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Old 08-11-2007, 01:45 PM   #1
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Hey guys

Have you guys had trouble with the A/C since installing the MSPnP?

My car idles great, but just a touch rich. I haven't done any real tuning yet with the exception of locking the timing and programming the LC-1...

Here's what happens... my car idles great at about 950 RPM. When I turn the A/C on, it starts to get funny. The compressor engages, and then the car dips way down at idle for about 2 seconds, climbs to about 1800 for about 3 seconds, and then bounces around.. as it dips repeatedly, it gets lower and lower rpm and finally stalls. I tried once playing with idle with my foot and kept the car at about 2000 RPM. After about 1 minute, I took my foot off and the car bounced around from 1500 to 2000 consistently. I could hear pressure releasing from the engine bay just before it would dip from 2000 and tracked it to a vacuum leak in one of my supercharger hoses. So I turned the car off, redid all the hose clamps....

When I restarted the car, I had the same problem with the A/C on. A/C off, the car's fine. A/C on... read above.

Took some carb cleaner to all the hose clamps.. no idle changes so I think my vacuum leaks are now negligible.

Anyone else have the same issue?
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Old 08-11-2007, 02:40 PM   #2
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2) Idle Dashpot Settings (prevent stalls when coming to a stop with the AC on)

* From the main MegaTune screen (with the gauges), right click on any of the gauges and choose SWAP TO. Choose tpsADCGauge near the bottom right.
* Look at the TPS ADC gauge you just selected with your foot off the throttle. Add 4 points to this number and remember that new number.
* Open the 'More Settings' Menu and choose 'Idle Control'.
* Near the bottom, set the 'TPS Threshold (ADC)' to the number you just calculated by adding 4 to your closed throttle TPS ADC.
* Click 'BURN TO ECU' and then click 'CLOSE'.
* NOTE-- you will need to know this same number for the next exercise as well.


i just read this and might help you
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Old 08-11-2007, 02:42 PM   #3
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The stock ecu has a circuit which opens the idle valve proactively when you turn the a/c on. MS acts reactively. So when you turn on the a/c at idle, you are going to get a bit of an idle dip. However, the MS should detect the dip, react, and stabilize your idle quickly. Like within 1-2 seconds. Mine will dip to like 500 rpm, then slowly go up to about 1100, then slowly go back down to about 900 and hold.

Your oscillations are curable. What I think is happening is the fast limit idle recovery is working so quickly, it overshoots. The fix is in the closed loop idle settings.
More settings:Idle Control (Closed Loop Settings)
Under Adaptive Idle Deviation Control you see the thresholds for fast and slow idle recovery, as well as their time definitions.
I would try 2 things
1> increase the lower limit (lo RPM) so that you it switches from fast to slow recovery sooner. I think default settings are 200 for upper limit and 100 for lower. Increase lower to say 130.
2> increase the deadband range slightly. Say 140. I think defualt value is 100.

Fix 1 should allow the ecu to go to slow recovery mode sooner, softening the transition between fast recovery and target, and hopefully preventing the overshoot.

Fix 2 will increase the "deadband" or range around the target that the ecu considers as acceptable. This should help by preventing some of the "hunting" oscillations you expierence.

If this isn't enough, you may also need to tweak the actual recovery definitions. Mine are 10 x.01 sec for fast recovery and 35 x.01 sec for slow recovery. This means that time between steps in fast recovery mode (when actual rpm is +/- target by 200 or more) is .10 seconds, and the time between steps in the slow recovery mode (as actual approaches target) slow down to .35sec. To slow down the fast idle recovery you can add a little bit of time between steps. IE change the fast idle recovery time to 15 (instead of default 10). This would add an additional .05 seconds between steps. You don't want to get too carried away and slow down the fast recovery too much. Just enough to give the MS time to transition to slow recovery before idle overshoots target and sets up oscillations.

Again, if you don't slow down as you approach target, you overshoot your target, leading to a cycle of obnoxious oscillations. But it should be totally curable once you get your closed loop settings dialed in. They are always going to differ to some degree, car to car. Not to mention you have the supercharger situation, and tons of throttled volume. Which probably would be more difficult to get tweaked out than NA or turbo set ups. And you probably have the first blown 1.8 w/ MSPNP.

LMK if any of the above is less than clear.

B
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Old 08-11-2007, 02:51 PM   #4
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Tom, your solution is for a slightly different problem. It prevents the car from stalling when coming to a stop w/ the A/C on, by using a linear TPS. You 1.8 guys are lucky to have them from the factory. My car did not, but I was able to add an aftermarket TPS. Doing this erradicated that problem for me. Not to mention gave me closed loop boost control (which seems to work correctly).

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Old 08-11-2007, 05:14 PM   #5
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hmmm. .it's gotten a bit better. I had to adjust my loRPM to over 200 and the deadband to 220. Don't know if that's bad or not... but the oscillation is better although not gone yet. Played with the time correction a bit, but ran out of time. I have to get ready to go to a party.

There is still a wicked dip in RPM when I first turn on the A/C... like down to 200 and the muffler rings and the car wants to stall. I actually got it to idle nicely at 850 real steady with the A/C on, but when I blipped the throttle it settled back into what it was always doing. almost stalling, then shooting up to near 2000, and then oscillating anywhere from 400 to 1100 rpm..

I'm glad I'm actually getting a weekend this weekend. I'll spend some more time on it tomorrow.

Good point on the supercharger... with the OEM MAF still on this car, there's a LONG way from the stock MAF to the intake manifold. I wonder if that means that I should change those recovery times drastically... perhaps double them?
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Old 08-11-2007, 05:38 PM   #6
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that sounds a bit extreme. i'd probably want to lower the deadband again, and then get into tweaking the step delays. but at least you were able to go out and make some progress. more importantly, you have at least some, if not full, understanding of the closed loop idle settings. so you're good to go.

you're always going to get the dip when your compressor kicks on at idle. the ms simply can't do anything about it until after the event occurs, then it reacts afterwards. something I've been wanting to try is adding a soft start circuit to the a/c. I haven't looked into it yet, but if the clutch is electro/magnetic it should be pretty easy with a 555 timer IC. My mercedes has a soft engage/disengage for the a/c compressor, and you can't feel it turn on or off at all.

Disntance between the MAF and cylinders won't matter. You're now running speed density, and load is based on manifold pressure via the MS' internal MAP sensor. The MAF doesn't do anything now except get intake temp, and create an intake restriction.

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Old 08-12-2007, 01:17 AM   #7
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Stan-- as you were beta testing you had an early version of the map. I know you've done some tuning so you probably don't want the full 'release' map now, but you may want to open it up offline and copy the idle settings (both pages) into your map. We did a bit more work on that between beta and release to smooth out some oscillation and improve control.

I'm out of town and will be back Wednesday-- I'll catch up and see where things stand then and make sure to help you get this lined out if it's not then.
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