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1995-2002 Range Rover P38A
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Discussion Starter #1
About 18 months ago I had a ‘Gearbox Fault’ message on my 1997 P38 4.6HSE (188,000km). Checked for fault codes with my Faultmate, but nothing. Continued driving for a few months with all seeming to be okay, then I got the same fault message, followed by rev counter, speedo and gauges all going to zero momentarily, ‘Fuse 17 Fault’ and ‘ABS Fault’. After checking through the forums I came across the suggestion (and TSB) to clean all earth points, which I did with great care and attention. Everything seemed fine for some time, until recently I got the ‘Gearbox Fault’ followed by the loss of gauges, speedo and rev counter plus blank message display.

This time I purchased some very expensive silver conductive grease which I lightly applied as I went through the entire cleaning and reconnecting process again, even down to making sure all connection were tightened to the specified torque. On the test drive everything seemed fine for about 10km, then gauges went to zero, no message display and so many fault alarms that I lost count. Spectacular! Obviously the conductive grease was increasing the resistance. Okay, go back and clean it all off, wash all connections with (no residue) contact cleaner and emery paper. Test drive and all seemed well for around 20km, then ‘Gearbox Fault’ and gauges to zero again.

I’d read a very interesting and helpful ‘sticky’ by ghind with a check list, which I did over the weekend. Here are the results:

1. Engine off, all accessories on for 30 seconds, then off. What voltage 12.46V
2. Voltage across battery at idle (no electrical load) 13.76V
3. Voltage across battery at 2000rpm (no electrical load) 13.85V
4. Voltage across battery at 2000rpm (everything electrical switched on) 13.32V
5. Voltage at ALTERNATOR at 2000rpm (everything switched on) 14.06V
6. Voltage drop between alternator body and battery negative (YES negative). Measure at max electrical load and 2000rpm 200mv (millivolts please)
7. Voltage drop between alternator positive and battery positive. 2000rpm, max electrical load 0.559V
8. Check Voltage drop from Battery Negative terminal to 1st groundpoint on vehicle 60.1mv
9. Check voltage drop from 1st ground point to block 1.8mv
10. Check voltage drop from Alternator Housing to block 3.3mv
11. Voltage from alternator positive to alternator housing 13.97V


It does look like there are issues with cables, which I intend to replace. The alternator also doesn’t appear to be outputting the correct charge rate. Does anyone have any other suggestions? One interesting point is that the alternator body bolts to the mounting bracket which is all part of the earth system, but there is no mention of cleaning any of these surfaces.

Although this is all rather annoying, I am getting some perverted enjoyment out of trying t get to the bottom of tis issue.

Thanks
paclx


 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

My sticky is wrong about the alternator voltage. Yours is fine

Get a 2 gauge battery cable from a battery shop and run it direct from alternator to battery. Your positive cable is very bad but your negative needs to be done too. Mine cost me in Australia $15each

I think I used 2 gauge but it may have been 4. Just get the biggest you can fit. No need for bigger than 2 gauge

Greg
 

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1995-2002 Range Rover P38A
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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

That's a good suggestion but looking at what is already there could isolate your voltage drop on the positive side. There is the connection on the back of the alternator. This then goes to the starter and is under the same terminal as the cable to the battery which is attached to the bolt on the battery terminal. So that's 3 connections and if any of them are dirty, that will give you the voltage drop. The bolt on my terminal came loose so my battery wasn't being charged despite the alternator working properly, the volts were just not getting to the battery (or the rest of the car!). Cleaned them all up and fitted serrated washers and the problem was cured.
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Mine used to occasionally display the gearbox fault message in the winter when there was a high electrical demand (lights, heater blower max, wipers , seat heaters)

Load tested the battery , it tested weak so I changed it.

No gearbox fault message since.
 

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Discussion Starter #5
Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Thank you all, especially ghind! I’ll change cables over the weekend. I’ve already ordered the negative set, but I’ll go and get some cable and make up a set from the alternator to the starter/battery. I’ll solder the lugs onto the cable as I really don’t trust crimping for the long term. That’s what I did with the wiring loom to the ABS booster that got fried. Don’t ask!

Any thoughts on cleaning the matting surfaces of the alternator where it fits the mounting plate? They are all negative connections after all.
paclx
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Gilberttd's suggestion of cleaning all the existing connections is a very good one. I did this and I should have suggested you did too.

However, even if you do that, the battery charging will still be marginal.

In a vehicle application, 13.8 volts will never, in practice, fully charge a lead acid battery. Sure if you ran the engine for 24 hours or longer non stop then you might come close to 100% but who does that? A proper battery charger will typically hold the battery at 14.4 volts until the battery is charged and then pull back to a lesser voltage to hold it on float. 13.8 volts is good for float charging not full charging.

When your alternator only puts out 14.0 volts, and then you lose 120mv in the negative wires and 120mv on the positive wires, you end up with about 13.7 volts at your battery. This is a best case scenario for a p38. Your battery will NEVER fully charge in the real world.

