Off throttle - the car seems to continue to fuel itself

[minke]

Hi,

I wasn't sure how to title this, and I'm really struggling to think of how to describe it.

Manual Mark 6 GTI 33,0000km 2.5 years old.

I'm noticing that when driving along with some throttle (in moving traffic) when I get out of the throttle (no application of brake, just coasting) it seems like the car takes a long time to respond. a second to maybe two, before the car starts to slow down against the compression of the engine.

Not only can I only feel it, but hear the exhaust not change significantly later than getting out of the throttle.

It is almost as if the car continues to fuel itself long after I've removed the input.

Anyone else experienced this?

Cheers
Justin

ps I'm aware that compression braking is not as aggressive in a turbocharged car. It seems it's more about the fly by wire throttle being slow to respond to my removal of input. (but not slow in application)

[h100vw]

Manual or DSG?

Can't see why compression braking would be different in a turbo car. My Polo slows down appreciably off throttle. Where my S3 rolls for ages. The difference in the 2 would be the vehicle weight and that the S3 has a DMF clutch, where the Polo is on a LWFW and clutch.

I am pretty sure if you were to log the fuelling with VCDS you would see the fuel cut as you came off the throttle. It would cut back in around 1500 revs to prevent stalling.

Gavin

[Snail Style]

Have VCDS? Make sure the clutch switch is working correctly.

[wai]

I experienced a similar effect when I was given a Jetta as a loan car. When I mentioned it to the dealer, he said it was something to do with the ECU trying to avoid unnecessary accelerator on/off cycles. The result was that the accelerator remained "on" for a short while after lifting off in case you were thrn going to re-apply the accelerator.

[minke]

Manual Mk6 GTI - Getting out of the throttle the car continues to fuel itself

Hi all,

I've described this issue before without much success. I've captured a video and would certainly like to hear from anyone that has experienced this, explained it to a dealer and had it resolved.

Here is YT clip https://youtu.be/Ri5GUdv1LtA

Issue
When you get off the throttle, there is a good two second delay before compression braking occurs. Car never did this before, friends manual mark 6 GTI doesn't do it either.

In the video (to help show the issue) what I do is knock it out of gear and get off the throttle and it is around two seconds latter before the revs drop. Also interesting to note that the car is still requesting that I pick fourth even though I'm in neutral.

Thoughts please

[Lucas_R]

Im not much help to you - but can only confirm that its not normal. I currently have a manual Mk6 GTI (and used to have a manual Mk6 Golf R) and neither of my cars have/had a delay like that when coming off the throttle.

These cars do have what is commonly referred to as "rev hang" when coming off the throttle, which is caused by the drive by wire throttle, but it's no where near as long as what you are experiencing.

If you apply the brakes immediately after coming off the throttle, does the engine back off immediately, or does it still take a few seconds as per the delay in your video. If so, it could potentially be dangerous (not to mention annoying) if the engine is still applying throttle when you want it to back off or slow down.

Does the car have this behavior ALL the time? Does it do it when cold, when casually driving around suburbs etc

Also, to possibly help your cause, is the cars engine modified in any way (ECU re-tune / exhaust/ intake etc etc).

There are a few clued up and helpful VW tech's on this forum, so hopefully one of them may be able to shed some light on what is causing this.

[minke]

Lucus. Thank you for your input.

To answer your questions :
Rev hang : yea knew that but wasn't aware it was worse for VW?

I thought it was temp related. Recently had a morning where it was ok (ambient around 6/8 degrees) but it was once off.

Most definitely does it under brakes. You can feel it fighting me

Not modified at all

Also had a recent oil change (to rule out).

This might seem far fetched but I think the car is protecting itself. Modern cars will fuel themselves to cool cylinder heads etc. (86s do this). So I think the car "think" or "senses" something is hot and is using fuel to cool inside the combustion chamber.

2.8 years and 36000km I've raised loss of coolant every six months (all test show pressure is maintained) and my oil can be 103-108 with city driving (moving not much traffic and no boost/ shifting early around 2000). My friends GTI never seems to crack 95

Hence I think logically the ecu detects it's hot and as such dumps fuel to cool.


Sent from my iPhone using Tapatalk

[zoolander]

Get it checked out by a specialist. Could be dangerous in a emergency situation.

[minke]

Get it checked out by a specialist. Could be dangerous in a emergency situation.

I have. Two dealers. All operating as normal. I disagree but I've nothing to argue. I was able to demonstrate the issue with the QA advisor at Barloworld Mascot. He himself said it seemed odd but wanted to compare another GTI Mark 6. Two days later I get the car back (supposedly reset ECU values - however I note that all the values relating to fuel usage and time since last reset and the number of km was still in there)

Meanwhile, I note that my engine oil always seems to run hot. As per below. After 14km of driving to/from shops. I left it idling for a few minutes (3?) and it dropped to 107. Oil is 2160.7km old and the approved Castrol oil as per what the deal would use.

Frustrating. If anyone has an idea and access to VAGCOM that might know what to look for I'm happy to pay beer.

