MTW Posted January 31, 2023 Share Posted January 31, 2023 Took the car out for a shakedown earlier, once the car was warned up I noticed a weird low rattle almost like a sawing sound only on idle, then about ten mins later in noticed the battery light was coming on and off very intermittently and voltage was at 11.9 and not increasing with revs etc,battery light would still be flashing on and off very intermittently, then when I got home and let it idle on the drive the volts started to climb again, and the sawing noise wasn’t there. seems like alternator is on the way out, but could it be something else causing the alternator to Intermittently charge? Slipping belt or tensioner? Loose wire? And tips on how to diagnose or things to check would be much appreciated! Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2023 Member Share Posted February 1, 2023 Most likely explanations would be a slipping belt or a fault within the alternator such as the shaft bearings.How old is the car, when was it last working properly, and has there been any recent work on it?I'd start by inspecting the belt and checking the tension, and feeling if the alternator shaft has any lateral play or excess friction.While you're down there have a look for a loose wire or a bad connection, but I wouldn't expect those to cause the sound effects....I have the wiring diagrams but nothing on the belt or how it is tensioned... anyone?Jonathan Link to comment Share on other sites More sharing options...
Area Representative DerekH Posted February 1, 2023 Area Representative Share Posted February 1, 2023 Hi Max,Check the light connection to the alternator, mine was very corroded.It sits right on the top of the engine next to the cam cover on a Sigma, directly under the louvres, so it can easily get wet. Battery voltage should go up to 13.8 volts if the alternator is working. Just pick the RPM up a little and see if it improves. From your description it sounds broken like mine.Put the Ford part number into Google, I picked up a new one for £75 delivered next day.Derek Link to comment Share on other sites More sharing options...
MTW Posted February 1, 2023 Author Share Posted February 1, 2023 Thanks for the tips chaps, I will check all those.the strange thing about the noise is (before I noticed the battery light and had suspicions over the alternator) it seemed to not be present when the bonnet was off, also when I held the springs at the exhaust collector it seemed to dampen it, so it might be unrelated? Fingers crossed anyway.also, one thing I did think, I did let the car idle for about 15-20 mins before I set off out, and had the lights on and the heated seat? Would that be enough to make a overwhelm the alternator and make it do it can't make up the charge when setting off? I would imagine not, but just a thought I had.I will try all the bits suggested, I'm hoping it's a loose connection as I have a Trackday Saturday, and only have Friday off to work on the car! Do doubt I would be able to sort a new alternator before then Link to comment Share on other sites More sharing options...
MTW Posted February 1, 2023 Author Share Posted February 1, 2023 Jonathan, the car is 2020 so not very old, work I have done recently is just general servicing, all the fluids and changed the rad.I did take out the heated seat. And it had two wires and plugs that are indentical on each seat, so there's a chance I didn't plug them back in to the right plugs, but the heated seat works fine so I assumed I had got it right! Link to comment Share on other sites More sharing options...
Andy135 Posted February 1, 2023 Share Posted February 1, 2023 I had a similar experience on my S1 Elise. The battery warning light flickered intermittently - it was one of the battery post clamps coming loose. A quick nip up with a spanner resolved it. Might be worth you checking your clamps as they can/do work loose over time. Could be a quick and cost-free solution. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2023 Member Share Posted February 1, 2023 "... the strange thing about the noise is (before I noticed the battery light and had suspicions over the alternator) it seemed to not be present when the bonnet was off, also when I held the springs at the exhaust collector it seemed to dampen it, so it might be unrelated?"It's notoriously difficult to localise sounds in Sevens. If it isn't clear where these are coming from I recommend the use of a stethoscope, either purpose-built or DIY.Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2023 Member Share Posted February 1, 2023 "also, one thing I did think, I did let the car idle for about 15-20 mins before I set off out, and had the lights on and the heated seat? Would that be enough to make a overwhelm the alternator and make it do it can't make up the charge when setting off? I would imagine not, but just a thought I had."I wouldn't expect so. What's the nominal current (or power) of the seats? And are the headlights incandescant or LED?"I did take out the heated seat. And it had two wires and plugs that are indentical on each seat, so there's a chance I didn't plug them back in to the right plugs, but the heated seat works fine so I assumed I had got it right!"Hmmm... is that one connector per seat for power and one for control?I don't think this is going to be the cause, but now it's in your mind you'll have to check! : - )Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted February 1, 2023 Share Posted February 1, 2023 Difficult to diagnose without seeing (or hearing) the car, but I'd start by checking whether the tensioner and alt pulley spin smoothly and silently. The serpentine belt is tightened automatically by the spring-loaded tensioner: To remove the belt, turn the hex centre of the tensioner anticlockwise with a 17mm ring spanner. Now spin the tensioner and the alt pulley by hand, checking for noise or roughness.JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2023 Member Share Posted February 1, 2023 Thanks, John.Is it possible to slacken the belt without removing it in order to test how the alternator spins?Jonathan Link to comment Share on other sites More sharing options...
MTW Posted February 1, 2023 Author Share Posted February 1, 2023 Thanks chaps, no sign of battery clamp issues, or any electrical connections as far as I can tell from above.I will have a look at the tensioner and alt pulley next, awfully tight around the alternator! I haven't got the car in the air yet, is it possible to change the alternator from bellow? Or is it coolant pipe and inlet off etc? Link to comment Share on other sites More sharing options...
ScottR400D Posted February 1, 2023 Share Posted February 1, 2023 #10 JK, it's pretty easy to do that. Changing the belt is simple and only takes a few minutes. As said, 17mm ring spanner on tensioner nut, try to turn AC and you pull against spring and slacken the belt. Very clear when you start to do it. Could there have been water on the belt? Was the 'sawing' something touching the underside of the hood? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2023 Member Share Posted February 1, 2023 ThanksJonathan Link to comment Share on other sites More sharing options...
MTW Posted February 1, 2023 Author Share Posted February 1, 2023 Thanks Scott, I will give that a try after work and have a look, I will check the underside of the bonnet for any marks also! Link to comment Share on other sites More sharing options...
John Vine Posted February 1, 2023 Share Posted February 1, 2023 #10: Is it possible to slacken the belt without removing it in order to test how the alternator spins?It may be possible, but there's really no need. The alt mounting is non-adjustable (unlike the K), and it's a doddle simply to remove the entire belt. Just release the tension and slip the belt off the alt, water-pump and crank pulleys. Easy peasy.(Which raises another thing for the OP to do: test the water-pump pulley as well for smooth operation.)And, in case a replacement is needed, the correct serpentine belt is the Gates 6PK1320:JV Link to comment Share on other sites More sharing options...
John Vine Posted February 1, 2023 Share Posted February 1, 2023 #11: ... is it possible to change the alternator from bellow?Well, it is on my wet-sump R400D S3 (see Step D26 in this Guide). But yours is dry-sump, I believe? Whether that makes a difference, I don't know. No doubt someone who knows will be along soon.JV Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 1, 2023 Member Share Posted February 1, 2023 Thanks, John.Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted February 4, 2023 Share Posted February 4, 2023 Just to complete the circle, the OP replaced the alternator.(This is the problem with multiple threads on the same topic!)JV Link to comment Share on other sites More sharing options...
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