1.9TD engine management timing

[MikeT]

I'm very interesting to learn how the ECU on my car operates - mainly to identify what's involved with the timing but it'll probably better if I get to know all the in's and out's of it. Is there such data available?

[CitroJim]

Mike,

Ive done a few posts in the past describing exactly how it works. A search amongst all my random amblings will be very tedious though...

Fundamentally, all the ECU does is control pump timing via the timing electrovale which varies the hydraulic presure applied to one side of the timing actuator.

The ECU does not control any aspect of fuelling. That's all mechanical.

The ECU contains a number of maps that contain timing values for various conditions the engine is working under. There is, for instance, a cold map, a light load map, a heavy load map and so on.

The ECU measures the set timinmg by comparing the time delay between the needle lift sensor and TDC sensor and adjusts until the measured value is the same as the ECU set value.

The ECU looks after driving the tacho and controls glowplug post-heat.

There's a lot more to it than that but that's the basic operation of the ECU. Ask if you want much more detail.

[MikeT]

Hi Jim, Sorry if I gave the impression I hadn't bothered searching as yes, I do want more detail if you have it, I'd be most grateful. Pretty please?
It's obvious to me I don't have the right wiring diagrams in my Haynes BoL so that's my first request please.
Additionally, the maps you refer to, do you have them in printed form, like in a table or similar? If not, any idea what the timing ranges are (for all the maps)?
If you do have those, would you also have the same for a non-turbo, for me to compare any differences at full load?
Again, apologies to ask so much, I know how busy you are - I'll make it up to you when I come up for a matrix change, ok?
I'm thinking after we've completed our individual projects would be a good time.

[CitroJim]

Hi Mike,

No worries at all

I found a thread here that may be of interest to you. It was the one I was looking for originally.

I can let you have a wiring diagram specific to your car. Remind me of your RP number again.

Sadly, I have no ECU maps and no way of getting hold of them. Not even the mighty Lexia reveals that kind of information

I've no detail either on remapping the ECU. Easier perhaps would be to knock-up a box of tricks to artificially change the time delays between the TDC and Needle Lift signals to "fool" the ECU into setting a different timing value. I'd not like to comment on how much difference this might make to performance. Methinks not a lot.

Diesels are a bit different to petrols as the timing is essentially a function of the ignition delay value of the fuel being used and the fuel has to be injected precisely at the right time with nothing except increased noise, to be gained by tring to inject earlier. There may be value in slight alterations to the maps if you're ruunning exclusively veg as the ignition delay value of veg may be a tad different but in conclusion, having studied the subject a bit, I'm happy to believe that Bosch and PSA have pretty much an optimum set of maps in the ECU amd little or nothing will be gained from playing with them. You'd be better off transplanting a mechanical Bosch VP20and playing with that. You can then set the static timing to where you wish and also, if you play with the timing piston pre-load spring rate, you can change the advance curve of the pump.

The non-turbo engine used the Lucas pump as a rule and apart from the EPIC, which was only seen on the 2.1TD, they were always fully mechanical, both in fuelling and timing. Paradoxically, a Lucas allows far more timing experiments to be easily carried out than a Bosch but the downside is, you're limited to diesel as a fuel.

[MikeT]

The diagrams will be most helpful, yes please Jim. I'm surprised the Lexia doesn't reveal the advancing/retarding live data, I would have thought it necessary. What about lift sensor live data? I assume the ECU gets engine speed from the crank sensor (I've neither looked for nor seen one)?

I was told there's a box of tricks that does intercept the timing signal and "adjust" it on the fly, (like you refer to in the old thread). This has created the questions about my car's timing range. I also learnt that some petrol turbo ECU's will retard the timing at full boost and again, I wonder if diesels do. Another reason for my inquiry - again as you refer, different fuels can create different delays as can other conditions, so it could prove very useful being able to adjust it.

As you may know, I'm up for doing a bit of tuning on these cars and looking to make improvements over stock timing when the car is operating beyond it's stock power, if that makes sense?

RP:07859 CJ 1 0018

[CitroJim]

I'm surprised the Lexia doesn't reveal the advancing/retarding live data, I would have thought it necessary. What about lift sensor live data? I assume the ECU gets engine speed from the crank sensor (I've neither looked for nor seen one)?

The Lexia does indeed give live timing data Mike. It presents it as two figures: the first being what the ECU desires and the second, what the pump is giving. Those two figures should be identical and it's a test that the pump and sensors are working correctly to enable the pump timing to follow that set by the ECU.

You could map the ECU by observing the Lexia display whilst driving under all conditions.

Live needle lift data is simply given as a mean voltage and is around 0.9V whereas the TDC sensor measures engine RPM. The sensor itself is mounted on top of the gearbox bellhousing and reads a toothed ring on the flywheel. It has a brown connector.

Petrol egines retard at full boost to obviate detonation (or "pinking") which can be very destructive. Diesels don't need to worry about detonation as they rely on detonation to run in the first place In any case, the ECU does not sense boost pressure; that's done in the pump and the LDA simply ups the maximum fuel delivery on boost.

Ignition delay is primarily a function of the fuel but changes both with temperature and barometric pressure. That's why a diesel needs the timing to be significantly advanced when cold to help it start easily. The ECU takes this into consideration by reading coolant temperature and barometric pressure. The Lucas EPIC takes this one step further and measure fuel temperature as well, as does I believe, the HDi. The ECU runs a "cold" map under such conditions. The map selection is also determined by the engine load via the pot on top of the throttle lever. Under light running, a map will be chosen that again advances the timing as it takes longer to ignite lower injection volumes as will happen with the engine on the over-run - just like the function of vacuum advance on a petrol engine.

I'll get the diagram scanned up for you Mike...

[MikeT]

The Lexia does indeed give live timing data Mike. It presents it as two figures: the first being what the ECU desires and the second, what the pump is giving. Those two figures should be identical and it's a test that the pump and sensors are working correctly to enable the pump timing to follow that set by the ECU.

You could map the ECU by observing the Lexia display whilst driving under all conditions.

It might be possible that I'll only need to know the range otherwise.... I'll take that option

....The ECU takes this into consideration by reading coolant temperature and barometric pressure.......

Is this sensor in the ECU box?

.....it takes longer to ignite lower injection volumes

I wasn't aware of this, interesting. Can I read more on this somewhere?

I'll get the diagram scanned up for you Mike...

Superb, you're a star Jim.

[CitroJim]

Hi Mike,

Here's the diagrams..

MK2 XUD9 Injection Circuit

MK2 XUD9 Injection harnesses

MK2 XUD9 Injection Component Locations

These are the diagrams specific to RP7668 onward and for the Aircon variant.

The barometric pressure sensor is located on the side of the ECU. It looks like a raised vent.

[CitroJim]

Mike,

If you really want to get to grips with diesel combustion theory, may I recommend a rather weighty tome entitled "The Diesel Engine Reference Book"

It's weighty both in size and content, especially the maths and chemical equations, but contains enough information to design a diesel engine for anything from a lawn mower to a cargo ship

[MikeT]

Here's the diagrams..
These are the diagrams specific to RP7668 onward and for the Aircon variant.

Thanks muchly, they're printed off and stored on file for future reference.

A few things not clear from Haynes diags, perhaps you know.... which of the outputs are from which key stage on the Ignition Switch Component CA00?