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Post by nickjaxe on May 2, 2023 21:35:39 GMT 1
Hi all....my daughter has a 2015 camper with the 2lt TDI common rail injecting system.
It developed a prob with its idle and slow running engine speed....idles quite lumpy....trys to stall pulling away....onbe underway its as normal....normal power and smooth running.
Took it to a garage...said needs a new fuel filter....that will sort it....I was not convinced....to me a restricted filter will make the motor struggle at higher RPM.
Anyway it made zero difference.
She wants to take it to the same garage....I suggest a diesel specialist....but she wants to take it back.
Guys any tips on what it could be.
Found a small diesel specialist near to me.....going to see if he want to take a look.
Has an odd think that I dont think is connected.all the HP fuel injection pipes and union nut are badly corroded....the one from the pump is very very flacky but not leaking yet.....never seen the likes before.
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Post by chippie on May 2, 2023 21:49:56 GMT 1
No warning light on dash? No codes stored?
Changing the fuel filter is an easy start….,
As it hasn’t resolved the issue, then it time to go back to basics, work thru the fuel system…..from tank to hp pump. Rail pressure readings?
Check the air side…intake thru to turbo…air leaks..etc.
Live data..?? Emissions?
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Post by nickjaxe on May 2, 2023 21:55:40 GMT 1
Would you goto a specialist diesel shop over a multi task garage?
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Post by OldGit on May 2, 2023 22:21:10 GMT 1
Could be air ingress into fuel, poorly fuel injector, charge air or induction leak or something else entirely - all of which can give the symptoms you describe, basically, higher revs can mask the issue due to the flywheel mass smoothing out any unevenness felt at lower revs. Personally I wouldn't pay the 'specialist' premium unless you know it's a fuelling issue, rather find somewhere that will put fresh eyes on it and diagnose it properly rather than suffering confirmation bias.
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Post by valhalla on May 2, 2023 22:42:45 GMT 1
It would point in the direction of a small air-ingress at the fuel-filter, but if you changed this without any effect, then that rules-out the sealing washers - most common leak-point.
The clue would be in the starting; does it struggle to start after parking overnight? If not, then that rules out (mostly) an air-ingress leakage.
One thing I have found is rail-pressure-sensor drift, which used to be a big issue on some Bosch systems, as this affects the low-pressure end disproportionately, but not enough to give a DTC. The problems were largely addressed by the time this van was made, however they stemmed from the sealing-washer under the head of the RPS being distorted by over-tightening or reuse after removal/replacement of the RPS. As the setpoint pressure on this will be low at/around idle, it might be going into a partial-misfire due to the reported pressure coming back higher than it really is - the PCV is driving the real pressure down. I'm not sure about VW (is anybody?) but one thing that some of these calibrations try to do is to run "closed-loop" pressure-control all the way through to idle-speed, and that is what affects the actual pressure in the rail if the RPS is drifted. More experienced calibration-Engineers  will ignore what Bosch / Continental propose with their systems, and run them near-open-loop to prevent pressure-fluctuations around low engine-speeds.
Other issues are associated with sticking throttle-plates and debris on EGR pintles/seats, all of which can be hidden at higher engine speeds/loads, but which will give a cold-misfire through excessive EGR. If the problem only happens hot, then it would point more towards a drifted AFM (air-mass meter) that was over-reading.
The clues are all with your Daughter; when does it happen, cold-engine/hot-engine, first thing in the morning, etc.
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Post by nickjaxe on May 3, 2023 9:02:02 GMT 1
It would point in the direction of a small air-ingress at the fuel-filter, but if you changed this without any effect, then that rules-out the sealing washers - most common leak-point.
The clue would be in the starting; does it struggle to start after parking overnight? If not, then that rules out (mostly) an air-ingress leakage.
