Intermittent Engine or Brake Issue?

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CageyJ0nnY
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Intermittent Engine or Brake Issue?

Post by CageyJ0nnY » Wed Jan 15, 2020 12:12 pm

Twice now I have noticed that it sounds like my engine is labouring even at a constant speed (50mph duel carriage driving).

Another symptom is getting 22-25 mpg when sat at 50mph when I normally get 55-60.

Im thinking that this is either an engine / drivetrain issue or something to do with the brakes binding.

Has anyone else had any issues like this? It's sods law that if I take it to the dealership that the issue won't present itself and they won't find anything.

Cheers

SRGTD
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Re: Intermittent Engine or Brake Issue?

Post by SRGTD » Wed Jan 15, 2020 12:22 pm

It could be the GPF carrying out an active / forced regeneration, especially if your motoring includes a high proportion of short journeys. Worth having a read of this discussion thread;

viewtopic.php?f=71&t=73177

monkeyhanger
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Re: Intermittent Engine or Brake Issue?

Post by monkeyhanger » Wed Jan 15, 2020 12:27 pm

My guess would be the car is doing an active GPF regeneration. How many miles has your car done, and roughly when (number of miles) did it happen last time? Is your exhaust a bit roomier than normal? When you say labouring at 50mph, what's the engine speed (revs) and what gear are you in?

My wife's 2019 GTI+ had 2 concurrent 8 mile journeys happen with horrendous mpg, then revert back to normal.

Is yours DSG or manual? I'm assuming 1.0TSI variant (which output?) due to your quoted "normal" mpg.

How long are your commute journeys typically? If you do 30 more miles and the car hasn't rectified itself, I'd get it to the garage.

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Re: Intermittent Engine or Brake Issue?

Post by CageyJ0nnY » Wed Jan 15, 2020 12:56 pm

monkeyhanger wrote:
Wed Jan 15, 2020 12:27 pm
My guess would be the car is doing an active GPF regeneration. How many miles has your car done, and roughly when (number of miles) did it happen last time? Is your exhaust a bit roomier than normal? When you say labouring at 50mph, what's the engine speed (revs) and what gear are you in?

My wife's 2019 GTI+ had 2 concurrent 8 mile journeys happen with horrendous mpg, then revert back to normal.

Is yours DSG or manual? I'm assuming 1.0TSI variant (which output?) due to your quoted "normal" mpg.

How long are your commute journeys typically? If you do 30 more miles and the car hasn't rectified itself, I'd get it to the garage.
My car has just ticked over 6000 miles and first did it a few month ago, i'd guess around 4500. The exhaust is boomier at 50 mph in 6th at around 1500 ish rpm. At those conditions it was doing 25ish mpg.

Mine is a DSG and my commute is 13 miles doing duel carriage way and country road driving.

From reading the thread linked above it does sound like a regen thing. It's frustrating though as I used a quarter of a tank today getting to work.

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Re: Intermittent Engine or Brake Issue?

Post by S_94 » Wed Jan 15, 2020 2:02 pm

Had the same issues around 5500 miles. Went for a long drive (70 miles) and it sorted itself out.

I could actually feel the car change halfway through the journey, everything just went quiet again all of a sudden, was very odd.

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Re: Intermittent Engine or Brake Issue?

Post by monkeyhanger » Wed Jan 15, 2020 3:34 pm

CageyJ0nnY wrote:
Wed Jan 15, 2020 12:56 pm
monkeyhanger wrote:
Wed Jan 15, 2020 12:27 pm
My guess would be the car is doing an active GPF regeneration. How many miles has your car done, and roughly when (number of miles) did it happen last time? Is your exhaust a bit roomier than normal? When you say labouring at 50mph, what's the engine speed (revs) and what gear are you in?

My wife's 2019 GTI+ had 2 concurrent 8 mile journeys happen with horrendous mpg, then revert back to normal.

Is yours DSG or manual? I'm assuming 1.0TSI variant (which output?) due to your quoted "normal" mpg.

How long are your commute journeys typically? If you do 30 more miles and the car hasn't rectified itself, I'd get it to the garage.
My car has just ticked over 6000 miles and first did it a few month ago, i'd guess around 4500. The exhaust is boomier at 50 mph in 6th at around 1500 ish rpm. At those conditions it was doing 25ish mpg.