[h100vw]

I have. Two dealers. All operating as normal. I disagree but I've nothing to argue. I was able to demonstrate the issue with the QA advisor at Barloworld Mascot. He himself said it seemed odd but wanted to compare another GTI Mark 6. Two days later I get the car back (supposedly reset ECU values - however I note that all the values relating to fuel usage and time since last reset and the number of km was still in there)

Meanwhile, I note that my engine oil always seems to run hot. As per below. After 14km of driving to/from shops. I left it idling for a few minutes (3?) and it dropped to 107. Oil is 2160.7km old and the approved Castrol oil as per what the deal would use.

Frustrating. If anyone has an idea and access to VAGCOM that might know what to look for I'm happy to pay beer.

Resetting the ECU doesn't do anything to the instruments.

You could only see it by checking the fuel trims with VCDS.

Does the oil temp stay up on the highway too?

Gavin

[minke]

Resetting the ECU doesn't do anything to the instruments.

You could only see it by checking the fuel trims with VCDS.

Does the oil temp stay up on the highway too?

Gavin

Gavin - Thank you for your input.

I assumed that resetting ECU would reset all values.

I assume the dealers checked the fuel trims. It's interesting to note that when I have instant fuel economy displayed and get out of the throttle it takes a long time before it displays 0.0L/100. My friend's GTI did not exhibit this delay .

I can think of two examples on high (what I think is high) oil temp.

* Sydney to Wollongong with an ambient temp of 13 degrees the oil was reading 106-107 at 110 in 6th gear cruise control
* Inner Sydney to Parramatta (lunch with a friend) then Parramatta (via M4) back to inner west. Great traffic flow, no lights run. 108 degrees. I think ambient that day was 15.

I wonder if the 'oil temp' is related somehow. Modern cars will fuel the cylinders to aid cooling. If the car thinks it is hot, it might be dumping extra fuel for cooling. I know many a modern car does this now so I would assume the Golf has that programmed into its ECU

[h100vw]

Gavin - Thank you for your input.

I assumed that resetting ECU would reset all values.

I assume the dealers checked the fuel trims. It's interesting to note that when I have instant fuel economy displayed and get out of the throttle it takes a long time before it displays 0.0L/100. My friend's GTI did not exhibit this delay .

I can think of two examples on high (what I think is high) oil temp.

* Sydney to Wollongong with an ambient temp of 13 degrees the oil was reading 106-107 at 110 in 6th gear cruise control
* Inner Sydney to Parramatta (lunch with a friend) then Parramatta (via M4) back to inner west. Great traffic flow, no lights run. 108 degrees. I think ambient that day was 15.

I wonder if the 'oil temp' is related somehow. Modern cars will fuel the cylinders to aid cooling. If the car thinks it is hot, it might be dumping extra fuel for cooling. I know many a modern car does this now so I would assume the Golf has that programmed into its ECU

There's probably over 10 ECU in the car. So you can assume nothing to be the case.

I doubt that VW would look at trims. The ECU would show a code if it was outside the limits it has been taught.

I have an AFR gauge on my Polo and it takes a lazy count to 2 to have the fuel shut off completely.

Modern cars have heavy flywheels which hold lots of inertia. My S3 will roll for ever compared to my Polo.

There's no way they inject fuel to aid cooling, it is often done during high loads to reduce cylinder temps but not for cooling. Why would they bother with water if that were the case. I think you have 2 concepts confused there.

IMO you are over thinking the Oil temp thing. They have taken nearly all instrumentation out of aircraft cockpits to reduce pilot workload. Only when something is outside of normal parameters will it be displayed as a caution.

Not sure where the oil temperature is sensed but if it's in the sump, then it makes sense that it is hotter than the water. As the pump would pass it around the heat exchanger afterwards reducing the temp before it lubricates most of the engine.

Gavin

[Snail Style]

Did you check the clutch switch yet? :S

[Lucas_R]

I have. Two dealers. All operating as normal. I disagree but I've nothing to argue. I was able to demonstrate the issue with the QA advisor at Barloworld Mascot. He himself said it seemed odd but wanted to compare another GTI Mark 6. Two days later I get the car back (supposedly reset ECU values - however I note that all the values relating to fuel usage and time since last reset and the number of km was still in there)

Meanwhile, I note that my engine oil always seems to run hot. As per below. After 14km of driving to/from shops. I left it idling for a few minutes (3?) and it dropped to 107. Oil is 2160.7km old and the approved Castrol oil as per what the deal would use.

Frustrating. If anyone has an idea and access to VAGCOM that might know what to look for I'm happy to pay beer.

No doubt there are some variances from car to car, but my Mk6 GTI's engine oil temp rarely sees above the mid to high 90's. Im going to Sydney this weekend and will be around the Camden area, so if that's close to where you live we could meet up and compare cars etc. I could bring my VCDS cable and laptop. I will have a bit of free time in the mid/late afternoon.

We could check fault codes (if any) and look at your fuel trims.

Not sure where the oil temperature is sensed but if it's in the sump, then it makes sense that it is hotter than the water.

Gavin

Yes Gavin its in the sump

[Lucas_R]

Did you check the clutch switch yet? :S

Listening to ^^^ this guy might be a good idea too. He is a VW tech.

Snail Style - do you know where in VCDS you can check the clutch switch operation? What module?