SOIA

What bumps up the engine speed when you're drawing to much power? and why isn't it doing it? When I have all my acesseries runnig the battery drains, and the car almost dies, as acessorys die off one by one and the engine won't compansate by bumping up the RPM?
Alt fuxored?
Battery Fuxed?
Something Else?
WTF?
Help?

Icemark

The ECU with the BAC valve raises idle based on the load of a couple of things, including load on the engine by some of the accessories (like power steering, air conditioning, headlights, foglights (the last two, only on the S5)).

HAILERS

Well doggies. My series fours are going in the shop come Monday. They must be done broke. Sitting at idle my BAC'S duty cycle is 37.5 percent and when I went and turned on my headlights the duty cycle went up to 43 percent. Then I turned the headlights off so as not to cause anymore damage and then turned my A/C on, and woe and behold the duty cycle went to 39.6 percent. Thank goodness I didn't have the fan on full blast, no telling what harm would have occured.

I was fit to be tied, so I turned the A/C AND the headlights on (high beam to boot). Eeeeek! Duty cycle up to 48.2 percent.

Yep, gonna have these puppies towed to the dealership first thing Monday. Darn series four thinks they're series five!

And, let me add:

HAILERS

That was just a very friendly dig at Mr Icemark. Not venemous. Not mean spirited. Not being rude. Just a friendly dig. What he said is correct in almost everyway. It was the part about the series four not being applicable to the A/C and headlight. The bac in my car/cars/all series four, have a bac response to to the lights being turned on or the A/C being turned on. The bac has a duty cycle of about 120hz. If you put a meter on it's input wire you'll see the duty cycle change as a load is put on the engine. Load as in A/C or headlights. I was trying to say that at idle, fully warmed up engine, teh duty cycle on my car was approx 37 percent. When the lights were turned on the bac's duty cycle up to 43percent which means the mixture was changed and the air input of the bac was increased.

He answered your question. I was just ribbing him about his remark about series four cars bac's not responding to a/c inputs.

Your HUH has been responded to. Fix your bac problem.

Icemark

No, I don't think you understood my post correctly... I said the last two, (which would be fog lights and headlights)...

Nothing about A/C... A/C always triggers the ECU and the BAC accordingly.

But on the S4 the headlights do not feed into the ECU as they do on the S5. The S4 BAC duty cycle change is due to voltage load, not the actual headlight operation.

This can be proven by the lack of a headlight feed to the S4 ECU and the same duty jumps, when the rear defrost is used (and again, no input to the ECU for the rear defroster).

Perhaps you mis-understood the S4 ECU control of the BAC... Hmmm I thought you had the shop manual

HAILERS

[QUOTE]Originally posted by Icemark
[B]No, I don't think you understood my post correctly... I said the last two, (which would be fog lights and headlights)...

QUOTE]

So we just proved I am a functional illiterate. Yup. No mention of A/C and the series four. I bungled that.

So, explain the duty cycle bumping up when the lights are turned on. Load on the engine? Probably. But frankly the results are the same. Lights on......bac duty cycle goes up.

I have the shop manual and know how to use it. You set your beer bottle on top of it while working on the car. Signed: Embarassed in Texas

SirCygnus

iTrader: (1)

does the car run when you unplug the battery? i men cqan you jump stqart it and have it run withought the battery? also i noticed that when i grounded everything, my idle was better and my votage gauge didnt show much of a drop if any from turning on my headlights.

Wankel7

Don't try that. It has been discussed and it is bad idea.

James

Icemark

NO NO NO NO BAD BAD BAD, do not ever do that on a internally regualted alternator. Its a good way to spike the alt and burn it and the electrical system of the car out.

The battery is used as a capcitor on modern automotive systems... disconnecting the battery while the car is running, can spike the alt up to 16 volts (some euro cars even higher)...

wanna see how long your ECU lasts as 16 volts (since most of it is designed for a max of 15 volts).

That disconnecting the battery method was something that shade tree mechanic did on an american car back in the 60s and 70s. Don't ever do that on a modern car.