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danes-on-tour · 03-19-2013, 08:09 PM

Going up the Colorado mountains, our engine developed a new noise/sound. We are now off the mountain, but the new sound continues.

The best way to describe the sound would be like the sound of a cicada. It comes on when the engine is being just slightly stressed fx at the start of a small climb. The "cicada sound" is quick repetitions of 1 second of sound and half a second of silience, and this is repeted say 3, 4 or 5 times. Once this is over, the sound stops, even if the climb continues. The sound is clearly audiable from the drivers seat.

We have no loss of power and al instrument readings looks normal.

The DW doesn't drive, so it is difficult for me to pin point where the sound/noise is coming from specifically, but she is adement that it's an engine sound.

Any ideas?

Muddypaws · 03-19-2013, 08:17 PM

Turbo stalling. Kind of a 'chirp chirp chirp' sound.

I've only heard it a few times from my 2001 F250. It usually happens after a hard pull when you let off the accelerator on the Ford 7.3, but other engines may do it under different conditions.

So far it's been harmless.

two sailors · 03-22-2013, 08:57 PM

I have heard the chirp sound many years ago while driving truck. May be broken head bolt.

RudyD · 03-23-2013, 02:46 AM

take notice of my posting on Cummins blog with my new Cummins engine - any "sound" out of the ordinary I'd suggest having Cummins specialists listen to -it doesnt cost anything out of warranty to have experts listen to the noise - its a pain I know but something you want to be sure is fixed if it sounds funny to your trained ears

J Walker · 03-23-2013, 09:27 AM

Localizing the source is necessary before making a good guess. I will offer the idea that the controls on the vents run on a vacuum motor and there is a buzz when they are moving vents. Mine have come on at random times when traveling at high altitudes.

3rd stage · 03-24-2013, 11:52 AM

Quote:

Originally Posted by J Walker

Localizing the source is necessary before making a good guess. I will offer the idea that the controls on the vents run on a vacuum motor and there is a buzz when they are moving vents. Mine have come on at random times when traveling at high altitudes.

My Spartan chassis Beaver also has a soft "chirp" at an unusual but predictable time. If the vacuum heater controls are calling for heat (at about 1/2 the temperature lever travel), when the engine rpms reach about 2000, there's a "chirping" noise that is very difficult to locate the source of. One day I turned off the heater control and it went away. Now I can induce the "chirp" at any time I choose by judicious placement of the "heat" control and then waiting until I reach 2000 rpm.
When it first happened, shortly after getting the coach, I thought it was an RPM alarm, since it came on at around 2000. Still don't know what causes it.

Worth a try- turn "off" the heater controls.
HTH
Andy

slemnah · 03-26-2013, 07:22 AM

3rd stage, what you are probably hearing is the small vacuum motor used to change the mode motors in your climate control system. When you put it into heat the mode motors (vacuum operated) move the doors into position in the heater box. Mine is bolted to the firewall and I can hear it every once in a while.
Steve 97 Imperial

danes-on-tour · 03-28-2013, 06:31 PM

Update:

As we come down from high altitude (11,000 feet) the strange noise gradually disapeared. It was still there occationally at 5000 feet although not as loud or intense as previously.

By the time we hit Phoenix, AZ the sound was gone, and I was not able to get the engine to repeat the noise, regardless of making the engine work hard.

I am by now well connected to the IRV2 Monaco group mafia

after several years of IRV2 membership, and today I had 2 of the expert King Pins visually inspect my MH engine. They saw nothing that would warrant the strange sound, so I will leave the matter at that for now. They did spot a leak at the exhaust manifold, and that I will have to get fixed in the near future.

A great thanks to the Monaco mafia

. Your assistance is much appreciated as always.

danes-on-tour · 04-17-2013, 10:56 AM

Another update.

On Friday the MH went into Rocky Mountain Cummins in North Las Vegas.

After a check-up, Cummins could announce that the manifold on both cylinder 3 and 4 was leaking. They could not (or would not) repack the manifold, and stated that is was warped. Happycarz had warned us that this was a likely outcome. A new 2 piece manifold was needed.

Work took all day for 2 guy's. Total price $1.513

. Parts was around $260 - the rest was labour.

They connected the diagnostic "gizmo" and found out that the engine otherwise was sound, and that it didn't have (now or previously) and reported problems.

This leads me to believe that the "cicada noise" that we was hearing earlier most likely has been air escaping at the cylinder 3 and 4 manifold. Makes sense to us - sort of - we think - possibly.