dolphins72

Hello:

I have a 2002 Audi A6 Quattro with 130,000 on it. About a month ago I started to have intermittent starting issues....no "rhyme or reason", although it became more prominent in the evening with cold weather. When I would go to start the car, it would be a very SLOW start....i.e., almost as if it wasnt getting enough juice. Last week in about 30 degree weather it took me 3 turns before it seemed to get enough juice to start up. Not wanting to get stranded as the winter is fast approaching, I took it to a mechanic who indicated that he believed it to be the alternator, as it tested slightly below average (his words not mine). He indicated that he could not say for certainty that is what it would be, but said if it was his car he would replace it. So I did, to the tune of around $800. Seemed to be fine for a day, but last night it did it again! Anyone have any other suggestions as to what it could be? battery is less than a year old, having been replaced at the dealer, voltage on the inside gauge read anywhere from 13 to 18. Anyone have any suggestions of what to look for? I certainly dont want to be dishing out more $$ on just flat out guesses! The mechanic said he has never replaced a starter on an A6, so he didnt think it could be that? Anything else that is possibly could be??? Thanks in advance!!

tcdesignguy

Did your mechanic check the starter?? There is a lot that can go wrong in a starter alone. You hear of people hitting them with hammers , that's typically because there is a dead spot in the armeture. For yours it can be as simple as oil spilling onto the starter soaking the fields inside. This would make it so it barely can crank the starter over.

He could have put the old alternator on a test bench (applied a load etc) to see if it was good. He would have known before you drove away if that was the problem.

Likewise, you can test a starter to know that was the issue.

Just my .02C (my dad owned a starter / alternator repair shop growing up so I have a background in this area)

Obviously, check connections at battery, and health of batttery and grounds etc before digging too deep. Try to keep it simple first...

Good luck

Just Me

Start from the beginning. So the problem is slow cranking, not slow to start per say?

So it could be:

1. wiring
2. ground strap
3. battery
4. alternator/regulator

I would begin by measuring Resistance from alternator to ground and from power lead (fuse removed) to alternator, switch set to crank.

Then i'd next think "battery". But this can be measured. At minimum measure off voltage and charging voltage. Should be ~ 12.5 and 14 vdc. Where does it fall to when cranking? 10V? 8?

You can also load test the entire system. But if the battery is fully charged it should crank fairly quickly even if you alternator is "marginal" - so long as you are not running a bunch of accessories.

Bottom line- i suspect wiring or battery. I worry about mechanics who don't give numbers adn replace $800 parts first. Charge the battery in another car and drop it in and see how it behaves. It should start 4-5 times with NO ALTERNATOR AT ALL.

Grant

Just Me

Checking a starter is not so easy when it takes hours to get it out.

I believe he said after swapping the alternator is cranked normally - briefly
(OP - pls confirm)
Then all went sour again

This says to me:

1. its probably not the starter
2. its also probably not the alternator

Note: a shorted battery can kill an alternator. Or at lest the voltage regulator portion of it.

How does it crank if you get it started, run it for 15 minutes, shut it off, and start it again?

When its running what does the voltmeter say? If its > 14V the alternator's working well enough to charge the battery under low load conditions.

What happens a you turn on lights, blower, radio etc? Voltage plummet, or just dip a little?

Clues, clues.

Grant

SloopJohnB@mac.com

There are no field coils on modern starter motors...they're permanent magnet coils.

That being said, rapping on a modern starter with a hammer can break or release a PM field coil...and that isn't good.

SloopJohnB@mac.com

Measuring resistance is often an (ahem) non-starter. What you want is voltage drop across the wiring, i.e., put a voltmeter across the battery and starter terminal and crank it. Anything more than 0.5-1.0 v is too much. V=IR; the current across the wire to the starter will generate a voltage drop depending on its resistance. The wire resistance is so small that it may not be measurable while throwing 400amps across it will generate enough voltage to be measurable..if not, the wire isn't the problem.

ECS Tuning-Audi

A weak start could just be from a bad battery. The battery is what turns the car over since the alternator is not really providing any juice at start up. The alternator charges the battery while the car is running to keep it from draining while running all the electronics/lighting.

A faulty crank position sensor can often cause intermittent starting issues.

Evidence of this could be viewed with VAG-COM or the computer diagnostics the dealer has.

I hope this helps!

Good luck!

Jason

Just Me

Why can't you measure resistance? Imputing it from IR drop means random guessing unless you know the draw, whcih you don't.

Grant

SloopJohnB@mac.com

. Voltage drop is the important parameter. Most multimeters can't measure say R if IR is 3v @200A. (.015 ohm). Should not have more than .5 v drop.

Just Me

The circuit must be disconnected from power
Most multimeters place a known voltage on the circuit and then calculate
The assumption is that within a reasonable band the wire has linear resistance with current

Yes, its very hard to measure very small resistances - but we are looking for a (relatively) large one.

My Fluke seems to be unable to resolve/measure under 0.1ohms

Let's say the draw of the starter is 75A and the max drop is 3V

That means the resistance must be at or below = 0.04 ohm.

So we might be able to discern it.

Its not precise, but i see the alternative (guessing the current draw) as even worse

Grant