INTERMITTENT POWER LOSS

[Alli26]

Hi fanatics

Hoping to pick someone's brain here that has perhaps experienced the same issue with the N47.

I have on occasion, over the past week, experienced intermittent power loss in my old 2009 pre LCI 120d N47.
Whilst highway cruising at half throttle (where the N47 usually has plenty of guts) the rpm would start to die, almost like I was completely off throttle. This would continue for a second or 2, until the car either eventually downshifts or wakes the heck up, "late spools" then pulls like a train again. It's weird, I've never experienced this before.

231 000km
Oil service done every 10k
Downpipe only, no other mods

I do have what sounds like a chirpy tensioner pulley which I will be getting replaced after the long weekend, already purchased a new tensioner, idler pulley and belt from Goldwagen.

Any advice would be welcome,

 

[Solo Man]

I had a 2005/6 120d with the m47 motor that would for a part of a second cut out and then carry on again. The rev counter would go to zero although the engine still ran. Long story short, turns out it was the alternator. Replaced with an aftermarket alternator and problem was over. Test the output of the alternator for at least a minute and see if it does not cut from around 14.4 down to 12 or even 11 volts just for a second or two. If it does that then the alternator is your problem. Seems to be fairly common problem on 120d's. Btw., car was an import from the UK. Alternator in question was a Valeo

 

[Alli26]

Thanks Solo

I had a 2005/6 120d with the m47 motor that would for a part of a second cut out and then carry on again. The rev counter would go to zero although the engine still ran. Long story short, turns out it was the alternator. Replaced with an aftermarket alternator and problem was over. Test the output of the alternator for at least a minute and see if it does not cut from around 14.4 down to 12 or even 11 volts just for a second or two. If it does that then the alternator is your problem. Seems to be fairly common problem on 120d's. Btw., car was an import from the UK. Alternator in question was a Valeo

I'd never considered the alternator. My rpm never drops to zero, but it's definitely worth investigating. I'll ask the mech to give it a test when installing the pulley.

Thanks again!