Accelerator Stuck Open at 4,500 rpm!
#1
Accelerator Stuck Open at 4,500 rpm!
Excellent Don!
I just had something strange happen to my '90.
Crossing a highway under green I goosed the engine and hit the brakes on the other side of the intersection.
The accelerator stuck open -4500 RPM!
Wouldn't return to normal after a hot restart.
The linkage is free so I'm thinking TPS or ECU?
Have the bonnet open to help cool it down and disconnected the battery to reset the ECU.
Any thoughts?
I just had something strange happen to my '90.
Crossing a highway under green I goosed the engine and hit the brakes on the other side of the intersection.
The accelerator stuck open -4500 RPM!
Wouldn't return to normal after a hot restart.
The linkage is free so I'm thinking TPS or ECU?
Have the bonnet open to help cool it down and disconnected the battery to reset the ECU.
Any thoughts?
#2
Join Date: Feb 2014
Location: Crossroads of America
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Hi Roger,
I've moved your post from the thread on oil cooler lines to start your own thread, since yours is a very serious issue!
Since the throttle linkage is free, what about the throttle plate/butterfly valve? Any chance it stuck open? The TPS would be another suspect, but I don't know how it could cause the engine to run at 4,500 rpm if the butterfly valve was closed and preventing sufficient air from entering the intake. If the Idle Air Control Valve stepper motor stuck open it could lead to high idle, but again, I don't know if it could be enough for the engine to run at 4,500rpm. Any chance the accelerator pedal got caught on the floor mat?
Cheers,
Don
I've moved your post from the thread on oil cooler lines to start your own thread, since yours is a very serious issue!
Since the throttle linkage is free, what about the throttle plate/butterfly valve? Any chance it stuck open? The TPS would be another suspect, but I don't know how it could cause the engine to run at 4,500 rpm if the butterfly valve was closed and preventing sufficient air from entering the intake. If the Idle Air Control Valve stepper motor stuck open it could lead to high idle, but again, I don't know if it could be enough for the engine to run at 4,500rpm. Any chance the accelerator pedal got caught on the floor mat?
Cheers,
Don
#4
Join Date: Feb 2014
Location: Crossroads of America
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Could something in the accelerator pedal pivot be loose or worn and have caught? Could your kickdown switch have stuck on (part 22 below)?
The parts list is here:
https://www.jaguarclassicparts.com/u...-from-v-594576
Cheers,
Don
The parts list is here:
https://www.jaguarclassicparts.com/u...-from-v-594576
Cheers,
Don
#5
I checked the throttle plate and all was well re moved freely, no binding open or closed and so on
I disconnected the battery to let the ECU reset and all is well.
Took for a decent drive around 4:30 and all is well.
Could hard acceleration and fast hard braking mess with the ECU, TPS?
Gotta be everything else appears to be as it should..? Puzzling for sure.
I disconnected the battery to let the ECU reset and all is well.
Took for a decent drive around 4:30 and all is well.
Could hard acceleration and fast hard braking mess with the ECU, TPS?
Gotta be everything else appears to be as it should..? Puzzling for sure.
#6
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Location: Crossroads of America
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Hi Roger,
Just trying to think this through:
1. On an XJ40, the TPS is purely a passive potentiometer and the throttle has no built-in motor that can open the valve; the throttle valve is strictly mechanical, controlled by the accelerator pedal and cable linkage;
2. If the TPS signal were corrupted such that the ECM read the throttle as wide open (WOT), it would increase the injector pulse duration to allow more fuel into the combustion chambers;
3. But it wouldn't matter how much the ECM increased fueling if the throttle valve did not open to allow sufficient air for proper combustion. If the throttle remained closed or not sufficiently open, the Air-Fuel Ratio might get so rich that it could not ignite, the definition of flooding, but the rpm would only rise a bit before the engine stumbled and choked and died.
The above points make me think that for your engine to have stuck at 4,500 rpm, either the throttle must have stuck open, or a large air leak must have opened up somewhere in the plumbing between the throttle and intake manifold (which doesn't seem very likely).
Or maybe my brain is just too tired to think of a better idea.
Cheers,
Don
Just trying to think this through:
1. On an XJ40, the TPS is purely a passive potentiometer and the throttle has no built-in motor that can open the valve; the throttle valve is strictly mechanical, controlled by the accelerator pedal and cable linkage;
2. If the TPS signal were corrupted such that the ECM read the throttle as wide open (WOT), it would increase the injector pulse duration to allow more fuel into the combustion chambers;
3. But it wouldn't matter how much the ECM increased fueling if the throttle valve did not open to allow sufficient air for proper combustion. If the throttle remained closed or not sufficiently open, the Air-Fuel Ratio might get so rich that it could not ignite, the definition of flooding, but the rpm would only rise a bit before the engine stumbled and choked and died.
The above points make me think that for your engine to have stuck at 4,500 rpm, either the throttle must have stuck open, or a large air leak must have opened up somewhere in the plumbing between the throttle and intake manifold (which doesn't seem very likely).
Or maybe my brain is just too tired to think of a better idea.
Cheers,
Don
Last edited by Don B; 04-29-2019 at 09:24 AM.
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I had similar happen yesterday afternoon, not as extreme but the throttle stuck open nonetheless. I found two things wrong and both involved the vacuum bellows
on the speed control. The linkage inside the bellows was sticking and what I think is the true problem. The linkage from the bellows was attached incorrectly to the throttle plate.
It was mounted to the top instead of the bottom of the throttle plate attachment. I didn't check this the first time I had a stuck throttle.
on the speed control. The linkage inside the bellows was sticking and what I think is the true problem. The linkage from the bellows was attached incorrectly to the throttle plate.
It was mounted to the top instead of the bottom of the throttle plate attachment. I didn't check this the first time I had a stuck throttle.
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