Low voltage intermittent, creeps up to full (video)

996t 2002 Just in case anyone else has seen this before and recognises the fault Normally from cold (but not every time it's started) the voltmeter goes to 11V holds it there for a few seconds then goes up to almost 14V. It creeps up. See video. I've had the chance to 'catch' this problem with a voltmeter and the 11V is all over the car i.e. lighter socket etc. So it's not a sticky needle voltmeter in the dash. Battery earth is fine to the body, checked that. Battery connections fine. Once, Whilst driving at night with lights on and wipers it dropped down to 11V and the wipers slowed down but crept up 5 seconds later. This has recently had a new starter, battery and new alternator so it isn't those. The problem was there before and after those were fitted. I have a feeling it's either a poor earth or poor connection somewhere. Just don't know where to start looking. Any pointers, would be appreciated. A useful thing would be to know if it's normal for the voltmeter (just a second after starting) swings up then delays slightly and then carries on swinging up to 14V or if it just shoots straight up to 14V. Mine does that every time it's started but occasionally it takes longer as seen in the video. UPDATE Solved See lower down in this thread.

There are threads concerning the electrical connections implicated & strategies to resolve problems there. I'd be more suspicious that your new alternator is not functioning properly. If it were a connection problem, you would expect the problem to be more consistent. Good luck with solution.

Thanks Mark, The fault was the same before the alternator was changed for a new Bosch one so the alternator is eliminated. Same with the battery. Changing that didn't fix the problem.

Hmmm...you've got a real head-scratcher on your hands. Don't think the delay is normal. There are some brilliant minds and experienced folks here - count on some good info soon.

The more I browse forums looking into this the more I add to my possible 'suspects' list is a slipping drive belt. It seems after heavy rain (constantly rains lately in the UK) and also after washing the car water gets on the belt. Another forum has several people saying their turbo does exactly this with low volts and no squealing sound until the damp on the belt goes and the alternator grips the belt and the volts go up some take 20 seconds to raise the needle.

Not normal on our cars. Voltage should swing to 14v as soon as the engine fires up. I also suspect belt slipping or belt tensioner too weak. You can try to reproduce by squirting a little bit of water on the belt (not to wet the alternator though) when idling. If it's the water making it slip, may be you want to consider a new belt and belt tensioner. Does the belt feel tight? Also, when it happened during a drive, was there water on the roads?

Perhaps the cable harness for the positive cable to the alternator and starter is corroded. Per several good threads on Renntech (several contributions by Ahsai, I believe), this harness is a well known weakness. I have a problem with slightly low voltage and a very slow starter especially when hot. Everything points to this cable. Here is a link to one of the threads: http://www.renntech.org/forums/topic...er#entry240001

Try this to verify there is a problem: 1) When you start the car, attach a good quality multimeter across the battery terminals and see if you actually have a reduced voltage. 2) If you have a genuine reduced voltage as per above, run a temporary wire (about 2.5mm) from the neg terminal of the battery to the engine block and another from the neg terminal of the battery to the chassis - say top of suspension. Make sure the connections are tight and clean. Start engine and check voltage. If you still have a voltage drop, then you will have to dig deeper, but the temp wires should circumnavigate any corroded cables.

Yea, that notorious "y" cable maybe bad too but I would expect it to be consistently bad for sometime or more temperature related and not just bad for 5 to 20 seconds then everything back to normal. Regardless, vdrop tests can't hurt and will eliminate other possibilities too.

Quotes source post: 11064297

Interesting. I had exactly that situation happen last week when I started my '99 in the parking lot after work to head home. It was raining all day, including on the commute in although that was 9 or 10 hours earlier. I noticed the gauges were dim and thought maybe I had hit the **** while at the gas station, then I saw the volt meter hovering around 11v. By the time I had pulled my flashlight out of the center console and popped both bonnets, it climbed up to the normal 13-14v. I checked the battery connections, alt. belt, positive box in the engine compartment... all in perfect shape. I haven't been able to replicate it since then, so the belt would make sense as it has been relatively dry.

I had that happened to me twice and both times I had the belt off and had got coolant on it. Never happned in any other conditions.

I think I am closer to pinning this fault down. Yesterday morning (a dry morning) I started the car and it was fine. Turned it off and started again it was fine, straight up to almost 14V. I opened the rear, lightly sprayed a fine mist of some water around the top of the belt area. Started it again and the fault was immediately there, 11V after about 5 seconds I gave it a couple of blips on the throttle to raise the revs and it went up to 14V. It has to be either the (particularly long) belt stretched a little or glazed AND / OR the tensioner. Ironically whilst the alternator was being changed I remember seeing a pool of water in the cup shape to the right of the engine where Pentasin is put in but thought nothing of it. It's booked in to have the belt changed next week. I'll post the results here in case someone else is searching for the same fault.

Good job tracking the problem. Also note carefully if the belt has abnormal and uneven wear top and bottom, which may indicate pulley misalignment.

Slippage might be due to a stretched belt, but it might also be due to excess drag caused by a problem water pump, AC compressor, or idler pulley. Also check that the belt tensioner is functioning properly, as a little stretch in the belt should be compensated for by the tensioner.

Many thanks to all of those who replied to this thread. I took the car to a local garage last week to have the serpentine drive belt changed hoping this would do something. While the old belt was off they checked the rollers and also the tensioner. New belt was easily put on, not a massive job. Half an hour. Before updating this thread I thought I would leave it a while before confirming whether this had fixed the fault. On the evening after the belt change there was no rain so I poured a couple of buckets of water over the rear lid. Started the engine, Volts fine, straight up to nearly 14V. Over the last few days of heavy heavy rain each time I've started it it has been fine going straight up to 14V no hesitation. The old belt 'looked' ok with a slight 'shininess' to the non-grooved side which runs on a couple of the rollers. I'm pleased to say it is now fixed (just before the belt change it was going 'wrong' almost every day when it rained). I hope someone else finds this thread with a search in the future and it helps them. Obviously an alternator can cause this problem so it won't fix all problems but for �20 it was worth a go.

Congrats. It's lot cheaper than the alternator

Just wanted to report I saw this same exact behavior the other day with my 03 Turbo that was parked outside in the rain for a while parked on a slight upslope. (The car has been in the rain so seldom here in the Livermore/bay area what with its drought the last couple of years.) I didn't hear any squeal/chirp like I hear when I start the engine after washing the car. I didn't rev the engine very high but I did raise RPMs to around 1500 for a moment or two several times. The voltage level didn't rise. The voltage reading read low enough long enough that I was starting to think it was not from the rain water but something else when the voltage started moving up then shot up to just under 14 volts. On a related note I spotted a nice white Turbo (997) at a dealer the other day. I heard the air box had water in it. Enough to slosh around... You have to check that all the air box seals are intact. (On a side note when I first bought my 996 Turbo I noticed the air filter element looked like it had been wet before. I had this replaced and have not seen any signs of the replacement (or its replacement) getting wet. I think the original owner was just a car wash fiend and managed to get water in the air box that would otherwise remain water free under normal circumstances. You should have seen the rotors... rusty! And the holes full of rust/dust.) Anyhow, you have to or should watch these cars in the wet.