loud chuffing sound under boost, power loss

[Lifespeed]

Lately I've been hearing a loud chuffing sound under heavy boost, which seems to coincide with the engine falling on it's face a little. Then the sound quiets, and the engine comes roaring back, followed by a repeat of the cycle - chuffing and falling on it's face. At first I thought this was a symptom of my exhaust leak getting worse (this post), but maybe I was just confusing two different problems. The exhaust leak problem has been around for a couple years, although I'm going to try to fix it now. The loud chuffing/roaring under heavy load is a newer problem that I at first chalked up to a worsening exhaust leak. But I don't think an exhaust leak would affect engine power when it is operating open-loop.

Has anybody experienced this problem before? The engine runs great, otherwise. It has a new MAF, supercharger isolator and oil, crank damper, crank trigger, water pump, thermostat and radiator, etc. It has been pretty well maintained. Could it be letting boost leak out under pressure through the lower intake manifold gaskets?

 

[Lifespeed]

Could this be the supercharger bypass valve failing to close under boost?

 

[Lifespeed]

OK, did a quick datalog. There is no indication of a problem reaching full boost, and it stays consistent. Also there doesn't seem to be a loss of power, just an illusion due to the chuffing sounds. Which are probably an exhaust leak.

 

[LT1roadmaster]

I would have guessed boost leak, as well, but you say boost is staying steady. Actually joined the forum to say this: it may be the plugs.

My turbo cars have occasionally had the plugs erode enough where they couldn't ignite the dense air fuel mixture under high boost. It is a terrible shock to the whole system when this happens.. I spent a ton of time trying to figure this out in the past; with any luck, you have the same issue.

Lesson learned, and frequently forgotten by me.. start with the maintenance stuff and make sure the basics are covered.

 

[Lifespeed]

I would have guessed boost leak, as well, but you say boost is staying steady. Actually joined the forum to say this: it may be the plugs.

My turbo cars have occasionally had the plugs erode enough where they couldn't ignite the dense air fuel mixture under high boost. It is a terrible shock to the whole system when this happens.. I spent a ton of time trying to figure this out in the past; with any luck, you have the same issue.

Lesson learned, and frequently forgotten by me.. start with the maintenance stuff and make sure the basics are covered.

Good point on the spark plugs. I'm not experiencing any missing or loss of power, though. I think it's just getting loud and another exhaust leak has opened up, possibly the bellows. I will do some diagnostics this weekend involving a shop vac blowing up the tailpipe and some soapy water.