14 replies to this topic

[STC19]

Hello! 

back again with another voltage/ charging related issue *sigh*

I have recently had a new alternator as the old one was kaput. 

 

When stationary, the alternator will charge the car more or less no problem, it occasionally takes a few minutes when the engine is cold.

 

However once i start driving, the voltage quickly drops to below 13 volts, even getting as low as 12v. (see image attached, taken at end of journey)

 

increasing the RPM doesnt seem to do help.

 

Car is a '95 Cooper SPI.

I have replaced the battery today with a new one - issue still persists.

I have also added an earth strap from the wok to a nearby chassis nut. - issue still persists

 

 

Does anyone know why this might be happening or has anyone experienced anything similar?

 

Any help greatly appreciated,

 

Sam 

 

Attached Files

•  20230409_202640.jpg   54.19K   5 downloads

[weef]

It may be worth checking that the drive belt is the correct section for the pulleys, is adjusted correctly, the alternater pulley is the correct diameter and the belt is not slipping.

[STC19]

thanks for your reply,

 

the belt does squeel a little when the voltage reads 14+ volts. 

 

will have a look tomorrow or next weekend 

 

S

[bpirie1000]

Is the gauge a true reading? May be best checking with a different testing method.

[stuart bowes]

it's not always easy to get good tension on the alternator, on other cars what I've done previously is loosen the bolt(s), then use a pry bar behind the alternator (go easy of course, maybe a rag under the leverage point to stop any paint damage if you have a pretty engine block) and hold that out while doing up the bolts again

 

it's just an easy way to make sure the belt is running nice and tight 

 

don't go too mad with it though it's possible overdoing it might cause bearing damage in the long term

Edited by stuart bowes, 15 April 2023 - 08:45 PM.

[Midas Mk1]

Multimeter at the battery test , my mpi volt gauge is vague at best.

[sonscar]

High resistance between alternator and solenoid?Does the charge light illuminate when you turn it on before cranking?Steve..

[bpirie1000]

I would also ask what electrics you have on when dropping to 12v... if you have heater on and rear screen and stereo and radio.

That is a fairdraw of current.. so long as it is above 12.3 or so should be good to rock n roll..

IF IT IS SLOW TO START OCCASSIONALLY(LIKE ME)...then try taking off started and cleaning contacgs and maybe grease the started cog and solenoid alitle..

Just thinking...

[STC19]

Hello, thanks for the replys,

appologies for the delay in replying.

I shall try the above suggestions over the next few weeks.

Stuart - Is there a way to guage if the belt is the correct tension? I read somewhere that 13mm play is about right, but could be mistaken

Sonscar - yes, it comes on when the key is in the second position, although sometimes it is brighter than others (might be imagining this). It does always come on though.

Bpirie - thanks for the suggestion I will try it one weekend. Even when driving with nothing on (light, heater, radio, wipers etc...) the voltage still goes down. 

 

I do have a faulty coolant temp sensor and broken Lambda sensor which I am about to replace over the coming weeks.

I did notice that heavy breaking does seem to be a huge drain also, is this normal?

 

 

Once again, many thanks, and i will report back with an update over the coming weeks   

Sam 

[viz139]

You haven't stated that the car is hard to start or that the battery is not charging fully so I would think the problem is a poor connection in the wiring loom or on the gauge it self. The brake lights causing a volt drop would suggest a problem in the Positive feed as these use a different earth point 

[STC19]

Hello! 

just a small update,

have still not managed to find the issue as have been away for a few weeks.

I did however notice that the battery light on the dash is dimmer than the oil light, photo attached.

 

Is this normal or should i look at replacing the bulb?

Sam

Attached Files

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[bpirie1000]

Usually this means that the voltage is charging just about right but not 100% (light goes out)

Sounds like you should have a look at the wires on the alternator and make sure no corrosion is there..
The D wire is the one you need to,look at for the bulb but checking them all is always a good idea...

[madalicesdad]

When my 92 SPi was still under warranty I had issues with battery being flat after a long run. At idle, charge was good but often battery would be totally flat after 2 hours on the motorway. Two different Rover dealers said no fault found.
In the end, an eagle eyed mechanic noticed that the tie bar bushes were worn and under load, the engine tilted forwards enough to pull the earth cable that runs along the tiebar such that the cable came out of the crimp.
A longer cable fixed it. One of the cheaper items the warranty paid for 😁

[STC19]

Hello! 

Good news, I have fixed my issue.

I am embarrassed to say it was extremely simple,

I had not checked that the alternator belt was tight enough.

It must have been tight enough to generate enough power when there was no load applied, but once engine revs increased or a load was applied, it would slip.

 

Tightened by rotating the alternator a fraction and now the car runs and charges perfectly. (have made sure not to tighten too much) 

Many thanks for all the advice none the less.   

Sam

[stuart bowes]

Stuart - Is there a way to guage if the belt is the correct tension? I read somewhere that 13mm play is about right, but could be mistaken

 

 

sorry I totally missed this at the time, yes according to google that is right, but there's no accurate way to measure that of course, 

 

it's just kind of a do it by feel kind of job really, nice and tight but a little bit of flex when you press on the belt.. not too tight.  until it stops squealing .. ? 

 

sounds like you found the right tension in the end though

Edited by stuart bowes, 01 August 2023 - 09:14 AM.