Cummins ISC 8.3 350 HP

[grant3791]

I have this cummins engine in a 2002 Winnebago Ultimate Advantage MH. When getting home from recent trip got out and walked to back of coach to make sure i was back far enough. I could hear a loud noise coming from engine area, as soon as the air built up and compressor cycled the noise stopped. I went back and stepped on brake a few times and went again back and it was making the loud noise until the compressor built up air and cycled. I forgot to say that this is intermittent, I have started and messed with it for awhile trying to make it act up and nothing happens. I am trying to get it ready for 1600mi round trip so today I took it for 100 mi shake down. I pulled over at 25 mi and got out to check, no noise. I drove another 25 mi and stopped for fuel, before I shut off engine i went back and it was making the noise until built up air and cycled noise went away. I talked to cummins and they had no answers except to get it to a cummins service center. I am 300 miles from the nearest cummins dealer. Has anyone had this trouble with their's? Can anyone give me any advice as what to do?

[esaulten]

That's you air dryer purging air. Quite normal unless the dissicant is used up and it won't dry. Also the motorhome has a air valve on the side of the block that controls the cycle time by loss of air pressure usually approx. 20-25lbs differential between high and low. If you never serviced the air dryer or had a mechanic look at the govener then before your trip I would suggest that you do.

[mackwrench]

Since you say noise stopped when air pressure built up, My WAG is compressor failure, worse news is it's a bear to change.

[palehorse89]

I can tell when my compressor is loaded and when it is unloaded.......I can hear the difference around the rear of the Coach and especially when around the fresh air intake up on the rear of the Coach for the engine air filter intake. My compressor's crankshaft snapped in half and left me on the side of the road.......years back, replaced once under a recall from Cummins............and again by me.........Cummins would not help the second time.....
How loud is the noise? is this something you just noticed that has changed?
I replaced the hex head mounting bolt's with socket head Allen wrench bolt's for ease of changing if needed again........

[grant3791]

The noise is very loud, not like a rod knock, more like a piston slap.

[grant3791]

It is still pumping, so piston probably isn't cracked or broke.

[twinboat]

Ok, not normal.

The compressor only pumps air when the governor calls for it.

The governor calls for air at 90ish psi.

During the time the compressor is pumping air, the large line to the air dryer, the air dryer itself and the large line from the air dryer, to the tank, is under pressure. One of them is leaking.

When the governor senses full pressure, it stops the compressor from pumping and sends a signal to the air dryer to purge. That empties the 2 lines and the dryer. The air stays in the tank, due to a check valve. That is why the leak stops.

Many times the air dryer exhaust port, ( purge valve ) gets sticky, doesn't seal fully and leaks. That would be the first thing to check.

Next would be the 2 large lines for leaks. I'v seen the lines leak behind the clamps that hold the line on place. But those leaks wouldn't be intermitent.

The trick is to look for the leak while the pressure is building.

[grant3791]

I don't know how I could change it I can't even see it. They build the body around the motor so you can't even get to the motor.

[palehorse89]

Originally Posted by grant3791

It is still pumping, so piston probably isn't cracked or broke.

Sound like the crank bearing's are going out.........if you look at the compressor from the bottom, you will see a 2-1/2" soft plug on the bottom of the compressor.........that is how they install it rod cap and nut's........when mine broke, it pushed out that soft plug, and there was Black oil all over everything.....clear to the roof on the rear, TOAD and bike were covered in black oil..........you can see the oil trail in the back ground of the photo coming off the highway ! it went 3/4 of a mile back up the road
You might want to get it checked out before traveling......

[grant3791]

I was thinking maybe not getting enough oil. Yes I just noticed this problem after getting home after trip and was parking it.

[grant3791]

Originally Posted by mackwrench

Since you say noise stopped when air pressure built up, My WAG is compressor failure, worse news is it's a bear to change.

Where would I get a compressor?

[mackwrench]

Originally Posted by grant3791

Where would I get a compressor?

Cummins, but I warn you, it's not a job for a novice. It'll be on the passenger side of engine .....you maybe able to see it through the rearmost compartment ...at least on mine you can.

[palehorse89]

Originally Posted by grant3791

I was thinking maybe not getting enough oil. Yes I just noticed this problem after getting home after trip and was parking it.

By design, it will get enough oil all the time. The compressor is fed with a oil line filling its crankcase, and then it just over flows back into the timing cover as it is bolted right to the back side of the timing cover......

http://salesandservice.cummins.com/locations

[mackwrench]

Originally Posted by grant3791

Where would I get a compressor?

You can go to Cummins quickserve and make a free account, get part #....