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loss of overdrive when ac is turned on

t-stack
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t-stack

t-stack

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Hey! ok so ple ase help me here I just bought a 98.5  cummins about a month ago and it has this issue that I just cant seem to tackle and its super frustrating! if I have ac on just cruzing along in overdrive (48+ mph) it jumps in and out of overdrive! but as soon as I turn the ac off.. no problem! it runs great.... turn it back on it goes right back into this cycle of going in and out of overdrive. when I first got it the ac worked but the fan didn't work so when I took it home and got to lookn at it closer I noticed a wire going to the + battery turminal and it had a blown fuse right there too.. replaced the fuse and fan works great now......    just tonight I put a APPS noise insulator on hoping that would fix it but it didn't... anybody got the same issue, or know a fix? thatd be super helpful!

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t-stack

t-stack

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I got the APPS idea thing from this forum.. What's it hurting?......Ok so I was out driving tonight and I noticed that if I turn my AC  off and really crank the radio it does it too! So now I'm totally confused!!

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Me78569

Me78569

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Please point us to where you found the apps filter as a good thing as we need to take that down.  I am guessing a old user recommend it without us seeing it and correcting it.

 

AC noise generated by your alternator is causing these issues.  When you increase load on your alternator, ruining ac or turning the stereo up, the issue gets worse. 

 

Now the problem is regardless of your issues your alternator is putting out AC noise all the time and that is RUINING all the computers on the truck.  The noise filter is just covering up the issue and prevents you from noticing ( for the most part) and causes your truck computers to get beat to death from AC noise.

 

The best way to fry an ECM / PCM / ABS module  etc is to pump AC noise through them.

 

Here is the article showing the diode pack being burnt up causing this

 

 

Test your alterntor for AC noise and replace when it fails the test.

 

 

Another thread showing more "weird" issues due to this same issue

 

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t-stack

t-stack

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17 minutes ago, Me78569 said:

Please point us to where you found the apps filter as a good thing as we need to take that down.  I am guessing a old user recommend it without us seeing it and correcting it.

 

AC noise generated by your alternator is causing these issues.  When you increase load on your alternator, ruining ac or turning the stereo up, the issue gets worse. 

 

Now the problem is regardless of your issues your alternator is putting out AC noise all the time and that is RUINING all the computers on the truck.  The noise filter is just covering up the issue and prevents you from noticing ( for the most part) and causes your truck computers to get beat to death from AC noise.

 

The best way to fry an ECM / PCM / ABS module  etc is to pump AC noise through them.

 

Here is the article showing the diode pack being burnt up causing this

 

 

Test your alterntor for AC noise and replace when it fails the test.

 

 

Another thread showing more "weird" issues due to this same issue

 

Ok so if I unhook the alternator fuse and take if for a drive it shouldn't do it anymore right?

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t-stack

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On June 6, 2016 at 9:39 PM, Me78569 said:

and the alternator lead wire.    

 

Ok so I checked the battery with the fluke 322 and got a reading of 0.0 volts AC at idol (900rpm) and 13.5 volts dc so should I try it again at 2000 rpm and see what does then or is my fluke 322 not reading right? And to fix the whole  diode problem I just have to buy a new alternator? Or are they saying  have the it checked before you buy it to make sure it doesn't already have the problem?

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Mopar1973Man

Mopar1973Man

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This should help...

 

0.010 to 0.030 normal good alternator.

 

0.050  and up is marginal... There is some people that report strange happenings at this level.

 

0.100 is a fail. The diodes are damaged and producing too much AC noise.

Edited by Mopar1973Man
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Mopar1973Man

Mopar1973Man

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Typically you need a fairly expensive meter like a Fluke or SnapOn that cane read as low a 2V scale or lower on the AC side. I see lots of cheap DVM in hardware stores for $10 to 20 and only measure in the 200 volt range this is not low enough it must have a 2V AC or 200mV AC setting.

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Mopar1973Man

Mopar1973Man

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Ok...

 

As for the PCM did you do any wiring mods or AC noise filters or voltage regulators (transmission)? If so make sure the power lead is still connected to the PCM. I've ran across @pepsi71ocean that his brother installed his voltage regulator for the transmission wrong and cut the power wire to the PCM. So this causes a weird issue of when the blower motor comes on the NO buss message and the transmission goes into limp mode (unlocks) and then as soon as you turn off again it goes back to working normally. So double check any and all wiring modifications you have. If you need to remove then from the PCM and return to stock form and see if thing work better.

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t-stack

t-stack

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ok so turns out i was NOT using the meter correctly... i tested it again the correct way and sure enough .1 VAC!!!... so to fix this i just  get any new alternator? or can a new alternator have this problem? should i make sure BEFORE i buy it that it has all good diodes by testing it with my fluke meter while they bench test it?

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t-stack

t-stack

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Cool! And should I get a heavy duty one? Or would I be ok with just a normal one? What is going to stop the next one from having the same problem? I have lots of acc.. Sound system.. Tuner.. Lights.. Piller gauges..  Would it be smart to go with one alittle more heavy duty?

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Mopar1973Man

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3 hours ago, Me78569 said:

The more load you put on the system the shorter the life span will be.  bigger alternators generate more heat as a result of more amps so that may not help either.

 

Absolutely true...

 

14.5 Volts x 140 Amps = 2,030 Watts (heat)

 

So now upgrade to 200 Amp...

 

14.5 Volts x 200 Amps = 2,900 Watts (heat)

 

So where is this heat going to be dumped? Right across the diode pack. The whole problem is every one is putting bigger and bigger alternators in that just means more and more heat generated. The only way around it is high quality diodes on a oversized heatsink... But there is still going to be quite a bit of heat generated on the diodes from switching.

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