Power supply problem for IAC driver

[midnightblue]

My setup is MS-II on a v3 pcb with a GM IAC stepper.

Had a lot of trouble getting the IAC to work on the bench, there was no movement at all.

Eventually I found there was noise on the 12V supply I was using (newish PC power supply with a HDD as a ballast). The noise was not enough to upset the MS-II CPU or anything else, but caused the UDN2916LB to give no output.

Once I had a clean 12V supply, the stepper worked exactly as expected.

This is just for info really, had me scratching my head for days.......

Matt.

[Bernard Fife]

The noise was not enough to upset the MS-II CPU or anything else, but caused the UDN2916LB to give no output.

Matt,

That's very useful info, thanks for posting it!

Lance.

[mattrampone]

Matt buddy what and where can I get a filter from? as I have a gm iac that also bearly moves (the wrong way too!)

[midnightblue]

I didn't add a filter the PSU I was using, I swapped it out for a 12V lead/acid battery instead, and haven't had any problems since.

If the pintle is going the wrong way, you may need to swap some of the wires over. Mine is wired exactly as the diagram from http://www.megasquirt.info/ms2/IAC.htm as if you're looking into the connector on the back of the stepper. That seems to work for me.

Hope that helps, Matt.

[mattrampone]

MSII v.3/MT2.25b759beta/2.3 firm

Matt my friend I appreciate any advise I get,
I have my MS already installed in the car though with a fully charged batt, I believe the power supply should be good (works cranking too) and the engine will fire up and run pretty well with a little foot in the gas.
I had the IAC wires installed as per the dia. (orienting the plug propper) at first when nothing happened at all, so I pulled out the car wiring dia and found that 1a,1b,2a and 2b were arranged a little different than the ms dia. so I changed them. The only problem is the car manual lables a-high, a-low, b-high and b-low. the a and b part is ez, but I guessed at the high and low, and wired the 1's as high and the 2's as low. If it worked backwards consitently I could have guessed to switch the wires around (wich I have also tried) and should work, correct? still not working. I jumped the two resistors under the daughter card (carful not to short now) and still made no improvment. I have tried changing all of the values and settings in MT and found that changing the step time will change the hz that IAC viabrates. It somtimes moves out and somtimes in or just viabrates when cycling power on, but no consistant pattern that might make any sense! I tried a new IAC ($90!)
same. Before I mess with the firm ware, I was wundering if maby I missed sumthin obvious (as this is still new to me).
Anyway, would u happen to know wich MS IAC wires are Hi and Lo? or if there has been any prob's with 2.3 firmware or MT2.25b759?
Thanks for your help!

[midnightblue]

Well, you seem to have tried all the sensible things.

The only thing I can think of is that the a and b in the different diagrams don't refer to the same thing, maybe the 1 and 2 in the MS pinout relates to and b on the car, with and and b on the MS relatin to hight and low. After all they were written by different people, we can't assume any similarities in their labling convension. Maybe worth a try?

If that doesn't work I'd start working through every possible permutation of connections to see the one that works. I don't think it's possible to break anything on the stepper driver with crossed wiring, but I'd remove those resistor jumpers while you check it out, just to be on the safe side. If my (very rusty) math is correct there are only 12 possible ways to fit 4 wires into 4 holes, so it shouldn't take too long to work out what they are and test them all.

Hope you get it all sorted soon, Matt.

[mattrampone]

Matt thanks alot, I think you are right, I'll try changing the wires around and let you know if it works!

[mattrampone]

I did some internetting and some multi-metre testing and got the wires connected properly. Took a little bit of doing, and your advice steered me in the proper direction, many thanks! Motor fired up and IAC has it warming up nicely, idles @ 850rpm right off the bat! lucky guess!

I got another Q for you if you feel like helping me some more,
The original ECM had base ignition timing set to zero (on the distributor with ECM controle disconnected), and advance was predicted when re-connected to the ECM. Does mega squirt do the same thing, or am I supposed to set the distributor to the full advance as base timing and MS just retards the output to the spark modual as a means of timing controle?

[jcorsaro]

I got another Q for you if you feel like helping me some more,
The original ECM had base ignition timing set to zero (on the distributor with ECM controle disconnected), and advance was predicted when re-connected to the ECM. Does mega squirt do the same thing, or am I supposed to set the distributor to the full advance as base timing and MS just retards the output to the spark modual as a means of timing controle?

If your using GM 7 or 8 pin HEI or Ford EDIS, they will go to base timing if the megasquirt is disconnected. I have tested it with my 8-pin HEI setup, the module looses the 5 volts at the "B" pin and goes into bypass mode.

[Bernard Fife]

The original ECM had base ignition timing set to zero (on the distributor with ECM controle disconnected), and advance was predicted when re-connected to the ECM.

mattrampone,

MegaSquirt-II works similar to that, depending to some degree on the module you are using and the settings you have.

With MS-II you can set the 'trigger offset' to values other than zero (TDC), so you can calibrate the timing with a timing light and ythe triogger wizard.

It's not necessary or desireable to set the trigger to more than the maximum advance, as MegaSquirt can advance the timing, it doesn't just retard it (this results from it being a 'next-cylinder' timing algorithm).

Lance.