Unfortunately, as we've all seen, with all these connections in the way, even if only a small amount of corrosion or oxidization builds up on each, we end up with really low charging voltage.

Per WayneB's suggestion, you could replace the battery and the car will be OK for a while. However, the reason the battery is weak is almost certainly because it isn't being charged properly. I've personally replaced two batteries in my own RR that were only 1 year old until I figured out it was the charging system that was the culprit. Then for a year I cheated and charged the battery once per month with a good 7 stage charger because it was easier than fixing it properly.

I would (and in mine have) run additional cable from the alternator direct to the battery. At least then your battery is getting decent charge. Also, your fuse box will then have two supply paths and get less voltage drop.

From memory, now I get about 26mv voltage drop in each of my positive and negative cables. In other words, even under load, I lose 0.05 volt total from my alternator to battery. My battery charges properly, has lasted many years and no more running problems.

I'm not so sure about soldering. This creates a hard point in the cable where it is likely to fracture. They are crimped from the factory for a reason. Either use the proper crimpers for the job or buy premade cables from a battery shop. I tidied up the existing wiring and then ran direct from alternator to battery. You could remove the existing cables and put bigger ones in but due to the low alternator charging voltage, I would suggest a clean direct run and tidy up/leave the factory wiring with all its stops in place. That solution is cheap, easy and very fast.
 

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Discussion Starter #7
Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Greg, are you recommending disconnecting the old cable from the alternator to the starter, and running a bigger cable direct from the alternator to the battery? I just want to be clear. The existing cable from the alternator to the starter is tiny in comparison to the one from the battery to the starter. I've got hold of some heavy duty 35mm2 welding cable, I think that's 2AWG. I replaced the cable from the battery to the alternator, then managed to fracture the small PVC coolant tube, which has obviously got very brittle over the years. So it's all stop till I get the new tube.
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Hi,

I had the same issue with mine, instrument panel would behave like it was possessed and then bam car just died during driving on the motorway. ADAC guy gave the alternator a thump with a rubber hammer and a quick battery charge and we got home. Was painfully clear that the battery wasn't getting enough charge. Changed the alternator for a new one and things got better.

Unfortunately for me this was only part of the issue as I am back to gearbox fault and issues electrical on going now after a couple of months. Battery is only 11.9V so its on charge at the moment but I think its been ruined from the poor alternator I had, and I have charged it up from flat more times than I should already.

I am in the process of looking for all earth points so I can check each, as you have done this recently would you mine just listing them all?

thanks

/scuba
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

It might be worth pointing out that unless your multimeter cost about as much as your Range Rover and is calibrated every year, you should disregard the 0.01V digit and take the 0.1V digit with a pinch of salt...
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Hi could someone point out the connection at the alternator that I would connect the 2 gauge too. Is it the connection closest to the lens?

Cheers

Tony
 

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Discussion Starter #12
Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

It's the one with the big red wire.
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Jos, is this your extra cable to the battery? Where did you route it?
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Hi

Yes this is an extra cable that goes straight to the battery terminal passing under the alternator.
This makes sure there is direct connection from the alternator towards the battery and is connected parallel to the original one that first goes to the starter motor.

If I think about it I can snap photo tomorrow when its light again and upload it.

Regards

Jos
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

Hi

Some extra photos








As you see I installed 2 extra wires from positive and negative sides of the battery direct to the alternator.

In case you wonder what the extra wires under the fusebox are, these are to external relays for the blowers to avoid the fusebox being overloaded at the relays.

Regards

Jos
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

It looks like you took the cable under the front of the alternator, over that metal cover that holds another loom in place. Right? That's how I broke the coolant pipe from the expansion tank the throttle housing, buy using cable ties and over tightening the, plus the pipe was old and brittle. Did you remove/cut the original cable from the alternator to the starter? Can't really see any point in keeping it. Mine is a lot smaller the the new one.
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

I made up a cable like this for a GEMS vehicle yesterday as there was excessive voltage drop between alternator +ve and battery +ve.

I routed it behind the alternator (so it's away from the moving parts), around the front of the rocker cover and then up next to the rest of the engine loom.
Held it in place with a couple of cable ties.

Before... charging voltage at idle was 13.8v, and about 130mv measured between alternator +ve and battery +ve
After... charging voltage at idle was 14.1v, and about 58mv measured between alternator +ve and battery +ve

I was amazed at how much difference it made.. The -ve cables all tested fine when we ran the electrical sticky on it previously and diagnosed the +ve cable as being the culprit.

Marty
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

I was concerned about the heat if I routed the cable between the rocker cover and alternator, though I also had concerns about moving parts. Hence routing the cable in front of the alternator, securing with cable ties and snapping the coolant hose to the throttle housing in the process.
 

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Re: Electrical Troubleshooting (Earth) Again - '97 P38 4.6 HSE

I ran this one inside a piece of plastic heat shield, the same stuff that the original wiring runs through - partly for heat and partly for vibration reasons, so the wire won't get damaged.

I don't think it ultimately matters which way you run it - as long as it's secure! It's not really something you want arcing out everywhere!
 
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