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Author Topic: STII S/C cars with rough idle due to A/C compressor coming on  (Read 9429 times)

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Offline TecSolOnt

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Re: STII S/C cars with rough idle due to A/C compressor coming on
« Reply #25 on: September 05, 2009, 09:50:07 AM »


 Thanks for the update Dave, not a huge issue for me just an occasional engine shake,  but as you say it varies from car to car. Car still runs like a charm  :brnout:


DDM ST II Supercharged , DDM Pro Beam, DDM Backbone, Solo Performance Mach Exhaust, Norms Diffuser Valance, Kappa Windscreen, Sound Deadener

Offline RevmanII

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Re: STII S/C cars with rough idle due to A/C compressor coming on
« Reply #26 on: September 09, 2009, 06:07:48 PM »
Part of the issue with the idle droop has to do with the location of the throttle body on the PD supercharger setups. Since it is moved from the stock location to the back of the supercharger, we introduce a lot of throttled volume to the system. With the stock setup the computer can react a lot quicker to load changes at idle since only the intake manifold is the throttled volume. With the intercooled supercharger setup, the intake manifold, charge tubes, intercooler and supercharger all become throttled volume. So when the ECM needs to add air to the system for increase in load, it is heavily buffered by all that extra volume. We have been working for awhile on tweaks in the program to make the ECM respond quicker to this load difference, and have made minor improvements over time with it, but the extra volume in the system really makes it tough. Also different cars are more prone to it than others, some idle like champs and some take the little dip sometimes.

And there you have it :). I had the drop/shudder for a little while with STII without A/C on. It did go away after a little driving. It will still do it now with the A/C on. But as Dave said, because of the location of the TB, the change takes a hair longer to reach the combustion chamber. For me it's not an issue. I can probably count on one, well maybe two hands how many times I've turned on the A/C in 3 years.

scdyne, the mp62 DDM uses has a vacuum controlled bypass valve, so it does not apply any boost at idle.

Offline Dave@DDMworks

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Re: STII S/C cars with rough idle due to A/C compressor coming on
« Reply #27 on: September 09, 2009, 06:47:45 PM »
and of course we always work on the tune to make it better and if we come up with any major revisions we will of course let everyone know and offer upgrades for the tune at no charge, as usual  :thumbs:
Dave Michel
DDMWorks
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Dave@DDMWorks.com

Stage 3 Supercharged 2.4L - 314whp - 93 octane
Rotrex Supercharged 2.4L - 303whp - 93 octane
2871 Hybrid turbo 2.0L - 371whp - 93 octane

 

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