Technical Alternator only starts generating after revving

[nigelvan]

Hi guys,

My 3.0 2007 X250 has a new annoying issue. I noticed when starting the engine the rpm would slowly rise to about 1100rpm, normal would be around 800. I thought the bad earth/ground issue I had before was back so I checked the voltages. Turns out the alternator is not producing any electricity whenever I start the vehicle. I need to hit the accelerator and rev the engine a bit (or start driving) and then it kicks in, producing a steady 14V, after that the rpm will slowly fall to 800 rpm again. I know from previous issues that the ECU will rise the idle rpm if the battery voltage is too low.
Anybody knows what would be causing this? Something similar did happen before a few months ago, when I was waiting in a queue, when the engine started idling higher again and there was a weird noise coming from the alternator or at least around it. Stopping the engine and restarting it fixed it, it happened only 2 times in a row and never came back, until now where every time I start the engine I have to rev it to get the alternator to kick in.
Does an alternator have a clutch of some sort? I checked the belt and the tensioner a while back and it seemed fine. However I already bought a new one and plan to replace it in the next coming months. However I don't think this problem is due to the belt...

 

[bugsymike]

May be irrelevant , but two things most modern alternators have a free wheeling clutch pulley, so a special tool is required to remove the pulley.
The other thing is recently my Citroen alternator packed up and it turns out the small field wire terminal actually via the ECU controls the alternator output to match other conditions, such as engine loading through aircon or steering etc. but also reduces output from alternator when accelerating to reduce power lost in charging battery when overtaking for instance.
So your issue could be a duff alternator, the ECU or the wiring in between.
It maybe a good Auto Electrician can test the output using a specialist bit of kit.

 

[mikefitz406]

Add or replace the earth strap from gearbox casing to chassis. You can see is just under the air filter housing. Adding an additional to suitable points is easier than trying to remove the original.
You may have an alternator or drive belt issue but the earth strap going high resistance is very common. The symptoms are intermittent high idle speed and sometimes starting problems. All 250/290 vehicles will suffer from this after a few years.

Mike

 

[Communicator]

With a previous generation of vehicles, I would have suspected a faulty alternator warning bulb, or an overloaded D+ node. There is also the possibility of a broken connection to the D+. This latter possibility could be still apply as nigelvan has not mentioned the battery/charge warning light.

There is a recent long thread here relating to an incompatible pattern alternator. If I have understood correctly with the x250 the alternator is controlled by the BCM, which needs to have its output pulled low when the ignition is switched on. Perhaps @koalar would like to join this discussion?

Somtime perhaps I will be able to study the linked thread in detail, as it seems to contain useful info.

 

[nigelvan]

Add or replace the earth strap from gearbox casing to chassis. You can see is just under the air filter housing. Adding an additional to suitable points is easier than trying to remove the original.
You may have an alternator or drive belt issue but the earth strap going high resistance is very common. The symptoms are intermittent high idle speed and sometimes starting problems. All 250/290 vehicles will suffer from this after a few years.

Mike

Thanks Mike, but as I said in my post, I had this issue before and checked and it is not a bad earth issue. I have checked and cleaned my two additional earth connections. There's also no voltage drop between chassis and engine block, as was the case before I added the extra cabling.
I verified the voltage between + terminal and engine block, it sits around 12.6 after starting, after hitting the accelerator pedal once it jumps right to 14V, same on chassis. And then the idle drops to normal rpm

 

[nigelvan]

With a previous generation of vehicles, I would have suspected a faulty alternator warning bulb, or an overloaded D+ node. There is also the possibility of a broken connection to the D+. This latter possibility could be still apply as nigelvan has not mentioned the battery/charge warning light.

There is a recent long thread here relating to an incompatible pattern alternator. If I have understood correctly with the x250 the alternator is controlled by the BCM, which needs to have its output pulled low when the ignition is switched on. Perhaps @koalar would like to join this discussion?

Somtime perhaps I will be able to study the linked thread in detail, as it seems to contain useful info.

Thanks! Correct, there's no battery/charging light now as was the case when I had a bad earth strap. I'll check the link in your message, thanks!

 

[nigelvan]

May be irrelevant , but two things most modern alternators have a free wheeling clutch pulley, so a special tool is required to remove the pulley.
The other thing is recently my Citroen alternator packed up and it turns out the small field wire terminal actually via the ECU controls the alternator output to match other conditions, such as engine loading through aircon or steering etc. but also reduces output from alternator when accelerating to reduce power lost in charging battery when overtaking for instance.
So your issue could be a duff alternator, the ECU or the wiring in between.
It maybe a good Auto Electrician can test the output using a specialist bit of kit.

That sounds like a smart alternator, but afaik the 2007 x250 doesn't have one, just an old 'dumb' one. But a faulty clutch pulley does fit the description, if it has one...

 

[koalar]

Right I start by saying i don't own one or worked on one or have a readable circuit diagram


Let start with what we do know


In a standard Ducato the alternator works the same as in any other Fiat


1/The body computer receives a ground signal from the alternator at ignition on

Without out it, the body computer recognises the broken D+ wire or faulty altinator and leaves the warning light on, it also disables the electric power steering to (conserve power (at least on other models))

Seeing as the light isn't on, it's highly likely the D+ cable is okay

2/The next thing that happen is. As you crank an excitation current is sent via the D+ to start the charging. There are no permanent magnets. Without this the alternator will not charge until the revs are raised

This is a possibility, check D+ voltage as you crank.

