Power loss when driving

[Manfridas]

Hi everyone

My van is T5 with 2.5tdi 174hp.

Did you guys ever came across to the problem when driving on a motorway and suddenly loosing power,but only happens in fifth or sixth gears and only when trying to eccelerate! Engine running but no power! Restarting the engine solves the problem. Drove 2000km east of Europe to Croatia and it happened 6 times.

 

[larrylamb]

Is it going into limp mode limiting your revs? Any engine management lights on?

 

[Loz]

https://vwcaliforniaclub.com/posts/297489/

 

[Manfridas]

Is it going into limp mode limiting your revs? Any engine management lights on?

Yes that’s correct,going in to limp mode and limiting my revs,but no management lights on.

 

[Steve Fuller]

Hi, my T5 recently did this, the management lights do not usually come on, yours doesn't sound as bad, yet. The problem was a leak of boost pressure, in my case the intercooler was split but first you should check that all the pipes from the turbo, throught the intercooler, to the inlet manifold are properly in place with no air leaks. Another clue is if you look in the mirror, when accelerating hard, you may see black smoke, this is because the airflow meter, in the aircleaner housing, is fooled into thinking the engine is receiving more air than it actually is and so tells the ECU to deliver too much fuel thus triggering the limp home mode. Once I repaced my intercooler the problem was cured.

 

[sidepod]

Could it be the air mass flow sensor itself? Every VW I’ve had has had a new one at some point!

 

[VW Guru]

Hi it all depends on the fault code if underboost then as @Steve Fuller said it would be a failure of the intercooler. Sometimes it’s a failure of the egr cooler change over valve diaphragm spliting. If you have a dpf and have underboost code and maybe a code for exhaust gas temp sensor 3 then you may have a broken up dpf blocking the exhaust.

If you have an overboost fault code then the variable vane unit in your turbo will be jamming up casing the ecu to see overboost for more than 3 seconds and putting you into limp mode. Then either a new turbo will be required or a competent mechanic who can strip your turbo down clean it up and rebuild it.

 

[Steve Fuller]

It could be the Airflow meter itself, when my intercooler was leaking the only clue was that I could hear the boost leaking out if I drove with th window open and accelerated, the hole was quite large but was on the back so it was only confirmed when I removed it. I'd take all the easy stuff first, check the pipework and hoses etc, perhaps airlow meter next and then intercooler, judging by the numbers sold on, Ebay, this must be very common and a lot of people fitt upgraded ones, I couldn't afford to or probably would have. The cheapest place I found, apart from Ebay, was Carparts4Less which is just Eurocarparts in disguise but much cheaper. Good luck.

 

[Steve Fuller]

Hi it all depends on the fault code if underboost then as @Steve Fuller said it would be a failure of the intercooler. Sometimes it’s a failure of the egr cooler change over valve diaphragm spliting. If you have a dpf and have underboost code and maybe a code for exhaust gas temp sensor 3 then you may have a broken up dpf blocking the exhaust.

If you have an overboost fault code then the variable vane unit in your turbo will be jamming up casing the ecu to see overboost for more than 3 seconds and putting you into limp mode. Then either a new turbo will be required or a competent mechanic who can strip your turbo down clean it up and rebuild it.

Oh yes forgot about DPF because I am lucky enough to have a pre DPF T5! This will give you the kind of synptoms you have if it is blocked, They are meant to re-generate but you have to drive in a certain way and avoid short journeys if possible, it may be too blocked to clear itself ( the warning lights notoriously don't come on until it's too late!) but don't, yet, let a garage tell you it needs to be replaced, I recently had one blocked on a friends BMW, I removed it and steam cleaned it through for a good half hour until it ran clear, it is working perfectly now. Info on driving to protect your DPF is widely available online. When you buy a vehicle the saleperson never mentions any of this because it would put buyer off of diesels.

 

[Steve Fuller]

Oh, one other thing, if you have a DPF you will never see any smoke at all, even if over fuelling/underboosting, but all the other faults mentioned would cause the DPF to clog up even more quickly and, if not sorted, re-occurance would happen very quickly.

 

[Steve Fuller]

Oh, one other thing, if you have a DPF you will never see any smoke at all, even if over fuelling/underboosting, but all the other faults mentioned would cause the DPF to clog up even more quickly and, if not sorted, re-occurance would happen very quickly.

Still going! If you vehicle is pre-DPF I would consider getting an EGR delete kit, they are all very well when everything is new but putting dirty exhaust smoke into the inlet never really seemed a sensible way to go, it may lower emissions ( debatable maybe when new) but actually makes the engine, overall, slightly less efficiant in terms of both performance and fuel economy.

 

[Manfridas]

Still going! If you vehicle is pre-DPF I would consider getting an EGR delete kit, they are all very well when everything is new but putting dirty exhaust smoke into the inlet never really seemed a sensible way to go, it may lower emissions ( debatable maybe when new) but actually makes the engine, overall, slightly less efficiant in terms of both performance and fuel economy.

My van is pre PDF,2004 model and I have recently new EGR changed. And other thing,it doesn’t give any black smoke at all,I’m thinking to change new air flow sensor and still want to block my EGR and reprogram it,see if that will fix my problem. Cheers guys for your opinions

 

[Stoneybroke]

Does it reset after stopping and restarting?
My T5 did this. The cause was overboost on the turbo, caused by sticking variable vanes.
First thing required is going up to VAGCOM or similar to get the fault codes.
If it is overboost, then it's a professional turbo clean out or a refurb.

 

[Manfridas]

Does it reset after stopping and restarting?
My T5 did this. The cause was overboost on the turbo, caused by sticking variable vanes.
First thing required is going up to VAGCOM or similar to get the fault codes.
If it is overboost, then it's a professional turbo clean out or a refurb.

