Engine Dies on overrun
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- Ian Anderson
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Engine Dies on overrun
Hi
Something that has always happened but I just drove around the problem.
In the GT40 RV8 3.9 JE102 cam balanced and a screamer! Hotwire ecu
So drive on road, lift off and use engine braking, once slow, put in the clutch and engine dies.
Same place, driving, dip clutch and brake to stop and the engine idles perfectly.
Only non standard thing that I can think of is that the normal take off for the advance on the dizzy comes straight up near the butterfly, but no height available under the deck lid means it was blocked off and a T taken from the fuel pressure regulator to plenum tube.
I presume that the vacuum reading is the same in bothtake off positions so this may be a red herring.
OR
does the standard advance take off sample the vacuum before the butterfly and hence will be at a different vacuum to the plenum at idle when the butterfly is closed?
Only reason I ask is my daughter drove the car for first time over the weekend and really battled not to engine brake and stall the engine each time she slowed.
Any thoughts guys?
Thanks
Ian
Something that has always happened but I just drove around the problem.
In the GT40 RV8 3.9 JE102 cam balanced and a screamer! Hotwire ecu
So drive on road, lift off and use engine braking, once slow, put in the clutch and engine dies.
Same place, driving, dip clutch and brake to stop and the engine idles perfectly.
Only non standard thing that I can think of is that the normal take off for the advance on the dizzy comes straight up near the butterfly, but no height available under the deck lid means it was blocked off and a T taken from the fuel pressure regulator to plenum tube.
I presume that the vacuum reading is the same in bothtake off positions so this may be a red herring.
OR
does the standard advance take off sample the vacuum before the butterfly and hence will be at a different vacuum to the plenum at idle when the butterfly is closed?
Only reason I ask is my daughter drove the car for first time over the weekend and really battled not to engine brake and stall the engine each time she slowed.
Any thoughts guys?
Thanks
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
- Ian Anderson
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Many thanks for that so would it be better to run no vacuum?DEVONMAN wrote:The dizzy advance take off point has no vacuum at idle or overun. If you have connected the dizzy advance canister to full plenum vacuum the timing will be all over the place unless your dizzy has been set up for that situation like on many Americam V8's
Not many miles done each year so any loss in consumption not to big a deal!
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
- Ian Anderson
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Thanks I will give it a try.
Just to clarify, if the vacuum take off is on the filter side of the butterfly, surely it only ever sees ambient air pressure? Or does the air rushing in cause a Venturi effect to generate the vacuum needed for the dizzy? Just I cannot see any Venturi near the butterfly / original take off position.
Cheers
Ian
Just to clarify, if the vacuum take off is on the filter side of the butterfly, surely it only ever sees ambient air pressure? Or does the air rushing in cause a Venturi effect to generate the vacuum needed for the dizzy? Just I cannot see any Venturi near the butterfly / original take off position.
Cheers
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
The vacuum take of is set just next to the edge of the butterfly so that it gets vacuum as the air rushes past it when the butterfly is just cracked open. (Light throttle conditions). The small gap between the edge of the butterfly and the bore effectively becomes a venturi point and the air rushing past causes a vacuum in the take off and advances the ignition only on light throttle.Ian Anderson wrote:Thanks I will give it a try.
Just to clarify, if the vacuum take off is on the filter side of the butterfly, surely it only ever sees ambient air pressure? Or does the air rushing in cause a Venturi effect to generate the vacuum needed for the dizzy? Just I cannot see any Venturi near the butterfly / original take off position.
Cheers
Ian
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Ian, If you have had this problem long term then I suspect that you may have a problem with your road speed sensor. Check that it is working correctly, google it, it can be dismantled and is only a magnetic rotor and a reed switch in series with a 120R resistor.
Failing that check/set up your base idle speed, again plenty of info on the net.
Hope this is of help.
Andy.
Failing that check/set up your base idle speed, again plenty of info on the net.
Hope this is of help.
Andy.
If the speed sensor is faulty then on engine braking it may be telling the ecu that the car is moving faster than it really is, and therefore the injectors pulse is switch off too long on overrun. However this switching off feature should also be controlled by engine revs.
On a down hill approach to a fast road roundabout my engine often dies if I have to suddenly dip the clutch and brake due to quickly appearing traffic from the right.
- Ian Anderson
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Thanks guys
No road speed sensor not on. 1990 system CUX Hotwire not CU flapper
And thanks for the explanation re the Venturi and butterfly just cracked open, certainly never thought of that, just one side of butterfly or the other.
Next time the car is out I will try with no vacuum connected and see how that goes
Ian
No road speed sensor not on. 1990 system CUX Hotwire not CU flapper
And thanks for the explanation re the Venturi and butterfly just cracked open, certainly never thought of that, just one side of butterfly or the other.
Next time the car is out I will try with no vacuum connected and see how that goes
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
- Ian Anderson
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- Location: Edinburgh
Exactly what happens on mine.DEVONMAN wrote:
On a down hill approach to a fast road roundabout my engine often dies if I have to suddenly dip the clutch and brake due to quickly appearing traffic from the right.
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
- Ian Anderson
- Forum Contributor
- Posts: 2396
- Joined: Sun Nov 19, 2006 9:46 pm
- Location: Edinburgh
Many thanks for the snip of the article which I believe is fully found here.
http://www.gt40s.com/forum/site-questio ... nside.html
So I have never had a road speed sensor, also have no spare connectors that are unused, other than purge valve. So where in the loom would these normally connect?
With this in a GT40 replica it is not a standard Rover /TVR / Morgan gearbox so no connections to a speedometer. I can sort out a bolt counter on the CV or similar that get a road speed signal, but where to connect the other end?
Also as this thing does about 160 top end I certainly do not want it to be limited by the same system that limits other vehicles to 115mph.
Perhaps I should still go carb, none of this electronic stuff getting in the way of driving it
Ian
http://www.gt40s.com/forum/site-questio ... nside.html
So I have never had a road speed sensor, also have no spare connectors that are unused, other than purge valve. So where in the loom would these normally connect?
With this in a GT40 replica it is not a standard Rover /TVR / Morgan gearbox so no connections to a speedometer. I can sort out a bolt counter on the CV or similar that get a road speed signal, but where to connect the other end?
Also as this thing does about 160 top end I certainly do not want it to be limited by the same system that limits other vehicles to 115mph.
Perhaps I should still go carb, none of this electronic stuff getting in the way of driving it
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.