P38A (Dis)Charging problem

Have spent last hour or so trawling the R/R Forum for guidance but don't seem to be asking the right search questions as not having much luck, so trying new thread instead.
Vehicle is '98 P38 with 4.6 Gems motor c/w LPG and when engine running, it seems to be actively discharging the battery at an alarming rate so that after a couple of minutes tick-over the motor dies from lack of spark power.
Recent events leading up to this point (which may or may not be relevant) are as follows:
Mid-week on 2 occasions the starter motor failed to immediately spin (with good battery power) but after a lot of key twisting (whilst waiting for RAC to answer) it finally burst into life and I got going again. Thinking it would probably be the starter solenoid I started the removal saga and noticed some bared section of the smaller (energizer?) wire to the solenoid and when I removed the f/o/s inner wing splashguard to access the top starter motor bolt I found the Lucar connector of the same wire had come off its terminal - I assumed this had been previously only just resting on the terminal causing the intermittent starting problem so I spliced in a new length with new connectors, reconnected and tried several startings - all were first timers with no misses! Result, or so I thought. Went for a short run (during which EAS failed to come up - poss due to having been jacked up?) , tried a restart but now battery appeared flat so put on trickle charge overnight.
Next morning started first time but after several minutes running, would not start a second time so checked around starter motor to see if all wires clear. By this time battery had recovered just enough to start engine but a check showed only appx 10v across battery terminals at tick-over and no increase when revved. Swapped alternator from another (donor) 4.6 but no improvement and engine wouldn't start without a jump start and again, would only run on tick-over for a few minutes before dying.
Without the motor running, the car's battery recovers to appx 12v so the discharge only seems to be related to when engine is running. I tried removing fuses and relays from the EAS then Starter Motor circuits whilst engine was running to see if the discharge stopped, but no change - Any ideas folks?

Sounds like the main + on back of alternator is not attached to battery,try a new bit wire or check for +at alternator....

Speculation, but does the alternator need a working ignition warning light to excite it & enable it to charge?

dubbleRR said:

Sounds like the main + on back of alternator is not attached to battery,try a new bit wire or check for +at alternator....

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Thanks dubbleRR, I think you're on the right track. I managed to check alternator output earlier (between showers) and it showed 14.8v between main terminal and the earth casing so I guess its producing OK - just not delivering a full charge to the battery. Next chance I get will be to try and follow the main cable out from the alternator to try and locate the problem area.
PS. I like your choice of RR colour - obviously a man of taste!

Ratae said:

Speculation, but does the alternator need a working ignition warning light to excite it & enable it to charge?

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Thanks Ratae, I can't remember that - I checked the battery symbol came on with the ignition OK and went out again immediately after the start-up. I'll look for the ignition symbol tomorrow, just in case it's necessary to allow the full charging power.

The early GEMS (not sure when it changed) had the main alternator feed
from the alternator to the battery run via the starter motor! It's a long run with a lot of potential for breaks and damage.
A well known mod was/ is to run a 25mm2 cable direct between the batt +ve and alternator output, and throw away the old bit of cable between starter motor and alternator.

Whid said:

Thanks Ratae, I can't remember that - I checked the battery symbol came on with the ignition OK and went out again immediately after the start-up. I'll look for the ignition symbol tomorrow, just in case it's necessary to allow the full charging power.

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If the battery symbol's on when ignition switched on & goes out when the engine is running I'd say it's OK & not your issue.

Orangebean said:

The early GEMS (not sure when it changed) had the main alternator feed
from the alternator to the battery run via the starter motor! It's a long run with a lot of potential for breaks and damage.
A well known mod was/ is to run a 25mm2 cable direct between the batt +ve and alternator output, and throw away the old bit of cable between starter motor and alternator.

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Wasn't there a second earth strap added to the later GEMS / Thor as well?

Grrrrrr said:

Wasn't there a second earth strap added to the later GEMS / Thor as well?

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Don't think so Grrrrrr, but can't say I've looked really.
When I did the +ve cable mod on my GEMS, I fitted an additional 25mm2 ground directly from -ve on battery to alternator body, just to give the weedy 105A alternator the best chance of coping.

Orangebean said:

Don't think so Grrrrrr, but can't say I've looked really.
When I did the +ve cable mod on my GEMS, I fitted an additional 25mm2 ground directly from -ve on battery to alternator body, just to give the weedy 105A alternator the best chance of coping.

