P38 DSE - Alternator error

Hello,

After about 5000km with a swaped engine (from a bmw 525tds), trouble free, my rangie show me it wasnt that ease..
(Kept all the "old" other parts: fuel injection pump, alternator, starter motor, turbo, flywheel, injectors...)

Idle, the revs are around 2000, 2300rpm...the rev gauge doesnt work, the injector light is on, on-board computer says "alternator fault" and all the suspension lights are on.
All of this happened suddenly.

First, a sensor from the fuel inection pump was replaced (its a re-builted one, under guarantee)...the symptoms remains..
Now my mechanic will swap the crankshaft sensor...

Any ideas?
..please...

Joao

jonasserra said:

Hello,

After about 5000km with a swaped engine (from a bmw 525tds), trouble free, my rangie show me it wasnt that ease..
(Kept all the "old" other parts: fuel injection pump, alternator, starter motor, turbo, flywheel, injectors...)

Idle, the revs are around 2000, 2300rpm...the rev gauge doesnt work, the injector light is on, on-board computer says "alternator fault" and all the suspension lights are on.
All of this happened suddenly.

First, a sensor from the fuel inection pump was replaced (its a re-builted one, under guarantee)...the symptoms remains..
Now my mechanic will swap the crankshaft sensor...

Any ideas?
..please...

Joao

Click to expand...

Yes your alternator has failed

Thanks John.

But, thats it?
The high revs at idle, the rev gauge dead....all of this at once...?
So, got to get a new alternator..?

thnks in advance...all advices are much welcome

Just talked with mechanic....its not the alternator..not from there..
(its charging..with around 13,9v)

The high rpm with idel engine (about 2000rpm when it should be 750rpm) is the big issue here..

If the alternator is okay, then you have alternator fault message caused by these normally in order first

1) dirty bcem plug- make sure you have EKA code and it works,discontent battery and clean only with contact cleaner or medical alcohol from chemists. DO NOT USE WD40

2) Broken Wire

3) Possibly FUSEBOX OR BCEM fault.

jonasserra said:

Just talked with mechanic....its not the alternator..not from there..
(its charging..with around 13,9v)

The high rpm with idel engine (about 2000rpm when it should be 750rpm) is the big issue here..

Click to expand...

If you removed pump top it will need sliding on it's slotted holes until RPM is 750. Unless you mark it's position and put it back in same place you alter fuel quantity, that is why it idles fast. You cannot just take it off and plonk it back on.

oh, forgot to mention....driving in low gear its hard (start driving the car from park, engage first gear and so on until a confortable speed, say around 50mile/h in fifth -about 2500rpm) ...have to use the cluntch or speed the car or else it seems the car will stall (lots of bumps), even with the high rev issue.

Will aks the mechanic if he removed the pump...and check the bcem plugs

Test-book detect fusebox or bcem malfunction?

i'm just guessing, (not based on real actual facts but what i've seen on mine) but i think the rev counter is significant.

Guess 1: the throttle electronic control is bust or connection probs. I know when i've got connector on mine wet rev counter didn't work.

Guess 2: ecu or conection fault. i reckon the rpm signal goes through it too, and that's where the idle speed setting must be stored. I could imagine some flash memory corruption in there causing this, might be corrected by resetting idle speed in testbook etc.

jonasserra said:

Just talked with mechanic....its not the alternator..not from there..
(its charging..with around 13,9v)

The high rpm with idel engine (about 2000rpm when it should be 750rpm) is the big issue here..

Click to expand...

13.9V is too low at the alternator.Should be 14.2 to 14.4 V

14.4 volts is the maximum charging rate of the alternator. You will only see anything like this just after startup when battery has been depleted by cranking. Or with headlamps turned on at around 2000 rpm. Anything above 13.8 volts in these circumstances is ok. The alternator does not constantly charge at 14.4 as many think, it depends on the battery voltage. Charging rate decreases as stored battery voltage increases. If it did charge at that rate all the time it would boil off the electrolite.

wammers said:

14.4 volts is the maximum charging rate of the alternator. You will only see anything like this just after startup when battery has been depleted by cranking. Or with headlamps turned on at around 2000 rpm. Anything above 13.8 volts in these circumstances is ok. The alternator does not constantly charge at 14.4 as many think, it depends on the battery voltage. Charging rate decreases as stored battery voltage increases. If it did charge at that rate all the time it would boil off the electrolite.

Click to expand...

