I have just blown through an ISV of the car, which supports that without power there is a fixed position that supposedly allows the car to idle, according to the info, slightly higher! I guess by that they don't mean 1200-1500rpm! If it is earthed via the ecu, I am wondering what happens if it was shorted to earth permanently. If it can open more than this default setting then that makes sense.
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Yes Robin the idle is the same with both sensor dissconected.
And I agree, with you I think it is a wiring issue.
I have already checked he main sensor wireing from the ecu for continuity,but I will check it again.
I cannot quite understand what would cause the car to run ok when cold and then run badley as it approaches tempreature, and this problem what ever it is,is definatly tempreature related.Comment
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What did you do with the N75 after?Comment
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N75 is still pluged in and vented to atmosphere.tomorrow I have a new piece of hos coming and will put it back to stock location.Comment
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Well if it is temperature dependent then it could be the coolant sensor in the head not the MFTS. It's a pain with the 3b as we only get those 10 measuring blocks and they are not expressed in a easily understandable way.
Nevertheless it would be worth noting those down and posting the results with the engine warm as it might allow us to spot something as simple as the ecu not seing the correct engine temperature!
Do some poor mans data logging using a sheet of A4 and a table for the 10 blocks.
Just write down the numbers every couple of minutes. As soon as the car starts to misbehave the numbers will become meaningless. For example the specified ignition timing will be out of spec once the idle isn't 770-830rpm! But we might strike lucky!Last edited by twoqu; 5 June 2012, 20:35.Comment
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Replaced n75 in stock position,and no change.Comment
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Temorarily remove the throttle cable from the TB and if its not too much bother take the whole damper assembly off without disturbing the damper. If we agree that the only way the engine can idle that high is by extra air, then somehow we need to establish whether the ISV is bypassing it or it is unable to control it.
Still trying to pin down the whether the ISV can pass more air than in its unpowered state. Presumably it can pass less. If there are no other leaks then the only way the engine can get more air in is through the actual throttle plate itself. There is a tiny gap at the bottom of the throttle plate. Might have to physically check it.
Actually if disconnecting the ISV make no difference, then put one of the other ISV's you have on the connector and see if it is being activated by the ecu. If it is, then we can eliminate the ISV/Idle switch and the ECU control.
Give some of that a go!Comment
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Robin,I took the connector of the ISV and connected it to a spare and the actuator opened when I pluged it in ,then closed and did not appear to move after that on opening and closeing the throttle.
Disconnected the throttle cable and checked that the damper was not touching,but no change.
the idel is at 1050 hot and cold with very slight needle movement,just noticeble .
The hunting starts at 1400 and ocilates from 1200 to 1500,the drone does not happen till 2000.Last edited by 220bhp; 6 June 2012, 14:17.Comment
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Right so it idles at 1050 hot or cold. I would say thats consistent with the ISV not doing anything as without being operated it has effectively a fixed orrifice, whereas to control the idle it would need to make that orrifice smaller.
Was that with the engine running? Would have thought that the ISV would have being moving trying to control the airflow. Unless of course its not being controlled. When you say it open and closed, can you blow through.
I know you don't have the a/c but does the idle increase when you turn it on?
Had my rad not took a dump, I could have tried to duplicate the fault on mine. Bit like NASA Mission Control!Comment
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Engine was running.when I plugged in the spare ISV and I did this three times just to check what I was seeing,each time as I plugged it in it opened half way and then slowly closed,did not apear to move after that ,and you could not see a gap.
Turning on the A/c makes no differance.There is no condensor,or compressor,just the pipes and the electrical conectors.Comment
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Lou, I have just had a fiddle with an ISV off the car and posted a thread!
I am not entirely sure thats a valid way of testing it!
There should be a gap as otherwise the engine will not be getting enough air to idle. Even off the car there is a gap which the air from the bypass channel passes. As the valve opens that is shut off and the valve opening should become visible.
My logic is that this fixed idle is symptomatic of the ISV not being controlled. Its allowing a fixed amount of air in thats why the idle is 1050rpm not 830rpm. When you put the aircon on it should open the ISV further increasing the idle. Thats not happening either!
So either the ecu is not aware that the car should be idling which points to the TPS or the wiring to the ecu or the signals out from the ecu are not reaching the ISV, again pointing to the wiring. I believe the aircon boost is a seperate signal out.
It sounds like there is power but no earth, which is how I understand the ecu controls the valve. It switches to earth to open it.Comment
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Pulse width modulation?
Basically the ecu controls the ISV through earthing it, pulsed earth activation duty cycle 25-95% according to the literature.
I am trying to establish whether they might be an earthing problem at the ecu end.Comment
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You have got me thinking hear, because when I removed the old engine I forgot to dissconect the earth strap on the left hand side looking fIom the front of the car,and it broke the eyelet of the chassy end.
I did not know this until we had the rebuilt engine in place,and tried to start it and could see the spark arching. We the put an intirely new earth strap from the battery to the engine mount,this was a very heavey duty strap that runs to both the underside of the battery tray,and to the engine mount,the old earth which was broken I did not reconnect
it.Comment
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I am more concerned with the ecu earths. There is some conflicting info!Comment
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