Engine Idle knock when a/c cycles

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staynlean
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Location: Memphis Tennessee

Engine Idle knock when a/c cycles

Postby staynlean » Sat May 18, 2013 12:07 am

As title states but it only happens when the truck has been driving for a while and then you come to a stop. Once at a stop and the engine is at idle with the a/c on there is such a drop in rpm's when the compressor cuts on that it causes the engine to knock and almost shake and vibrate the truck, almost violently.

It just started this, worries me of course. Any suggestions? Be back later this afternoon...


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ShipFixer
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Postby ShipFixer » Sat May 18, 2013 12:49 pm

Mine gets pretty lumpy, especially when the compressor is working hard on a hot day. It's not abnormal...

staynlean
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Postby staynlean » Sat May 18, 2013 10:57 pm

Thanks Ship, mine was not as bad today when we took the 3 year old through the drive through at Wendys. Actually it never made a rumble at all.

Who knows, i was just thinking maybe it was like an idle air sensor or a knock sensor or something like that failing.

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smj999smj
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Postby smj999smj » Sun May 19, 2013 12:09 am

You might want to check the serpentine tensioner.

staynlean
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Postby staynlean » Sun May 19, 2013 12:44 am

smj999smj wrote:You might want to check the serpentine tensioner.
Tensioner and belt replaced with Nissan OEM parts about 500 miles ago...

staynlean
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Joined: Wed Oct 17, 2012 11:28 pm
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Postby staynlean » Sun May 19, 2013 12:46 am

Air blows cold as it possibly could, actually the coldest air conditioner i have ever felt but what about the compressor going bad?

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smj999smj
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Postby smj999smj » Sun May 19, 2013 12:39 pm

It's possible. If you can duplicate the noise, a mechanic's stethoscope can be used to try and pinpoint the source of the noise.

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volvite
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Postby volvite » Sun May 19, 2013 2:54 pm

smj999smj wrote:It's possible. If you can duplicate the noise, a mechanic's stethoscope can be used to try and pinpoint the source of the noise.
If you don't have a mechanic's stethoscope, you can use a screw driver. The noise will travel up the blade of the screw driver.

staynlean
Posts: 197
Joined: Wed Oct 17, 2012 11:28 pm
Location: Memphis Tennessee

Postby staynlean » Sun May 19, 2013 11:56 pm

Think i have figured it out, the exhaust, (somewhere) is giving me this fierce vibration. Will look under the Path son to se if anything looks loos and then maybe add some exhaust weights here and there...

Any other suggestions...

staynlean
Posts: 197
Joined: Wed Oct 17, 2012 11:28 pm
Location: Memphis Tennessee

Postby staynlean » Mon Jun 10, 2013 11:42 pm

Bumping for more suggestions, when this does hapen the RPM's do drop a hair, i mean like 50 or so but not enough to be abnormal. What could it be. Still need to look at the exhaust piping as i fell it's whats rattling...

FLpathFinder
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Postby FLpathFinder » Tue Jun 11, 2013 6:21 pm

Happens with me as well, seems to me normal. Actually when mine cycles my voltage gauge drops a little.

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ShipFixer
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Postby ShipFixer » Tue Jun 11, 2013 10:02 pm

Check your engine mounts too...

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ThePainClinic
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Postby ThePainClinic » Wed Jun 12, 2013 3:24 pm

Same thing happens to me. When the a/c kicks on, you can tell. It seems its a strain on the engine even the battery gauge moves. I was thinking mounts too.


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