Mine is a DSG and my commute is 13 miles doing duel carriage way and country road driving.

From reading the thread linked above it does sound like a regen thing. It's frustrating though as I used a quarter of a tank today getting to work.
13 miles each way should be ample for the GPF to regen passively (it is for a diesel with a DPF), considering how hot the exhaust gets on a petrol car.

There was a big discussion on this within the Golf GTI forum recently.

There are 3 things needed for combustion - fuel (in this case, soot), heat (in this case, exhaust heat, 550-600C to burn the soot) and oxygen (in the air).

For a DPF, diesel combusts under an excess of air, so oxygen in the exhaust is plentiful, and you have the soot, so limiting factor is how hot the exhaust gets - an issue on shorter journeys.

For a GPF, we have the fuel (soot), we have the heat (so much energy kicked out through the exhaust as heat for a petrol car, so exhaust warms up quickly), but there's a lack of oxygen because petrol engines bring in only as much air as they need for combustion with the fuel injected (stoichiometric mixture).

The only time a petrol car puts a lot of air (containing oxygen) through the exhaust is when it is overrunning - when you take your foot off the accelerator and the engine is still motoring the car with no fuel input and you get engine braking.

My theory as to why GPF regenning doesn't seem to be a doddle compared to DPF is that DSGs aren't set up for allowing overrun, if you take your foot off the accelerator, the drop off in speed is minimal, compared to engine braking on a manual. The DSG is still fuelling the engine to a degree, when you take your foot off the accelerator to avoid heavy engine braking. If it is, then it's depriving the exhaust of oxygen containing air too, as it's taking in just enough air to burn the fuel it's still putting in under deceleration.

GPF regenning passively needs engine braking to provide the oxygen to convert soot (carbon) into CO2. Seems this happens far more readily with a manual box where you can do effective engine braking.

The puzzling thing is, during an active GPF regen, I haven't a plausible reason why the mpg suffers so much. It needs oxygen, not more fuel for the GPF reegen to happen. There must be some other factor at play too which makes the engine run ridiculously insufficiently with the fuel it's getting, but I can't find any explanation for it. My wife's mpg dropped from a normal 30mpg on her commute to 19mpg during the GPF regen. That's a far bigger penalty than for a diesel engined car with a DPF that is actively regenerating.

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Re: Intermittent Engine or Brake Issue?

Post by l3rady » Fri Jan 17, 2020 2:03 pm

Makes you wonder if all these cars running around with GPFs are actually making less of a negative effect on the environment compared to those without a GPF.

Petrol engines run pretty clean as is, by adding a GPF to capture those last few noxious emission is it worth it when the main trade-off is lower fuel economy?

These GPFs/DPFs in cars are making the only viable car for regular short journeys and town runs, EV's.

My long term MPG is only 32MPG in this new car and only see 45+MPG when I visit my mums after a 3.5hr drive away.

I'm seriously considering getting a cheap EV to do the local day to day driving and keeping the GTI for the road trips and visits back home.

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Re: Intermittent Engine or Brake Issue?

Post by monkeyhanger » Fri Jan 17, 2020 2:43 pm

l3rady wrote:
Fri Jan 17, 2020 2:03 pm
Makes you wonder if all these cars running around with GPFs are actually making less of a negative effect on the environment compared to those without a GPF.

Petrol engines run pretty clean as is, by adding a GPF to capture those last few noxious emission is it worth it when the main trade-off is lower fuel economy?

These GPFs/DPFs in cars are making the only viable car for regular short journeys and town runs, EV's.

My long term MPG is only 32MPG in this new car and only see 45+MPG when I visit my mums after a 3.5hr drive away.

I'm seriously considering getting a cheap EV to do the local day to day driving and keeping the GTI for the road trips and visits back home.
I wouldn't consider petrol hugely clean since direct injection became the norm.

Even only considering particulates, a DPF equipped diesel is a hell of a lot cleaner than a petrol with no GPF.

My 2018 GTI+ without GPF has sooty tailpipes, my wife's 2019 GTI+ with GOF has spotlessly clean tailpipes.

The tailpipes on my 2015 Golf R were filthy too.