3/ once the ECU see above 750 Rpm the excitation current is switched off and the body computer moitors the voltage, anything below 12V and it puts the warning light on,

Often overlooked is the red cable that goes between the alternator and starter, it's not unknown for one end come loose

 

[bugsymike]

May not be relevant, but an Auto electrician once told be whilst an alternator may work with warning light bulb blown eventually it damages the alternator. Though how that is affected by computer controlled systems and digital dashboards etc. I don't know.

 

[koalar]

May not be relevant, but an Auto electrician once told be whilst an alternator may work with warning light bulb blown eventually it damages the alternator. Though how that is affected by computer controlled systems and digital dashboards etc. I don't know.

Not relevant any more

The dash Led is purely switched on and off by the body computer via a network signal

 

[nigelvan]

Right I start by saying i don't own one or worked on one or have a readable circuit diagram


Let start with what we do know


In a standard Ducato the alternator works the same as in any other Fiat


1/The body computer receives a ground signal from the alternator at ignition on

Without out it, the body computer recognises the broken D+ wire or faulty altinator and leaves the warning light on, it also disables the electric power steering to (conserve power (at least on other models))

Seeing as the light isn't on, it's highly likely the D+ cable is okay

2/The next thing that happen is. As you crank an excitation current is sent via the D+ to start the charging. There are no permanent magnets. Without this the alternator will not charge until the revs are raised

This is a possibility, check D+ voltage as you crank.

3/ once the ECU see above 750 Rpm the excitation current is switched off and the body computer moitors the voltage, anything below 12V and it puts the warning light on,

Often overlooked is the red cable that goes between the alternator and starter, it's not unknown for one end come loose

Hi Koalar,

Thanks for your input. I'll have to check where to get the D+ signal. I installed an intelligent DC-DC charger to charge my Lifepo4 battery 2 years ago and I remember getting to D+ was quite hard, hence the charger runs in voltage sensing mode. I'll check the eLearn CD of the Ducato to see if I can get to it somewhere without crawling under the vehicle.
Without the initial voltage to excite the coils I would think the alternator wouldn't be able to generator any power at all, even at higher revs.
I think if I leave the vehicle to idle (without 'kickstarting' the alternator) the battery light would eventually come on.

 

[koalar]

Every fiat I have seen has a coupling within the D+

Possibly a yellow/red alternator side and brown/green at body computer side of the D004 connector near/under the fuse box


But I have no idea what year car circuits diagram I have found

 

[Kahcorp]

I have just had the exact same thing as per your post on a 2010 3.0lt Ducato. The voltage was not consistent day to day but to my experience not an alternator problem.
As you did I fitted extra earth with no change. I changed one at a time the alternator cables thinking maybe a cable fault with no luck.
Finally got hold of a 2008 alternator & swapped them out. Note both 2008 & 2010 did not have a clutch pulley.
The 2nd hand 08 alternator fixed the problem.
I then had an auto electrician put the alternator on a test bench and he found that "end play within the unit was giving a low voltage but only sometimes."
I do not know as yet what this "end play" is as there is next to no end play measured at pulley shaft.
As I said this has just happened to me so I have not had time as yet to look into the old, (2010) alternator, first thing I will do is fit a new regulator & test.
Removing
The alternator will come out the bottom without removing axle or anything else. Remove rear cover of Alternator while in place as you will need every millimetre to get it out.

New alternator in Australia $660.

 

[Communicator]

I have the attached drawing for x250, provided by another and downloaded from the forum. Quality is not good but may be readable? You are looking for pin 2 of connector D004 which may be larger than 2ways. Wire colour is?????

It may help.

 

[koalar]

I have the attached drawing for x250, provided by another and downloaded from the forum. Quality is not good but may be readable? You are looking for pin 2 of connector D004 which may be larger than 2ways. Wire colour is?????

It may help.

Pin 2

Different colours either side the connector brown/green and yellow/red

 

[nigelvan]

@koalar @Communicator Thanks for helping me with the diagrams and help me locate the D+. I'll get back at this thread once I measure the voltage. I never accessed the BCM so I need to plan in some time to find it, as we are on the road right now with this van in France...
If I understand correctly what I've found out about the wiring of this alternator, D+ is both used to supply the exciter current and measure the voltage the alternator is maintaining once the engine is started, right?

 

[vexorg]

Not relevant any more

The dash Led is purely switched on and off by the body computer via a network signal

The power through the bulb to kick start the alternator power was such an elegant solution, how is the initial power fed on (not-so) smart modern cars/vans?

 

[nigelvan]

The power through the bulb to kick start the alternator power was such an elegant solution, how is the initial power fed on (not-so) smart modern cars/vans?

Well according to the diagrams it's the BCM that powers the D+ and afterwards uses the same pin to measure the voltage, if I understood correctly.

 

[bugsymike]

The power through the bulb to kick start the alternator power was such an elegant solution, how is the initial power fed on (not-so) smart modern cars/vans?

As I mentioned towards the beginning of the thread from recent experience with a 2012 C3 Picasso alternator, on later units the control box inside (that originally was just a form of diode pack to give DC voltage) the alternator takes a signal from the ECU/BCM and depending on load required can increase or reduce the output from the alternator, if this is the case on yours then the voltage on the little wire may not be 12volts, but a lower signal voltage and that is why my auto elcetrician had to use a special bit of equipment to tell the Alternator what output to generate when he had it running on his test bench, whereas in the past he used a primitive loading system of headlamps etc. to measure the output.

 

[koalar]

Well according to the diagrams it's the BCM that powers the D+ and afterwards uses the same pin to measure the voltage, if I understood correctly.

Correct for the diesel

The petrol is wired completely different