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Mk2 Nb Slow Cranking, Battery And Alternator Issues


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#1 -Rich-

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Posted 01 September 2020 - 07:28 PM

The car is only used in the summer so doesn't do much mileage. For the last year or so it felt like it was taking too long to start up. It now takes at least 4 seconds to start but always does first time. I really need to get it sorted as it'll just get worse.

The alternator pulley is always stuck after winter so I free it off first and it seems fine afterwards. It's still the original and the car is on 98k miles so I think it could do with being replaced. But I've read it's a pain to do and also not all pattern parts are compatible. Is this true and what's the best one to get? Genuine is far too expensive for me! Or should I wait until it does need replacing? The belts do need replacing too though.

The battery seems to only hold a charge at 12.33v with the engine off. After a long 70 mile drive that's the reading I got. Even after charging it with my Ctek charger I watched the meter drop from 12.45v down to 12.33v. The battery is at least 7 years old so probably needs replacing. I've yet to test it with the engine running to see if the alternator is charging it properly.

There's also the starter motor to consider but how can I test this? Is there anything else that can cause slow cranking problems?

I do have a video I can put on if it helps.
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#2 Martin Y

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Posted 01 September 2020 - 07:56 PM

Hmm.  How long did you leave the Ctec charging?  (depending on the model) it's a conditioner as well as a charger and can revive sulphated batteries quite well just by charging them really slowly.  Might take a couple of days to charge a low battery.

 

One other thing which can cause slow cranking is a bad ground and there's a point which is notorious for cable fractures:  Look under the car in front of the right rear wheel and you'll see a thick cable which ought to be bolted to the powerplant frame next to the differential.  That's the far end of the battery ground cable and it often fractures at that point.  It's the main ground connection between the bodywork and the powertrain.  There's a smaller one, a braided strap, in the engine bay next to the dipstick, but it's not really up to the 100+ amps the starter motor wants.


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#3 -Rich-

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Posted 01 September 2020 - 08:54 PM

The Ctek is the MXS 5.0. It was charging for a couple of hours and I always leave it until it reaches step 7. So according to the charger the battery is still ok. I charge it on AGM mode too.

Thanks for the info about the ground cable, I will have a look. Something I forgot to say is that I have a cut off switch fitted to the negative terminal, similar to the one MX5 parts sell. But I always make sure it's tight and it didn't crank for this long after fitting it.

Here's the video, hopefully it works.


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#4 Martin Y

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Posted 02 September 2020 - 09:57 AM

One thing you might try is using the Ctek on its Small Battery setting. That limits charging to 0.8A instead of 5A. MX-5 batteries seem to respond well to slow charging. I read that very slow charging gives time for built up sulphates to gradually dissolve in the battery acid while it charges and clearing that can free up more available area of the plates.
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#5 -Rich-

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Posted 20 September 2020 - 03:43 PM

I charged the battery up on the small setting but it didn't need long for a full charge, under 2 hours. It's been sitting for over a week now and the voltage has barely dropped. Hopefully it'll last a bit longer yet.

I bought a new battery for another of my cars and tried it in the MX5 to see how it started. It cranked about 1 second quicker and definitely felt stronger.

Today I had time to look for this ground strap - it's no longer attached to the bolt!! I tried to undo the bolt and the head snapped off so I'm not happy!

How can I fix this? Does the PPF undo easily, it looks like there are 5 bolts? I don't think I'll be able to drill the old bolt out or a new hole in situ. Can a bolt and nut be used instead?

If I cut the end of the cable off what size terminal would I need to replace it and do you need a special tool to crimp them as they're pretty thick?

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#6 Martin Y

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Posted 21 September 2020 - 12:19 AM

That's the other end of the battery ground lead. 

 

It starts at the battery negative terminal and fixes to the side of the boot and then forward and down through the offside rear wheel well to the PPF. I managed to unscrew the original bolt on mine, but in your position I would either drill a new hole and tap it to M6 or drill a clear 6mm hole and use a nut and bolt but be sure to sand down the aluminium surfaces to make a solid contact as it needs to carry 100+ amps while cranking.  You'll need about 1.5m of 16 sq mm cable to reach from the PPF to the spot in the boot where the original cable fixes to the chassis.


