Jaguar S-Type 2.7D with hesitation at idle

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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby aux_r » Tue Jul 09, 2013 5:40 pm

Valhalla wrote:Remembering, of course, that the first rule of Diesel injection HP pump design is to drive it at a ratio that does not match the camshaft or crankshaft, for the very reason your example shows above!


Sorry, I can't agree with this point of view on this kind of pumps. If we see the technical information of Denso, the HP3 pump is constructed with two plungers and is actuated at 1/1 or 1/2 the engine rotation (this second option matches with the example). The same it can be said about others, for example the CP4 pumps have a relation of 2/1 of engine rotation. The reason is synchronized the pulses of pumping with injections at the point of design. This explains why some pumps in CR must be timed.
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Valhalla » Tue Jul 09, 2013 11:40 pm

Is the 2.7 TDV6 a Denso 2-piston HP pump then? :wink:
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Fat Freddy » Wed Jul 10, 2013 6:41 am

at 1/1 or 1/2 the engine rotation (this second option matches with the example)


Thats what it is. Something to take a note of in future.


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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby aux_r » Wed Jul 10, 2013 8:48 am

Valhalla wrote:Is the 2.7 TDV6 a Denso 2-piston HP pump then? :wink:

No, the jaguar S-Type 2.7D CR has a Siemens system PCR 2.3 Lion V6 with a 3 plungers radial HP. The Denso system with 2 plungers is about the example of Fat Freddy.
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Re: Jaguar S-Type 2.7D with hesitation at idle

Postby Valhalla » Wed Jul 10, 2013 10:59 pm

I had a look at a '57 Toyota Avensis D-4D today, just a routine first-service and check over for a local chap that has just acquired it. Unfortunately for me, time did not permit me to measure the rail pulsations in the same way as FF, but now I fully appreciate the points that you were trying to make with FF's example.

What strikes me the most is how daft the Denso design is! In almost every way, it tries to break the rules established (the hard way) over many years of injection pump design for Diesel engines. A notable example seen on the Avensis is a non-symetrical displacement of the rail inlet fuel line to the outlet lines (the inlet line has been positioned at one end of a row of five evenly-spaced HP rail ports). So any timing of pulses from the HP pump to the respectively fired injector is going to require a lot of skill, bearing in mind that each cylinder will have a slightly different delay to its adjacent cylinders. Any timing of pulses will be an approximation of many disturbance factors.

In both the cases of Bosch and SiemensVDO, the applications of their equipment would not be allowed to go to production with the layout seen on the Toyota. The German application Engineers for these firms have learned over the years that you have to be very careful about management of reflections of pulses back to the pumping elements. One example of this on the 2.7TDV6 is the use of different diameter fuel lines to feed the two HP rails, compared to the feed pipes from rails to injectors. The lines have different criteria to achieve; the former to provide a steady flow of fuel to the rails, the latter to provide a pulse of fuel in a short burst to the injector. Having narrower bore line for the rail supply not only makes it more durable, it also goes some way to isolating the rail pressure fluctuations back to the pumping elements (and the pump mounted PCV). So if the RPS is reporting one injector influencing the rail pressure differently from the rest, you can be sure it is likely to be the injector.
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