 | Home > Puma (Tdci) > Eratic Idle especially when cold |
 
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233   
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Thanks that's how I have understood it should be like. The coil of the solenoid is built into the body of the valve and center part as you illustrate shuttles back and forth inside of the coil, against a spring. It works a bit like a carburetor but in reverse. Instead of the tapered needle being moved in and out of the jet to increase or decrease fuel flow in this case the jet (the centre component which must have an iron content) is moved in and out of a fixed tapered needle that is in the body. The position of the jet is controlled by the ECM by pulse width modulation of voltage applied to the coil so the longer the pulse width the further the jet moves thus reducing Fuel flow as the spring holds it in the open position. The pulse train frequency is fast such that the mass of the jet is unable to respond to individual pulses due to its moment of inertia so a mean position is attained depending on the pulse 'on' to 'off' ratio. I can only assume that the center jet component is sticking occasionally and not moving freely particularly when the whole thing is cold. I have read that the coil should be about 500 Ohms however the new VCV that I have just received is 2.4 Ohms. Thats a bit more realistic as the spring is actually quite stiff so the solenoid force needs to be quite substantial. The current will be around 5 Amp pulses. Assuming on average it's sitting mid position with duty cycle of 50:50 that's a consumption of 30 watts.
Hopefully soon I can have a better look I my one when I get it off. John "You are never to old to learn something new" |
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9th Feb 2017 2:02am |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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I now have the old and briefly the new replacement VCV to compare. The operation of the VCV is slightly different to how I describe above but the principle of operation remains the same. The main body of the VCV has two diametrically opposed holes positioned between the large corner O ring seal and the piston O ring. When the valve is fitted into the HP fuel Pump, low pressure fuel must be ported to enter into the region between these two O rings and hence can flow into the centre section of the valve through the two diametrically opposed holes. The two holes are not circular they are a circle with a small slit in one side (shaped). Internally the bore of the body is ground and highly polished to receive the piston to a high degree of accuracy for just a sliding fit with minimum friction. The piston is likewise ground and mirror polished on the outside and has an internal bore of approx. 1.5 mm. The recessed sections of the Piston have holes drilled through to the inner 1.5 mm bore to let fuel in these sections flow into the central bore. The piston itself has a significant pure Iron content (i.e. it is attracted to a magnet but does not retain any magnetic field of its own) It is designed to be pulled by the magnetic field of the solenoid coil built into the body of the VCV. This means the piston will be pulled into the body as the current pulse width is increased from the ECU control signal. The piston (jet as I called it above) operates against a spring as described above and a circlip holds the piston inside the bore of the main body with slight spring compression. In this relaxed position the two External holes in the valve body align with the central recessed section of the piston (just). This allows fuel to flow through the outer holes, into the recessed section of the piston and then through the holes in the piston to the centre 1.5 mm bore and then into the HP pump (one assumes). As pulse width modulated current is applied to the solenoid coil the piston is drawn further into the body of the valve. Any movement of the piston starts to close off the two diametrically opposed fuel entry holes as the raised centre section of the piston moves over the slotted holes. Its only a few mm of movement from fully open to fully closed or covered holes. Hence by modulating the pulse width the piston position controls the effective orifice and hence flow rate to the HP pump intake side.
The whole valve is precision engineered (hence why it is quite pricey) and relies on virtual friction free sliding of the piston without excessive leakage past the raised section of the piston when in the partial or fully closed position. Now for the interesting bit 
On examining the piston of my old VCV I find that the ground mirror finish is very slightly rough and dulled on one side for approximately 30% of its circumference indicating wear or effects of contaminants. I also find it doesn't feel as smooth in movement compared to the new valve. I cannot examine the inner bore easily but assume this is similarly worn around part of its circumference. Now this is my theory and it may be wrong 
As the body heats up from the power driven into the solenoid coil (30 to 60 watts) and the heat of the engine it eventually attains a temperature slightly above that of the inner piston which is being constantly cooled by fuel and hence the expansion of the bore in the body is greater than the piston. This reduces the friction between body and piston and that is maybe why effects are observed to be worse when everything is cold at start up. The important part is on replacing the valve the unstable idle and occasional fuel starvation to near stalling problems disappeared in my case completely and instantly. Any other theories are welcome, the case remains open. 
I have included some pretty poor pictures (sorry) but it tries to show the fuel orifice (hole) positions in the body and piston.  Click image to enlarge Click image to enlarge Click image to enlarge Cheers, John "You are never to old to learn something new" |
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15th Feb 2017 12:09am |
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| agentmulder Member Since: 16 Apr 2016 Location: Outer Space Posts: 1324 
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You've got me wanting to open my old one up now.