Sorry Wammers, the output voltage of an alternator is fixed by the regulator at around 14.2 to 14.8 volts, they are not very accurate in my experience. The voltage of the battery will be down to around 12.2 volts or less immediatly after starting the engine, it is the potential difference between the alternator output and the battery voltage that governs the rate of charge. So straight after starting the charge rate in amps will be very high but the measured voltage will be below the maximum regulated output of the alternator, as the battery voltage recovers due to the charge, so the charge rate in amps will drop as the battery voltage approaches the alternator regulated output voltage thus reducing the potential difference between battery volts and alternator volts and the measured voltage will increase.

Datatek said:

Sorry Wammers, the output voltage of an alternator is fixed by the regulator at around 14.2 to 14.8 volts, they are not very accurate in my experience. The voltage of the battery will be down to around 12.2 volts or less immediatly after starting the engine, it is the potential difference between the alternator output and the battery voltage that governs the rate of charge. So straight after starting the charge rate in amps will be very high but the measured voltage will be below the maximum regulated output of the alternator, as the battery voltage recovers due to the charge, so the charge rate in amps will drop as the battery voltage approaches the alternator regulated output voltage thus reducing the potential difference between battery volts and alternator volts and the measured voltage will increase.

Click to expand...

You know more about electricary than i do Keith. But the fact still remains that when the battery is low you get a higher measured voltage across the terminals when the alternator is charging than you do when the battery is full. The regulator controls the maximum charge rate. It also measures the battery voltage and feeds the field coils to regulate alternator output voltage. The higher the voltage the higher the amperage. If you own a dual rate battery charger of say 10 amps max rating and measure the trickle voltage it will be around 13.5 volts. Switch to fast charge it will be around 14.75 volts. If you own a garage charger/starter of say 150 amps. As you turn the selector knob the voltage is increased the higher the voltage the higher the amperage. Think from memory the one i had went to 20 volts for fast charge. That would boil a battery in minutes and had a thermal cut out probe to switch it off if the electrolite got too hot.

wammers said:

You know more about electricary than i do Keith. But the fact still remains that when the battery is low you get a higher measured voltage across the terminals when the alternator is charging than you do when the battery is full. The regulator controls the maximum charge rate. It also measures the battery voltage and feeds the field coils to regulate alternator output voltage. The higher the voltage the higher the amperage. If you own a dual rate battery charger of say 10 amps max rating and measure the trickle voltage it will be around 13.5 volts. Switch to fast charge it will be around 14.75 volts. If you own a garage charger/starter of say 150 amps. As you turn the selector knob the voltage is increased the higher the voltage the higher the amperage. Think from memory the one i had went to 20 volts for fast charge. That would boil a battery in minutes and had a thermal cut out probe to switch it off if the electrolite got too hot.

Click to expand...

The regulator on the alternator is a simple constant voltage device unless they have changed out of all recognition since I used to repair them. It has no means of measuring the battery voltage, it simply tries to pull the battery voltage up to it's set voltage. A battery always has a lower voltage immediately after a heavy drain such as starting, giving a greater potential difference between the alternator and the battery which is why the current is higher. As the battery voltage rises, so the potential difference falls causing the charging current to also fall. You have effectively confirmed this yourself by pointing out that higher charge currents are produced by increasing the voltage set point on battery chargers. Ohms law covers it.
I need to add a bit to the above and make a small apology to Tony, I got my internal rsistances muddled, old age strikes again!
A totaly flat battery has a high internal resistance, so high that it may not take a charge from a normal charger, so in that situation, you would see full alternator voltage 14.2 to 14.8 volts at the battery, as the battery starts to accept a charge, the voltage will drop as the current rises. As the battery approaches full charge the voltage will rise to the alternator voltage.

Datatek said:

The regulator on the alternator is a simple constant voltage device unless they have changed out of all recognition since I used to repair them. It has no means of measuring the battery voltage, it simply tries to pull the battery voltage up to it's set voltage. A battery always has a lower voltage immediately after a heavy drain such as starting, giving a greater potential difference between the alternator and the battery which is why the current is higher. As the battery voltage rises, so the potential difference falls causing the charging current to also fall. You have effectively confirmed this yourself by pointing out that higher charge currents are produced by increasing the voltage set point on battery chargers. Ohms law covers it.
I need to add a bit to the above and make a small apology to Tony, I got my internal rsistances muddled, old age strikes again!
A totaly flat battery has a high internal resistance, so high that it may not take a charge from a normal charger, so in that situation, you would see full alternator voltage 14.2 to 14.8 volts at the battery, as the battery starts to accept a charge, the voltage will drop as the current rises. As the battery approaches full charge the voltage will rise to the alternator voltage.

Click to expand...

