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MS - 3.5 with Thor heads - IAC valve settings


=jon=

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Hello All,

On my recently acquired 110, the idle control valve isn't connected up, and it's not setup in MS - idle is only set mechanically at the moment. Does anyone have a rough set of starter settings to get me going?

It's a 3.5 v8 with Thor heads if that makes any difference :)

Cheers

Jon

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Be careful. I haven't tested the thor IAC valve, but at 0v they're not necessarily closed. You could stick a variable voltage supply onto it and find what voltage closed is.

G

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Which type of IAC is it ?

The Thor IAC is a 3 wire one that can be driven from Megasquirt as a PWM IAC with the addition of a resistor.

The Hotwire IAC is a 4 wire stepper that can be driven from MS2 but not MS1 without additional hardware.

The Flapper IAC is a 2 wire bimetal electro mechanical one which just needs a 12v supply from the ignition.

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Just did some checking - it's a 3 wire one, and one of the pins is 35Ohms to earth. Plugging it in and selecting PWM closed loop in tunerstudio causes the revs to hunt, so it appears to be working...

Does anyone have a set of base settings (idle speeds, duty cycles, PID values etc) to get me started along the right track please?

Thanks

Jon

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Had another play with the settings, and no matter what I select in tunerstudio plugging in the IAC valve causes the revs to climb to about 2000 and hunt a bit... I've played with the valve settings, PID values etc and nothing changes...

Doing a bit more digging - it seems that if you are trying to use PWM and you are using a relay board, you need to jumper out the relay:

http://www.msextra.com/forums/viewtopic.php?f=94&t=30394

Next thing on the list to try - although I don't hear the relay clicking as it suggests I should, but I'm not sure I would from the engine bay over the v8....

Edit - just took the cover off the relay board - if the FIdle relay is closest to the DB connector, it's jumpered already...

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Not sure I follow, have you attached the external resistor ?

By providing power to the centre pin of the IAC and a resistor to earth on one of the outer pins, the IAC will close (assuming you've connected the correct pin to the resistor. If it opens then you have connected the resistor the the wrong pin. The three pin IAC is like a 2 way motor, 12v on the middle pin and it will move one way or the other depending on which side has the best earth. The resistor on the "closed" side acts like an electrical spring, trying to return the IAC to a closed position if there is no input from the ECU. The ECU uses a series of pulses to momentarily connect the "open" pin to earth, the higher the ratio/percentage of earth pulses, the further open the IAC moves against the "spring" provided by the other side.

Once you have the IAC closing when power is connected to the centre pin (via the ignition) then you can start trying to open it with the PWM "output" from the MS. The PWM settings are a bit of a pain to get right and will depend on the version of the MS firmware and software you are using. You can use a low power 12v bulb (sidelight bulb, for example) to test the output from the ECU by connecting it between a 12v supply on one side and earthing through the ECU IAC pin. The bulb will light up at it's brightest when the IAC would be fully open, the bulb will be at it's dimmest/off when the IAC would be closed.

I'll be honest, I've never bothered using PWM on these types of IAC, preferring instead to just use them as a cold start on/off valve using the MS to open the IAC when the engine is cold, I then restrict the airflow through the IAC mechanically by restricting the air pipes to it.

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Hi,

Yeah, If I open up the relay box there's a big resistor inline, and it looks like the FIdle relay is jumpered out.

Some good things to test there - many thanks! I hadn't thought of using a bulb across it to check the operation from the ECU..

I'll carry on fiddling over the weekend :)

Jon

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Did some playing today - the IAC valve is working when connected directly to 12V - it'll open/close depending which pin you connect.

However, it doesn't look like the output from the MS is working - I can force the duty to 10% / 90% in tunerstudio, but the bulb didn't change brighness at all, so it looks like something isn't wired up right...

We blocked off the IAC valve and the idle speed dropped low enough that it wouldn't run, so we upped the idle and now if anything it runs better than with the IAC valve present but disconnected - I guess it had been set up previously with the valve present but slightly cracked open which was almost the same as having an air leak all the time...

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Hi,

I know very little about this other than following threads in prep for a possible build however an observation/question.

Are you talking about the same things here? As far as I saw the Extra EFI web page (should we be quoting other forums without rference to them?) is about adding a PWM fitting in replacement of an IAC and this thread appears to me to be about a IAC which is a stepper motor in which case the votage is pulsed not variable so the bulb will stay the same brightness!

If I have it wrong then ignore me!

Marc

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Its coming back to me a bit now i read this thread. I suspect i got to the same point that you are now.

Good you have tracked it down to the signal.

Hi Paul,

Can you remember if you made the optional hardware mods inside the MS to drive an IAC? It appears you have to swap out one of the transistors internally:

http://www.diyautotune.com/catalog/megasquirt-pwm-iac-valve-control-tip120-39modkit39-p-134.html

If you can't remember I'll go check but it's a mission to pull all the centre console apart to get to it!

Cheers

Jon

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Are you talking about the same things here? As far as I saw the Extra EFI web page (should we be quoting other forums without rference to them?) is about adding a PWM fitting in replacement of an IAC and this thread appears to me to be about a IAC which is a stepper motor in which case the votage is pulsed not variable so the bulb will stay the same brightness!

Hi,

The Thor IAC is regulated via PWM - so a square wave pulse of varying frequency. If you put a bulb across a PWM feed it'll flash on and off very fast (probably quicker than the human eye can see) - the slower the PWM frequency the dimmer it'll get :)

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Yes pretty sure i did the mod, i remember ordering the TIP121.

Hi,

Comparing what you've done to what's listed at:

http://www.diyautotune.com/catalog/megasquirt-pwm-iac-valve-control-tip120-39modkit39-p-134.html

They say wire the big transistor across Q4, remove Q20 and D8, and jumper R39.

Your MS has B & C connected, A is jumpered across R39, and there's a diode that goes back to S12 (which looks to be +12v)...

Pic of the board at: https://www.dropbox.com/s/zw61sre1yww331z/2015-04-04%2016.31.01.jpg?dl=0

Any pointers. My electronics skills are pretty basic compared to yours!!

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OK - so I found another link that has it wired up like you had yours on the MS Extra side - the diode is the flyback diode, but it should be easy enough to put back...

It also looks like the transistor needs a mica insulator beneath it, if one isn't there it'll appear to be full short all the time - and I can't see one on the pic...

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OK- wired this up and tested yesterday, the idle valve now works as expected and it starts and ticks over very nicely on closed loop from cold when on petrol...

However - when on gas it's not so happy - come up to a queue of traffic, stop in gear (it's an auto) and it will slowly get rougher and rougher and then stall. I think it's because it's a single point LPG system, and the IAC valve is essentially bleeding air past it, so it gets weaker and weaker, the MS compensates for the drop in revs by opening the valve more, until it stalls.

I guess the solutions are:

Only use the valve for warmup (which happens pretty quickly) when it's likely to be on petrol anyway.

Find some way of disabling the valve when it's on gas somehow. I can't just disconnect it as it doesn't 'park' fully closed. Any suggestions?

Thanks

Jon

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Yep, mine's similar to that, with the cooker ring on the throttle body....

Guess I'll have to see how it runs with just control during warm up when before it's not been happy at all on petrol..

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Been and had another play, with just Open Loop idle control during warmup it seems a lot happier, and now its fine when you switch over to gas...

Playing with the values during cranking have also made it a load easier to start as well, and it'll even start on gas at a push... :)

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Well done Jon, sorry about that. Even electronics engineers can miss things...

I used to usually start it on gas. The fuel tank was just a reserve for me.

IIRC the gas evaportator has its own idle screw.

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