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1995-2002 Range Rover P38A
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Discussion Starter #1
Help! Electrics Pulsing, in the middle of trip, tried everything

Greetings,
We’re driving my sons 95 Classic County LWB Softdash from Lousiana back home to Maine. It became such a problem child for him that he turned its care and feeding back over to me. Lovely solid vehicle, no rust, but a real harridan so far in upkeep.
We’ve made 1200 miles in her so far and are fetched up in Virginia at the moment. I’ve just spent all morning going through every detail of the sticky and am out of ideas and energy. The only thing left to try is replacing the alternator. However, I have two alternators in my possession that both pass a test stand check with flying colors, but fail once placed in the vehicle.

1. Engine off, all accessories on for 30 seconds, then off. What voltage _13.5 Brand new Battery____
2. Voltage across battery at idle (no electrical load) _15.3___________
3. Voltage across battery at 2000rpm (no electrical load) _14.8_______
4. Voltage across battery at 2000rpm (everything electrical switched on) __12.8_______
5. Voltage at ALTERNATOR at 2000rpm (everything switched on)____13.0_______________
6. Voltage drop between alternator body and battery negative (YES negative). Measure at max electrical load and 2000rpm ___120mV________ (millivolts please)
7. Voltage drop between alternator positive and battery positive. 2000rpm, max electrical load ___230mV__________
8. Check Voltage drop from Battery Negative terminal to 1st groundpoint on vehicle___disconnected/checked SAT/cleaned/ reconnected___________
9. Check voltage drop from 1st ground point to block_____Visual check SAT_____
10. Check voltage drop from Alternator Housing to block____Visual check SAT______

Also:
-What are your symptoms
1) All vehicle electrics pulse at approx. 3-4 cycles per second (pumps, lamps, etc.) Engine RPM does little to affect pulse frequency, except occasional multiples of 3-4 cps. Hard to explain. It’s like there’s a regulation trigger point that effects the pulse rate switching and smoothing.
2) No Load idle – pulse smooths out with minor load added (headlights on, or heater on, or fan speed increased)
3) Pulse comes back once engine speed is increased
4) 2000 rpm under full load (everything electric on) pulse smooths out
5) Travelling at night with normal load, headlamp/interior lamp pulse is super irritating. Other vehicles occasionally respond…
6) Alternator makes audible whining in time with pulses.
7) I’m in the middle of a trip from Louisiana to Maine (presently in Northern Virginia) and the symptoms are worsening.
-What have you done to fix it so far
1) Renewed battery two days ago. Original battery read 12.4v and wouldn’t take charge on Autozone machine
2) Have two alternators (one less than a year old and very clean), both test SAT on Autozone test stand, both fail once installed in vehicle. Autozone used portable load test device on the installed ones and they failed on voltage regulation
3) Have gone through and cleaned all connections on the positive charging side with no improvement.
4) Subbed in a new jumper cable in place of original positive cables with no improvement (other than the mV measurement from the alternator to the battery) (dropped from 230mV original cables to 50mV direct to battery, jumpered around the 100 amp alternator fuse with its two cables and numerous connections, a very silly arrangement IMHO)
5) Checked and strengthened the D+ connection. (original fastener did not make up securely)
6) Broke the generator suppression capacitor, so removed it (no difference in operation/malfunction noted)
7) Don’t see the 820 ohm Phase tap resistor on the W connection, but wire tap appears original condition, so maybe it was never there, or hidden in the sheathing further down the wire.

I’m out of ideas, tired, and throwing in the towel… can two alternators really be bad and still pass on a test stand?

Thank you for any and all help/ideas.

Sandy
 

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Premium Member
1995-2002 Range Rover P38A
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1,131 Posts
Discussion Starter #2
Re: Help! Electrics Pulsing, in the middle of trip, tried everything

OK... for future reference, this was all alternator. I just hunted down and replaced the alternator with a new/reman'd unit and the problem is 100% fixed. No more pulse, rock steady juice. It's important to note that my exchange core alternator passed the "bench test" machine with flying colors... the sales rep had to disconnect a lead and purposely fail the alternator in order for the core transaction to be allowed in the point of sale system. So, lesson learned... alternator testing at your local auto parts sales establishment determines absolutely squat. Don't waste your time.
 

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Re: Help! Electrics Pulsing, in the middle of trip, tried everything

I am glad you found it. My hint was line four at only 12.4. Internal VR is goinna fight to keep to keep things up and running IF it is the VR failing. The alternator itself may pass on a bench test, but a full draw test will fluctuate and "hopefully" fail on the bench.
 
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