As petrol is less efficient, it uses more fuel and creates more CO2 per mile.

Petrol generally has the edge on NOx though, as it doesn't combustion with an excess of air, and combusts cooler, making it less likely to create NOx. Diesel has a solution for that though - newer diesels use adblue to convert NOx.

When not doing a regen, the wife's GTI+ is only marginally less fuel efficient than mine.

Buying an EV for better cost of fuelling in addition to your Polo is not going to save you any money. People spending thousands chopping cars in early and getting hit hard on depreciation to save maybe £500 a year at the pumps is crazy enough.

I'm averaging 35mpg now. If I'm sat on a relatively busy but free flowing motorway/dual carriageway, I can get 45-52mpg. Pretty good for a 200ps petrol car.

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Re: Intermittent Engine or Brake Issue?

Post by Dark_cze » Fri Jan 17, 2020 3:00 pm

monkeyhanger wrote:
Fri Jan 17, 2020 2:43 pm
My 2018 GTI+ without GPF has sooty tailpipes, my wife's 2019 GTI+ with GOF has spotlessly clean tailpipes.

The tailpipes on my 2015 Golf R were filthy too.
I have gti made in 11/2018 spain. With GPFand my tailpipes are black like my old diesel Audi A4 B6 :D no fluids are missing and consumption is fine so I guess no technical problems there.

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Re: Intermittent Engine or Brake Issue?

Post by RUM4MO » Fri Jan 17, 2020 3:37 pm

Dark_cze wrote:
Fri Jan 17, 2020 3:00 pm
monkeyhanger wrote:
Fri Jan 17, 2020 2:43 pm
My 2018 GTI+ without GPF has sooty tailpipes, my wife's 2019 GTI+ with GOF has spotlessly clean tailpipes.

The tailpipes on my 2015 Golf R were filthy too.
I have gti made in 11/2018 spain. With GPFand my tailpipes are black like my old diesel Audi A4 B6 :D no fluids are missing and consumption is fine so I guess no technical problems there.
That is interesting, I'd expect that you would find the same as monkeyhanger finds with his wife's GTI+ with GPF, so what exactly is your GPF doing when it is passing the soot that appears on the tips?

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Re: Intermittent Engine or Brake Issue?

Post by SRGTD » Fri Jan 17, 2020 3:51 pm

Dark_cze wrote:
Fri Jan 17, 2020 3:00 pm
monkeyhanger wrote:
Fri Jan 17, 2020 2:43 pm
My 2018 GTI+ without GPF has sooty tailpipes, my wife's 2019 GTI+ with GOF has spotlessly clean tailpipes.

The tailpipes on my 2015 Golf R were filthy too.
I have gti made in 11/2018 spain. With GPFand my tailpipes are black like my old diesel Audi A4 B6 :D no fluids are missing and consumption is fine so I guess no technical problems there.
My previous generation Polo GTI with VW’s 1.8 litre EA888 192ps dual port injection engine keeps its exhaust tailpipes clean - I’ve never had to clean any sooty deposits off the tailpipes in almost 4 years of ownership.

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Re: Intermittent Engine or Brake Issue?

Post by l3rady » Fri Jan 17, 2020 4:28 pm

monkeyhanger wrote:
Fri Jan 17, 2020 2:43 pm
I wouldn't consider petrol hugely clean since direct injection became the norm.

Even only considering particulates, a DPF equipped diesel is a hell of a lot cleaner than a petrol with no GPF.

My 2018 GTI+ without GPF has sooty tailpipes, my wife's 2019 GTI+ with GOF has spotlessly clean tailpipes.

The tailpipes on my 2015 Golf R were filthy too.

As petrol is less efficient, it uses more fuel and creates more CO2 per mile.

Petrol generally has the edge on NOx though, as it doesn't combustion with an excess of air, and combusts cooler, making it less likely to create NOx. Diesel has a solution for that though - newer diesels use adblue to convert NOx.

When not doing a regen, the wife's GTI+ is only marginally less fuel-efficient than mine.

Buying an EV for better cost of fuelling in addition to your Polo is not going to save you any money. People spending thousands chopping cars in early and getting hit hard on depreciation to save maybe £500 a year at the pumps is crazy enough.

