 | Home > Puma (Tdci) > Rough idle and no throttle response |
 
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| DaftOldGit Member Since: 20 Sep 2015 Location: London Posts: 52  
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I have a 2007 2.4 TDCi
It starts first time and runs great in all conditions until, and this is only intermittently, I stop at a junction and the engine is idling, the idling changes to very rough and the throttle has no effect at all. No warning lights come on, it just ticks over really rough as if its only running on two cylinders. I turn off the ignition (and the engine stops as it should) then restart the engine first time and the throttle response is normal and all seems fine and i can drive away as normal. This might happen several times when im driving in traffic, but then it might be fine for a couple of days. It can happen when it's cold but other times it's been fine all day and plays up just as i get home. Long journeys or short journeys make no difference. It seems completely random. I had a very similar issue about a year ago and cleaning and remaking the earth connection from the ECU appeared to cure the problem. I've done this again now but no change this time. It seems clear that it must be an electrical or ECU issue. If it was an alternator problem (causing low power to the ECU) then i would expect the Battery light to come on. Presumably the next step is to swap out the ECU. Any thoughts anyone? |
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1st Jul 2017 9:44am |
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| DaftOldGit Member Since: 20 Sep 2015 Location: London Posts: 52
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Thanks Steve
Ive just got an Ultraguage, so i can monitor all different readings, although ive no idea what they mean! What is the normal operation of the EGR valve? I've just been out for ten minute drive to see what it tells me. When i'm driving the guage shows varying EGR% flow between 0% and 65%. When im stationary it reads around 98% and after about a minute it gradually drops to around 20%. The motor behaved fine this time but i'll keep the guage plugged in to see what it reads when the motor is playing up. The Ultraguage has two Mass Airflow guages: MA1 g/s and MA2 g/s. These both vary around 8-15 is that normal? The MAF sensor was replaced about a year ago, ive done about 10 000 miles since then. I have a spare one that i could put in. I don't know what a MAP sensor is. What is it and how do I clean it? |
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1st Jul 2017 11:25am |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720 
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EGR should stay fully closed at idle and when the engine is cold. It should only open when you're cruising with a warm engine. If it gets stuck open it'll be choking the engine with fumes which will upset the idle.
But it could also be a blown pressure relief valve on the fuel rail or a worn VCV on the pump. Neither give a fault. |
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1st Jul 2017 2:18pm |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20351
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I'm not sure about the parameters to be honest a bit out of my scope of knowledge.
Although many members on here will know, or a call to the main dealer you may get after a while some answers. There is also the possibility of the VCV, however, in my opinion it's best to check the other things I suggested first as they are easier and generally cheaper fixes. It's very easy to shell out for a perfectly working part and there is nothing wrong with it. The MAP created a rough idle on mine, and your MAF sounds to me to be quite okay. Ther EGR can cause rough idle but usually coupled with poor performance is that so? Typically hesitation in acceleration. The VCV does cause erratic idle also, and can be a real pain as it doesn't put up any MIL at all $W33T $0U7H3RN $UG4R 🇬🇧🏴🏴🏴🇮🇪🇺🇸⛽️🛢️⚙️🧰💪 |
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1st Jul 2017 2:22pm |
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| SteveNorman Member Since: 16 Sep 2008 Location: Somerset Posts: 18
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I would suggest the VCV (volume control valve) on the back of the injection pump too.
If you look at the high pressure readings when it's playing up, they vary when faulty. Also you can usually hear quite a diesel knock intermittently. Be warned though, if it is the VCV valve, renewing it may not be the end of your problems, as one reason they fail is sticking because of contamination, so check the fuel filter, by draining. If it has water or debris in it. drain remove & clean the tank & renew the split tank vent hose(s) & reposition the breather behind the splash shield in the N/S rear wheel arch. regards Steve |
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1st Jul 2017 2:46pm |
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| DaftOldGit Member Since: 20 Sep 2015 Location: London Posts: 52
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Thanks for your input.
The general performance seems fine normally, although it's never been particularly smooth when i first manoeuvre in the car park where i live. I'll go out for a longer drive and keep an eye on the EGR readings and try to see whats going on. Should it shut (0%) as soon as I stop and the engine is idling or is it normal to gradually close. Even then, mine doesn't fully close when i'm idling, it just drops to around 20% flow. It does drop to 0% when I'm driving and I accelerate, so i guess that tells me that it's not stuck and it does fully operate. What actually triggers the EGR? Could this be the pressure relief valve or the VCV that zsd-Puma mentioned? Is there some other attribute that I need to monitor to give more clues? |
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1st Jul 2017 3:00pm |
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| zsd-puma Member Since: 09 Aug 2016 Location: Kent Posts: 2720
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the EGR is electronically operated by the ECU, depending on load, engine revs etc.
The PRV is just there to dump the fuel out of the fuel rail if the pressure goes too high, if the PRV fails though it intermittantly leaks fuel back into the tank, so the fuel pressure will fluctuate when it shouldn't. |
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1st Jul 2017 8:46pm |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233  
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So what was the end result of all this. Was it the EGR or the VCV or something else? "You are never to old to learn something new"
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18th Jul 2017 8:58am |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17372 
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The pressure relief valve on the common rail is more of a safety valve than a relief valve, it is non-resettable and uses a ball bearing crimped into a seat designed to pop out at a certain pressure. Although it is possible for the valve to weep slightly without popping, once popped they are not resettable and normal operation is not possible - there will be consistent low fuel rail pressure, poor running (if running at all), as well as stored DTCs. |
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18th Jul 2017 9:34am |
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| DaftOldGit Member Since: 20 Sep 2015 Location: London Posts: 52
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Frustratingly, the problem seems to have gone away again. So I'm none the wiser. |
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18th Jul 2017 10:06pm |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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DO you know if the ECU controls the position of the EGR using pulse width modulation? "You are never to old to learn something new" |
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19th Jul 2017 1:48am |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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I'm sure it will come back just when you don't want it to! "You are never to old to learn something new" |
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19th Jul 2017 1:50am |
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| B4Lamb Member Since: 21 Mar 2015 Location: Abergavenny, Wales Posts: 233
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If any of you have any EGR valves from 2.4 TDCi engines that stopped working I woukd love to get hold of them so I can build up a picture of what is the main failure mechanism. I've heard of drive pinions coming loose and in my case bad electrical contacts inside but I'm sure there are others. Most, like those I have identified I'm sure are repairable but maybe not cost effectively by a garage with their hourly charge rate. "You are never to old to learn something new"
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19th Jul 2017 1:59am |
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| DaftOldGit Member Since: 20 Sep 2015 Location: London Posts: 52
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Sure enough, it's started happening again.
Very intermittent. Always when idling. Sometimes when I first start the engine, sometimes when I've been driving all day and just stop at a junction. I set the UltraGuage to monitor the fuel pressure. At idle, it's generally around 2800-3400psi. When it plays up and I have no throttle response, it's around 950-1100psi. Sometimes the engine cuts out and sometimes it continues to idle (roughly) and doesn't respond to the throttle at all. Usually I can restart the engine ok and all seems fine, but sometimes it's still the same and I have to restart a couple of times, but the it's fine for a few days. |
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5th Aug 2017 8:05pm |
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