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Discussion Starter · #1 ·
A couple of times now my cruise control seems to have started accelerating as I come over the brow of a hill. It seems that as I climb the hill, the throttle is opening but as I come down the other side, it is as if the throttle is staying open and I start accelerating. If I flick the throttle pedal, it returns to normal. I have also had a similar occurance with the cruise control turned off when I ease off the throttle the car keeps accelerating. Dipping the clutch shows that the engine is idling at around 1500 - 2000 rpm, again, flicking the throttle brings it back to normal.

Obviously, there is no throttle cable to be sticking and as it affects the cruise control and the throttle pedal, would this mean the injection pump has a problem, or is there a sensor that can be causing this?

It's happened 3 or 4 times so far.
 

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What happens if you dont flick the throttle? Will it pickup in excess of the set speed?
 

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Hi Mark,

That's a curious one! If you look at the following graphs of accelerating to 70 mph and then releasing the throttle you'll see the effect on fuel injected, rail pressure and boost pressure. Without really much experience of this my guess would be that excess rail pressure was the most likely cause of your continuing acceleration. I don't think maintaining boost without fuel would make much difference and I can't see the injection pulse widths being maintained when the ECU didn't command it. My advice would be to replace the Inlet metering valve on the injection pump.

Peter



You can see the effects of injection pulse width and rail pressure on the quantity of fuel injected in the graph below.
 

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Will the ForDiag give a throttle position reading when in cruise control?

I think i used the Bluetooth OBD reader and that didn't
 

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Hi Purple,

It will give the three accelerator pedal position sensor readings just as F-Super does but for cruise control you want to know what the ECU thinks is the Fuel Demand and again both Fordiag and F-Super will display this. So it would be useful to monitor these parameters whilst running with either cable.

Following on from my guesswork both cables can monitor rail pressure and that would be my favourite target but all these parameters can all be recorded simultaneously.

Now who do we know in South Wales with an F-Super???


Peter
 

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Discussion Starter · #6 ·
If I don't flick the throttle it keeps accelerating. I noticed yesterday that I was up to 75 MPH on a gentle downhill slope despite cruise control being set at 60.

Its been a chaotic weekend so not had time to look at it yet. I have an F-Super so I'll plug it in and see if it picks anything up. It only deems to happen every few days so it's going do be difficult to pick anything up with live data. Hopefully it will throw a DTC up though.
 

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Peter, I would have liked the throttle position it used so i could repeat runs in different gears.

Fuel demand doesn't look as simple as the throttle % position required.

Thanks
 

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Peter, I would have liked the throttle position it used so i could repeat runs in different gears.

Fuel demand doesn't look as simple as the throttle % position required.

Thanks
Hi Purple,

I guess if you were recording F-Super's live data then you would see the accelerator pedal position at the point when you engaged cruise, as you would then take you foot off the pedal and you'd see that on the recording.

Thereafter the ECU will ignore pedal movements unless they exceed the cruise point. Vehicle speed will also appear in the recording.

Peter
 
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