IAC tuning. Am I crazy? (Solved!)

JSC · Post by **JSC** » Tue Apr 11, 2006 9:08 am

Bud;

Of course I'll share my solution, when I find it.

Update from last night. All indications have been that if the IAC motor needs to really go somewhere (ie 50 to 100 steps at a time) it works fairly well, however, if it needs to move just a few steps (ie 1 to 5 steps at a time) it doesn't work. In the idle steps table, with the engine at temp,
I changed the 160 deg bin from 200 to 100 and the idle increased, back to 200, idle decreased, 150 - idle up, 200 - idle down. Worked as advertised. Then took the bin to 150, idle up, down to 149, 148, 147,... to 200, no change in idle. Checked voltage to IAC, no voltage. Checked IACEnbl on the UDN2916LB motor driver, it was still enabled. Conclusion, the 2916 is going in to some sort of fault mode.

Question for the Gurus: The component values for the oscillator RC network on the 2916 are out of the range specified in the Allegro 2916 datasheet. Could this be an issue?

Scott

69 1/2 Six Pack Bee · Post by **69 1/2 Six Pack Bee** » Wed Apr 12, 2006 2:56 pm

Well,
The NEW MS-II chip is in place, wired the resistor jumpers accross R5 & 6. The BRAND NEW IAC is installed. And as I had expected it is still exactly the same as it was prior to when I pulled out the old daughtercard.

The stepper DOES NOT follow the temp curve even though the "IAC Steps" leads me to believe it does. Once again I tried different algorithms, step speeds...the same old scenario and it is just as unreliable as it was from the get go. I also notice that after about 7 or 8 starts the stepper only goes to a number shy of the 215 fully closed number I have in the step table. For example, I have the "start" steps set at 155 and a taper time of 6 seconds. It goes to the start position and then will only go to 189 (as indicated in mT) and it just stays there. If I shut it off and restart it this time it might only step to 178. I have started the engine up 14 times and the last 6 have had IAC counts that ARE NOT at the fully open position of 215 but rather an odd ball number....it just stops there and goes no further.

Once again I have rang out all of the wiring and all is well. Battery voltage is at least 13 volts (14.3 when runing) and fully charged.

Now I have definately run out of ideas, time and I am not going to invest any more $$ on new parts. One of the main reasons I upgraded to the MS-II was for the IAC function but that is clearly not working as I had anticipated. And now with the added complexity of the tuning (at least to me) this is quickly becoming a "back burner" project now.

I will more than likely put the Q'jet and the old HEI distributor back on it and call it a day. I may revisit this at a later date in time but as summer is quickly approaching I need to carry on and get this truck ready for vacation and I have run out of time, money and lastly, patience.

Thanx to all who have helped and keep up all of the concerted efforts each and every one of you "squirters", beta testers and developers and a big thank you to Al & Bruce for the fun project and to Lance for his superlative knowledge and help but I think it is time to bail.

Thanx again for the ride!

Bud Weaver

bluetrepidation · Post by **bluetrepidation** » Wed Apr 12, 2006 3:34 pm

I just tried bypassing those resistors on the MS II board since no matter what I did settings wise made any difference. Now I have a spare IAC motor I hookup to see what it going on. It pulls all the way back from fully forward and has decent holding power but my guess is somehow the high vacuum at idle is sucking the valve closed. Hopefully jumping these resistors will give it more holding power. We'll see.

A.J.

bluetrepidation · Post by **bluetrepidation** » Wed Apr 12, 2006 4:03 pm

Well it seemed to make some difference though it is still fishy. I won't say for sure till I drive it for a few days.

A.J.

JSC · Post by **JSC** » Thu Apr 13, 2006 8:14 am

Question for the Gurus: The component values for the oscillator RC network on the 2916 are out of the range specified in the Allegro 2916 datasheet. Could this be an issue?

I'll answer my own question, YES. If I force the 2916 motor driver into an over current condition, it disables the output, this happens because the oscillator will not run with component values shown on the MSII schematic.
I changed the values on my test setup to .001uf cap and 47K res, (left overs from the V3 board) and now the current limiting osc runs and the output will not disable.

