P38A Voltage drop

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5

5amw1se

Member
Posts
22
Location
Somerset
Hi all,

Yes, it is another of those electrical posts...

Pulled the RF antenna last week as I was suffering battery drain since we got a new wifi router at home. Also gave my battery a good overnight charge and gave it a test, which gave it the all clear (90 percent health). It is a 920CCA and 1050AH battery so it should have plenty of oomph even for this tractor.

As a precaution, I check the drain (which is now as it should be, BECM going to sleep as it should, always-on LPG ECM drawing negligible current) as well as the alternator voltage etc. Had no glamorous assistant so only been able to get the readings at idle so far, but even the results of that are quite telling.

Alternator is kicking out between 14.28-14.36 at idle, which seems fine. However, only 13.83-13.93 of that is reaching the battery.

The voltage drop between the alternator body and the battery negative is 50mv, so well within tolerances. However, I detected a 0.43v drop between the alternator positive and battery positive. Am I right in thinking I need to clean the positive terminals at alternator and starter motor, then replace the cables if that doesn't fix it?

All the best,

Sam
 
If it hasn't already been fitted, then fit a lead directly from the alternator output to the battery positive, leaving the connection to the starter in place. It seems some trucks had this done as a dealer mod, some ex factory and some not at all.
 
Thanks gents, always good to have your suspicions backed up.
Is there actually any need for the positive feed to go to the alternator en route to the battery? In other words, if cleaning the contacts doesn't improve things (flagging a dodgy cable) would there be any point replacing the one from alternator to starter, or just add the direct one?
 
The plot thickens... went out to clean the positive terminals up, thought I would turn it over to test, and lo and behold it was dead again. A fully charged battery drained to the point where it would only turn over once (not enough to fire), then gave the "gearbox failure" error, in just over 24 hours.

So it isn't the rf problem (at least it isn't now).

Around the same time the problem started, I had to call the RAC out because an inaccessible coolant hose had come off while I was out and about, ****ing coolant out and causing overheat. The RAC guy managed to get the hose back on, filled up and tested the block, but in the process I reckon either coolant has got in somewhere or he has dislodged something else. Any ideas?
 
5amw1se said:
The plot thickens... went out to clean the positive terminals up, thought I would turn it over to test, and lo and behold it was dead again. A fully charged battery drained to the point where it would only turn over once (not enough to fire), then gave the "gearbox failure" error, in just over 24 hours.

So it isn't the rf problem (at least it isn't now).

Around the same time the problem started, I had to call the RAC out because an inaccessible coolant hose had come off while I was out and about, ****ing coolant out and causing overheat. The RAC guy managed to get the hose back on, filled up and tested the block, but in the process I reckon either coolant has got in somewhere or he has dislodged something else. Any ideas?
Click to expand...

Which wire did you unplug on RF receiver? If signal is strong enough it may still get through. My interference was from a wireless weather station. WiFi unlikely.

Always on LPG sounds a bit odd although I know nothing about LPG. @Saint.V8 is more knowledgeable.

Has it got an aftermarket stereo fitted? Switched and permanent 12V the right way round? Or does it have wipers on the headlights and are they parked?
 
The engine tested out ok and doesn't seem to have suffered, I was able to switch off within minutes so no apparent damage.

I am going to get a decent ammeter today as my multimeter doesn't seem up to the task of tracking down this issue, will update once I have accurate figures.

The front windscreen wipers will not park amd operate at normal speed even when set to intermittent. When the battery is low and the gearbox fault shows, the wiper will not switch off at all and I have to pull the relay. Could it be a faulty relay and/or wiper park sensor causing the drain?
 
It does have an aftermarket stereo, but this drain issue has only just started the past couple of weeks. Have pulled the removable face off the stereo to see if that makes a difference, but no luck so far. And it was the blue wire I pulled
 
OK now even more confused. Removed the battery to charge and it is still reading as 12.7v, but the tester is now showing State of Health as 0%-replace. It tested at 88% SoH yesterday?!?!

So it appears the battery might be duff. But I will try to charge it again so I can do a draw test and establish if there is an ongoing underlying problem that would quickly knacker a new battery.
 
5amw1se said:
The plot thickens... went out to clean the positive terminals up, thought I would turn it over to test, and lo and behold it was dead again. A fully charged battery drained to the point where it would only turn over once (not enough to fire), then gave the "gearbox failure" error, in just over 24 hours.

So it isn't the rf problem (at least it isn't now).

Around the same time the problem started, I had to call the RAC out because an inaccessible coolant hose had come off while I was out and about, ****ing coolant out and causing overheat. The RAC guy managed to get the hose back on, filled up and tested the block, but in the process I reckon either coolant has got in somewhere or he has dislodged something else. Any ideas?
Click to expand...

Has the battery been tested under load, for dead or dying cells ?
 
No got a proper load tester, just one of the electronic ones. It isn't flagging any bad cells, but it seems it may be sulphated. Regardless, it should have enough life left to run a few tests on the draw
 
wifi 2.4 GhZ and key fob 433 Mhz are completely different frequencies, so no issues there, although there a plenty of other devices that can use 433mhz.

If you have wiper issues then that cd be causing your problem. A BeCM awake will draw about 2/3 of an amp IIRC - when asleep it should 30-40mA. So if your BeCM doesn't sleep (cos your wipers aren't parked ) then your +/- 100AH will drain in a week or so. Once the battery is left in that state even for just a few days it will start deteriorating, but if you trickle charge it from time to time, a V8 should not care.
I have no excessive drain on mine, but if I know I will leave the car standing for a week I disconnect the battery negative, just to protect the battery.
 
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@5amw1se @RisforRacingnotReverse just went through something similar. Battery tested on a digital tester at 2/3rd of its original capacity but was shot. The new mf31-1000 by hankook has put an end to that problem. It turns over really fast and does not get the chance to do full stroke before it fires into life. We also had the green pins to deal with on the white plugs behind the passenger kick panel under the dash. If you've not been there, take a look. ;)
 
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OK so I have discovered that the problem is not the battery (although the problem may have knackered the battery). I tested the current across the battery with the engine off, and it blew the 10amp fuse (twice). Something is drawing an awful lot of current when it shouldn't.

Upon further investigation I found the driver's side footwell was sopping wet. I am hoping it is from a door seal that had come away (now fixed) but will have to wait and see on that. No sign of water anywhere else...

Have disconnected the battery for now to stop it getting immediately drained again, and set up a heater and dehumidifier in the cabin to try to dry it out.

Once everything is dry I will take a look at the becm connectors to see if there is any obvious damage. I can only imagine the water is causing a short somewhere and keeping a circuit active (not the wipers as I have pulled the relay for that, must be a separate issue).

Anyone had similar flooding and can offer advice on where else it could be coming from? Or what sort of damage to check for?
 
I also recently had a wet driver's side floor, and water in the sill channel, where the wiring goes down the RHS of the vehicle. I fiddled with a seal, but other than that, I am generally mystified, other than sometime during the summer the a/c drain came free, and may have been a source at one point... so , I'm also interested to see what folks come up with....
 
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