Well unless i am reading it wrong that is not how the volt regulator works. Of course there has to be some charge in the battery or the exiter windings cannot be energised. According to what i read the regulator measures the battery voltage and increases voltage to the coil windings to induct greater voltage and current (amps) output. When the battery voltage reaches it's preset value the regulator reduces the voltage to the coil windings reducing the voltage output of the alternator and therefore the current. In other words the regulator controls voltage between around 12.6 volts (Low amp trickle) to a maximum of 14.4 volts (high amp fast charge). There will always be a slightly higher alternator output shown on modern vehicles because of the number of systems that are fed directly from the generator. This i suppose is so the battery does not constantly deep cycle with the constant draw on it. Otherwise you would need a battery the size of a suitcase.

wammers said:

Well unless i am reading it wrong that is not how the volt regulator works. Of course there has to be some charge in the battery or the exiter windings cannot be energised. According to what i read the regulator measures the battery voltage and increases voltage to the coil windings to induct greater voltage and current (amps) output. When the battery voltage reaches it's preset value the regulator reduces the voltage to the coil windings reducing the voltage output of the alternator and therefore the current. In other words the regulator controls voltage between around 12.6 volts (Low amp trickle) to a maximum of 14.4 volts (high amp fast charge). There will always be a slightly higher alternator output shown on modern vehicles because of the number of systems that are fed directly from the generator. This i suppose is so the battery does not constantly deep cycle with the constant draw on it. Otherwise you would need a battery the size of a suitcase.

Click to expand...

Unless they have switched to smart regulators as used in the yachting business, automotive regulators have a fixed output limit of nominaly 14.2 volts. At low revs/high load the alternator will not produce enough power to reach 14.2 volts. You can run an alternator on the bench with no battery (assuming an exciter voltage) and it's output will limit at 14.2 volts nominal. It will maintain that voltage as the load is increased up until the point is reached where it is at maximum power, the voltage will then decrease if the load is increased further. This is not a function of the regulator but of the inablity of the alternator to produce more power.
On the smart regulators I used to install, there were 3 or 4 wires from the regulator to the battery, Pos & Neg power wires and a pair of voltage sensing wires, plus a thermocouple to sense battery temperature. The sense wires carried no current and provided the regulator with an accurate reading of battery voltage allowing the regulator to adjust the charge rate and compensate for volt drop in the current carying wires and also the drop across split charge diodes. This enabled maximum charging current to be maintained (subject to battery temperature) for long after an automotive regulator would, by virtue of it's fixed voltage, have limited it. It would then switch to float charge mode.
You may be more up to date than me, but I have never seen an automotive alternator with anything other than a not very accurate 14.2 volt fixed voltage regulator. I've googled a few makes and all the schematics I have found are fixed voltage.

You are absolutely right to say that the regulator controls the voltage to the armature windings to increase/decrease the current, but it is actually doing this to try to maintain it's internally set target voltage output of 14.2 volts. Nothing more complicated than that.

Lastly there are no systems fed directly from the alternator. The alternator and battery are in parallel. The battery acts as a smoothing device for the raw alternator output and compensates when the load is greater than the alternator output. Generally it is the alternator that provides the power to run everything except perhaps at idle with high load when there will be draw on the battery equal to the difference between the load and the alternator power output.

Wooohh....thats a master degree in alternators!!!!!

Well...the mechanic will fit a new crankshaft sensor today..
Will ask him to overhaull the alternator..
Meanwhile, bought a fuse box from ebay...

Theres a sensor in accelarator (throttel potenciometer) for the DSE? Or is just for the petrol ones?

jonasserra said:

Wooohh....thats a master degree in alternators!!!!!

Well...the mechanic will fit a new crankshaft sensor today..
Will ask him to overhaull the alternator..
Meanwhile, bought a fuse box from ebay...

Theres a sensor in accelarator (throttel potenciometer) for the DSE? Or is just for the petrol ones?

Click to expand...

Diesel is fly by wire. No throttle cable. The EDC ECU takes care of all that for you. Alternator will possibly just need new brushes regulator comes with these.

...not from the crankshaft sensor..

jonasserra said:

...not from the crankshaft sensor..

Click to expand...

Crank sensor tells ECU engine speed, that together with number four injector controls injection timing. The throttle pedal is attached to a potentiometer, position signals from this are recieved by EDC ECU and the fuelling is changed to match the desired RPM read from the crank sensor as indicated by position of the throttle sender potentiometer attached to the pedal. Throttling is achieved by adjusting the fuel quantity.

Mechanic is cheking the connections at the fuse-box...

I heard it could be also a faulty ECU...
So, things to check:
-Fuse-box
-ECU
-Bcem
-Trottle potentiometer

Could it be the flywheel?