Hiccup on gear change, what is it?
08 August 2003, 10:03 AM
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Mornin all
When I boot the car and change gear from say 2nd to 3rd, i find that if i release the clutch quickly and get straight back on the power, the car kinda hiccups! It's like fuel cut but not as aggressive, almost like drivetrain shunt or slack being taken up but it's dictated by the engine. It's like theres a blockage somewhere and the engine has to cough it out first before it can get on with the power delivery.
Getting round it is straight forward, if i pause for a second with my foot on the clutch, let the revs drop a bit and THEN release and accelerate, it's fine.
The car has done it since new so i know it's not something going wrong and most other scoobs i've been in do it to.
Folk often call it over boost but i'm not sure.
Any ideas anyone?
Mikey
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>
When I boot the car and change gear from say 2nd to 3rd, i find that if i release the clutch quickly and get straight back on the power, the car kinda hiccups! It's like fuel cut but not as aggressive, almost like drivetrain shunt or slack being taken up but it's dictated by the engine. It's like theres a blockage somewhere and the engine has to cough it out first before it can get on with the power delivery.
Getting round it is straight forward, if i pause for a second with my foot on the clutch, let the revs drop a bit and THEN release and accelerate, it's fine.
The car has done it since new so i know it's not something going wrong and most other scoobs i've been in do it to.
Folk often call it over boost but i'm not sure.
Any ideas anyone?
Mikey
<Wanting to know more >
08 August 2003, 12:27 PM
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Hi Mikey
Some people reckon it's turbo lag, but I'm more convinced it's something to do with the centre diffs redistributing the power through the drivetrain. Movement in the rear diff might also have a contribution. When it does it really bad you get a bang from inside the boot, which apparently is the rear diff moving up and hitting the underside of the car
Could be talking out my asre though
Cheers
Simon
Some people reckon it's turbo lag, but I'm more convinced it's something to do with the centre diffs redistributing the power through the drivetrain. Movement in the rear diff might also have a contribution. When it does it really bad you get a bang from inside the boot, which apparently is the rear diff moving up and hitting the underside of the car
Could be talking out my asre though
Cheers
Simon
08 August 2003, 12:53 PM
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Hmmmm, maybe.
I reckon it's got summat to do with turbo's, manifold pressure etc. The action of being hard on the gas, lifting of to change gear and then slamming all that boost back through the system again could be triggering summat in the ecu and the car is just protecting itself. Maybe.
By pausing slightly before re applying power, the "system" has time to kinda get ready before the next onslaught.
Just a thought
Anyone really know?
Mikey
I reckon it's got summat to do with turbo's, manifold pressure etc. The action of being hard on the gas, lifting of to change gear and then slamming all that boost back through the system again could be triggering summat in the ecu and the car is just protecting itself. Maybe.
By pausing slightly before re applying power, the "system" has time to kinda get ready before the next onslaught.
Just a thought
Anyone really know?
Mikey
08 August 2003, 01:01 PM
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I don't think it's an ecu thing because I've datalogged it and there is no abnormal readings re fuelling/timing/boost. Definately a drivetrain prob.
If you imagine full load to no load to full load, the amount of movement and forces through the drivetrain will be significant, especially as it's all rotational forces. Just look at the engine when you blip the throttle - the whole engine rocks.
Simon
[Edited by SiHethers - 8/8/2003 1:04:17 PM]
If you imagine full load to no load to full load, the amount of movement and forces through the drivetrain will be significant, especially as it's all rotational forces. Just look at the engine when you blip the throttle - the whole engine rocks.
Simon
[Edited by SiHethers - 8/8/2003 1:04:17 PM]
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