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Caterham

Member Since: 06 Nov 2008
Location: Birmingham
Posts: 6276

2011 Defender 110 Puma 2.4 XS CSW Stornoway Grey

the good old manual choke...

I believe I'm not the only one to have suggested the engine seems to run smoother while cold and then once was the diesel know becomes more obvious.....

got me thinking - as we are now in an age of low emmissions etc could it be that while the engine is cold its fueled with a rich mix (like with the good old choke of petrol engines in an era gone by) and once warm the mixture is soo lean that it causes what sounds like 'pinking' / knocking noise all in the quest to reduce emmissions.

so do the remaps we hear about where customers talk about 'it should have left the factory like this' a simple adjustment on the fuel mix plus a bit more in terms of additional perfomance..... (I use the word 'simple' very very losely and no offence intended).

this is by no means a way of rubbishing the remaps because if the engine run better but uses a little more fuel I'm all for it. If driven right I believe an engine running well will be more economical than one that has had its fuel starved to within an inch of stalling.

1st Dec 2013 12:27pm

Lorryman100

Member Since: 01 Oct 2010
Location: Here
Posts: 2686

First of all you need to understand the injection process in that each injector solenoid is controlled separately by the ECM (which is why the 16 digit hex codes on top of each individual injector are important for the relearn procedure), which provides an earth path to open the injector nozzle at the correct time and for a calculated period to provide a metered injection of fuel into the cylinder. The ECM uses signals from other sensors (MAF, MAP/T, CHT, CMP, CKP etc) and a pre programmed fuelling strategy to ensure that the precise amount of fuel is injected at the correct timing for maximum fuel efficiency and minimum emissions. Also the injectors are opened by way of a solenoid on top of each injector, the EMS applies current in three stages, 18 amps, 8 amps and 4 amps so at the beginning of the injection process, the solenoid valve is actuated with a higher pick-up current so that it opens quickly (ps as these values are known they can help you diagnose an immobilizer fault). After a short period of time, the pick-up current is reduced to a low holding current. So when the engine is cold ( the EMS knows the head temp through the CHT sensor) more fuel is used to help start the engine and then keep it running ( EMS keeps injector solenoid open longer which gives more fuel into the burn) until the CHT starts to rise then the EMS reduces the solenoid opening times reducing the amount of fuel being injected into the cylinder. These values are stored within mapping strategy files within the EMS.
So in effect if the EMS is receiving false information from a faulty sensor in that the values received don't match up to stored values of that sensor compared to other sensors values for a know set of parameters then it will cause an issue, whether that is to log a DTC, put the Puma into limp mode or to compensate for the wrong information by upping the fuel delivered to the cylinder as you get with a faulty MAF.

HTH

1st Dec 2013 1:11pm

Caterham

Member Since: 06 Nov 2008
Location: Birmingham
Posts: 6276

Lm100

Always most helpful.

Kind of what I thought however but I could never have put it together with so much detail.

Presumably if the map was faulty it could lead to under fuelling in the same way a faulty MAF could result in over fuelling?

1st Dec 2013 2:12pm

zone30

Member Since: 07 Sep 2012
Location: Gent
Posts: 669

2011 Defender 110 Puma 2.4 X-Tech LE Nara Bronze

As I understand it:

The crankshaft is connected to the camshaft(s) by a belt. This determines the timing of the opening and closing of the valves.
Today the can electronically monitor these shafts and change it bit to be mire efficient.
So having a manual choke is rendered useless.

A diesel needs air to breath. The more air the better is runs, hence why people with raised aur intakes mention a loss of a bit of power somethimes. Cold contracts material, also air, so this means more air is goung to the engine within the same volume. So when cold, yes your engine runs more exficient.

1st Dec 2013 2:53pm

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