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Does not build at idle?

I have an 06 ISX. It builds to 60 psi but will not build past 60. Pressure builds fine when driving!

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You have one of two issues: either an air leak or a bad compressor. First, you should get out of the truck during your pre-trip and listen for a "hissing" noise with the engine idling. If you hear hissing, you should be near the source of the leak. Often a loose hose fitting on the compressor, a leaking hose or a leaking air bag will cause this noise.

Also during the pre-trip, watch your suspension air pressure gauge if you have one- it should be steady at 5-10 pounds when you're bobtail or empty (once the air bags inflate and the system reaches correct air pressure) and hold a steady PSI between 25 and 70 when you're loaded on level ground at idle. Usually if the pressure on the primary and secondary air gauge is below 85, the air bags do not inflate and you likely have a compressor or air suspension problem.

If you don't hear or see anything unusual other than the primary/secondary gauge during the pre-trip, take the truck to a mechanic and have them test the air system. They'll likely have to replace/repair the compressor.

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also be sure there is no water,sluge,oil in your air tanks...


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I just had the same problem last week with my 07 ISX, took it into transpower kenworth in Valdosta, Ga where they changed the compressor out, air builds up fast and excellent now

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When was the Air dryer filter changed? this will also cause this problem. Cost $75 give or take $20.

when was your governor replaced the low side can also do this... cost $25 give or take $10.

Beware of compressor replacement some times is just the Un loader valve,on the compressor head it will be beside the brass blow off valve. the top of the valve is held down with 2 screws and is about the size of the avg thumb. with these new EGR type engines there is more carbon in the air compressor intake and it will gumm up the vales O rings(rubber seals) and the plunger.

if you take it out (engine off) use carb cleaner to remove the soot carbon...and rinse with winter washer fliud.

(never use WD-40 or anything similar...they dry out the rubber seals)

inspect the rubber seals and re install You can use a light film of RTV red or black sealant ( reads Oxy sensor safe) let it set up before you tighten it down...

Me I just replace the Unloader Valve Bendex is about $50. i have found that the bendex parts are updated fast and are cheaper than the ones from engine mfg.


you wanna extend the life of your compressor?

Don't Idle.(the bonus is you save Fuel Too)

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