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Old 9th January 2007, 15:30   #46
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Originally Posted by Sideways View Post
In my experience fuel cut is normally related with speed and not RPM or gears. I may be wrong about GM's theory and am open to further details.
Hi Farhan,

You are absolutely correct. This car has been limited electronically by GM. Those donkeys out here themselves dont know or dont want to tell how hence the stupid answers. Had given Boom the same suggestion that you did as well. Gonna take the car in a day or two to install the same. Have another possible remedy as well am confident we should get around this quite easily just a matter of time and patience.

Will let Boom post on results and whether it made a diff or not.

Viper

Last edited by viper : 9th January 2007 at 15:31.
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Old 9th January 2007, 15:33   #47
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Maybe the fuel cutoff only corresponds to a 180 kmph top speed, which was 6300 rpm in 4th but 5000 rpm in 5th, so it won't go any further. So it could be a speed and rpm based pickup signal, so then 180 kmph at 5000 rpm for the engine would correspond only to 5th gear for a certain set of fixed gear ratios , no?
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Old 9th January 2007, 15:36   #48
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Originally Posted by ported_head View Post
Maybe the fuel cutoff only corresponds to a 180 kmph top speed, which was 6300 rpm in 4th but 5000 rpm in 5th, so it won't go any further. So it could be a speed and rpm based pickup signal, so then 180 kmph at 5000 rpm for the engine would correspond only to 5th gear for a certain set of fixed gear ratios , no?

I doubt their system is that advanced / complicated. You would have to programme gear ratios into the ECU for which you would have to have a seperate sensor to send a signal.

Or there has to be a link between the 5th gear and the ECU so that the ECU knows that the car is in 5th and then induces fuel cut with input from the RPM pick up.

Lke I said, i might be wrong and am open to a better explanation.

Last edited by Sideways : 9th January 2007 at 15:43.
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Old 9th January 2007, 16:44   #49
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Farhan, its not hard to conceive that there is a way that the ECU would know which gear the car is in. Heck, my 1979 Suzuki GS had a gear indicator display.

I'm not saying that GM has installed such a sensor on the Optra, highly unlikely actually. Its almost certainly just a simple speed restrictor placed by GM due to the speed rating of their OE tyres.
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Old 9th January 2007, 17:10   #50
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Originally Posted by Sideways View Post
As an example, in most jap spec cars the top speed is limited to 180 KMPH. After which the Ecu induces a fuel cut irrespective of the gear or the rpm.
O.T. - Is this why my OHC 1.5 doesn't cross 180kph?

p.s. - sorry BS, don't mean to hijack your thread.
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Old 9th January 2007, 17:12   #51
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Farhan, its not hard to conceive that there is a way that the ECU would know which gear the car is in. Heck, my 1979 Suzuki GS had a gear indicator display.
Agreed Robin.

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Its almost certainly just a simple speed restrictor placed by GM due to the speed rating of their OE tyres.
I doubt they have a speed restrictor in place. Seans problem is something else actually. He is going to make some changes. Lets see if it works.
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Old 9th January 2007, 17:20   #52
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Quote:
Originally Posted by Sideways View Post
Seans problem is something else actually. He is going to make some changes. Lets see if it works.
hmm...seems you know a bit more than most, so lets see what the end result is. keep this thread alive!
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Old 9th January 2007, 18:22   #53
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The ECU will know which gear your car is in with two variables one is engine RPM & other is Vehicle Speed (using vehicle Speed sensor) these values must have been calibrated with gearbox/gear ratios in use, the data is fed in ECU during development process by GM engineers. Hence when at X RPm when X is speed then = fuel cutoff.
So the ECU goes reverse way say eg when in 1st gear you are at 6000 RPM =55KMPH so ECU will read RPM (6000) & Speed (55KMPH) & it will know its 1st gear.
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Old 9th January 2007, 23:16   #54
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Originally Posted by Boom Shiva View Post
Goes up to the redline (6.3k) in 4th. But the speed doesn't go past 177-180.

When you shift to 5th it drops to 5k and doesn't budge. Speedo also remains annoyingly stuck at the same place.

I got in touch with the GM people and they told me about the fuel cut off. So at least I know what's causing the issue. Now to figure a way around it!
this does sound very strange and hard to digest but you never know it may be true
btw its better you stay under 180 on indian roads no matter how good they be
try checking the gearbox and its vicinty for a gear sensor
or else it may limited via the way jitu suggested or may be speed limited
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Old 9th January 2007, 23:34   #55
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Arrow Bypass surgery

Care to share the workarounds with the rest of the community, gentlemen (sideways/ viper)? We have enough *classified* information doing the rounds on team-bhp anyway. So this can't hurt too much.

sAP
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Old 10th January 2007, 01:27   #56
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I guess they're waiting for the workarounds to be proven before announicing them here. Rest assured that if they do find a solution they WILL post it here for benefit of other people too.
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