Low voltage while running - alternator changed

Buzza9

Idling at the Lights
Location
NSW
First Name
Nathan
Drive
Magic School Bus
Hey folks

I have an issue with my legnum that while running it is only putting out 11.8v and doesn't change under load (Measured with multimeter). My first thought was alternator, so I changed that with a second hand one but still have the same issue.

I also replaced the battery with a new one at the same time.

Am I missing something? Any idea's on where to look next?

Thanks in advanced.
 

Brett

Idling at the Lights
Lifetime Member
Location
Adelaide
First Name
Brett
Drive
2000 Mitsubishi Galant VR4
Where are you testing the charge rate? Test it on the output and casing of the alternator using your multimeter and compare it to what you're getting when testing on the battery terminals and you'll be able to see if you have a wiring issue.
 

Buzza9

Idling at the Lights
Location
NSW
First Name
Nathan
Drive
Magic School Bus
Alright I will give that a go; I was testing it at the battery..
 

trotty

3 AYC Bars
Location
nsw
First Name
Daniel Trotman
Drive
2000 vr4 Legnum 5 sp man
2006 Suzuki Swift Sport 5 sp man
U should still see between 12.8-14.4 at the battery when charging. Mine does float depending on load. I'll see it sit at battery voltage of about 12.2-4 they it will ramp up as reeves rise or headlights turned on.
 

Kaldek

2 AYC Bars
Premium Member
Location
Melbourne
First Name
Ed
Drive
2000 Legnum VR4 Manual, Ford Territory family runabout, BMW K1300R.
Alternators on these cars are ECU controlled. If the control circuit from the ECU is damaged, the alternator will not supply a charge.

Remember that the alternator is always spinning. The charge it puts out is controlled by secondary windings. Supplying power or "exciting" these windings is what controls alternator output. And it is the ECU that supplies that field excitement power.
 

Kaldek

2 AYC Bars
Premium Member
Location
Melbourne
First Name
Ed
Drive
2000 Legnum VR4 Manual, Ford Territory family runabout, BMW K1300R.
Also does your charge light come on at all?
 

Buzza9

Idling at the Lights
Location
NSW
First Name
Nathan
Drive
Magic School Bus
No lights were coming on the dash at all.. I gave it a rev while I had the meter hooked up to the battery and it got a reading of 14.2v and was alright after that until turned off. I restarted it then got my wife to slowly build the revs up and it started charging again at around 3k...

I stopped and started it a few times, took it for a drive and it has been working alright since... I am curious as to what it will read in the morning on start up.

It has me confused but it is working at the moment.. I am going to book it in to TME for a service so I might get him to have a look at it also..
 

Tony_T

Leaving Skid Marks
Location
Hamilton New Zealand
First Name
Tony
Drive
Legnum VR-4 1997
Did you get it sorted yet? If not just a thought:
Does the lamp in the dash for the alternator come on when you switch the key on i.e. during the self test? Some alternators (and I'm not sure if ours are like this) use the current through the lamp to start them and lamp failure will cause them not to start unless revved quite high such that residual magnetism in the field winding produces enough output to start the regulator.
If ours is not that type this won't apply.
 

Buzza9

Idling at the Lights
Location
NSW
First Name
Nathan
Drive
Magic School Bus
Nah still haven't got it sorted, I have a new alternator ordered so should come this week.. The light comes on the dash with the reds so I am not sure.. Still need to work out a time to get TME to check it over for me
 

pretzil

2 AYC Bars
Location
Qld
First Name
Rick
Drive
Legnum VR4
Thread revival.
I am having a similar issue, have spotted the battery light flicker very occasionally.
Fitted a cig plug volt meter and have seen it dip down to around 11V randomly and stay there, but also up around 13.9V at other times.

This thread doesn't appear to have been resolved, but any ideas?
 

Gav

1 AYC Bar
Lifetime Member
Location
Sydney
First Name
Gav
Drive
Galant
Thread revival.
I am having a similar issue, have spotted the battery light flicker very occasionally.
Fitted a cig plug volt meter and have seen it dip down to around 11V randomly and stay there, but also up around 13.9V at other times.

This thread doesn't appear to have been resolved, but any ideas?
Your alternator could be starting to die or could be a faulty plug on the alternator. I got a new plug off eBay for mine. Has a friends leggy do the same too. Fixed his problem when he put the new plug on.
 
Top Bottom