Idling question

[zak_62]

Hi guys~
I have been driving more of my HC recently, and I noticed that my engine idle speed are lowered when I switches on my headlights, and it will snap back up as soon as I turn the lights off. The volt meter still shows around 13V at idle after I switch on the light. Is there something I should check? Or that's pretty normal to an esprit?
By the way, how about electronic ignition magnifier stuff? Any one tried those toys with their S3? I also heard something about removing the vaccuum hose connected to the distributor and advances ignition timing. Could someone please tell me more about it? Thanks.

[lotusguy]

Hi guys~
I have been driving more of my HC recently, and I noticed that my engine idle speed are lowered when I switches on my headlights, and it will snap back up as soon as I turn the lights off. The volt meter still shows around 13V at idle after I switch on the light. Is there something I should check? Or that's pretty normal to an esprit?
By the way, how about electronic ignition magnifier stuff? Any one tried those toys with their S3? I also heard something about removing the vaccuum hose connected to the distributor and advances ignition timing. Could someone please tell me more about it? Thanks.

Hi,

The slowing of the engine idle when you apply an electrical load is definitely not normal. But, the causes can be many, spanning from a poor battery which is at the end of it's service life, to an under-capacity battery, to a bad voltage regulator in the alternator, to a loose alternator belt, to a failing alternator, to having too much electrical load for the alternator capacity.

Your alternator essentially freewheels most of the time applying little load on the engine. All of the car's electrical needs are supplied by the battery. When the voltage regulator senses a reduced capacity from the battery, the alternator kicks in to re-supply electricity to the battery. When this occurs, the engine comes under a bigger load which is why your idle speed is dropping.

But, remember, we are talking capacity here which is amperage and not voltage so, any voltage check will normally come up ok.

Having now thoroughly confused you, let's just say that your problem is that your alternator senses a reduced capacity in your battery, or thinks it does.

This can be from an old battery which has degraded plates or leaky cells (making it incapable of storing the proper level of amperage), or a loose alternator belt (which makes the alternator incapable of re-supplying the needed amperage, especially at low engine speeds), or a faulty voltage regulator (which lives in the alternator) which thinks the battery's capacity is low whether it is or not.

If your battery is old, think about replacing it. Check your alternator 'V' belt for tightness. Proper tension should allow you to deflect the belt at it's longest point no more than ½ in. total deflection. This means no more than ¼ in. in either direction.

If these fail to correct the problem, review the total electrical load you are applying. Do you have an aftermarket power amp, cell phone, alarm system? You may be creating a demand which is greater than the alternator's 90 Amp capacity. If so, you need to consider a larger capacity alternator.

Also, check and clean all ground cables to insure that a clean electrical path is available to the charging system. If none of these improve the situation, remove your alternator and have it checked to see it is working properly. If not, have it rebuilt.

I suspect you will find one or more of these circumstances to exist which are causing the problem. Happy Motoring! Jim'85TE

>> Edited by lotusguy on Monday 21st April 15:50

[lotusguy]

Hi,

As far as electronic ignition, you already have this. You have a magnetic induction device which initiates your ignition spark through a phenomena known as a 'Hall Effect'. This simply replaces the conventional 'points'. It is more efficient, and doesn't fall out of spec as points do when they wear. Essentially, it is maintenance free and requires no chronic adjustment as points do. Also, it eliminates a phenomena known as 'point bounce' where at high speed, the points can actually bounce open and closed reducing the time that the coil charging curcuit is closed. This results in a depreciating coil current and poor combustion.

The vacuum line which goes into the distributor provides an advance to the ignition timing when the engine is producing high vacuum. It uses this vacuum pressure to physically move the 'reluctor' closer to the ignition point allowing the spark to occur sooner.

You can remove it provided that you plug the vacuum line and either advance your static timing to make up for it or have the distributor 're-curved' so the mechanical advance comes on sooner. For a street car, this is best left in place. Happy Motoring! Jim'85TE

>> Edited by lotusguy on Monday 21st April 16:06

>> Edited by lotusguy on Monday 21st April 16:07

[zak_62]

I see~ Quite an interesting system~

So, just out of curiosity, what is the advantage/disadvantage of having an advanced ignition timing?

[zak_62]

So, basically, the alternator "Freewheels" as a mean to reduce energy consumption at idle? And when the regulator senses an excess current loading, the alternator kicks back in to assist the battery?

[lotusguy]

zak_62 said: So, basically, the alternator "Freewheels" as a mean to reduce energy consumption at idle? And when the regulator senses an excess current loading, the alternator kicks back in to assist the battery?

Hi,

No, your alternator freewheels until it senses a demand. It is a function of how the system works and not specifically to reduce the load on the engine.

The alternator draws mechanical energy from the rotating crankshaft and converts it to electrical energy for the battery. When no demand is placed upon it by the battery (or actually the voltage regulator), it isn't working, so it does not draw much mechanical energy from the crank.

Once the alternator energizes, the attractive/repulsive magnetic force created when the coil on the armature spins past the magnets surrounding it is transmitted to the pulley creating drag (or load). Mechanical energy from the crank, transmitted via the 'V' belt must overcome this drag, (or load) to keep the armature spinning.

Of course, as we do not live in a friction free environment, there is always some load on the system, but very little. Also, due to friction, mechanical inefficiencies etc., very little of the energy supplied by the crank is actually converted to electrical energy, the rest is lost mostly as heat. Happy Motoring! Jim'85TE

[lotusguy]

zak_62 said: I see~ Quite an interesting system~

So, just out of curiosity, what is the advantage/disadvantage of having an advanced ignition timing?

Hi,

Most engines have some form of advance to allow the engine to best perform at all rpm and temp ranges. Ideally, you want to give your fuel sufficient time to burn completely releasing as much of it's energy as possible. This 'flame travel' is the time it takes for the air/fuel mixture to completely ignite. The flame quite literally travels across the cylinder from the point where it initially ignited some of the air/fuel charge.

When the engine is turning low RPMs, the piston takes longer to complete a cycle and spends a little more time at each stage, (intake, compression, combustion and exhaust), than when it is turning at higher (faster) RPMs.

At extremely high RPMs, there may be insufficient time for the flame to travel the entire mixture while the piston is still at the top of it's stroke, so by advancing the timing, (or producing the ignition spark earlier), the fuel can more completely combust in this shortened environment.

Conversly, once the engine slows down, the ignition spark must once again be delayed (or retarded) or the fuel won't be properly compressed when the ignition spark occurs and may not even ignite at all.

On modern, ECU controlled cars, this controll of the spark occurs electronically. But, on older cars, with conventional distributors, a different control mechanism was needed.

One such mechanism is called the centrifugal advance. On a centrifugal advance, a series of weights, held by springs are attached to the baseplate inside the distributor. When the distributor shaft turns, a centrifugal force is applied to these weights. Once enough force is applied, the spring pressure is overcome and the weights cause the baseplate to physically move, this also changes the place in the rotation where the spark occurs. Centrifugal advance is often used to adavance the spark just off idle say between 2k & 3k RPM.

At higher RPMs, a vacuum module is connected to the baseplate in the distributor and once sufficient vacuum is created, this module moves the baseplate even further to provide additional advance. Hope this clears things up for you. Happy Motoring! Jim'85TE

[zak_62]

I see I see~ So in theory, we would like to advance the timing as early as possible to achieve maximum efficiency.
Heading out of the country for a few days, will catch up with you folks on tech classes later if you don't mind. Thanks Dr. Jim.