Megasquirt Support Forum (MSEXTRA)

Has anyone had any success in setting up the typical Dodge/Chrysler 4 wire stepper IAC, ~50 ohm per coil?
I've studied the documentation, researched anything I can find on the web, and tried as many combinations as I can find, but I still get inconstant results. I don't tend to give up easily, but this one is challenging me.
If anyone can say it is working well for them I'd sure appreciate in knowing what your settings are so I can try them out.

We've run one on a 318 Magnum. It didn't seem to have any particular challenges that I could recall.

Do you recall what the settings were?

It might be more productive for you to post the settings you are trying to use. What sort of "inconsistent results" are you getting?

Well now, I think I've tried almost every combination of settings there are to try, except possibly the right one, so I don't know if posting them all would help.
As far as inconsistent results is concerned, I'd have things set up with the throttle body off the engine so I can observe what the pintle is doing. I could get it to the point where when under test, the pintle would move to home position as well as move to the run position and cycle reasonably well. But, when I put everything back together and run the engine it never seems to end up on the correct run position no matter how I set things. Some times it will be barely running, if at all, and other times it will be running about 1400 RPM or anywhere in between. The "step" display looks reasonable, but doesn't seem to have any bearing on the actual position. I've experimented with step times, home steps, WOT steps and direction is about as many combinations as I can think of, but still no joy.

About the only thing I haven't done is physically reverse the wires on the motor. It shouldn't make any difference because I should be able to do that with the software, but that's the next thing I will try.

I'm putting together a stepper driver that I can control manually to see what I can do with that. It might give me some clues as to where I am going wrong. It may be a few days before I get it ready, but when I do some testing with it I'll report back.

Why such a reluctance to post the MSQ (any one tried)? Maybe it won't help, but surely you can't think it will hurt efforts to help you. Your choice, though. Good luck, but I have to give up here.

I never had success reversing the motor direction using software.

It's also possible that you don't have the correct pinout at the motor. Both GM and Chrysler use extremely similar, but use different pinouts. From what I recall there was one pinout that I tried that would ALMOST work, but not quite (GM, but they work the same), and it wasn't until I got the pinout exactly right that it worked as expected.

So basically you likely have it wired wrong.

IAC problem solved.

Well it looks like Dodge threw a curve at me. In the factory service manual, all wiring diagrams for the IAC motor that show pin numbers and wire colours have the pins in line, 1,2,3,4 with one coil on pins 1&2 and the other coil on pins 3&4. Assuming that the official shop manual must be correct, that is how I wired the IAC up. When I tested the pins on the motor plug itself I found that the motor coils are arranged with one coil on the two outer pins (1&4) and the other coil on the two inner pins (2&3), both coils measure ~ 50 ohms each.
I found this conflict to be very strange, and did some more digging into the manual. Then, on page14-34 I found another general system schematic, no pin numbers or wire colours, but the illustration had the coils arranged as I had found them to be. This is not the first conflict that I have come across.
I changed my connections to match that configuration and things began to work as expected on a bench test. I found that I moved 215 steps between home at the fully extended closed position and open at the fully retracted position. With homing steps set to 225 and cranking and idle warm up steps at default values it got me in the ballpark. I warmed the engine up and tweaked things a bit so now at least I have a repeatable stable idle and a place that I can start the tuning process.
I’m not sure just what range of vehicles and years this might cover, but for the ’95 engines here are the connections that worked for me:

MS3Main DB37 pin 25 IAC1A) to IAC motor connector pin 1 Cct K39 #18 Gy/R
MS3Main DB37 pin 27 IAC1B) to IAC motor connector pin 4 Cct K59 #18 Vt/Bk
MS3Main DB37 pin 29 IAC2A) to IAC motor connector pin 2 Cct K60 #18 Yl/Bk
MS3Main DB37 pin 31 IAC2B) to IAC motor connector pin 3 Cct K40 #18 Br/Wt

I’m attaching my latest .msq in case it might be of help to anyone else, but note that these are all initial values only with just a minimum of no load tuning being done so far. I’ve got some other issues that have to be resolved before I can get out on the road to do some serious tuning.

"Moving only" is the least-reliable control for a stepper. Use "Always on" or "Hold current", at least.

What are the potential consequences of using "moving only?

The pintle valve may move/shift without a change of step number. Always on or hold current keep the coils energised, basically an electric lock, so the pintle can't really move. You are supposed to check the motor does not get hot if you try always on or hold current. Always on is the strongest hold, then hold current and no hold for moving only.

That is the assumption I made, so I'll give it some time. If I find that my idle speed is drifting with no other changes I'll experiment with different settings. If it doesn't drift then I see no need to heat the motor for no reason. I would expect that if it does drift it would probably be in the opening direction ,especially if manifold pressure is low, as in prolonged idle or decel conditions when there would be more of a pressure drop across the valve, which may tend to try to open it.

Bumping this because I also wired the same IAC per the manual. Admittedly, the pin assignments on the diagram didn't really make sense to me from the get go, and I was not making any headway on troubleshooting the issue. I re-pinned the connector, per this thread with pins 1/4 as 1A/1B and 2/3 as 2A/2B and the stepper began behaving as expected.

I just wanted to bump this in hopes it makes it easier for the next person to find. Also, thank you OP for updating this with your findings!