ISCV Diode help
Discussion
Hey folks,
Chasing a long term idle problem I'm trying to sort out the lack of a diode in my ISCV system as per the TVR wiring diagram and the 2.9 Cologne diagnostics article. Having put a multimeter around multiple bits of the ISCV system, I defo don't seem to have a diode anywhere to be seen. I've tested from the ECU end of pin 21 (ISCV) to the ISCV itself, across the ISCV, and the other end and resistance is pretty much zero throughout.
So, my questions: is anyone able to provide any photos or guidance on the location of the Diode? I provided the wiring diagram to an autoelectrician and enquired about him sorting it and oddly his advice was "Mate, my minimum charge is £60 for an hour, you'd be better off paying 10p for a diode from Maplin and sorting it yourself!". So that is what I'm going to do (and then get the pro when it doesn't work! Does anyone have any photos or experience of replacing the Diode on the idle end of the ISCV?? What is the recommended Diode? I have severaly ready to go, just in case!
Chasing a long term idle problem I'm trying to sort out the lack of a diode in my ISCV system as per the TVR wiring diagram and the 2.9 Cologne diagnostics article. Having put a multimeter around multiple bits of the ISCV system, I defo don't seem to have a diode anywhere to be seen. I've tested from the ECU end of pin 21 (ISCV) to the ISCV itself, across the ISCV, and the other end and resistance is pretty much zero throughout.
So, my questions: is anyone able to provide any photos or guidance on the location of the Diode? I provided the wiring diagram to an autoelectrician and enquired about him sorting it and oddly his advice was "Mate, my minimum charge is £60 for an hour, you'd be better off paying 10p for a diode from Maplin and sorting it yourself!". So that is what I'm going to do (and then get the pro when it doesn't work! Does anyone have any photos or experience of replacing the Diode on the idle end of the ISCV?? What is the recommended Diode? I have severaly ready to go, just in case!
I don't know that ISCV system, but the most likely reason for a diode is to provide a flyback circuit for the actuator. If you have a wiring diagram, you could confirm that's what it's for. The diode would just need to be able to handle the current and voltage supplied to the actuator, and physically robust enough to survive wherever it needs to be installed.I doubt it'll need to carry more than a couple of Amps and 12V which means it's going to be cheap and readily available.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
I agree, if it needs a diode to prevent back emf (flyback) a 1N4001 will probably do the job. 10p or less anywhere.
I agree, if it needs a diode to prevent back emf (flyback) a 1N4001 will probably do the job. 10p or less anywhere.
I took it for a drive last night and swung past Maplin so for 60 pence I have variety of 4000 series diodes (1N4001, 1N4004, 1N4006) which are all 1 amp and a 1N5408 3A Silicon Rectifier, so one of those should do the trick. Where I wire it in is the trickier bit. This is the best I have seen:
"Finally, if the idle problem persists it's worth remembering that there is a diode fitted across the idle speed control circuit (in between pin 21 of the ECU and the supply from the main relay). This diode which prevents a back feed, is taped into the vehicle's wiring harness along the top of the engine in between the two cylinder banks...".
Is it as simple as just separating the yellow wire from pin 21 of the ECU to the ISCV at some point and putting the diode in series on that? Couple of wiring diagrams here and here...
"Finally, if the idle problem persists it's worth remembering that there is a diode fitted across the idle speed control circuit (in between pin 21 of the ECU and the supply from the main relay). This diode which prevents a back feed, is taped into the vehicle's wiring harness along the top of the engine in between the two cylinder banks...".
Is it as simple as just separating the yellow wire from pin 21 of the ECU to the ISCV at some point and putting the diode in series on that? Couple of wiring diagrams here and here...
ukflyboy said:
I took it for a drive last night and swung past Maplin so for 60 pence I have variety of 4000 series diodes (1N4001, 1N4004, 1N4006) which are all 1 amp and a 1N5408 3A Silicon Rectifier, so one of those should do the trick. Where I wire it in is the trickier bit. This is the best I have seen:
"Finally, if the idle problem persists it's worth remembering that there is a diode fitted across the idle speed control circuit (in between pin 21 of the ECU and the supply from the main relay). This diode which prevents a back feed, is taped into the vehicle's wiring harness along the top of the engine in between the two cylinder banks...".
Is it as simple as just separating the yellow wire from pin 21 of the ECU to the ISCV at some point and putting the diode in series on that? Couple of wiring diagrams here and here...
Is it as simple as just separating the yellow wire from pin 21 of the ECU to the ISCV at some point and putting the diode in series on that?"Finally, if the idle problem persists it's worth remembering that there is a diode fitted across the idle speed control circuit (in between pin 21 of the ECU and the supply from the main relay). This diode which prevents a back feed, is taped into the vehicle's wiring harness along the top of the engine in between the two cylinder banks...".
Is it as simple as just separating the yellow wire from pin 21 of the ECU to the ISCV at some point and putting the diode in series on that? Couple of wiring diagrams here and here...
In answer to your above question, no don't wire a diode in series with anything - Read On
Read page 12 of this PDF as this will save me explaining things - http://www.autoshop101.com/forms/hweb2.pdf
The Diode fitted in parallel with a ISCV works in exactly the same way
Be careful here, read page 12 of the PDF I have linked to and once you understand it you can carry out the work
You will be ok to think of the ISCV being the same as a relay coil when learning from that PDF
I have looked at those 2 diagrams you have posted links to. The above diagrams are different.