Is it possible to get an MSII daughterboard with different value components in the osc RC network? Or should I change the components on my board? Can I get the component specs for the MSII?

Thanks
Scott

69 1/2 Six Pack Bee · Post by **69 1/2 Six Pack Bee** » Thu Apr 13, 2006 8:44 am

JSC,
Did you see this?:

I'm game...which of the components ned to be swapped out?
I'll do it on my card. Maybe this is the fix I need.
I'll try one last thing before I sail into the sunset and maybe we have a fix that the others can use.

Lordprimate · Post by **Lordprimate** » Thu Apr 13, 2006 10:47 am

JSC wrote:Question for the Gurus: The component values for the oscillator RC network on the 2916 are out of the range specified in the Allegro 2916 datasheet. Could this be an issue?

I'll answer my own question, YES. If I force the 2916 motor driver into an over current condition, it disables the output, this happens because the oscillator will not run with component values shown on the MSII schematic.
I changed the values on my test setup to .001uf cap and 47K res, (left overs from the V3 board) and now the current limiting osc runs and the output will not disable.

Is it possible to get an MSII daughterboard with different value components in the osc RC network? Or should I change the components on my board? Can I get the component specs for the MSII?

Thanks
Scott

So Basically , A Capacitor and a Resistor are allowing too much current into the chip causing it to shut down??....

And changing the components with the .001uf CAP and the 47k resistor will solve that issue with the output droping out..

So yea which components do you swap... because I had, HAD the same problem and it was just dismissed as a Wiring issue... when I knew I had my wireing right...

JSC · Post by **JSC** » Thu Apr 13, 2006 12:07 pm

Bud;

Yes, that is the schematic I used for the component values on my test setup. The components that I am going to change are C14 & C16 which are now .056uf and R7 & R8 which are now 1K. The 2916 datasheet shows 820pf cap and 56K resistor. So I'll change C14 & C16 to 820pf and R7 & R8 to 56K ohms. These components are ity bity surface mount components on the bottom of the board close to the crystal, may have to cut away some of the silicone around the crystal to get at the capacitors, it's going to be a tricky operation. I ordered parts from Digikey and will change the parts this weekend, unless someone gives me a good reason not to. If it works, I'll let everyone know and I'll have Digikey part numbers.

Lordprimate;

The 2916 motor controller uses PWM (pulse width modulated) current control. The pulses for the PWM are generated buy an oscillator circuit using an external RC (resistor/capacitor) network. The problem I'm seeing is that the oscillator will not oscillate with the component values installed on the MSII. The basic operation is that when the output current to the motor increases to the current limit setpoint, the output to the motor is turned off for 1 cycle of the oscillator, then turned back on. If the current reaches the setpoint again, it's turned off again for 1 cycle, then back on. This continues as long as the current is above setpoint. If the oscillator isn't running it can't turn the output back on after the setpoint turns it off. The only way I've found to turn it back on is a power down reset. Hope this make sense.

Scott

bluetrepidation · Post by **bluetrepidation** » Thu Apr 13, 2006 12:21 pm

So looks like we all are having the same problem. So I'm game about doing something about it. I can solder surface mount no problem and I also have access to an oscilloscope. I did drive my car to work today and didn't have the IAC drop out like it did the last two days after jumping those resistors. But I haven't drove home yet. ;) Are well all running GM steppers here? Can we compare ohm ratings for the field windings? Is there a fault output for this chip we can hook an LED to?

A.J.

69 1/2 Six Pack Bee · Thu Apr 13, 2006 12:25 pm

bluetrepidation wrote:yet. ;) Are well all running GM steppers here? Can we compare ohm ratings for the field windings? Is there a fault output for this chip we can hook an LED to?
A.J.

That's a big 10-4..I am using the GM "o" ring inline stepper that is found on a zillion different cars and trucks the oly really difference is the diameter of the pintle end and the angle of the taper but they are all around 50 ohms. My "a" coil is the first two wires and the "b" the last two.
Maybe we'll get some resolve to this finally