One thing I have found is rail-pressure-sensor drift, which used to be a big issue on some Bosch systems, as this affects the low-pressure end disproportionately, but not enough to give a DTC. The problems were largely addressed by the time this van was made, however they stemmed from the sealing-washer under the head of the RPS being distorted by over-tightening or reuse after removal/replacement of the RPS. As the setpoint pressure on this will be low at/around idle, it might be going into a partial-misfire due to the reported pressure coming back higher than it really is - the PCV is driving the real pressure down. I'm not sure about VW (is anybody?) but one thing that some of these calibrations try to do is to run "closed-loop" pressure-control all the way through to idle-speed, and that is what affects the actual pressure in the rail if the RPS is drifted. More experienced calibration-Engineers will ignore what Bosch / Continental propose with their systems, and run them near-open-loop to prevent pressure-fluctuations around low engine-speeds.
Other issues are associated with sticking throttle-plates and debris on EGR pintles/seats, all of which can be hidden at higher engine speeds/loads, but which will give a cold-misfire through excessive EGR. If the problem only happens hot, then it would point more towards a drifted AFM (air-mass meter) that was over-reading.
The clues are all with your Daughter; when does it happen, cold-engine/hot-engine, first thing in the morning, etc.
The fault is there from cold.....and stays when warm....its a bit harder to start cold.....but not massively. I just dont want it pulled apart unnecessarily. |
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Post by valhalla on May 3, 2023 21:33:55 GMT 1
As chippie mentions, this is pointing a little bit more towards airpath - not a VW speciality-area IMHO.
It would be worth a separate garage, one that specialises in diagnostics, to have a closer look at either EGR main valve sticking open slightly, or have a very close look at the turbocharger VNT-actuation system ; basically anything that is involved in moving the vanes, including the accuracy of the manifold pressure sensor (MAP).
From the way it does it cold, as well as hot, it would lean away from a MAF sensor fault, as one would expect, even of VW, to have much higher MAF setpoint figures for cold-start and warm-up, compared to the hot data. So the pressure-side of the airpath is more likely the culprit here.
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Post by OldGit on May 3, 2023 22:00:07 GMT 1
Could be worth a smoke test to check for a failing EGR not closing properly - it'd also pick up any induction or charge air leaks.
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Post by Rhubarb on May 4, 2023 8:20:34 GMT 1
Gummed up egr/manifold is my educated guess.
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Post by nickjaxe on May 4, 2023 22:16:48 GMT 1
Guys these injector or diesel system cleaners.....are they any good.....is so should I try injector cleaner or system cleaner.
Any particular brand....I see the price vary lots.
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huffo
Tea Maker
Posts: 243
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Post by huffo on May 5, 2023 7:24:14 GMT 1
Even the most expensive injector cleaner isn’t going to fix a problem with you EGR valve or turbo vanes.
Don’t waste your money on injector cleaner when most of the advice you’ve been given is that injectors aren’t the most likely candidate for the cause of your issue.
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Post by OldGit on May 5, 2023 11:34:13 GMT 1
Guys these injector or diesel system cleaners.....are they any good.....is so should I try injector cleaner or system cleaner. Any particular brand....I see the price vary lots. Snake oil in the main, most vehicle manufacturers explicitly prohibit their use except when directed by their technical assistance dept. those that are mandated & used by dealers are pretty much just a dose of detergent & Kerosene to increase the burn temperature. Fuel additives (such as the one I use, Dipetane) generally have some detergent in them and compensate for the lack of lubricant (Sulphur) in modern fuel as well as being a 'combustion improver'. - none of which will cure your issue.
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Post by chippie on May 5, 2023 13:15:00 GMT 1
Here’s a very simple check….
Look at the fuel trims at idle, post up the readings….
An unmetered air leak can be caused by the oil dipstick ( really? Yes…)…so check it is pushed fully home and seats properly..
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will ignore what Bosch / Continental propose with their systems, and run them near-open-loop to prevent pressure-fluctuations around low engine-speeds.
