[ds968]

Today, for the very first time since I got the second car I used the windshield defogger. The moment I pushed that button, the car started vibrating, and I would say about twice as much in comparison to turning on the AC . The AC I can understand because of the additional load from the compressor activation, but what the hell causes the drop in rpm and ensuing vibration when you switch on the defogger ? Particularly even more so than the AC ?!

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[flash]

was the vent selector to the windshield open?

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[speedysprocket]

Does it do the same if you just turn the AC on and turn the fan speed all the way up? The fan draws current and loads the alternator and thus engine as well...

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[Bulti]

I had a problem once with a screeching sound. It was only there when using the defogger. It turned out to be the cooling fan of the alternator grinding against the housing.



Maybe it's the bearing of the alternator going bad and starting to 'wobble' when the load is increased. Perhaps this creates vibrations.



Am I making any sense? :-)

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[flash]

very possible. could also explain some of the other vibrations. seems to me there was also a voltage issue on that car. am i losing it?

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[ds968]

I think the vent was open , it defogged the windshield right away, but I'll check it nonetheless .

When I turn on the AC whether the fan is at the lowest setting or at the highest setting it makes no difference to the load effect which I am able to detect, anyway..

So let me understand this, the ONLY extra "load" caused by activating the defogger is the current drawn on the alternator ?

If I have just the regular air / heater on , at any setting there is absolutely no vibration or similar effect that I can sense. If I turn on the AC, there is a noticeable difference, and the then of course the defogger switch even more pronounced . I'll have to check the other car and see if the defogger causes the same reaction.

The voltage reading in both of my cars have always been a little odd , ( but it has never caused any issues ) , I think the instruments readings are is probably screwed up, and not the voltage regulators . When its cold outside , as I start the car it's a hair under the 14 bar, a minute later while driving and all the time thereafter it a hair above the 12 bar. Both cars ! Ever since I've owned them. And whether the battery is new or old or in between ..

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[94SilverCab]

Dan,



Do you have the A/C support that D1R designed to keep the ears of the compressor from breaking off? (A known defect).



Thought it was worth asking,



Jay

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[flash]

um - i didn't design an AC support. i just changed the way the tensioner mounted, so it moved the load farther back. it comes with the SC kit, so yes, he has everything available.



dan cracks me up. voltmeters read volts (electricity), not bars (pressure).



anyway, if the bearing is going, you'll usually still get volts, but not as many amps. not sure what the vibration would be like with the SC though. there is a lot less slack on the belt, so it could transmit more vibration under load.

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[Bulti]

"dan cracks me up. voltmeters read volts (electricity), not bars (pressure)"



Lol, how did I miss that? Strange how you CAN measure beer in meters...

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[ds968]

[quote name='flash' timestamp='1417623471' post='164207']

dan cracks me up. voltmeters read volts (electricity), not bars (pressure).

[/quote]



Yo, ( both you and Philippe ) what I meant by the "BARS" is the indicator lines on the voltmeter gauge. Ya' bunch of literal clowns ! <img src="/forum/images/smilies/968/tongue.png" class="smilie" alt="" /> Besides, I told you guys that english is my fourth language, so I may not always use the most appropriate terminology, lol.



Back to the vibration; the vent selector was in the open position, but I omitted to specify that I only notice this pronounced change when I activate the switch while the rpm is around 800 ( you know, the BAR which corresponds to the 800 on the gauge <img src="/forum/images/smilies/968/laugh.png" class="smilie" alt="" /> ) Turning on the switch seems to cause an approx. 100 drop in rpm, so at 700 rpm that vibration becomes rather noticeable . If I'm at a higher RPM, even in N or in P, it's barely noticeable, and of course if I push the switch on while driving, I can't tell the difference at all. Essentially anything above 1 K rpm is undetectable .

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[Bulti]

The manual -if I remember correctly- mentions 800 +/- 50 RPM for idle. Maybe the idle becomes too low causing vibrations?

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[ds968]

I have my idle set at 1K. When I'm in gear and on the brake it drops down to about 850-800. If I turn on the AC it drops just a hair below the 800 mark ( well call it 775 ) . If I turn on the windshield defogger switch it drops to 750-ish or lower. I hesitate to turn on both the AC and the windshield defogger at the same time, the car may stall <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />

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[paulzebo]

a) Idling speed



ldle speed check value for engines at operating temperature:



840 + 40 rpm with manual transmission

880 + 40 rpm with Tiptronic



Isn't the Idle is supposed to be controlled electronically by the idle air control valve or as Porsche calls it, an idle speed positioner?

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[ds968]

[quote name='paulzebo' timestamp='1417660585' post='164223']

Isn't the Idle is supposed to be controlled electronically by the idle air control valve or as Porsche calls it, an idle speed positioner?[/quote]

Yes, but you can manually adjust the idle ( there is an inverted screw just under the throttle body lift arm which allows you to do that ).

I manually set mine a bit higher than the factory setting because the vibration at 850 rpm is annoying.

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[paulzebo]

NIce. But if you manually set the idle up too much, the programmed ECU looks at the throttle valve switch voltage and sees its at a position where the throttle is open and the air control valve is not needed. Did you reset the throttle valve switch to read the voltage it was supposed to be at the programmed RPM? It really should not fall below the programmed rpm noted above unless your throttle valve switch is not calibrated correctly or the Air idle control valve is bad. In the 2000's, Bosch delveloped a program so the the ECU would self calibrate the throttle valve switch because of this. In those later vehicles, it would look at the voltage at the sensor when the vehicle started and set that point as closed throttle. The RPM should not fall to 700, or even below 840 if the system is operating correctly. If anything, calibration engineers increase the idle RPM when the A/C is on or during other high load situations to smooth out the idle. Do your vehicles still have the stock ECU chip?



Secondly, don't confuse your voltage reading as an indicator the alternator is good. The voltage can be 14.5 volts, yet if the alternator is only putting out 80 of the rated 115 amp output, problems arise.The voltage in mine never goes below 13 volts. Above 1500 RPM it stays at 14. Yours seems to be doing the opposite. Voltage regulators are a know issur with these Bosch alternators. I doubt that's the problem though because the ECU will fully function at any voltage above 9.6 volts.

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[flash]

the odd thing about the figure given in the manual is that it does not say whether it is in gear or in neutral. almost all automatics idle higher in neutral than they do in gear.



before we go looking for gremlins, dan has a supercharger on his tiptronic. he is the only one. i did a test of the ICV and it passed. that doesn't mean that it is doing everything it needs to be doing, but it passed the test in the durametric, which was all i could do, short of swapping it out. it could simply be a case of the added load of engaging the transmission drops the idle.

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[ds968]

Tested this on the six speed today, and it's not even close to the tip's reaction . The rpm drop is insignificant in that car , and even though there is a very slight difference that can be felt, you really have to pay close attention and " look for it " to recognize it, whereas with the tip...well, it hits you over the head with a mallet so waaay more pronounced . But like I said , it's only when I'm on the brake while in gear so I'm not going to bother with it , since it really does not affect anything other than annoying me if I happen to be stopped at a light and running the defogger at that time.

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