While cruising home in traffic yesterday, the exhaust suddenly went from sounding like a prop plane to sounding like a helicopter. It will still idle on its own, it will rev through the whole range in neutral or under load, power seems low below 3k rpm, but I can still start on a hill. Above 3k, power seems fine, but I can still hear that something isn't right in the sound of the exhaust, like it's missing every other beat. Decel engine braking feels and sounds the same as always.



I had my injectors cleaned most likely less than 25k miles ago. Spark plugs were replaced within the last 10k miles. Spark plug wires were replaced a few months ago.



I figured if my engine was blown, the power would be low all throughout the range, right?

afm unplugged? they run really weird and laggy that way



or check engine light?

No check engine light. I'll check the AFM.

Gee thats tough. Yea id check your whole intake system. Idles fine right? Im think if it didnt then maybe u have a leak. God theres so much to check for. What if ur exhuast clogged up. Ok maybe im throwing things out there.

check to make sure your Catalytic converter isn't clogged up, along with your afm

No cats, pretty much straight thru exhaust. Header, resonator, straight-through muffler. AFM was not unplugged, no frayed wires around the plug. A spark plug wire looked like it wasn't seated all the way, but that didn't make any difference.



I can also hear it sound differently when the starter is spinning the engine, which worries me. Instead of a solid "chug chug chug" it's more like "chug wrrr chug wrrr", if that makes sense.



If I lost compression in one rotor, would it still have about the same amount of power above 3k rpm? This is just really weird.

ive seen em chip a seal, or very occasionally the seal will split in two, and when that happens it will run ok up top, but idle poorly.



compression check?

When I get to feeling better (hope sick today) I'll pull a spark plug from each chamber and turn the start to listen.



Could a seal have gotten stuck? Should I do the AFM jazz if it sounds like there's low compression somewhere?

I did the compression test today, and sure enough I have 2 faces with very little pressure on the rear rotor. Oh well, I'm just going to keep driving it as long as possible. We don't have another car besides the mazda 5, and I don't have money for a rebuild or an engine. Either that, or I take some sort of loan for a new engine. I like the no-money-involved option, for now anyway.



Honestly I'm surprised how well the car drives with a busted apex seal. Will driving it with a bad seal cause more problems?

it can, if the seal is cracked and then comes out. but if the seal is already gone, or it just chipped a corner then you've got nothing to worry about, its already been done