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#7 -Rich-

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Posted 21 September 2020 - 12:40 PM

Thanks. I'll see if I can get some grips on the bit of stud that's left first before I start drilling new holes. I don't have any taps so it would need to be a nut and bolt if a new hole is needed. Can the frame be removed that's to the right of the bolt to make access easier?

You can see how rusty that is in the photo so I'm a little reluctant to try undoing those bolts though! I could only get a small socket or spanner on the ground bolt with a pole on the end and even after spraying it I could feel it would snap on the first turn!

Would you advise replacing the cable completely and not just the end terminal? The other end in the boot looks in good condition. Can I leave the old cable there or should that be removed? I couldn't jack the car that high where it's currently parked so it was difficult to trace the cable's route. I'm guessing it needs to be quite high. Does the wheel and arch liner need to come off?

I'm amazed I've not had any other issues other than the car cranking slowly. It does suffer with idle droop when cold though.
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#8 dadbif

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Posted 21 September 2020 - 02:21 PM

Could you not drill through the crimped end of the cable and then bolt it up to a fresh hole in the frame? Making sure that everything is clean between cable and frame of course.
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#9 Martin Y

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Posted 21 September 2020 - 05:21 PM

If the cable end isn't in bad condition then yes you can just crimp a new end on and keep using it.

I doubt if there's enough material in the remaining part of the crimp terminal to drill it and use that.
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#10 dadbif

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Posted 22 September 2020 - 06:57 AM

It’s worth stripping the end back to see if it would take a new crimped end, assuming you have crimps big enough
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#11 -Rich-

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Posted 22 September 2020 - 09:55 PM

Yeah I'm not sure drilling a hole through the crimped end would leave much material left. I'll definitely try a new ring terminal first. So that's 16mm² for the cable end but when I measured the bolt hole and the bolt itself they seem odd sizes.

Do you know what size the Mazda bolt is as it doesn't seem to be M6 but closer to M8? The ring terminal hole is nearly 9mm.

I had a look behind the trim in the boot earlier. The cable seems to go down under the parcel shelf and is all taped up to the wiring loom. So if it needs replacing it looks easier just to leave it and put a new one in somewhere else but following the same route.

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#12 -Rich-

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Posted 28 September 2020 - 08:16 PM

I tried and failed to remove the snap bolt today with some grips but there just isn't enough space. I'm going to drill it out and just use a nut and bolt. Can it be accessed if I take the rear wheel off? I didn't get time today but it looks like the suspension and chassis may be in the way.

Also, will these crimps fit or can you recommend anywhere to buy some that are the correct size. I'm not sure about these looking at the thickness of my cable and going by the Q&As on Screwfix.

https://www.screwfix...ack-of-10/54720

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#13 Martin Y

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Posted 29 September 2020 - 09:04 AM

Those look like the right size crimps for the cable.  16mm² cross sectional area wire is about 5mm diameter.


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#14 -Rich-

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Posted 17 October 2020 - 09:40 AM

So I drilled the remaining bolt out, fitted a new crimp and it made no difference at all to how the car started. Considering the ground wasn't connected at all I'm surprised at that.

Could it be worth adding a new one if I get some cable. Removing the old one looks like a pain so I'll just leave it there.

I didn't clean the one by the dipstick but if this didn't make any difference I can't see that doing anything. When operating the windows the clock light dims but I've not noticed any other issues.

Where is the starter motor located as I'll try cleaning the terminals up and check they're tight?

As the car started better with another more powerful battery, could it be the Panasonic one is knackered? Apart from that and the Westco what other GEL batteries fit these cars? I'm not keen on using a normal one as it'll probably leak.
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#15 Martin Y

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Posted 17 October 2020 - 09:53 AM

I think you're probably right that if restoring the main ground didn't improve it, the remaining problem is probably that the battery just can't supply enough cranking amps, especially if a stronger battery worked better.  Starter is at the offside rear of the engine quite low down.

 

It's a few years since I bought a battery and then I just went with a Westco so I'm not sure what the best deals are now.


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#16 -Rich-

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Posted Yesterday, 11:57 AM

Thanks. I found the stater but what a pain for access! Looks like it's a wheel off job to check the connections.

One thing I hadn't mentioned is this slow cranking also seems to happen when the car is warm. Could that also point to the starter beginning to die?

I've decided I'll get a new battery after winter and go with the Bosch S5. As it's a sealed wet battery it should be fine and I'll get some clear tubing for the vent. I did look at the Westco but the price and short life from what I've read put me off.
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