Ticking sound under acceleration, but only while in gear?

[armstrong486]

Hey guys, I got a 1999 5.9 Cummins, automatic transmission, and it started making this weird ticking/tapping noise coming from around where the turbo is, and it gets alot louder and noticeable under hard acceleration. I checked the turbo, no play in the shaft. No leaks in the boots. Then I was driving today, I tried to duplicate the noise while I was at a stoplight by revving it in neutral...no noise. Then I start driving, I hear the noise, so I put it in neutral and rev it...noise stops....I put it back in drive and accelerate... noise comes back.

So basically, what would cause a noise (like a leaf flapping in a fan or a playing card on a bicycle wheel) but only when i'm in gear and accelerating and not when I'm in neutral? and the noise goes up in volume and speed as the RPM's go up. I can't figure it out

 

[Rich Poirier]

Hey there, nice truck. I'm thinking exhaust leak. Are you running the stock exhaust manifold? They are prone to cracking after years of heat cycles etc.. And tend to crack on the underside of the manifold where you can't see it. Could possibly just be a loose manifold or turbo at the flange, or even from the turbo to downpipe. Tighten these when cold, along with the manifold bolts. Each one a little at a time. If you have a mirror, take a peek on the underside of the manifold, looking for soot, or rust colored stains. This is a big reason why aftermarket has gone to a 3-piece manifold, for our engines, and others for that matter.

 

[armstrong486]

Hey there, nice truck. I'm thinking exhaust leak. Are you running the stock exhaust manifold? They are prone to cracking after years of heat cycles etc.. And tend to crack on the underside of the manifold where you can't see it. Could possibly just be a loose manifold or turbo at the flange, or even from the turbo to downpipe. Tighten these when cold, along with the manifold bolts. Each one a little at a time. If you have a mirror, take a peek on the underside of the manifold, looking for soot, or rust colored stains. This is a big reason why aftermarket has gone to a 3-piece manifold, for our engines, and others for that matter.

It’s funny you mention that, I actually just replaced my stock one with a 3 piece aftermarket 2 months ago. The OEM one cracked on me. Would it make sense that it’s an exhaust leak if it only makes the noise while I’m moving? Revving in neutral I don’t get the same noise

 

[DavidC]

It would probably be more pronounced moving as more load on the engine.

 

[petersonj]

Would it make sense that it’s an exhaust leak if it only makes the noise while I’m moving?

Yes. There is very little exhaust drive pressure when revving the engine with no engine load. When the engine is loaded, exhaust drive pressure between the head and the turbo inlet on the exhaust side increases significantly. The closer an exhaust leak is to an individual cylinder, the more pronounced the "tick" will be under a load. The closer the exhaust leak is to the turbo, the leak will represent the combined exhaust flow from all of the cylinders - so a "tick" is not likely to be heard.

- John

 

[armstrong486]

Yes. There is very little exhaust drive pressure when revving the engine with no engine load. When the engine is loaded, exhaust drive pressure between the head and the turbo inlet on the exhaust side increases significantly. The closer an exhaust leak is to an individual cylinder, the more pronounced the "tick" will be under a load. The closer the exhaust leak is to the turbo, the leak will represent the combined exhaust flow from all of the cylinders - so a "tick" is not likely to be heard.

- John

Awesome! Thanks for the heads up, honestly I think this is my problem, being that I just took all these bolts out to replace my exhaust manifold. Wouldn’t surprise me at all if one of them backed out from the vibration

 

[armstrong486]

Found the issue. Exhaust manifold is loose, one of the bolts backed out completely but aside from that it just needs to be tightened

 

[Rich Poirier]

Nice, good job! Keep checkin em for the next 1000 miles or so til the gaskets find their sweet spot and you should be good to go.