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I've been through the various threads - have a question about something in the sticky under electric troubleshooting.

Ghind says 11. This test tells you if your alternator is producing 14.4 volts or not. Strictly not essential to do this test as the numbers above let you work it out mathematically but it gives you a quick idea. For example if your alternator is producing 14.4 volts but your battery is only seeing 13.8 volts then you can see there is a voltage drop somewhere that needs fixing. However, if your alternator is producing less than 14.4 volts, fix all other issues above before replacing it as there is probably nothing wrong with your alternator.


My alternator is producing less than 14.4 volts (about 13.64) when I test it at the positive lug and the alternator housing, idle or at 2,000 rpm.

If the alternator isn't producing 14.4 volts right at the alternator then why should I go fix "all the other issues" first?

Doesn't that tell you right there that the alternator is not putting out enough current?

Its true I am losing about 0.2 volts between the alternator and the battery but the voltage starting at the alternator seems to be almost a whole 1 volt too low.

Appreciate any help here but i am about to order a new alternator pending some good info from you all.

thanks
 

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OK, you are checking by placing the negative probe on the Alt case and pos probe on the "Positive Lug".......By lug, do you mean the ring "Lug" on the alternator output post, or the pos Lug on the battery?
Correct check is Alt Pos post to alt case first, then pos post of batt and neg post of batt.
This will give you total voltage drop through both paths.
Then do alt+ and Batt-, then Alt case to Batt plus to see which path has the most drop.
Note that these checks should be done with a constant load on like heated windscreen, seats, and headlights. Also, you should confirm the meter is reading correctly as some cheepo digitals can be 20% off on the 12v scale (From personal experience)
 

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The alternator contains a voltage regulator that prevents the output voltage rising above 14.x volts (they do vary a bit). If the voltage isn't reaching the set-point (and yours isn't). There are two possibilities. 1) The alternator / regulator is faulty, 2) The car is trying to draw more current than the alternator can supply. If you put your negative probe on the battery negative terminal and measure both the alternator output and the battery positive, the difference will give you some idea of how much current is being drawn. If you turn all the electrical loads off then there shouldn't be more than around 1/2 a volt difference. If that's how you got the 0.2V then I would condemn your alternator.

In my experience alternator / regulator failures are more common. The brushes that supply the field coil can wear / stick and (less common nowadays) diodes in the rectifier can fail which usually means the alternator only gives 2/3 of it's rated output. The voltage regulator chip can also fail.

For most alternators you can replace the brushes and for many the entire regulator is replaceable, though it may involve soldering. Generally the coils and bearings are pretty robust. The P38 has an automatic belt tensioner which prevents it being set too tight and killing the bearings, so second hand units are worth considering if you're on a budget.
 

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Discussion Starter #4
I did all the tests recommended in the sticky note and here's what I got. Tests 6 & 7 suggest there are some cable issues but test 11 seems to suggest that the alternator itself is not putting out 14.X volts. What do you guys think??
Worksheet

This is a cut down version of the tests, see above for detail on how to complete each test.

1. Engine off, all accessories on for 30 seconds, then off. What voltage _12.6_____
2. Voltage across battery at idle (no electrical load) __13.36__________
3. Voltage across battery at 2000rpm (no electrical load) _13.4_______
4. Voltage across battery at 2000rpm (everything electrical switched on) __12.96_______
5. Voltage at ALTERNATOR at 2000rpm (everything switched on)___13.52________________
6. Voltage drop between alternator body and battery negative (YES negative). Measure at max electrical load and 2000rpm ____171mv__________ (millivolts please)
7. Voltage drop between alternator positive and battery positive. 2000rpm, max electrical load _179mv____________
8. Check Voltage drop from Battery Negative terminal to 1st groundpoint on vehicle__4.4mv____________
9. Check voltage drop from 1st ground point to block__62mv________
10. Check voltage drop from Alternator Housing to block___1mv_______
11. Voltage from alternator positive to alternator housing13.64

since I am not seeing that 14.1 to 14.4 volts ANYWHERE it makes me think I have an alternator issue. I did clean up the cable connections on the negative side of the system but saw no change.

Would you recommend changing out the alternator?

