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Old 03-11-2017, 02:42 PM   #1
zenith
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Drives: 2013 Golf Silver 2.5 5 speed
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2.5 fuel does not cutoff

I had bought a 2013 VW Golf with the 2.5 5 cylinder and 5 speed manual recently and one thing I noticed about it is that under most circumstances, the fuel does not cut off when you take your foot off the gas. In fact, even when braking it doesn't cutoff. I can see this when I set the MFI display to instantaneous mileage and I still see a MPG reading and not --.--

I own a ScanGuage II and I plugged it in and I saw that the throttle would mostly close, but the engine was still receiving fuel and the spark plugs were firing.

There are some circumstances where it does cut off, but only when;

I'm over 3500 rpm in any gear,
I'm in 5th gear over 1500 rpm (over 50 mph).
If I'm in 1st it seems to only cut off over 2500 rpm.
In 2nd it will cut off but only after a few seconds over 2k rpm.
3rd seems to take about 10 seconds for it to cut off, and only above 1500 rpm.
If the engine is cold, it seems to cut off at a lower rpm, and in a shorter amount of time as well.

It just seems annoying to me because it makes low speed driving somewhat of a chore as I have to shift to neutral any time I want to slow down, or I just have press harder on the brake pedal, which to me is a waste of brakes and waste of gas to brake while the engine is firing. I came from a 97 Civic HX 5 speed before this car and I guess I'm just used to the car engine braking immediately when I'm slowing down.

I had a dealer look at it and they say the car does this by design. They seemed puzzled by my description of my issue, so I'm not sure if they knew what they were doing or not. They claimed that the engine has to fire in order to generate vacuum for the brake booster and so that the electric power steering has power to operate as well.

But the engine doesn't lose vacuum just because it's not receiving fuel, the engine is still spinning with a near closed throttle, which should generate plenty of vacuum. A bicycle air pump generates vacuum from pushing up and down on its handle without combustion. The alternator should also be spinning and generating electricity as well.

It may be to the point that I'll have to get a different car if this is truly part of its design to do that, but now I'm wondering if all new manual cars do that now (got nothing against autos I just prefer manual is all).

Hopefully what I typed here makes sense, thanks to anyone who took the time to read!
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Old 03-12-2017, 02:34 AM   #2
madbikes
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Drives: 2012 Golf 2.5L 5-speed
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Mine is a 2012. Unfortunately, I have addressed similar to what you are describing to at least one dealer and the response I got is somewhere along the lines of normal. Modern age manual cars (usually after year 2000 with drive-by-wire) have what is called rev-hang and how severe it is will depend on the make and car.

From what I read, it's designed to improve emissions on manual cars. It's not a VW only thing, Honda, Subaru do have them. Some claims rev-hang destroys clutches, but if it hangs at high RPM, it can. When I replace my clutch at 62K with a lighter single-mass flywheel and clutch kit, there was enough material to keep driving and no hotspots on the OEM flywheel.

The way mine happens, drivability-wise, felt like the throttle is stuck open for a small amount of time after you let go of the gas, which leads to engine still want to speed up as you shift up. If I shift up at lower RPM, it can hang and I have to wait.

A tune may relief the problem, but may not completely solve it. A lighter flywheel will also help out, but the issue still exist after doing both. Even for me, I can drive better with an older drive-by-cable manual car, which I did drive a 00' SI owned by someone I used to work with and did way better. So don't feel too bad.
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Old 03-12-2017, 06:24 AM   #3
stevenj
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Quote:
Originally Posted by madbikes View Post
..... Modern age manual cars (usually after year 2000 with drive-by-wire) have what is called rev-hang and how severe it is will depend on the make and car.

From what I read, it's designed to improve emissions on manual cars. It's not a VW only thing, Honda, Subaru do have them. ...
If you want to learn more about rev hang in recent model cars, you may want to look at my website with charts and videos. It will confirm your own findings and suggest a way how to deal with it.
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Old 03-13-2017, 01:07 AM   #4
madbikes
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Is there such device for VW in development?
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Old 03-13-2017, 08:50 AM   #5
stevenj
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In order to adjust software of my module to suit other cars, I need either access to the car (e.g. VW) or an interested owner of such a vehicle to take measurements of some ECU signal levels. In any case, ECU pinout diagram is required first to identify the relevant signal wires.
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Old 03-13-2017, 11:00 AM   #6
gugu1981
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Drives: 2012 JSW 2.5 5MT
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The OP mentioned it taking 10 seconds before throttle is really closed, that's not rev-hang. Rev-hang is a second or so.

I would say inspect your throttle body and see if it's sticking in any way. It might be worth cleaning it, including the rotating assembly of the valve and then go through a throttle body alignment procedure.


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