Just a tidbit of information if you are seeing odd voltage drops, particularly as your Disco warms up and you have a known good alternator and battery. Your starter may be the culprit after replacing my starter I noticed an odd voltage drop I have been chasing vanished.

Some research confirmed my suspicion, the "simplest test" is to use a multimeter with the negative to battery casing and the positive to the positive cable on the solenoid it should be within .1 or exactly the same as the the reading at the battery.

This occurred even when my starter was still spinning ok

As requested by @Harvlr The voltage situation in my case (monitored via torque and OBD port):

• Voltage at the alternator was 14.3 and at the battery 14.2
• On startup voltage would be 14.1 or so dropping to 13.8 after a short time indicated by Torque and ODB monitoring
• Once the Disco was fully warm voltage would drop to 13.6 - 13.5
• But I would get sudden drops to 13.3 and as low as 12.9 sometimes leveling out at 13.3

Sometimes hitting a bump would bump the voltage up, I started checking and cleaning all the grounds assuming a loose ground as well, as checking the battery cable ends to no avail. Once the starter was replaced voltage returned to normal, 14.3 at start dropping to 13.9 once the battery was charged and staying there. With everything on seat heaters, low beams & driving lights, heated windshield heater fan on high and defrost. I drop to 13.6 to 13.5.

 

Hey Richard, can you explain what you were observing? I’m not really following what kind of voltage drop you were having.

 

Updated with details of voltage fluctuations

 

Monitoring the voltage via ODB doesn't give accurate numbers. I measure (using a high accuracy method) at the battery terminals and I always see around 14V when driving around. The voltage is fluctuating short term, but this is due to changing loads, rpm and the control loop of the voltage regulator isn't perfect. You see an improvement because you did some work on the wiring which impacts the measurement result, but the starter itself can't influence the voltage when it's not engaged.

 

@Discorama That was my thought too until I did some research, the starter being and on/off device if you will. The gist of the article was a form of parasite draw, in the form of a short. Up until the starter I had pretty much checked, cleaned and tightened every ground. However I am happy to proven or found wrong because that damm heat shield makes diagnostics hard.

 

One determines a parasitic draw with an ammeter. A voltmeter can only suggest a problem, and then only with the help of an electrical theory; an ammeter tells you directly what is happening or not, in such a case.

 

Thanks Richard. As I see it, the only readings of yours that would have concerned me are the drops to 12.9-13.3V. And you’re saying that those went away after replacing the starter?

 

If it’s as I’m understanding then, the starter solenoid was allowing some current to leak through, even perhaps through the main starter motor part of the circuit? With all the vehicle noise as you’re driving, I don’t imagine that you ever heard the starter motor spinning when your voltage dropped to 13ish?
I’m still trying to wrap my head around what you were experiencing. If this thread was started by some new member I’d be very skeptical about what I’m reading, but you’re a guy who’s very experienced with these vehicles, and a guy that I respect.

 

@Richard Gallant You are right, there can be parasitic current draw from stuff like metal shavings, dirt and possibly salt collecting outside or inside.

 

@Harvlr @Discorama It is just very weird, I am with you guys I sound a bit like a lunatic snake oil guy. I have put a call into the shop that did the starter to see if they found anything weird or replaced anything.

Maybe they found something loose and just tightened it up,but the primary Ground /Positive path is pretty simple in these and I covered all major stuff the before the starter.

And yes after the starter replacement the voltage is perfect, at 3C with heater fan on max,headlights on and driving lights on my lowest dip was to 13.5 for a few seconds stopped at light then back to 13.8 as soon as the revs when back up as I moved off all normal stuff. I drove from Chilliwack to the Vancouver airport and back on Monday (240 KM/150miles) and never dropped below 13.8