I’m looking for technical help or recommendations on: Alternator, battery or grounding problem
Hi All, I’ve been putting off checking my alternator/battery for a while but it finally hit me today - had the car idling for a little and it just completely stalled. The battery did feel weak before as when I turn on lights the car seems to struggle a little for the last month ish.
I turned on lights and hazards etc to check and the rev dropped significantly but it caught up, other times it won’t and will completely stalled. Some other times when its left idling, itll just stall on its own without any additional electrical load. I had a long drive two days ago but didn’t notice this.
Started the car again and it seems to start fine (started a couple of times to try and diagnose problem and each time seems to start ok with the odd times that it takes slightly longer to start).
Checked my ground straps (PPF ground and one thats next to dipstick under bonnet), both seem to be in good condition and not loose or corroded.
All things seem to lead to a bad alternator (car starts fine so maybe battery is ok). I’m waiting for a friend to bring my multimeter back so I can test it. But before I take off my alternator, is there anything else I should/can check to eliminate taking it off unnecessarily?
I’d ask myself what condition is the alternator belt in ? Is it tight ? Similarly what is the condition of the wiring to the alternator and starter, are the connections clean and tight. If not garaged and dry stored any signs of corrosion round the fuse boxes particularly down the back of them, obvs check battery terminals are clean and tight. Hope you find the cause of the problem.
Hiya, thanks for the response! The alternator belt was replaced a month ago and seem to be in good condition - tensioned well and no squealing either. The fuse box is a good shout, will check this now!
I had a small problem where my battery negative terminal was left loose by mistake a couple of weeks ago (though the car wasn’t driven a whole lot back then), but it did leave some corrosion product especially on the positive terminal. Is this likely to cause problem like this? I did do quite a bit of driving since retightening the battery terminal but didn’t seem to have any immediate problem (albeit the slight ‘shaking’ when headlights are on) until now, which has been around 2 weeks.
An iffy battery can cause all sorts of obscure problems to chase your tail around. I’d fork out for a new one unless you have proof it’s newish. Even the cheap brands have a three year guarantee.
I haven’t changed mine yet on the MX, but the first sign of electrical trouble and it will be replaced.
The big sheds do free battery tests with sophisticated gear so try that as a first move?
I’ve just gotten my multimeter back and resting voltage of the battery is 12.56V (I drove the car today so fair enough). But when I turn on the car, voltage shoots to 15.15V at the terminal (crazy!). I wonder if its my voltage regulator that’s doing things? I heard mk2.5 has it in the ecu unlike the mk1. Would anyone have any thoughts on this?
My understanding is the regulator is in the ECU under the seat, might be worth checking connections for corrosion, no idea how to determine if it is faulty.
Yes, alternator output is controlled by the engine ECU (PCM) on the NB, this is in the passenger footwell under the glovebox protected by a metal cover secured with shear bolts Check for water damage at the pins in the first instance.
Thanks All! I have checked under passenger footwell, all seems dry. Changed a battery to a new one, voltage still shoots high. Seems to be a problem with the voltage regulator itself, I’ve purchased an oem used alternator stripped off another mk2.5, and picking up this weekend. Hopefully this is the answer to my problem!
Thanks! I’ve checked under the passenger footwell, all seems dry (didn’t get the time to take the plate and casing off to check). Car was never sat out for long (dry parked mostly) and never had leaks inside so corrosion is unlikely. Strange that I wasn’t getting any battery light, and car just shuts off randomly with no rev drop warning before hand. I’m guess the pcm isn’t gone yet - however will check this tonight.
What I fail to understand is that the car turns off on its own (essentially stalling), when there is no other symptoms (no battery light, no flickering light, nor christmas lights on dash) other than a high voltage. I’m guessing there might be a relay somewhere that does over-voltage protection (?), as the car seems to start up just fine the next time around (did a couple of times to try diagnose the problems and when changing out battery etc. And then will die randomly when idling, almost like turning off the ignition key - which is why I think it might be a protection relay somewhere.
Not at the moment as my friend borrowed my OBDII from me (will get onto this soon but at the moment alternator & battery are both out so can’t do that), but the voltage problem seems to dominate because of the occasional misbehaving electronics in relation to revs both pointing toward my alternator VR at the moment.
Crank sensor was replaced early last year and late last year the engine was refreshed and at the end of that I had no fault codes nor problems as such. Only recent occurrences with my battery volt shooting high and stalling while idling etc.
Hi all, a small update is I have changed out the alternator but the problem persists…
A good news is maybe I have found the problem which is the grounding wire that runs to inlet manifold - the blu/blk & blk and the red/blk & blk crimped in ring terminals. They seem to be super corroded and when I measure their resistance against manifold it shot super high. Will be cleaning it tomorrow. Fingers crossed this is the final answer to my problem
Good luck! It’s a week now, which is nothing when us amateurs try to fix electrical problems on the modern car.
Sorry my suggestion of a new battery didn’t fix things but it’s solid basis if anything else goes wrong.
Fault finding via the OBD port is key to isolating without expensive substitutions. Even if you fix this problem before your reader is returned it might be interesting to recreate the problem and see what codes come up. But, if your like me,you breathe a sign of relief and forget about it😀
Thanks mate, hopefully this would be the end of it
Yea I had my obd2 back end of last wk and had a read but no fault code was found anywhere… which sounds more just like a mild grounding issue that I’ll take a look into tomorrow
After almost a whole month of fiddling around the problem is now solved! It was the combination of a bad alternator (do not get a Lucas alternator - in my case the car came with one but I wasn’t aware of it), and a bad base idle setting which happened after battery disconnection to change out alternator.
All seems to be normal now so hopefully that was all it was!
Hiya, a super late response to this again - turns out I have more than just voltage problem and bad base idle. I had a sudden cut out today again when sitting in traffic. I thought I would just check all the connectors to my air and fuel related parts. Turns out I had a very loose (broken) injector connector on my injector rail, when I wiggled it, it replicated exactly what happens when I sit in traffic (runs rough, feels like misfire).
Now all epoxied back and car runs super smooth and idles well! I have bought an injector rail stripped from another mk2.5, will have it installed over the weekend.
It makes sense why no fault code was stored at all since its only a loose connector
