) Alternator Branch of that B+ Cable;
4) Primary Engine Ground Strap at Starter;
5) Loose Battery Terminal;

Your Voltage Readings, taken together with Intermittent slow/suspended Starter Crank, suggest an issue in B+ Cable at a point that affects BOTH Alternator Output Voltage to Jumpstart Terminal, AND Battery Voltage Supply to Starter Motor. But AT LEAST there SHOULD be higher Voltage readings (> 14.0V) measured at JS Terminal & Lighter Socket with engine running.
George

[hi rpm]

Originally Posted by gbalthrop

...Your Voltage Readings, taken together with Intermittent slow/suspended Starter Crank, suggest an issue in B+ Cable at a point that affects BOTH Alternator Output Voltage to Jumpstart Terminal, AND Battery Voltage Supply to Starter Motor. But AT LEAST there SHOULD be higher Voltage readings (> 14.0V) measured at JS Terminal & Lighter Socket with engine running.
George

Thanks. I felt the cable again this morning about a minute after starting and it was pretty warm--warmer in the original aluminum wired section than the splice. Valve cover cold. (And yes, the reason for the splice was the crimp end falling apart and causing poor cranking.)

I better replace it.

[marvinstockman]

Check you multimeter on another vehicle.

[hi rpm]

It was the cable. Got worse before I got the part so I cut a section out and respliced it, lighter voltage went from max 13.5 to max 14.7. The wire end or crimp must have gone bad in an invisible way.

Barely related but I had to jump the car and blew the footwell module, so fml and be careful.

[gbalthrop]

Originally Posted by hi rpm

It was the cable... I had to jump the car and blew the footwell module, so fml and be careful.

Glad to know you correctly identified the Cause. Sorry to hear about the FRM. Sure it wasn't one or more of the 4 FRM Fuses: F41,F81,F84,F86 on 2008 & later?

"fml" reminds me of the NYC Trial: "DJT, This is Your Life"
For those (MOST) of you who are too young to remember that TV Series:
https://www.google.com/search?q=this...hrome&ie=UTF-8
George

[hi rpm]

Originally Posted by gbalthrop

Glad to know you correctly identified the Cause. Sorry to hear about the FRM. Sure it wasn't one or more of the 4 FRM Fuses: F41,F81,F84,F86 on 2008 & later?

Nope, guess I better check them. I should be so lucky that it's multiple fuses instead of a $$$ repair. But the headlights are messed up, no dash lights, no turn signal, no windows, no seatbelt handoff.