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"Puffing" sound?

2000 Crown Victoria, 207K miles, 111K on current engine

My car has been an absolute champ since I took ownership of her at 133K miles, and to this day runs trouble-free. However, it’s just started making a noise that’s got my scratching my head. I can only describe it as a “puff” sound. It’s consistent with engine speed (higher RPM = faster puffs), and seems to get louder the more open the throttle is. If you let off the gas and coast, the noise goes away.

What’s kinda confusing me is that the noise does not occur at all while the car is not in gear. If you park and rev the engine, the noise doesn’t happen at all. All fluid levels and conditions are good, and there’s been no loss of power or other issues from the engine or transmission.

My only guess is perhaps I have a teeny-tiny pinhole leak in my exhaust somewhere. The sound seems to be coming from somewhere very close to the engine, but since it doesn’t happen when parked I can’t pop the hood and look around for where exactly the sound might be coming from. Anyone have an intelligent guess?

I don’t know if that car has the old doughnut between the exhaust manifold and tailpipe but if it does that would be my guess.

Exhaust manifold gasket leak.

My only guess is perhaps I have a teeny-tiny pinhole leak in my exhaust somewhere

Probably right. I suspect the noise just gets louder when you’re driving, but it may still be possible to find the leak when parked. If you want to track this down yourself, spend ten bucks on an automotive stethoscope and start hunting around the exhaust system. Start where Barkydog and jesmed suggest. If you don’t find it, you might just check all along the manifold or exhaust pipe. You might need to get a helper to partially block the tailpipe outlet to help accentuate your pinhole leak.

My old Nissan pu developed a hole in the manifold where two sections merged into one. In that case, it was a big enough hole to be LOUD. I used an epoxy repair material specific for exhaust systems to plug the hole. Then I improvised a bit of metal and a hose clamp to physically support the epoxy so that it didn’t blow out. Figured it would at least get me home from a long trip, but I was still out for a week or more. I knew I’d replace the manifold sooner rather than later. Dang thing was still in there 10 years later when that good old truck went to the crusher. Truly sad to see it go…400k. Bought it for next to nothing 22 years previous.

The bottom line is that the puffing sound is a classic symptom of a typical exhaust leak. I’ll bet if you look closely with a work light you’ll see a carbon spot at the leak.

That’s sort of what I figured. The way this engine sits in the bay you can’t see or feel much of anything from the top, but a quick check around the areas of both manifolds didn’t reveal an obvious leak to me. Didn’t see carbon marks or feel any puffs of exhaust gas. I’ll have to get the car up on ramps and try looking around underneath. Hopefully it’s small and easily wrapped up with muffler tape or something.

I think sound will be the biggest help, especially considering your followup post. It can help you get close even if the leak is completely out of line of sight. To isolate the sound, you need a stethoscope. If you find something that’s possible but unconvincing, have your assistant alternately restrict and then remove restriction on the tailpipe, while you listen to see if the sound changes in the same pattern. Good luck!

Sounds like an exhaust leak to me. I’ve used something as simple as a length of garden hose for a beer budget stethoscope, probe with one end and listen to the other, to isolate to where your puff sound is coming from. You may not be able to find it now, since it might not make enough noise when you are parked and rev-ing the engine in the driveway, but eventually it will make more noise as the hole widens, and then you can find it.

Well guys, it turns out this wasn’t an exhaust issue at all. I can say that because this morning the spark plug in cylinder #3 blew out of the head. This is not uncommon with Crown Vics, I’ve seen numerous mentions of this happening on the crownvic.net forums. I’d replaced the plugs about 30K miles ago and was just going to remove and inspect all of them tomorrow…guess I should’ve done it LAST week.

Car’s now sitting at the shop, hopefully a Time-sert away from being back on the road. Argh.

Thanks for posting back. i’m glad it was something simple. The irony is that of you had checked your plugs last week you might not have realized one was about to blow.