Tuning Nissan PWM idle (Solved)

[JamesBroChill42]

Hi everyone,
I have a 93 nissan 240sx that has been running MS2 3.57 for the last two years. In all that time I have been using the throttle plate as idle control. Now that I have a decent (not complete) VE tune I figured I would tackle the PWM idle valve.
The problem is I cant get MS to treat the valve like anything other than an on/off valve and in my case its just always on. The valve I am using is the AAC valve for those of you familiar with early 90's Nissan IAC valves. I just recently updated to firmware version 3.3.2 in the hope that it would help (it didn't).
My setup has the idle valve powered by the fuel pump relay. The grounding is controlled by the Fidle port on the relay board. I have the Fidle relay jumper-ed. I have tried using the Can-bus idle valve test but I cant get anything to happen. Also while trying to adjust duty cycle values in the drive way, the RPM's never change even with crazy values. I've also noticed that while the PWM valve is active there will be the occasional dip in the idle every couple minutes.... I have no idea if that is a separate issue though.
Thanks for looking.
-James


I've attached a copy of my MSQ in case any of you want to take a look.

[JamesBroChill42]

Minor update: I've been attempting to bench test the valve. I've plugged one end into a fused 12 volt source and the other into the Fidle port. Upon switching the 12 volts on, the valve will snap open. Removing the 12 volts snaps the valve closed. Even in this configuration I cant get the valve to do anything other than snap open and closed using various duty cycles in Tunerstudio. The weird thing is that if I power down megasquirt but leave everything connected, the valve starts to hum at what I assume is the frequency i left it at in the settings. Does anyone have any ideas? I know that this bad for MS so I've stopped testing it that way.

-James

[elutionsdesign]

You probably aren't getting much response as no one with Nissan idle valve experience is reading, I certainly don't have any. But do you have access to an oscilloscope to determine if the PWM is working?

[JamesBroChill42]

Sadly I do not have access to an oscilloscope. I suspect MS is just grounding the valve when on and not fluctuating the signal at all. If I discover anything new I'll be sure to post it in this thread.
-James

[jsmcortina]

It almost sounds like there's an internal wiring fault causing voltage backfeeding. Quite difficult to know remotely.

Can you try replacing the idle valve with a small lightbulb (e.g. a number plate light). See how that behaves in test mode. It should be off at 0% duty and full brightness and 100% duty.

Note that the valve/bulb should not be powered when the Megasquirt is off or weird things will occur due to backfeeding for sure.

James

[JamesBroChill42]

So I just tried the bulb idea and in both I/O test mode and the idle valve test mode I could not get any change to the lights. No matter what I tried the lights were at maximum brightness. In I/O mode i tried a number of pulse frequencies and a number of duty cycles. Same with Idle valve test, I tried a number of duty cycles and no change in the lights at all. These results mirror what i was experiencing with the idle valve. I'm beginning to think my problem might be software based?

-James

[jsmcortina]

I'm beginning to think my problem might be software based?

The MSQ you posted has idle control disabled?? It isn't going to work like that.

You might want to consider upgrading to the current firmware though, the idle valve test is a lot easier to use.

James

[JamesBroChill42]

Woops! My mistake that is not the most current MSQ . It has been enabled for all of my previous tests. I have updated to 3.3.2 as of yesterday morning.
*edit* I forgot to mention, this whole time I've been using a %Idle PW gauge in tuner studio and it reads what it should be but I don't see any indication that its actually doing anything.
-james

[JamesBroChill42]

I was doing some tests with the I/O test mode in tunerstudio and I found MS isn't turning the Fidle output off. To start with I turned idle control completely off. I then connected a volt meter between a 12v+ switched source and the Fidle output. Before doing anything it read 0volts which shows that the output is not currently grounding(shorted). Then in I/O test mode I turned the Fidle "on" and the relay clicked on and I was getting 12v+ on the multi-meter. I then tried to turn the output off and I still get 12 volts. So my conclusion is that MS is able to turn the output on (grounding) but isn't able to switch it off for some reason? Has anyone ever heard of this happening?

-James

[jsmcortina]

I've never heard of that happening before. Very strange.

James

[JamesBroChill42]

Do you think reflashing or even flashing to a different firmware version might help?

-James

[JamesBroChill42]

To add to the weirdness i just tested my other outputs (because why not). They all behave exactly how they should. I can pulse them, toggle them, and add conditional statements to them. Would it be possible to run a PWM idle valve off of IAC2 or IAC1 or any of the s1-s4 on the relay board?

-James

[jsmcortina]

The IAC outputs are not rated at enough current to run a typical PWM idle valve.

It sounds like somehow U8 is faulty. It isn't an expensive component. Do you know anyone who could repair your board? I would be tempted to swap out U8 which is a VNS3NV04D-E.

James

[JamesBroChill42]

I hate to bring this back up, but, I was messing around in the options and found that if my Fidle relay (On the relay board) isn't jumper-ed I can make the relay turn on and off and oscillate. So my question is why does the U8 chip seem to work as intended when the relay is part of the loop but when the relay jumper-ed out of the loop it doesn't function as it should?

-James

[cukali]

Have two of my ka24de running fine using the idle valve....be aware, the year car you have has three idle valves. One is only on/off and cannot be used as a pwm valve. Another is a heat based valve that has power to it at all times the car is running. The third is your PWM valve. Adding any kind of frequency to the on/off valve results in your symptoms.

If the valve your using has a 17mm hex shapes body then your using the WRONG valve. That is the A/C / Power steering idle up. The one you want to use is shorter, round and much wider.

[JamesBroChill42]

Turns out I'm an idiot....I didn't realize that when jumper-ing the relay socket on the relay board you don't put the relay back in
Anyway, the system works great now. I've even started playing around with Closed loop idle

Thanks for everyone's input!

-James