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Pretty sure @MrGorsky fitted a more powerful alternator to his so I think you can upgrade.

Grrrrrr said:

Pretty sure @MrGorsky fitted a more powerful alternator to his so I think you can upgrade.

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I did consider upgrading it, mainly to get the benefits of the 14.4v setpoint and keep the MF31-1000 alive for longer, but that's now 3 years old and still going strong on 13.8v.
The old GEMS is now the other half's daily driver and has moved from "improvement" to "maintenance and servicing only" status though so that aspect probably won't get any more attention until it shows signs of failing.

Orangebean said:

I did consider upgrading it, mainly to get the benefits of the 14.4v setpoint and keep the MF31-1000 alive for longer, but that's now 3 years old and still going strong on 13.8v.
The old GEMS is now the other half's daily driver and has moved from "improvement" to "maintenance and servicing only" status though so that aspect probably won't get any more attention until it shows signs of failing.

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I upgraded the gubbins in mine to get the 14.5V setpoint. Cost less than £15. Seems to be working OK so far.

I did the same only took 45 mins to do

Grrrrrr said:

I upgraded the gubbins in mine to get the 14.5V setpoint. Cost less than £15. Seems to be working OK so far.

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What is this Gubbins of which you speak? I have a failed 150A P38 Alternator in my garage it would be good to be able to fix it as a spare.

DanClarke said:

What is this Gubbins of which you speak? I have a failed 150A P38 Alternator in my garage it would be good to be able to fix it as a spare.

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The 150A alternator already has the 14.4 (or 14.5 depending on who's blurb you read) volt setpoint regulator.
It depends what has failed on your alternator really, you can buy regulator/ rectifiers, brushes, bearings, even get them rewound.

DanClarke said:

What is this Gubbins of which you speak? I have a failed 150A P38 Alternator in my garage it would be good to be able to fix it as a spare.

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Setpoint regulator is what I replaced but as Organebean says you can get diodes etc too.

Grrrrrr said:

Setpoint regulator is what I replaced but as Organebean says you can get diodes etc too.

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The problem is that it just "stopped" producing power one day when (of all things) I went over a large pot-hole (or was it a pedestrian, I forget).
Suddenly.... No Alternator output. ZIP, De-Nada, Zilch.
No idea what blew/went in the Alternator but it was expensive to get another 150A one fitted.
If it is easy enough to pull out the diode-block and or replace the slip-rings/brushes whatever then it would seem a cheap way to have a spare ready & waiting for the next one to go "POP".

DanClarke said:

The problem is that it just "stopped" producing power one day when (of all things) I went over a large pot-hole (or was it a pedestrian, I forget).
Suddenly.... No Alternator output. ZIP, De-Nada, Zilch.
No idea what blew/went in the Alternator but it was expensive to get another 150A one fitted.
If it is easy enough to pull out the diode-block and or replace the slip-rings/brushes whatever then it would seem a cheap way to have a spare ready & waiting for the next one to go "POP".

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I would suspect the diodes. The alternator generates alternating current (the clue is in the name!) so it has diodes so that only the positive part goes through. If these fail then nothing much happens as the voltage is effectively switching between + and - which DC electrics don't like.

The top part of the alternator comes apart quite easily and all the connections are different sizes so very hard to cock it up!

Problem solved - Partly!
Following dubbleRR's original advices and continuing my own efforts I went back to Rave and saw the starter solenoid terminal was a joint en route back to the battery +ve and, importantly, it was something I had disturbed to give access to replace the energizer wire terminal !
Hindsight tells me that you should always clean old terminals when you get the chance, preferably before you refit them !
After cleaning and refitting, surprise surprise, 14.4v charge across battery terminals at tickover and EAS & Heater both working superbly again!
Unfortunately the original problem of intermittent non-starting was not cured with the new wire to solenoid, so I'm back to Square 1 and a bit more forum trawling - peculiar that the problem only seems to occur when motor is hot, cold starts are fine??
Many thanks to everyone's advice though - keep the Faith!

http://www.roverparts.com/TechTips/hot_start_problems.cfm
Problem is that the price is eyewatering so hopefully someone will suggest a way of checking it that doesn't involve spending £100 & then finding it doesn't cure the problem!