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Old 07-28-2008, 05:17 AM   #1
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Default My Megasquirt thinks its a pipe organ

Thanks to Joe and ScottFW (and remembering to hook up my FP feed ) my MS is now running.

A short while after starting the engine I get the most bizzare "harmonic drone" from the idle valve. How do I know its the idle valve? I hear you say. Well when I changed the frequency for the PWM in the idle settings the pitch of the drone changed! I could get my car to play god save the Queen like the Renault F1 car in Top Gear.

I am using the MSPNP msq with only a few tweaks and with a little massaging of the throttle after starting the car it will settle into a fairly stable idle at ~500rpm!!? even though the fast idle is set for 1400rpm and slow for 1000.

The setup ATM is as follows:

94 1.8 de-catted, COPS, MS1 in stock case, LC-1, Owner who is ambitious but rubbish.

Anyone have any ideas?

P.S. How do I post my logs as attachments?

EDIT: I think I may have found the problem, I have the flyback diode installed on my tip120 like Joe and my PWM frequency is 26 and Joe's is set at 62. Do the MSPNPs have the flyback installed?

I Will load up Joe's stable idle settings tonight and see if that cures it. Whilst I'm there I think I'll also have a go at loading up 10g. No point in tuning up the old firmware when I know I'm going to upgrade and have to do it all over again.

Last edited by Duckie_uk; 07-28-2008 at 07:13 AM.
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Old 07-28-2008, 09:29 AM   #2
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The flyback diode isn't the issue - it's just that the IAC valve makes noise if you get the frequency wrong.
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Old 07-28-2008, 10:13 AM   #3
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Thanks Matt, I have been sifting through old threads regarding closed loop idling and found similar symptoms(my original search for noisy idle valve didn't turn much up)

I had 26 set as the divisor as per your MSPNP settings (thanks for publishing those btw) and its making a horrible humm. I was going to change it to 62 as per Joes settings thinking perhaps the numbers got transposed on your msq but then noticed that there are 2 different idle valves and Joe has a 1.6. My next best guess is 33 which Aussie Driver uses with his TIP120 on a NB engine.

Can I just play with the divisor untill it goes quiet or am I going to fry something by dicking about?
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Old 07-28-2008, 10:18 AM   #4
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I use 26 on my US 94. No noise.
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Old 07-28-2008, 10:31 AM   #5
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Mines a Jap and I've been finding lots of annoying subtle differences recently. Maybe theres a diff in valves.

I suppose I can try diff settings and just keep an eye on the temp of the valve without doing much damage right?
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Old 07-28-2008, 12:55 PM   #6
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On the US cars, the IAC valves on the 1.6 ('90-'93) and 1.8 NA ('94-'97) are different. My idle frequency came straight from DIY's basemap for my year car, though the rest of it was established by trial and error tweaking.

My idle characteristics did change considerably after installing the flyback diode, though there was no audible noise prior to it.

Not sure how old the settings you were looking at are (though it's been a while since I've changed it) so here's my current idle:



Apart from the idle frequency (and perhaps the exact cranking, closed, and and minimum dc), this should work for a 1.6 or a 1.8.
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Old 07-28-2008, 03:07 PM   #7
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I just loaded 10g and the idle went to hell, it was oscillating from 600 - 1200 rpm at about 0.5hz. Using Joes settings posted above (with the exception of frequency left at 26) the car now idles at 950 very nicely with the occasional missfire and consequent surge. Can I attribute the missfire/surge to the VE table needing work?

I did try setting the frequency divisor to 62 and the noise got 10 times worse but the idle was rock steady. 33 was also noisyer but more stable.

Should I put the old ECU back in and scope it to see what the frequency is?

Other than the frequency what could be causing the valve to be making such a racket?

Am I causing any damage by using the valve with DIYs value of 26?
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Old 07-28-2008, 05:24 PM   #8
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Quote:
Originally Posted by Duckie_uk View Post
P.S. How do I post my logs as attachments?
XLS and MSQ were added to the list of approved file types for attachments. Click on the paper clip thingy in your reply, then browse for your file and upload.

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Old 07-29-2008, 02:49 PM   #9
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Thanks Scott,

As with most things, the more I work at this the better it gets

I was trying to do too many things at once before. So I changed idle to warmup only. I then tuned the cells around the idle for the highest rpm (afrs) didn't change!?) I now have a rock steady idle in warmup and damn close in closed loop. Even the noise is greatly reduced.

But I still get occasional misfires and an rpm spike which blows the closed loop to hell. I have a .1uf cap between JS8 and gnd.

I have attached a quick log of my idle. First is closed loop, after the 3 tach spikes in quick succession I changed to warmup only.

Can someone offer some sage advice on what will stop my spikes?

Thanks
Attached Files
File Type: xls datalog200807291719.xls (118.9 KB, 57 views)
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Old 07-29-2008, 03:12 PM   #10
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That's definitely suggestive of the sort of tech spikes I used to have with my funky CAS, though with mine it never happened at idle- always around 3,000 to 4,000 RPM.

Since I never really fixed mine per se (I trashed the CAS and went VR) I can't offer any specific advice, other than that either your CKP or CMP signal are in need of filtering.
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Old 07-29-2008, 06:16 PM   #11
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The answer I was hoping for was "My tach spikes were different because X,Y,Z. Yours are due to a bad earth"

I was always intending to go for a wheel I guess I go sooner than originally intended. I'm going to try and find me a pully in a scrap yard from either a ford/GM car with the teeth already part of the body and then make the bolt pattern fit the crank. Should save me a bit of work on the lathe and look a lil bit neater (though I do love how Joe's table saw looks)

In the mean time are these tach spikes going to cause me any tuning problems in other parts of the map? I can live with an open loop idle for now.

Other than that I think its about time I stopped talking about the damn thing and got out there to do some logged runs.

Thanks to all who helped. If anyone is in my area for some reason swing by and I'll treat you to a few pints from my village brewery.
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