Anyone ever see this?http://www.napaechlin.com/tmt10.htm I am going to check this tonight on the car.

 

Ok I checked it and when initially putting the meter on the output post I see 3vac and then it bleeds off. Likely because its all going to ground I can do this over and over and its the same everytime. Could be on to something here.????

 

Sounds interesting. I will be checking it also, just to be sure everything is ok.

 

Im not sure of the exact testing or dynamics here but I believe this may be a very real problem for some cars that have had idle problems and no part thrown at it would fix it.

I have a 91 chevy lumina daily driver with 181,000 miles on it.It has had a strange idle the last year or so.Sometimes the idle would be fine then drop low,then high and sometimes make the car feel like it wants to stall.Sometimes there would be an overly rich condition where the exhaust would have a smell.With several scanner readings and tests,nothing showed up as being bad or out of the ordinary.

My alternator was acting up this week so I put a new one in along with a new battery and Bingo,the car idle and runs brand new again.
When my alternator was going bad,the battery light came on sometimes.Sometimes the dash or headlights would dim on braking or etc.

Also,before I changed the alternator,When I used the turn signal the rpm tach would blip with it.I knew something wasnt right.Its fixed now and doesnt do it anymore.

So I believe that was the problem with the car the last year or so.
Must be why 2 batteries have died in the car,but the alternator test kept showing it was OK.It wasnt a consistant problem,just once in a while until it got worse and worse.

 

Do you remove the output cable and check between the cable and the terminal or go from the terminal to ground? Thanks

 

Whoohoo it worked!!!!! Showing AC voltage from terminal to ground with it running rough and after about 5 minutes (normal time that it would take to start running right) it smoothed out and NO AC VOLTAGE, yippee. Will replace alt. asap. Thanks Onetrackmind, I owe you one (or 2, or 3).

 

I've been chasing an intermittant high idle problem. Checked the obvious, IAC, vacuum leaks, etc. What exactly was the procedure you used to check the alternator? Using a multimeter, did you read the AC voltage probing the ALT output to ground with the ALT output line connected to the power distribution block with the engine idling? TIA.

Larry

 

Guys, the way I checked it was simple putting the positive lead of the multimeter on the output post of the alt ( should have a rubber boot over it) and the negative meter lead to ground. I thought about this some more and the next thing I want to try is to warm the car up. then shut it off and disconnect the output lead from the alt and see how it runs for a few minutes just on battery power. I would think that if the problem is the output of the alt this would help confirm that.

 

I was showing 31 VAC while it was running like crap and as soon as it smoothed out NO AC voltage. Once the alt. heated up it stopped producing AC voltage. Tried to buy a new alt. tonight and no one has in stock. I'm going to check into having it rebuilt.

 

Are you sure it wasn't 3.1? Why did it smooth out after it warmed up. The symptoms on that web page were refering to the idle being bad after warm up, I assume this is because the car goes into open loop.

 

Very interesting. The heat up and go away thing may be caused by a cold solder joint making contact when warm.It makes very good sense as an alternator generates AC voltage that is converted by the diodes to DC. Diodes can and do fail over time and can leak through AC voltage in a rectifier circuit.

 

I just ran this test too. I'm having all kinds of major problems with a rough engine and then it dies with a DTC 41 for the ignition control module. I have a post running in Tech/Perf.

I got sometimes a 2-3. volts but then it would go right back to .06 volts. I wonder if this means my diode's are flaky?

 

Measure between the alternator terminal and ground or the negative terminal on the battery (It doesn't matter which lead - red or black - is connected to the alternator (AC voltage is non-polar over time). With the (digital) voltmeter set to AC, the meter will indicate the amplitude of the AC component on the DC circuit after a couple seconds. (The meter may read some higher value initially, but that is b/c the meter reads the instantaneous DC level as an AC pulse. After being connected for a second or two the anomoly is negated, unless a good connection is not constant for any reason.)

Hope this helps,

P.

 

That's pretty much what I did. I used two grounds just to verify what I was seeing. I used the ground for the horn and the one on the engine under the throttle body where the ground wire from the ignition control module attaches to the engine.

So does that mean mine is ok or not? When I first touch them it counts up to about 2.x volts then falls off to a fraction of a volt.

 

Solid state junctions fail in various ways under different situations. Temperature sensitivity is what breaks down most solid state devices, sooner or later. The temperature can be induced externally, or as result of current and resistance of the NP junction of the device.

Somtimes they will work until a certain temperature is reached and either go kaput all at once, or do so with agony and crying and sputtering and moaning until it finally fails completely. Some will "revive" when the temperature is right, and some not. No telling how it will be.

Bottom line: It might fail completely, or only under certain temperature conditions. Neither failure mode is uncommon, in my experience w/ solid state rectifiers. (Tube type rectifiers have different failure characteristics, but I realize I'm dating myself!! )

P.

 

Rechecked mine and got ~31 VAC. Bought a rebuilt alt. and now get 32!!! I checked my truck and I get 0 VAC. Did I get a bad rebuilt alt.? On top of that I found a gas leak around one of the injectors so until I fix that I'm not able to start car.

 

i just checked mine and with it idling i get 37 v ac and 17.25 v dc
its the original alt from 96 on the car. so which alt do you guys recommend? the best? autozone, pepboys, napa,?
tia

 

whatever you do DO NOT BUY THE CS ALT FROM AUTO ZONE. I had a brand new one from them cost me 5 ecm's and about 60hrs of labor before I found the a/c ripple that was wreckin house. I filed a labor claim on it and they never made good on it. F autozone parts. I now only buy alt/electronix etc from GM or Napa.

 

i just called advanced and they want 116.00 for one. i checked my 99 f150 truck with a new alt on it and it does the same thing... right at 17.v dc and @35 v ac

 

Dude your Dorf has an external regulator/rectifier. At least mine did anywho.