I'm averaging 35mpg now. If I'm sat on a relatively busy but free-flowing motorway/dual carriageway, I can get 45-52mpg. Pretty good for a 200ps petrol car.
My thoughts were strictly on GPF vs No GPF in petrol cars. I understand that my comment of "Petrol engines run pretty clean as is" has triggered the conversation on diesel vs petrol, but I was trying to gauge if a GPF given it's higher fuel consumption is actually beneficial to the environment than no GPF. It has however triggered a debate on sooty poop shoots 🤣

My understanding of a GPF is that its primary purpose is to clean up the exhaust gases from particulates - hydrocarbons (HC), nitrous oxides (NOx) and carbon monoxide (CO). Those particulates are shown to be damaging to our health so without a doubt, they do a good job at making the air in high traffic areas more breathable. I don't fully understand how the GFP gets rid of the particles but from what I read they are converted to small amounts of CO2. So a GFP actually increases a cars CO2 emissions...? I need to read up more to confirm this.

Given a GFP car that is used mostly in short journeys and has to constantly regen and we know regen tanks fuel economy, then that would lead me to believe that a GPF fitted car has the ability to emit more CO2 than one not fitted. The polo gti is rated for CO2 134 g/km but that's at it's rated 49mpg (UK). If the car is constantly doing regen due to its usage type and is only returning on average 32mpg then its CO2 is more like 204 g/km.

I doubt these new WLTP tests take into account a GPF fitted car during a regen cycle. So the CO2g/km figures are always going to take the car at it's best working condition.

Further thought 🤔 What if your car in for MOT and the GPF starts a regen during its emissions test. Could it fail because of that?

Still, these are thoughts and welcome debate and correction.

Regarding earlier comment about EV's. I was thinking about the second-hand market to supplement my driving style to improve efficiency. After a few hours looking, I have determined at the moment, it is not cost-effective. EV cars on the second market hold their price very well, especially when they don't come with the battery. Looking at the battery hire programs I'd be looking at £50/month min and I wouldn't use up all the mileage allowance so it would actually make the cost of motoring for me more expensive than to keep using my polo at 32mpg average for all driving. I will revisit this in a couple of years to see how pricing has hopefully improved.

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Re: Intermittent Engine or Brake Issue?

Post by l3rady » Fri Jan 17, 2020 5:20 pm

monkeyhanger wrote:
Wed Jan 15, 2020 3:34 pm
There are 3 things needed for combustion - fuel (in this case, soot), heat (in this case, exhaust heat, 550-600C to burn the soot) and oxygen (in the air).

For a DPF, diesel combusts under an excess of air, so oxygen in the exhaust is plentiful, and you have the soot, so limiting factor is how hot the exhaust gets - an issue on shorter journeys.

For a GPF, we have the fuel (soot), we have the heat (so much energy kicked out through the exhaust as heat for a petrol car, so exhaust warms up quickly), but there's a lack of oxygen because petrol engines bring in only as much air as they need for combustion with the fuel injected (stoichiometric mixture).

The only time a petrol car puts a lot of air (containing oxygen) through the exhaust is when it is overrunning - when you take your foot off the accelerator and the engine is still motoring the car with no fuel input and you get engine braking.

My theory as to why GPF regenning doesn't seem to be a doddle compared to DPF is that DSGs aren't set up for allowing overrun, if you take your foot off the accelerator, the drop off in speed is minimal, compared to engine braking on a manual. The DSG is still fuelling the engine to a degree, when you take your foot off the accelerator to avoid heavy engine braking. If it is, then it's depriving the exhaust of oxygen containing air too, as it's taking in just enough air to burn the fuel it's still putting in under deceleration.

GPF regenning passively needs engine braking to provide the oxygen to convert soot (carbon) into CO2. Seems this happens far more readily with a manual box where you can do effective engine braking.