 

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since I am not seeing that 14.1 to 14.4 volts ANYWHERE it makes me think I have an alternator issue. I did clean up the cable connections on the negative side of the system but saw no change.

Sounds like you have possibly nailed it.
Just to be sure, beg, borrow buy or steal an expensive meter and double check. As you did not specify meter.......If it cost less than 20 bucks, it could be a bit suspect, so before buying a new alt, it would be prudent to confirm Batt volt readings and compare in real time.
BTW, even my $350 buck Fluke meters will drift over time and need to be re calibrated. When my cheepies go wrong, they get binned!

Oh, out of curiosity. You never said what the issue was that sent you to the sticky in the first place........
If there was one? Dim lights? not starting?
 

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Discussion Starter #6
Bolt, I am using a $75 Dr. Meter multimeter - made in China - so I can't say its necessary real good BUT, I run all the time with a scan gauge plugged into my OBD2 and displaying voltage on my dash. The voltage varies from 13.2 to 13.8 depending on what's on while I am driving but I never see 14 volts (never have since buying rover 2 months ago). By comparison my jeep and Disco II always show +14.X on the scan gauge (i have scan gauges in all my cars - particularly useful is the water temp in the rovers).

What got me looking into this was that the other day my car cranked slowly (first time since buying it 2 months ago). It did start but when I got home I checked and battery was down to 12.5. I charged it and have been trouble shooting this ever since. The battery is 2 months old - I replaced when I bought the P38. What I think happened is that the alternator issue has always been there but in the last few days its been real cold here and for the first time since owning the car I am running demisters, seat warmers etc enough to put a real drain on the system.

As a side note my alternator has "land Rover 4.0 1999" hand painted on it in a yellow marker so I know it came out of a junk yard somewhere before I bought the rig.

My leaning is to buy a reman alternator like from Atlantic British and hope to see +14.X when I install it and then track down any cable issues that might be there.

Alternatively I could buy new but they are about $600.

But I really appreciate working with folks on the forum to make sure my thinking is well-based before spending significant $$.

I had a Defender and it had a lot of electrical issues that I eventually sorted out but my experience is that troubleshooting electrical issues can be tricky.
 

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Classic case then, good to know you have confirmation. Hate to see folks apply "hand grenade" method of troubleshooting.

Have you checked the local auto parts places there? I am finding a lot of parts I would not expect to at Napa, Car Quest, and O'Riley here. Then if it is duff, you can just bring it back!
Shoot! Find one that does "Free alternator testing" and bring it in! (Napa, I think)
For that matter, there could be someone in your area that can test, and repair yours?
 

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In my 2 years of P38 ownership I have read and reread and learned that the 2 things you pay OEM full price are the Alternator and the Fuel Pump.
Both are $600 bucks and both are needed.
Im a big fan of buy once.... cry once... just a thought. I have switched to all LED lamps in mine to ease the power draw. The P38 is a power hog. Hence the 950 CCA battery. How long and how much do you love your truck? ��������*♂
 

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Please to respectfully disagree with you?
I am a big fan of "Pay the price or cry twice".....Like don't put in the cheap water pump......
However, I have lots of experience with Alternators of all sizes, and there is nothing wrong with a competently performed rebuild there. Case and coils rarely fail, and new bearings brushes and Reg (as needed), will do just fine. I have done 3 P-38 jobs with no issues whatsoever.
Fuel pump? Yea, as it is a serious PITA to change, and a bugger when it fails!
Carry on!
 

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Do you actually have an issue with electrics? Battery slow to charge, difficulty starting, ... ? If not, it would seem you're chasing a ghost to replace something that is working OK. In my experience, a lot of (older) vehicles don't have an output of 14.4V, but as long as it's considerably more than battery voltage with engine off, there is no problem. The alternator will charge the battery just fine. If you really want to know the charge going into the battery, you need a good DC current meter and do measurements in different situations to see how the current varies (low and high rpm, low and high load etc).
But again, unless you have a clear indication of something not being right, it looks like you're looking for an excuse to replace rather than a cure.
I also agree a good recon alternator will perform just as good as a new original one, at a fraction of the cost.

Filip
 

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Discussion Starter #11
The issue is that the engine is sluggish to crank with a 2 month old battery. Voltage check at the positive lug (and alternator case(-) on alternator shows only 13.4 volts.

