Alternator Gearbox faults on start up only in the morning..

Some mornings (not every one but becoming more frequent) when i start the '99 P38 DSE the revs shoot up to 2500 and an alternator fault warning comes on. After driving for two or three min the revs drop to normal but then the gearbox fault comes on and the box stays in third... Two min later i stop, walk the dog for half an hour get back to the jeep and its perfect and stays that way all day and night.. I have put a new 110amh battery in after reading other threads but no change.. Starting to annoy me now as its really sore on the car in the mornings that it happens.. Anybody had a similar issue / solution..

How old is the battery? The voltage drop during cranking could play havoc with all the ECUs on board a P38.

Sounds like your altenator is not charging sufficiently. If you have a voltmeter you could measure the voltage across the terminal with the engine revs held around 2000rpm. It should be around 14.8 volts. If it is much less try measuring at the back of the altenator. If you now have a higher voltage start looking for bad connections on both the power and earth circuits. If it is crap at the back of the altenator then you need to have it repaired or replaced.

I have exactly the same problem and cannot figure it out. i think i posted the question a few weeks ago but to no avail i'm afraid.
But i can tell you this :
If you turn the ignition on and wait for the glowplugs to go off ,don't start it but turn it off and back on again wait a second or so back off and back on and this time start it you will get no alternator or gearbox fault and the car will rev and drive perfectly.It's a -3 turn of the key cycle- if that makes any sense.
if you start it on the second turn of the key it will tickover normally and only the gearbox fault will be present,if you start it on the first turn it will behave as you describe.
This is what mine does anyway and yours sounds eerily similar.
I just hope some wizard out there will be able to figure it out.
same car by the way 2.5dhse

Wow speedie replies.. Thanks..
@rodntod I have tried all of these little tricks and jiggles and somedays good and somedays not so much.. Its a real pain but tomorrow i'll try it on the third turn only and let you know...

@jt_armstrong I understand that it could have been the alternator but when i fitted the new battery I had the charging levels checked and they were spot on. The fact that its only in the morning could def lend towards connections.. Will investigate, thanks.

@StuckAgainSteve Brand new.. the old battery was also in good nick but was only an 80amh so i replaced it with a 110amh one but with little or no difference...

Petie i am keen to hear what happens if it runs ok when started on the third turn of the key as that would mean i am not the only one :tea:

petie said:

@jt_armstrong I understand that it could have been the alternator but when i fitted the new battery I had the charging levels checked and they were spot on. The fact that its only in the morning could def lend towards connections.. Will investigate, that

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The fact that only happens in the morning points right at the altenator. In the morning when its cold there is a lot of extra energy needed to start the car (glow plugs and extra cranking) and if its dark and frost then you need to factor in lights and screen demisters. All this energy puts extra demand on the altenator so faults are more likely to be unvieled at this time. Give it 10 mins till your finished with blowers etc and the altenator can handle the reduced load hence the fault messages stop.
I would go for a second opinion on the health on the altenator.

That pretty clear information JT, thank you... I will def have it rechecked and re-post the results..

As above, most likely to be the alternator especially as the car has kindly informed you of an alternator fault. If not that it will be a connection or the underbonnet fuse box.

thanks for that datatek and i will be chasing up the JT, and your advice, come Monday.. In fairness though, and don't get me wrong here, but it also kindly informs me of a gearbox fault when none exists.. Thanks again..

rodntod.. Just so as you know i did the three turn trick this morning and it worked, thanks.. But as I'm sure you can guess I'm keen to get it sorted and so will let you know how it works out.. As I'm sure you will if anything happens..

Glad it worked for you Petie ,but like you i would rather find out what it is and get it fixed rather than work round it.Let's hope one of the geniuses on here will recognise the traits and point us in the right direction.

As JT has said it could be a loose connection. You'd be surprised how often that happens. Check battery terminals, check the cable crimps on both the pos and neg cables, check the alternator connections. Measure the alternator charging volts both at the battery and the alternator outs, a significant increase implicates the charging cable/terminals. Charging volts should be around 14.5 as far as I can recall. Check all the earth connections you can find. RAVE is a bit fiddly to use for this but valuable if you want to make sure you haven't missed any. Datatek mentioned the fusebox which should be checked periodically anyway as corroded terminals are a common failure.

petie said:

thanks for that datatek and i will be chasing up the JT, and your advice, come Monday.. In fairness though, and don't get me wrong here, but it also kindly informs me of a gearbox fault when none exists.. Thanks again..

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That message always appears when there is low voltage which is consistant with an alternator faullt

So I checked all the connections and then the voltages... 13.9 - 14.0 at both battery terminals and the back of the alternator.. From the information given here ( and thanks everyone ) that would appear to be too low and so the fault is now pointing directly at the alternator.. So I'll order one and see how it goes.. Thanks again and I will report back with progress..

petie said:

So I checked all the connections and then the voltages... 13.9 - 14.0 at both battery terminals and the back of the alternator.. From the information given here ( and thanks everyone ) that would appear to be too low and so the fault is now pointing directly at the alternator.. So I'll order one and see how it goes.. Thanks again and I will report back with progress..

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Or you could overhaul your existing one with a new diode pack, regulator and brushes

I'm liking it.. who would be the best supplier of a refurb kit..

I have already fitted an alternator from emmets,a new battery(the biggest one that fits in) as recommended on here ,and fitted a new earth lead between chassis and engine,which instantly brought my charge rate up to 14.3v+ at the battery at tickover.Still get the message if i start it on the first turn of the key though???
More curious as you have experienced petie ,why would starting it on the third turn of the key stop these warnings from coming up altogether???

It's magic i tell ye and not the good kind!!!

Bcem plug corrosion,need eka code that works.
Disconnect battery, clean plugs with electrical contact cleaner only and check all earths
as per rave and clean.

Is also another known issue

Oh dear, not too sure what to say to that but I have to do something.. Having said that it started perfectly this morning again - on the third turn - but thats freaky.. It would appear that my voltages are low anyway and so I will have to get that sorted and see how I get on from there... They do sound very similar mind and a little worrying... Sure 'ever onward' as they say and see what happens..