The puzzling thing is, during an active GPF regen, I haven't a plausible reason why the mpg suffers so much. It needs oxygen, not more fuel for the GPF reegen to happen. There must be some other factor at play too which makes the engine run ridiculously insufficiently with the fuel it's getting, but I can't find any explanation for it. My wife's mpg dropped from a normal 30mpg on her commute to 19mpg during the GPF regen. That's a far bigger penalty than for a diesel engined car with a DPF that is actively regenerating.
Sounds spot on there. This is the explanation I found here:
GPF regeneration can only be performed in “non power” conditions, meaning that regeneration is normally achieved under deceleration. Deceleration increases the amount of oxygen following through the engine and exhaust system. This in turn raises the temperature of the GPF to around 400c – 700c, igniting the soot contained within the filter.

In conditions where this is not possible, the vehicles engine management systems alters timing causing it to run lean. This “lean” burn increases oxygen and therefore GPF operating temperatures, allowing a regeneration to occur.
So in DSG models the ECU simply runs the engine lean to increase the temperature and get more oxygen into the exhaust. To me, that would explain why the engine revs on average higher when regening as running lean reduces engine power output so has to compensate with higher revs. Would that also explain the lower fuel economy? Given that the engine is running leaner when it normally wouldn't, it is further away from the ideal fuel to air mixture so that its efficiency is reduced? But everything you read on burning lean in engines supposedly improves fuel efficiency... Confusing...

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Re: Intermittent Engine or Brake Issue?

Post by monkeyhanger » Fri Jan 17, 2020 7:20 pm

SRGTD wrote:
Fri Jan 17, 2020 3:51 pm
Dark_cze wrote:
Fri Jan 17, 2020 3:00 pm
monkeyhanger wrote:
Fri Jan 17, 2020 2:43 pm
My 2018 GTI+ without GPF has sooty tailpipes, my wife's 2019 GTI+ with GOF has spotlessly clean tailpipes.

The tailpipes on my 2015 Golf R were filthy too.
I have gti made in 11/2018 spain. With GPFand my tailpipes are black like my old diesel Audi A4 B6 :D no fluids are missing and consumption is fine so I guess no technical problems there.
My previous generation Polo GTI with VW’s 1.8 litre EA888 192ps dual port injection engine keeps its exhaust tailpipes clean - I’ve never had to clean any sooty deposits off the tailpipes in almost 4 years of ownership.
My 2018 GTI+ and 2015 Golf R have dual fuelling via port injection and direct injection, and both have sooting of the exhaust. The difference between my wife's 2019 GTI+ and mine is the GPF, it is what's keeping her exhaust clean. My GTI+ exhaust is a lot cleaner than the R's was, but still noticeably sooty. Port injection keeps carbon from building-up on the backs of the intake valves, but the source of that carbon build up is oil that escapes the intake valve seal and cooks onto the valve back without port injected fuel to wash it off.

Exhaust soot is all from the direct injection combustion process in the cylinders - having port injection capability doesn't prevent the formation of soot when the car is running with direct injection.

Not sure why your exhaust stays so clean (without you cleaning it) unless your exhaust terminates with a cut pipe rather than cosmetic tips, and possibly the cut pipe gets hot enough to burn off the soot (whereas an attached tip wouldn't).

Or maybe you drive extremely frugally (soot formed in greater quantities when a rich mix is direct injected, less complete combustion)?

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Re: Intermittent Engine or Brake Issue?

Post by Dark_cze » Fri Jan 17, 2020 7:26 pm

RUM4MO wrote:
Fri Jan 17, 2020 3:37 pm
Dark_cze wrote:
Fri Jan 17, 2020 3:00 pm
monkeyhanger wrote:
Fri Jan 17, 2020 2:43 pm
My 2018 GTI+ without GPF has sooty tailpipes, my wife's 2019 GTI+ with GOF has spotlessly clean tailpipes.

The tailpipes on my 2015 Golf R were filthy too.
I have gti made in 11/2018 spain. With GPFand my tailpipes are black like my old diesel Audi A4 B6 :D no fluids are missing and consumption is fine so I guess no technical problems there.
That is interesting, I'd expect that you would find the same as monkeyhanger finds with his wife's GTI+ with GPF, so what exactly is your GPF doing when it is passing the soot that appears on the tips?
Doing what all others gti do ... driving :-D I mean sometimes I drive it like a normal person on highway, some driving to work (that is around 8km one way) and then a lot of driving around like I stole it :-D it is manual transmision so this might be my fault because of keeping wrong revs. Dsg might be cleaner because ecu is shifting better than me :)

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