I did the full range of 11 tests with multimeter (see previous reply). I would agree that as long as alternator is putting out a voltage greater than battery then it will charge the battery.

The issue seems to be when I have a real load on (heater, heated seats, lights, windshield wipers) it puts too much load on the car and seems to run the battery down.
This is an indication that the alternator is not putting out enough current to run the car and accessories.

I notice the alternator on my P38 is an aftermarket (no bosch on it anywhere) and I cannot even find a data plate to say what its output is. So I am getting a remanufactured 150 amp bosch (original equipment) and going to see if it helps.

thoughts??
 

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If the issue is with cranking, have you checked the cables to the starter and it's earth connection? I agree low battery voltage will cause sluggish cranking, but then it would disappear if you charged the battery (with an external charger). If it does, the alternator is the likely culprit. If not, the problem is elsewhere. Would be useful to check battery voltage before trying to crank.
 

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Modern Calcium batteries need a higher charge voltage. The alternator on an early (pre-97) P38 only put out 13.8V but with the fitting of modern technology batteries the alternator was changed for one that puts out 14.4V. I don't think a GEMS alternator will fit a Thor but you probably have an alternator that would have been fine with an old battery but not a new one.
 

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Discussion Starter #14
Escape - yes the problem went away when I charged the battery - so cable to starter is assumed good. I also removed/cleaned all the ground cable connectors between battery/chassis and alternator housing. did not seem to help voltage readinge anywhere.

New alternator will be here in a couple days and I will report on outcome.
 

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Fair enough, looks like you tested and checked everything, so it does sound like the alternator. Should soon be fixed then. ;-)
 

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In my 2 years of P38 ownership I have read and reread and learned that the 2 things you pay OEM full price are the Alternator and the Fuel Pump.
Both are $600 bucks and both are needed.
And in my 10+ years of ownership, I say BS to both.
The Airtex fuel pump me and Scotty put in many many years ago, is still running strong. Strong enough to be powering the LSx engine in fact.
Same with alternators. I've fit them to Disco's and P38's without issue. And not a single one came from a dealer, or is genuine LR in any way. Why would windings and a few electrical parts HAVE to be LR??
For ease of return, even if those two parts didn't last, a local supplier is the way to go. I'd rather run an alternator to a local parts place than try to return to AB etc, and heaven forbid to a dealer.
I'd go as far as to say that the only "Genuine LR" stuff on any of our collection of FIVE Rovers (2-MkIII's, 2-P38's, a DII), is the stuff that can't be had in a reliable aftermarket brand. Otherwise,they all get whatever is around from a known supplier, at a fraction of the cost of LR stuff.

Martin
 

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Discussion Starter #17
In my case its in between aftermarket and genuine. Remanufactured Bosch through Autozone so any return should be doable.
 

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Autozone, Pepboys, OReilly's all have rebuilt and OReilly's has a lifetime guarantee for Bosch. OReilly's also carries rebuilt original magneti marelli for GEMS years, again with a lifetime guarantee.
 

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Discussion Starter #19
i installed a remain 150 amp alternator yesterday. Started it up and voltage was 14.4. I never saw over 13.8 with the old alternator. So I took one step ahead. But as I used the car to run errands the original issue (slow starter cranking) raised its head. The pattern is that the starter cranks fine in the morning when cold but cranks slower after it s hot and after errands today was getting worse - when I finally got home I turned it off and then went to restart and just a click. I checked connections at battery, Battery voltage is 12.9 and I even jumped a second battery to the car and still a click. So it seems I need a starter now. I will go under and check the connections at the starter next though. Sorting out a new rover (new to me, this one) can be a journey.
 

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You are on the right track. A starter positive connection can get loose when heated, as can the brushes inside the starter. If the connections are clean and tight (Of course, you should have checked those already)? Then the starter is indeed a likely suspect. To test for stuck, or just plain worn brushes, have someone hold the key in the start position while you give the starter a good thump with a heavy blunt object. If the starter kicks in when thumped, Go get a new one or rebuild yours.

Sorting the issues in these beasts can be a journey?? Well yes, but I like to think of it as more of an adventure!!!
Anything that takes this much of your time and $$$ has just GOT to be fun! :dance: Right??
 
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