The first diagram (290 S Wiring Supplement) Shows a diode wired in parallel with the ISCV and that means it is connected from pin 21 of the ECU to Pin 58 of the ECU
The second diagram (ford29diagnostics) Shows a diode wired in parallel with the ISCV and that means it is connected from pin 21 of the ECU to Pins 37 and 57 of the ECU
The good news is that in both of those diagrams there is a diode wired in parallel with the ISCV and you can do no harm in wiring a diode in parallel with the ISCV fitted to your engine
You can do no harm by fitting a 3 AMP rated diode
Make sure you wire the diode the correct way round, if you wire the diode the wrong way round it will be like wiring in a short circuit and the ECU or Relay wont like that
Finally, the diode can be wired at the ISCV connector plug or further up the wiring harness or even back at the ECU, it will serve its purpose where ever you choose for its location as long as it is in parallel with the ISCV and the correct way round
Consider the temperature when choosing where to locate the diode as they dont like too much heat, you could even mount the diode in a nice not too hot area and use cable to run from the diode to the ISCV connector plug
Further to my above help, there is nothing to say that the fitting of a diode in parallel with the ISCV will cure your problem, the diode only comes into play when the ECU has switched power off the ISCV and what the diode does is prevent a back EMF from discharging through the ECU or supply relay contacts
ukflyboy said:
Chasing a long term idle problem .....
If I remember correctly, there was a YouTube video where you unplugged the ISCV and the revs dropped back to normal.Have you taken apart the ISCV and cleaned it inside ? If it is a Hitatchi type, it is easy to clean, just two screws on the solenoid side.
Also there is a rubber O-ring separating the valve body and the solenoid. This might also need replacing, as it may be leaking.
Thanks kindly for the info, I'm thinking I need to find another auto electrician! I agree that this isn't likely to magically solve my idle issue, but it will at least be another thing ruled out. With my limited electrical knowledge, I was kinda hoping that the issue might have been caused by the flyback voltage activating the ISCV.
I have had several ISCVs on there, including a brand new one, and the problem remains. The ISCV seems to work, it just seems to be getting a signal to work too much! Think I'm going to either have to live with it or take it to a very knowledgeable pro.
I have had several ISCVs on there, including a brand new one, and the problem remains. The ISCV seems to work, it just seems to be getting a signal to work too much! Think I'm going to either have to live with it or take it to a very knowledgeable pro.
Before you go to far down the route of repairing and replacing ISCVs, think about how it works...
The ECU gets a number of signals from a number of sensors - air flow meters (or Lamdas if it's a cat model), fuel temp, engine temp, etc, and uses those to control other things, including ignition timing, fuelling and idle speed - for example, if the coolant sensor was duff, or had a poor connection, the ecu might think that the engine isn't at operating temp yet, so increases the idle speed to "fast idle" through a signal to the ISCV.
So now you have a fast idle. If you disconnect the ISCV, the idle returns to normal - but that's not because there's anything wrong with the ISCV, it's because the ISCV isn't connected to "bleed" air in to keep the idle high.
You can put as many ISCVs on there as you like, but you're not curing the cause - the coolant sensor or its wiring.
That's just one example, there could be a number of causes for the fast idle signal from the ecu.
So I would suggest that the first step is a good fault code reader, such as the Ford STAR tester - there are a couple circulating around this group. That might give a clue as to the cause, or at least, where to start further tests. If you need advice, ask somebody who knows what they are doing, not somebody who just keeps changing bits (at your expense) until they stumble across the cure.
The ECU gets a number of signals from a number of sensors - air flow meters (or Lamdas if it's a cat model), fuel temp, engine temp, etc, and uses those to control other things, including ignition timing, fuelling and idle speed - for example, if the coolant sensor was duff, or had a poor connection, the ecu might think that the engine isn't at operating temp yet, so increases the idle speed to "fast idle" through a signal to the ISCV.
So now you have a fast idle. If you disconnect the ISCV, the idle returns to normal - but that's not because there's anything wrong with the ISCV, it's because the ISCV isn't connected to "bleed" air in to keep the idle high.
You can put as many ISCVs on there as you like, but you're not curing the cause - the coolant sensor or its wiring.
That's just one example, there could be a number of causes for the fast idle signal from the ecu.
So I would suggest that the first step is a good fault code reader, such as the Ford STAR tester - there are a couple circulating around this group. That might give a clue as to the cause, or at least, where to start further tests. If you need advice, ask somebody who knows what they are doing, not somebody who just keeps changing bits (at your expense) until they stumble across the cure.
I have a Draper fault code reader that Mark gave me with the car, but I've not been able to get a fault code out of it; even with the ISCV unplugged it comes up as no faults. I am trying to avoid just aimlessly changing bits and have spent considerable time with a multimeter checking all the readings into the ECU and they all appear to be operating with limits, so there is nothing obviously wrong sensor wise. Now that I have fixed (or rather no longer have!) the rough running problem I'm going to get it to a garage with a SmokePro tester to chase down any air leaks. As I think you noted in another post, it shouldn't run with the ISCV blanked off, so there must be some extra air getting in there somewhere.
Mark and I have been trying to find a solution for some time so it might be that I just have to give up finding a solution. It drives well at the moment and I'm enjoying getting out and about in it, but it would be nice to have it running as it is designed
Mark and I have been trying to find a solution for some time so it might be that I just have to give up finding a solution. It drives well at the moment and I'm enjoying getting out and about in it, but it would be nice to have it running as it is designed
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