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  #1  
Old 11-26-2010, 06:11 PM
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RPM Fluctuations @ idle

Often my truck will have idle fluctuations between 620-650ish and you can hear a change in the tone of the engine. Originally I had a bad alternator connector, the tab securing it down was broken, replaced. Problem still exists. A friend of mine looked at it and said there was play in the clutch fan, said this could be the cause of the problem. Does this somewhat diagnosis sound legit? If I am going to change the clutch fan, I might as well do the water pump at the same time. I don't notice any other difference with how the truck runs, only at idle. He told me that I would be fine with it, but it is driving me insane. I don't have a ton of cash to just throw at this and would like some experienced input before I go ahead and order these parts.

It almost sounds like the voltage regulator is working too much. I am going to have my alternator checked out again to make sure that it is just not the alternator going. I replaced both batteries 6 months ago with 850 CCA Ford batteries. Whatever it is it is putting just enough of a small demand on the engine to cause this variation. Any help is greatly appreciated.

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  #2  
Old 11-27-2010, 03:39 AM
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Is this fluctuation like a quick stumble like a miss or a long stumble? Do you have the EGR valve still plugged into the wire harness? Are the heater controls turned on, with the HVAC system on in any heat setting, the A/C compressor will cycle on and off.

It may just be your turbo going thru the normal idle cycling program.
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Old 11-27-2010, 07:26 AM
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It is like something is putting a load on the engine. In the mornings, I can see my headlights intensity change with the fluctuations. I do not have the EGR pluggged in still. My valve was bad so I put a block off plate in its place. I do not notice any change in my boost readings when this happens.

This on-off cycle of the compressor, how quickly does this happen?

If I plugged the EGR valve in, the connector, but not the valve to intake, would this help. The only reason I say this is because I know the valve is weak and don't want to run into other issues. I will try it to see if it does anything and reply back. It can't hurt.

Does the normal idle cycle program happen everytime you come to a stop? Does this cycle begin at a certain rpm, like when at idle or stopped (in gear)?
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  #4  
Old 11-27-2010, 12:43 PM
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Quote:
Originally Posted by Heathrm View Post
It is like something is putting a load on the engine. In the mornings, I can see my headlights intensity change with the fluctuations. I do not have the EGR pluggged in still. My valve was bad so I put a block off plate in its place. I do not notice any change in my boost readings when this happens.

This on-off cycle of the compressor, how quickly does this happen?

If I plugged the EGR valve in, the connector, but not the valve to intake, would this help. The only reason I say this is because I know the valve is weak and don't want to run into other issues. I will try it to see if it does anything and reply back. It can't hurt.

Does the normal idle cycle program happen everytime you come to a stop? Does this cycle begin at a certain rpm, like when at idle or stopped (in gear)?
With certain year trucks and certain PCM stadegies there are side effects with unplugging the egr valve. Some of the side effects are, VGT won't cycle, Clutch fan won't reach full RPM speed, and CEL will come on.

The A/C compressor will cycle on/off with just the heat turned on, this allows the R-134 freon to keep the seals conditioned for the A/C system. When you start the truck, with the heater controls turned off, open the hood and the a/c compressor should not be spinning. Now with the truck still running, turn on your heat and take a look at the A/C compressor, it should be cycling on/off. When the heat is turned on at first the compressor should run about 1 minute, after that it will turn off and cycle evey 10 seconds. This is perfectly normal. You need to take notice when the compressor turns on if your lights are dimming. The dimming lights may be a loose ground cable, look at and try to move your battery cables for a loose connection. Also crawl under the truck on the pass side at the bottom front of motor and look for the main battery ground cable, see if it's loose or a coroded connection.


The VGT cycle is controlled by the PCM, I'm not sure how or when the PCM decides to cycle the vanes, but it should cycle whether your in park or in gear at a stop light, This is not a constant program, it will only cycle in certain conditions. I believe the real early stradegies didn't have this VGT cycle program.

Let us know if you notice any difference after you plug in the egr valve, you can just plug it in and tie up the valve to the side somewhere without bolting it back into the manifold.

If the lights are only dimming in the morning when you first start it up, it's the glow plugs that are turning on for about 1 minute, after that they step down in power. You can pick up a cheap voltmeter from walmart or a parts store that plugs into the cigarette lighter to check your volt output. Before start up the volts should be 12v-13v, then after start up they should be around 11.5v while the glow plugs are on for about a minute. When the glow plugs turn off the volts should jump up to around 13v-13.8v

Another way to test is to but a clamp on DC amp meter and check the amps from the red wire coming off the alternator. The amps at start up should be around 80amps, then slowly drop as it idles, to around 40amp.

It's possible that the the alternator took a dump. Even though you replaced both batteries 6 months ago, your first alternator that failed may have weakened or damaged them. A weak charging system on the 6.0 can result in damaging the FICM. And that could lead to failed injectors.
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  #5  
Old 11-28-2010, 06:30 AM
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Well, connected the EGR valve and tied it off, and performed a KAM reset and VGT relearn. I had forgotten that my buddy updated the strategy shortly after the EGR delete. Coincidentily, I think that is when I started noticing the fluctuating idle. It is running good, but I think I can still hear/see some fluctuations in the idle, not as pronounced as before. I don't know if this is me hearing things and being overly concerned. Other than this issue the truck runs perfect.

I am still going to check out the alternator, just for piece of mind. No one ever chimed in on whether play in the clutch fan could cause idle fluctuations? I will post a reply later when I check the alternator.

Thanks for the help Lilpooh.
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  #6  
Old 11-28-2010, 06:35 AM
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You will hear some fluctuations with the new strategy.

The VGT is opening and closing at idle to prevent sticking vanes.

If you have the new strategy you need to have your EGR plugged in
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  #7  
Old 11-28-2010, 08:27 AM
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Had the alternator checked and everything tested good. There is a noticeable difference since I plugged the EGR valve in. I will have to get used to the sound of the idle cycles and the learn cycles that come with the new strategy. Maybe I should put the radio on instead of listening to the sound of the engine and not be so worried. I am getting no codes. If things were problematic I think I would have gotten something. I will reply back if things change, but again thanks for the help.

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Old 11-29-2010, 03:04 PM
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Well, I don't think that plugging in the EGR did anything. On the way to work, I had the heat and rear defrost on and the voltage would not go over high 12's. I shut off everything and it jumped to 14 and stayed in the high 13's or better. On the way home, had the same systematic like fluctuations. It is more like a constant "Waa, Waa, Waa" sound when at idle or at a stop sign. When I got home, shut off all the heat and electronic components, and the headlights were still flickering. Is it possible that the alternator could pass the test from autozone and still be on the way out? Or could this be from the "clutch fan play" putting a demand on the engine that is causing it?

At this point it is becoming more of an annoyance than anything. I might change out the alternator just to give it a shot. If it doesn't fix anything, I will have a spare. Anyone have anything else to try. I don't think this fluctuating is from the strategy change.
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Old 11-29-2010, 03:11 PM
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why change the alt just to change it? if your worried about it take it to be load tested.
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  #10  
Old 11-29-2010, 03:14 PM
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Is that any different than the test that I had done at AutoZone?
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