[Morgzy]

The serpentine belt on my M135i Auto 2014 broke apart the other day whilst out on a drive. The belt must not have been turning the alternator before breaking because when I attempted to restart the car the interior lights flickered and I could hear a clicking noise from engine that I suspect was the starter relay. A friend came and jumped the car and it started for about 10 seconds but as soon as I put it in drive and applied some throttle the car died again. At this point I looked under the bonnet and realised the belt had completely shredded apart so called a recovery truck and got towed back home. When I got home I took the battery out and I put it on charge over night, checked voltage with multimeter the next day and it’s showing 12.5V so seems that seems okay. Put the battery back in and replaced the serpentine belt but now I’m having a crank no start issue. Car sounds like she wants to go and will sometimes fire for a second then die again. I attempted to start while spraying some easy start into the air intake but didn’t make any difference which makes me think it might be a spark issue. Checked all the fuses out everything good that side. Checked the fuel pump under the rear seats and it’s receiving power and fuel is being pumped so not that.

I’ve been looking around online for information from people who’ve faced similar issues and from what I’ve found so far seems like could be a issue with either the HPFP, spark plugs / coil packs, injectors or DME. Had a friend plug in a diagnostic tool and car didn’t show any codes however this might be because it was a fairly budget scan tool. I plan to test for pressure on the high pressure fuel rail before even attempting to checkout the HPFP. Also want to remove injectors and coil packs to test these. Basically I want to try and diagnose the problem myself or if failing that at least be able to diagnose what it isn’t.

Sorry for the long post just wanted to give as much information I have to hand as possible. Any help would be much appreciated �� also if anyone can recommend a BMW garage in the North West London area that specialises in diagnostic / repair of these types of issues or even anywhere in London that won’t charge me a arm and a leg would be appreciated.

Thank you

I’ve uploaded a video of the issue I’m having to better show the issue I’m experiencing.

*Update *

I placed the battery on charge overnight till fully charged and checked voltage under no load and not connected to the car. Battery’s showing 13.37V while disconnected. Once hooked up to the car terminals checked voltage again with auxiliary power turned on and battery shows 12.78V. Then monitored voltage while cranking, battery shows a lowest reading of 10.78V and averages around 11.1-11.2V mid crank. During cranking the engine almost fired for a cycle or two during which the multi meter spiked to 11.45V which makes me think the alternator is giving off power. I have OBD cable on the way in the post so hopefully once it arrives and I get hooked up to ISTA / INPA that will reveal some more info.

*Update 23/05/2023*
Unfortunately after a closer inspection I found a small piece of the serpentine belt that broke wrapped around the rear of the crank shaft pulley. After searching online about it seems to be a common issue with the 3.0-litre N5X model engines. I've yet to find out how much damage has been done but from what I have read online if the belt has made its way through the crankshaft seal and into the timing cover it can cause all sorts of issues. If parts of the belt have become wrapped around the timing chain then chances are it's thrown the timing off which would explain the no-start issue I've been experiencing. Also any smaller sections of the serpentine belt could have made their way into the oil pan and from there into the oil pickup tube causing oil not to reach the engine.

Could anyone advise me where to start in terms of checking the engine to see if this is the issue? I'm assuming removing the crankshaft pulley and inspecting the seal however, it may be easier to remove the valve cover and inspect from there, or even drain the oil and check it for any signs of a frayed belt.

[IJO]

If the battery is the original from 2014, I'd replace it.

Off load voltage does not tell you much, and nothing at ll about the remaining capacity.

Until you have a new battery and reliable charging, I'd not change anything else or do you believe in coincidences? Charging problem and now all sorts of other problems - not coincidence in my opinion, but related.

[Morgzy]

If that’s the case I’ll get the multimeter on the battery while cranking, what voltage should I be looking for while the battery is under load of starting ?

I’m pretty sure it’s not the original battery that came from the manufacturers however the car had been sat for at least a month before the day that this issue occurred. I’ve also seen online that jump starting the car could have caused some issues with the fuses that are sealed inside of the integrated supply module. I tested the coil packs today and they’re all good so it’s not a spark issue. From what I can tell I’m down to 3 different possible issues those being either fuel pressure, compression or battery/fuse issue.

[IJO]

Anything below 10.5v - 11v will cause ecus to misbehave.

Jump starting can cause problems if not done correctly. Contrary to what is said, the donor engine must not be running otherwise the sudden voltage drop when you crank the host can cause the donor alternator to overreact.

You view the donor battery as if it's a standalone jump start battery booster and also do not disconnect for a minute or so to allow the voltage to stabilise as much as possible.