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2007 CXN ROUGH IDLE WHEN AIR COMPRESSOR IS PUMPING


bgblk1968
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2007 Mack CXN has a rough/loping idle. Has to be operating temperature or warmed up a little. Noticed when air compressor is pumping it goes away. As soon as air dryer spits off, it goes to loping. No codes. Checked and even replaced cam and speed sensors. No power complaints. Supply pump? Doesn't make any sense.

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i wrote to you about this post... well, here you are.. I figured its an MP. then could there be a relationship because of the drive gears. air comp. runs the tandem pump....

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yes sir... well on this one, because I have lost a lot of knowledge on MP's since its been over 2 years since I diagnosed one, I feel it's best if I just watch.... You and "F" and a couple others will be a good source of help..  JOJO✌️

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I actually had this issue with Volvo and Mack with 13L engines. Turned out to be the double idler gear. When the compressor was in operation the timing gears loaded up and the engine would run smoother after the drier purged then it would run rough. Usually you would hear some strange noises from the rear of the engine.

V

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1 hour ago, bgblk1968 said:

2007 Mack CXN has a rough/loping idle. Has to be operating temperature or warmed up a little. Noticed when air compressor is pumping it goes away. As soon as air dryer spits off, it goes to loping. No codes. Checked and even replaced cam and speed sensors. No power complaints. Supply pump? Doesn't make any sense.

What engine is fitted in the vehicle?

V

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Well, I'll sing the same song I always sing....   Have you checked fuel pressure?  it should be at 100 PSI, but 80 will be ok too..  

Edited by Joey Mack
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So I've been sitting here for a while thinking about how the air compressor affects the idle smoothness.... I'm stumped... do you hear any noise behind the timing cover? like whining gears or chatter for example...

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Don't know how it would effect idle, but the compressor is pulling air out of the intake manifold and has a short hose on each end of the metal pipe that routes behind the engine.  One of those could be split and your losing intake pressure until the compressor kicks on and is sucking more air thru the system?

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Interesting perspective....  the only thing I can think of, is that the compressor is failing and has a vibration that may simulate a rough idle... I dont know...  I hope to learn something when the answer is posted.. jojo

Edited by Joey Mack
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Okay I had 80 plus pounds on fuel pressure gauge and  even changed supply pump out. No change. Pulled nozzles out and had checked. I had previously(month ago) put a 736GB421M2X in it. When injector shop checked, other five were not popping correctly because surfaces being blown out between plate and the tip. The one new one was not a M2X, but a MX. Apparently packaged wrong from factory. After all this truck still has same symptoms, rough idle, etc. Could the air compressor drive gear be loose. Wouldn't it give me times of not pumping at all?

Still puzzled....Besides erratic idle, runs great down the road!

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OK I have checked everything in SB. I eliminated everything except for air compressor. If air compressor is pumping motor is smooth. I replaced air compressor and still the same. I'm about to pull my hair out. Doesn't make sense. Tach gauge goes from 740 to 760 when it does it. i do not like throwing parts at a problem but I am baffled by this

HELP!!! 

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