Be interesting to look for wear as you describe... Solved the bowel problem, working on the consonants... |
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15th Feb 2017 5:24am |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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Well its only a circlip you have to remove to get the piston out. I'd be interested to see if you observe the same.
I've only been running the Defender for a few days now since the change and it's like a new motor. Seems to have more lower down torque and so much smoother. I've yet to get the pump relearn done but I'm wondering if it will make no further difference at all. Does the diagnostic tools tell you what the existing coefficients are stored in the ECU and the new ones that it calculates when it does the learn? If not, how can you check it has made any changes at all? If anyone knows this I'd love to know. Cheers, John. "You are never to old to learn something new" |
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15th Feb 2017 10:43pm |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720  
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After reading this thread i've just ordered myself a new VCV, mine isn't that bad, but it's always seemed worse than the Transits i've driven when it comes to cold idling.
122 from Land Rover with discount, but 48 from PF Jones - same numbers but in a Denso box. Looks like the LR one comes with a gasket, but i can just make one of those from gasket paper. https://www.pfjones.co.uk/294009-0260-ford...-0260.html |
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15th Feb 2017 10:53pm |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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Blimey, that's the cheapest yet, I've seen, I was ripped off when I paid 65. Does that price include postage? You will be able to use the old gasket I'm sure, it's a sort of thin plastic material. Does it come with a new corner seal O ring, its not shown in the picture from that company. It's that O ring that stops any fuel leaks, the gasket doesn't really do much. Again I'm sure the old O ring is perfectly serviceable if you look after it when you dismantle.
Cheers, John "You are never to old to learn something new" |
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15th Feb 2017 11:15pm |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720
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It was 54.60 with the postage.
If it doesn't come with the large O-Ring i have a large range of sizes in my workshop, so i'm sure i'll have one that fits. I suspect it probably does though, as the other valves they sell of the same design come with them. There are other much more expensive ones for various other vehicles. I double checked all the numbers though and it matches, the more expensive ones don't. I expect the gasket is just there to stop the flange from seizing on and keep a bit of dirt out of the joint, if it's not servicable, it will only take 10 min to cut a new one from paper. At over 60 less than the Land Rover one i can afford to have an oring custom made and still save money. 
The thing with most diesel parts is they're used on a variety of engines from different manufacturers, so you can usually get them cheaper than from the dealer. Take the copper injector washers, they're 18 each from LR, 8.50 each from Ford, 7 from Citroen or 1 each (or less) from a Diesel injection specialist - they're matched to the injector not the engine. And Denso injectors are in all sorts. |
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15th Feb 2017 11:56pm |
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| agentmulder Member Since: 16 Apr 2016 Location: Outer Space Posts: 1324
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Yes!
Noticeable gain in torque at lower RPMs here too  Solved the bowel problem, working on the consonants... |
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16th Feb 2017 12:08am |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 19572
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I've got a Borg and Beck Waterpump 68 off eBay, been brilliant. The LR part is over. 300! Diesel$ Live$ Matter. ⛽️🛢️👨🔧🧰⚙️ RED, WHITE & BOOST! 🇬🇧
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16th Feb 2017 12:25am |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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That's 10 quid cheaper than I paid at UKDieselparts.com but mine did come as a kit with gasket, O rings, new M6 cap head screws and two funny shaped soft poly mouldings that looked like electrical connector over protectors...no idea what they were for? On the box it said it was a Nissan Valve Kit Regulating A6860-VM09A yet the invoice states part number 294009-0260. Anyway it all fitted well and looks identical to the old (assumed original Ford/LR fitted) one I took out. "You are never to old to learn something new" |
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16th Feb 2017 1:04am |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720
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Same Denso part number as the one i've ordered then. Chances are it comes with the gaskets and seals but they're not pictured, will find out when it turns up.
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16th Feb 2017 2:08am |
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| agentmulder Member Since: 16 Apr 2016 Location: Outer Space Posts: 1324
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When I removed my old one a small section of a layer of something like paint chipped off the gasket and stayed on the pump mating face. Had to clean that off with a gasket scraper and retractable mirror which, as you can imagine, was hard to get in there. Glad I got a new one in my kit (Denso via Bearmach). Solved the bowel problem, working on the consonants...
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16th Feb 2017 7:20am |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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I kept the old gasket and large corner seal 'O' ring and they look good to reuse so if you need them I could pop them in an envelope for you. Let me know? B4lamb "You are never to old to learn something new" |
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16th Feb 2017 7:55pm |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720
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Thanks for the offer, i'll see what turns up on Monday.
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16th Feb 2017 8:09pm |
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