Hello! New poster but long-time lurker here. (Sorry about wall of text)

A week ago, I spliced my PCV hose that goes from the crossover (between both sides of the engine) to the lower intake manifold behind the throttle body since it was hard and cracked to all hell. (I'll post pics if you guys need) Here's the part where I may be an idiot... I used a little in-line 3/8 particulate filter. I figured, "Why not clean the air and oil coming through here? Worst case, it'll feel a little down on power and I'll just replace it anyway." I was waiting on a new hose to come in so I figured I'd experiment.

Car ran just fine and honestly a little bit smoother afterwards for a few days... Until about 4 days ago. I was driving to work on the freeway when I noticed my RPMs slowly declining and loss of throttle response. Only scary noise sounded like a small back-fire out the passenger side exhaust. I thought I'd blew it-- that I killed her.. first thing I checked was the particulate filter. It had a little bit of oil in it, but that was it. I checked my dipstick, no glitter. Anxious and in a bout of hope and denial, I try to start the car again. Cranks right up with no issues whatsoever.... EXCEPT it's CONSIDERABLY Quieter and the torque/power is There, but it's toned wayy back-- like the ECU is in "Valet Mode".

I finish the drive to work (Parts Store) and I immediately replace the particulate filter with a fresh solid hose we had laying around. Now, there's a little bit of power back and a little bit of sound is back, but it's still way quieter and still down on power.

Since it's my daily I've been forced to drive it semi frequently since the incident. It's given me zero problem so far outside of these issues. I've already tried a throttle body relearn and that didn't help. There's no CEL, no Pending codes. Everything else works fine. Please Help, guys!

*NOTABLE THINGS ABOUT MY CAR:*

--Has Injen Cold-Air Intake (Has been on for years w/no issue and has a fresh filter)

--Has modified True Dual Exhaust w/muffler delete and brand new manifold OEM Catalytic Converters/O2 Sensors. (This is how I was able to tell it was notably quieter because it used to be LOUD. Now, it sounds like I re-installed a muffler. I've also had this setup for years.)

--There was a Bank 2 lean code two weeks ago that I cleared and it hasn't come back.

--I'm 400 miles away from my next oil change. (Every 3k)

--Gas mileage is notably worse after this incident

--Car has 129.5k miles as of this post.

--No new noises or other odd behavior.

--Drivability is otherwise completely normal. If I didn't know any better, I wouldn't have really noticed a difference aside from the slight lack of power.

You're going to need to stream some engine parameters to figure out what's going on. Try a power balance test on both banks, see if one whole bank is weak compared to the other. That backfire makes me very suspicious that one of your new cats may have come apart.

VStar650CL wrote: ↑

Sun Jul 16, 2023 9:41 am

You're going to need to stream some engine parameters to figure out what's going on. Try a power balance test on both banks, see if one whole bank is weak compared to the other. That backfire makes me very suspicious that one of your new cats may have come apart.

Do you think a cat busting up would cause a shutoff at speed but no CEL?

Also I don't think I have the equipment to power balance test.. I just have a $40 OBD scan tool.

The ECM doesn't have any good way to detect an exhaust blockage, and since the two banks have separate injector and power parameters, if one side is partially blocked then the ECM will simply compensate and not throw codes. If you don't have work support on your scanner, take a look at your STFT's (A/F-alphas) and see if there's a major difference between banks. That won't confirm that the cat is the cause, but at least you'll know you're chasing an issue affecting only one bank.

You could do an exhaust back pressure test at the upstream o2 bung.

Or just pop the front O2's one at a time and see if one of them lets it rev normally. Loud but effective, although I dunno how hard they are to get at on an M45.

VStar650CL wrote: ↑

Sun Jul 16, 2023 6:59 pm

Or just pop the front O2's one at a time and see if one of them lets it rev normally. Loud but effective, although I dunno how hard they are to get at on an M45.

Yeah they're very difficult to get to and in very hot spaces. Not a lot of room in that V8 engine bay..

UPDATE:

It stalled out on the highway again this morning. Almost mirror conditions. For sure sounded like a backfire this time on passenger side, and engine lost power the exact same way.

This time I tried to crank it up right away and it started up like nothing ever happened. Is considerably quieter again though. Just barely louder than stock now. Felt the exhaust pressure at the tail pipes. Pressure/pulse on passenger side is normal, but driver side was barely emitting heat.

Checked over all my PCV and everything is properly connected and sealed.

Man, this sucks. I think I need to get under it and see wtf is going on

I'm thinking you need to bite the bullet and see what's inside that exhaust system.