One weird electrical problem

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Team Lazy

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I've searched around for info to see if anybody has experienced my issue, but if they have I couldn't find it. So maybe, hopefully somebody can help sort out my strange issue.

This is an 08 5.7 QC 4x4 with 119,000 km on it, so just over 60,000 miles. I've had it for a couple months but don't drive it often. It's just for towing and as my toy carrier. Here's the issue.

Randomly, the electrical system goes ***** and will completely cut the fan motor out. The headlights go slightly bright, then dim, and the volt meter will show an increasing charge. Those are the symptoms I have seen. Then, it will behave, and then repeat the problem. It seems to do it as I accelerate, mostly doing it as I hit about 2000 rpm and accelerating hard for example to climb a hill as I leave my house. So as I pull out of my driveway and turn, accelerate, the fan blower will go from high, to completely off, maybe the lights are always dimming but I can only tell at night, the voltmeter starts to increase, then the fan starts blowing on full again. Then it repeats. And it seems to do this mostly for the first half hour or so I use the truck. The radio doesn't go quiet, dash lights don't flicker, just the main thing is the heat/fan completely shuts down, then starts again.

Any clues? Tired alternator? Bad connection that every Ram owner but me knows about? I'm all ears so any leads would be appreciated. I hate driving my little guy somewhere as much as he loves the big red truck, just in case we end up dead in the water...

Thanks in advance!
 

HeavyD

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alternator sounds right.
Do you have a multimeter?
Check you voltage at idle & then at 2000 rpm.
It should be close to the same & over 13.5 - 14.4v
 

justin13703

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I'd also look into the fan motor resistor or the fan motor itself. The lights going bright, then dimming back is typical of the 06-08 rams when an electrical load disappears, because voltage is controlled by the computer. The fan goes out, voltage goes up because this load goes away, the computer sees this and dials the voltage back. It's an incredibly dumb and over engineered system in my opinion.
 

KarL45

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Is it possible you have an idler pulley that the tensioner is sticky or seized? You would get the discharge more frequent just after starting as the alt is attempting to replenish the battery as well as run accessories. Just a thought. Sometimes belt slip, especially with serpentine belt, is more difficult to hear.
 
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Team Lazy

Team Lazy

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Thanks for the awesome ideas guys, much appreciated.

Short of somebody coming along with a magic diagnosis i guess I'll just do the standard electrical diagnosis and start by replacing the cheapest and easiest parts first. theres a new Optima yellow in there so thats dealt with. I'll research the fan resistor etc while I Google some more and order up an alternator for good measure.

Thanks for ALL the ideas. I'm still all ears!
 

justin13703

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Thanks for the awesome ideas guys, much appreciated.

Short of somebody coming along with a magic diagnosis i guess I'll just do the standard electrical diagnosis and start by replacing the cheapest and easiest parts first. theres a new Optima yellow in there so thats dealt with. I'll research the fan resistor etc while I Google some more and order up an alternator for good measure.

Thanks for ALL the ideas. I'm still all ears!

The resistor is next to the blower motor under the passenger side dash. There's I think 4 wires coming out of it. The harness unplugs and there's 2 screws holding it in and it comes right out. I think a new one is like 20 bucks. If you're good with electrical I'm sure you can test the resistor and the blower motor to see if they're both good or not. I'd also replace any fuses or relays related to the blower motor.

I believe the problem will be somewhere either in the hvac controls or after them, such as the resistor or blower motor, because you said it will completely shut off. If there was a voltage drop the blower would simply slow down, but since the truck was still running there is obviously enough power still coming from somewhere to spin a blower motor. So if it was actually a low voltage issue the fan should still have been spinning, just slower. This is why I'm thinking its in or downstream of the controls.

Something you could do, is unplug the fan motor. Go for a drive where you know it would act up. If you don't see any funny voltage or light fluctuations, then you probably don't have a battery/alternator problem. I'm willing to bet that the lights getting brighter and dimmer is a result of the blower motor going out and coming back on and each time it does that the computer sees it and adjusts the voltage accordingly. The computer isn't instant when it does this so it can lead to excessive voltage drops and spikes for about a half second each time an adjustment is made. So if you remove the blower from the electrical system and find out if it still has voltage issues, that will give us an idea of where the problem might be.
 
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nybasspro

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Pull out the resistor and direct wire the blower motor. You will only have low and hi blower settings while the resistor is out. But if it solves the problem then you know you have a resistor issue.
 

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