Hissing Diesel Engine

NickfromWI

NickfromWI

King of Splices
Joined
Mar 30, 2005
Messages
4,992
Location
Snowless California
So I got this truck. Totally love it. 2002 Chevy 4500. It's a cab-over. Technically speaking it's an Isuzu engine. But it's a chevy truck so I can pretend it's made in the USA...right?

Anyway- a while back it started making this hissing sound. At first it was only occasionally and if you shut the truck off and immediately restarted it, the problem went away. And it only happened on colder days (keep in mind I mean "los angeles cold")

But now it happens all the time. You can hear it pretty good in this video. When the engine starts you can hear it kick in a half-second after

<iframe width="560" height="315" src="https://www.youtube.com/embed/xB6NvOfqtX0" frameborder="0" allowfullscreen></iframe>

Any hints as to what might be causing this? I've snooped around a little and haven't figured it out just yet. I am about to contact our mechanic, but I'd love to have a better understanding of what might be going on before I do that.

love
nick
 
Might have a turbo boot leaking. Easy fix. All the big diameter hoses coming out of the turbo, into intercooler (looks like a radiator), out of intercooler into engine. While engine is running grab those and shake them, if one is leaking at connection that's going to hiss
 
Yeah, I bet a hose slipped off or loosened up. MAYBE got a hole but generally not. You know what the turbo is?
 
If you can't start it with the cab up just check all those hoses I mentioned. Loosen the clamp, re set the hose and tighten clamp
 
I'll second the turbo boot leaking. Is it low on power? Also does the isuzu have an automatic exhaust brake? I'm not familiar with isuzu's specifically but drive fusos for a few years.
Another thing that might be worth doing is tilting the cab forward to pinpoint the noise or feel for air leaks.
 
  • Thread Starter Thread Starter
  • #13
sotc said:
Yeah, I bet a hose slipped off or loosened up. MAYBE got a hole but generally not. You know what the turbo is?
Click to expand...

I know WHAT it is, conceptually...but not sure I know WHERE it is.

Lemme get my nose in there and see what I can find.


love
nick
 
That's a dropped valve seat, I'd know it anywhere, but it wouldn't hurt to check the hoses while ya have the head off.
Just kidding.
 
:lol:

I was kind of thinking it sounded like it was keeping time with a compression stroke, had a tempo to it any way.

I have heard air compressors make that noise, unloader valves, even engine breathers, head gaskets and such.

Good advice to start by checking the hoses from the air cleaner first. What kind of aftercooler does this truck use? Air to air or air to water? Any kind at all?

Make sure you check every connection from the cleaner, through the turbo, to the intake. Would not hurt to check the exhaust side too.

Remember, that sound might not be pressure escaping, but it could be air entering a less than atmospheric situation as well.

Make sure the screen on the air cleaner is clean too.
 
I was thinking in line with these guys about a turbo hose. But. Share this with you.
My 7.3 decided to make that noise one day and then it went away after a restart. Then i had a water pump leak. Not related. While I was removing and than replacing the water pump I saw a loose power steering mount bolt behind the pump pulley. That is what was making the hissing noise. A bump in the road or torque movement from a start or stop of the engine would make it happen or cease it. Just rubbing metal. Take a looky.
 
You guys both beat me to it. Intake hose or exhaust brake. Most likely hose fitting. Our IH 4900 wasn't running very well a couple of years ago. Changed fuel filters, no change. I finally found a clamp off the intake hose going to the intercooler. It was like a new truck after that.
 
Oops. There's an extra page of replies in the middle there that I didn't see. Kindly disregard my rambling.:lol:
 
Those Isuzu motors use the exhaust brake to warm the motor on cold mornings. At idle it will close the brake to put back pressure on the motor and get it to operating temp or keep it at temp.
 
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