idle problems, is it my setup?

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idle problems, is it my setup?

Postby arnold » Thu Jun 08, 2006 7:51 am

I find it very hard to tune my idle, I cannot get it stable and strong. Please have a look,am I doing something wrong here?
Supercharged Austin Healey Sprite, Intercooler, spark control
MS1, MT2.25, extra code 029t
http://www.kmnet.demon.co.uk/arnold/
arnold
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Postby jharvey » Thu Jun 08, 2006 9:22 am

Problem with the idle probably means your driving to slow ;)

There is some information missing that makes it a pinch hard to help you out. How many cc/min are the injectors? What is the expected HP? How many cc, L, in^3 is the motor? Does it run OK under load?
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Postby arnold » Thu Jun 08, 2006 12:37 pm

it runs oka, sometimes a small hesitation, but that is not worrying me. I am afraid I need idle air control, which would rather not have as I run MS1 stock code
Supercharged Austin Healey Sprite, Intercooler, spark control
MS1, MT2.25, extra code 029t
http://www.kmnet.demon.co.uk/arnold/
arnold
Master MS/Extra'er
 
Posts: 556
Joined: Sun May 16, 2004 1:08 pm

Postby jharvey » Thu Jun 08, 2006 1:46 pm

My guess would be that the injectors are over-sized for the idle. Your pushing a fair amount of HP out of the injectors and demanding a large flow variation.

Hmm at idle your probably running a fairly low duty cycle, it's possible that the injectors are running at the threshold of their lower limit. If the injectors take 4ms to open and your running 4.5ms at idle then your really only running .5ms of injection. If the tolerance is +/- .1ms (8 bits for 255 or 25.5ms) then your going to see quite a fluctuation at idle. Do you know how much lag you get from the injectors? If this is the case I'm not certain the idle bypass would help.

When your running idle / wide open what is the minimum / maximum your injectors PWM gauge goes to? You can check the log for this. If you are less then 21.5ms or 85% duty, then you might be able to decrease the size of your injectors and increase the PWM at idle. I don't believe the 85% is a cut in stone figure, if your at 90% you can probably still decrease the injector size.

Another possible idea is to use two injectors/cyl one with low lag time and low flow rate and another with a long lag and hi flow rate. That way when you approach idle the large injector simple stops squirting. It's a hack I know but a possible alternative.
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