Battery voltage relation to spark quality?
 

Not a long story short...

I'm experiencing some alternator issues STILL, I know the solution, but I recently realized that my alternator problems could be effecting my ignition systems ability to keep the car running smoothly. The last thing I did to the car was change the distributor cap. It was corroded on the terminals, and carbon tracked inside. While I had the car in the shop, I also had it on a battery charger...After changing the cap and rotor, I took it for a spin, and wow what a difference!, or so I thought. That was on Aug 24th. I doubt that my cap can be fouled up again, but the idle quality has lessened since then, and today, I needed to boost it. I also needed to boost it before I brought it into the shop. (hence the charger)
I drive this car DAILY. There seems to be a pattern emerging. If I charge the battery, the car runs awesomely for about two weeks. as my time spent idling increases as opposed to amount of time at higher RPM's, the idle quality begins to decrease developing a miss. I KNOW that with idle time (remember I have a faulty alternator) the battery is draining, and charging when I am 1000rpm+
Can this slow drain of the battery be enough to effect the efficiency of the ignition system?
Having a decreased voltage to the ignition system would have the same effect as an out of whack Dwell setting on a conventional ignition system right? (coil is not given enough voltage to build voltage in the secondary winding to it's required voltage.)

seeing as how the spark system on that engine is wired so that the current goes through ballast resistor i would expect low battery voltage to have an effect.

FYI
 

The slow drain/voltage drop of the battery will directly effect the efficiency of the ignition system...

The decreased voltage + spikes will directly impact the CONTROL BOX, and can cause it to fail/burn out. :eek:

Ignition Control Unit (Rebuilt), NOTE: Only Bosch number 0 227 051 024 is acceptable as core.
MB# 000 545 84 32

PROGRAMA $275.16




..

I don't know why I didn't make that connection earlier :P! (no pun intended)

Read through this

http://www.landiss.com/battery.htm

And then get your multi meter out.

Interesting read! So, I look at my voltage regulator if it has a resistor it should be a low volt regulator and one without should be a high volt regulator?
This Alternator that I have is rebuilt, and does have warranty, I am then led to suspect that there is something wrong with the voltage regulator.. I have a new-used one that I'll try out..

OK. Alternator belt is tight, I DID find some badly corroded wires underneath the battery tray (116) and replaced them, I was hoping it was my problem.

Fully charged the battery..Here's the test results

after charge, the battery disconnected was giving 13.8V
running, at Park idle alternator was putting out 14.1V great! not so. As teh engine warmed up the RPM's came down and so did the voltages. 14.0-> 13.8 -> 13.0
warmed up, idling, it held 13.0. the INSTANT I put it in drive and the RPM dropped to 550RPM voltage dropped off and sat at 12.3V. idle was smooth and no misses with no additional loads on the alternator. the moment I turned my headlamps on, battery voltage dropped to 12, Fog lamps, then it developed a miss and it started idling erratically.. When I was idling it cold, as the RPM and voltage dropped I revved the engine and it would come back up to 14, but back down as soon as I let off the throttle.

With the loads on and the battery voltage down at around 12 I revved the engine to approx 2000RPM and the voltage did not go up AT ALL. If it were raining, and cold, and dark, that car would die within probably a couple hours of driving around.

turn off loads, rev the engine up and idle smooths out and voltage comes back up, but won't stay up.....

BINGO
 

We have a winner... :)

Your idle speed is too low... :)

Correct idle is 650 - 750 RPM set between 60° - 80° C :D

650-750 in N or D?

Chiltons says 650-750 in D
MB says 800-900 in N

For me 650 in D translates to a 2000-2500RPM cold Idle.
Alternator doesn't charge below 1000RPM.

650-750 engine temperature 60° - 80° C

I prefer 750 - 780.

If you have not replaced the voltage regulator yet, do it now.

In Drive? Really??

With my car, if I had the loaded idle that high it'd want to get away from me...Set right now, to what I think is too high, is a 1000rpm unloaded idle (2000 cold) and in drive, I judge the needle to be at about 600, and it's trying to go..

But at any rate, I was COMPLETELY on the wrong path with the alternator. I had it tested and the alternator is fine, I was kind of disappointed to hear that it makes 80A and 14.2V.

It seems, that the pulley, and the belt engineering is somewhat sub standard, as having the alternator driven by too big of a pulley. I noticed that the pully on my alternator was a 2 piece pulley, and I thought about it, and I took the pulley off, put a washer in between and in distancing the two plates, it makes the pulley smaller. I gained 2.5 volts at idle, however with headlamps, fog, radio, heater, and wipers it still drops to 11.9V@idle, but does increase, albeit slowly to 12V@idle. I still think I should have maybe a minimum 13V@idle with all loads..

OK
 

It sounds like you are on the right path.
If the pulley is to large = low alternator RPM.
At 11.9 you may want another spacer, or need to find a smaller pulley.
With the correct pulley you can lower the idle to your comfort level.

Idle speed is a very personal question for many people.
I have several local diesel owners demanding 450 - 500 RPM idle speed, difficult/impossible to get smooth idle + correct alternator charge that slow.

I agree, I've always set my idle speed as low as possible. Actually, the adjustment procedure describes it as just low enough for the engine to overcome the friction and drag of ancillary equipment. Another previous hunch I had a few weeks ago. Perhaps my tach has some discrepancies..I should really be using a diagnostic tachometer to measure RPM I'll just bet that my dash tach is off by at least 50-75 RPM.
I've had her running smoothly, hot at an even 500~550rpm in D, Oil pressure was .75 bar, it was awesome..That's another thing I use to determine my idle speeds, Oil pressure.

I was looking at the pulley system earlier today, and I noticed that the water pump\fan is being driven by two belts (M117.986) The Water pump pulley is quite a bit smaller than the crank pulley, but is exactly 1 inch to the rear of the alternator belt path. I have a gap of approximately 2" from the face of the fan and my radiator. I think I can re-route the outboard water pump belt over to the alternator if I space the fan pulley out 1" with a solid machined spacer and longer bolts. I know the risks involved in adding length to a spinning body, so I'll demo it without the fan. if it works, and I can maintain at LEAST 12V at hot loaded idle, with partial loads then I've succeeded, and I'll use the E-fan from my SD.

If it doesn't work, at least the entire thing is reversible, and I guess I start looking for a AL129X :rolleyes:

seems you need a new alternator . i had similar problem; great charging when cold 14.1 v
dropped to 12.1V after some time ,the regulator was not the culprit
mak
300se

Alternator was new in January, still under warranty.