Yep it resets after restarting the engine. And about 4 months ago I had a 5000km journey and it happened maybe few times only,spoke with one of my friends who has also same van and he travels a lot,he said it happened to him to a few times,so never thought it’s an issue,but now we took her out to Croatia from Lithuania just under 2000km and it happened 6 times (not looking forward to go back when it is something not wright with the van)

 

[Stoneybroke]

Sounds like sticky turbo vanes causing overboost.

 

[Manfridas]

Sounds like sticky turbo vanes causing overboost.

If it is,would it show some code on a computer scan?

 

[VW Guru]

If it is,would it show some code on a computer scan?

Hi yes it would have an overboost fault code

 

[Stoneybroke]

Hi yes it would have an overboost fault code

P0234 is a diagnostic trouble code (DTC) for "Engine Overboost Condition".

 

[Steve Fuller]

My van is pre PDF,2004 model and I have recently new EGR changed. And other thing,it doesn’t give any black smoke at all,I’m thinking to change new air flow sensor and still want to block my EGR and reprogram it,see if that will fix my problem. Cheers guys for your opinions

You should not need to reprogramme a 2004, you don't really even need to buy a kit, all you have to do is unbolt the egr pipe and place a blanking plate in. Another mod is to unclip and tie to one side the little diaphragm unit that operates the spindle where the egr connects and then cable tie the spindle open, this stops theengine oil that seep out around the spindle and make a mess. The diaphram thing is supposed to help the engine stop more smoothly but I haven't noticed any difference. As regards the black smoke, it doesn't do it all the time and it is quite hard to see, the best way to be sure is to get someone to follow you, that's how I found out mine was smoking.

 

[Manfridas]

Hello again
So now after a long journey from Croatia I’ve been trying to search what is the problem with my engine power loss. Took her for diagnostic and visual check found nothing else apart from the fault code P0234 for the turbo overboost,also decided to put her on a rolling road to measure the power (just curious) and was dissapointed with the result. Stock should be 128kw and 400NM but found 96kw and 303NM. So after this everyones opinion was the same,need to take turbo out and check on them veins (not sure the correct name for it)but it’s part of turbo. And yes turbo was faulty,veins were stuck and wings on turbo itself was slightly broken,replaceted it in to new turbo and went back to rolling road. After the test still found less than it should be (104kw and 340NM). I got to say after turbo been replaced it drives a little better/smoother,engine sounds great,no faults on diagnostic,injectors works perfect (checked) EGR valve brand new,no smoke as well,intercooler has no leak,catalic converter new,full service by VW recently,not sure what else could be the problem. I only have one idea,it’s the engine itself not producing enough power... Milage now 148000 miles. Any thoughts?

 

[WelshGas]

Hello again
So now after a long journey from Croatia I’ve been trying to search what is the problem with my engine power loss. Took her for diagnostic and visual check found nothing else apart from the fault code P0234 for the turbo overboost,also decided to put her on a rolling road to measure the power (just curious) and was dissapointed with the result. Stock should be 128kw and 400NM but found 96kw and 303NM. So after this everyones opinion was the same,need to take turbo out and check on them veins (not sure the correct name for it)but it’s part of turbo. And yes turbo was faulty,veins were stuck and wings on turbo itself was slightly broken,replaceted it in to new turbo and went back to rolling road. After the test still found less than it should be (104kw and 340NM). I got to say after turbo been replaced it drives a little better/smoother,engine sounds great,no faults on diagnostic,injectors works perfect (checked) EGR valve brand new,no smoke as well,intercooler has no leak,catalic converter new,full service by VW recently,not sure what else could be the problem. I only have one idea,it’s the engine itself not producing enough power... Milage now 148000 miles. Any thoughts?

Ignoring the Rolling Road results, how does the vehicle drive now that the Turbo has been replaced? Better than before or the same as?
Most engines lose overall performance as the miles clock up. To get back to it’s original power output then the engine would probably have to be fully reconditioned.

 

[Manfridas]

Ignoring the Rolling Road results, how does the vehicle drive now that the Turbo has been replaced? Better than before or the same as?
Most engines lose overall performance as the miles clock up. To get back to it’s original power output then the engine would probably have to be fully reconditioned.

Yes drives better than before but I got to say before was not bad as well. If not a long journey to Croatia I probably would never know that I hade I faulty turbo. So I have my van back 2 days now and driving around feels a bit better,accelerates better,but not a great deal.

 

[WelshGas]

Yes drives better than before but I got to say before was not bad as well. If not a long journey to Croatia I probably would never know that I hade I faulty turbo. So I have my van back 2 days now and driving around feels a bit better,accelerates better,but not a great deal.

Well the power has only gone up by 8kw. All engines lose power over time and miles. As I said I would think this is normal. If you want to spend money and investigate further then you are looking at compression tests, Injector refurbishment and the list will go on, as will the cost.
If it is doing all that you want then I would just enjoy the van and your trips.

 

[Manfridas]

I decegree on your thoughts that over the years and especialy this kind of milage engine looses that much of power is normal,my last van was a T4 2.5tdi with red i (111kw) and I went for the remap,so tried her on the roling road before and after and figures showed 110kw before and 120kw after,Nm was increesed more but I cant remember excact no. And the milage was even higher on that van. And before that I had another T4 with the same engine but it was with the blue i (65kw) engine,also done remape,and before and after roling road that was also very close to what the stock should be,after remap went up to 85kw. Most of my cars I owned I had them remaped and I got to say never had such a high difference in what should be.

 

[westfalia]

Like sidepod said in post #6
Have you replaced the mass air flow sensor.