Sudden loss of power

[1 Lucky Texan]

knock sensors have been known to be bad without setting a code. Plus, many folks have had good luck with cheap sensors from ebay or wherever.

[brus brother]

Not sure but there are brighter bulbs on the USMB than myself who might explain the metallic shavings external to the cat. Did you remove the cat or just disconnect it from the upstream flow? I would suggest you remove the cat entirely and have a look from each end to see what the damage looks like. also shake the converter to see if there are any rattling sounds indicative of loose honeycomb material.

Assuming that spray cleaning the MAF was unrelated to the improvement, at this point, simply disconnecting the cat as you have only tells you that there is an obstruction somewhere beyond the area you disconnected. The honeycomb certainly appears to be failing but it would seem that for your situation, I would expect pieces of the material the size of grapes and larger to have caused a clog.

I had started posting the above but then stopped, thinking you had solved the problem but it appears that you may have a restriction further down the line.

Disconnect the exhaust and run again.

If power restored then you still have a restriction

[89Ru]

Ok let's recap, starting with the anatomy of the exhaust system from the engine to the mufflers.

1.  Front cat/manifold.  Picture of degradation above, outlet side.  No access to opposite side w/o bore scope.  No obvious chunks or rattles when shaken.

This section was removed completely and car had restored power.

New aftermarket cat installed and connected to rest of original exhaust system.  Power loss as before plus some weirdness that I think is explainable, below. 

2.  2nd cat pipe.  Unable to see any side of cat due to piping bends.  

This section was removed today.  Car ran with aftermarket cat only.  Power restored and no weirdness.

3.  Resonator pipe with flanged y.  Wired with coat hanger.  Unconnected. 

4.  Muffler RH 

5.  Muffler LH 

So today I removed pipe #2.  New aftermarket cat in place.  Power restored.  No stalling, flashing CEL, or other strangeness.  No knocking sounds.  I'm thinking that I have actual preignition when the obstructed part is in place due to increased cylinder temps.  And the knock sensor picked it up and flashed the CEL.  No codes thrown.  I'm not sure that it should have flagged a code for knocking.  Just my guess.  Now whether the ECU is throttling back timing due to the knock and that is the reason for power loss, is unknown.  

So in the interest of keeping things simple, I want to focus on the restriction.  So far #1 pipe is not the primary restriction.  That leaves four other suspects.  

A.  #2 cat pipe.  Need a bore scope to visualize.  Or maybe there is some other way to diagnose. 

B.  #3 resonator pipe.  Maybe there is a rusted baffle that is blocking flow.  Have no idea how these things are built, just a guess. 

C.  Either muffler.  I kind of suspect the RH due to slightly less pressure felt on my hand at the tailpipe while running at 2-3k rpm.  

I'd rather not guess and start replacing parts willy nilly.  Walker mufflers are $80 each aftermarket.  Yes, they are original, 12 years old, and could go at any minute so not a wasted investment.  Subaru Sakamoto mufflers are $270 each.  The resonator pipe is about that also.  I'm going to get a borescope so I can make some kind of educated decision...

Love some input on this plan and thanks for hanging with me on this long winded post. 

[brus brother]

While you wait for your bore scope to arrive, disconnect then reconnect exhaust components sequentially until the symptoms disappear.

Seems pretty simple although tedious. You would have to do this to use your bore scope anyways.

If you trust your suspicion, then start in the rear with that R muffler although it could be a restriction just ahead of that component then move L and then forward.

Each time evaluate to see if symptoms improve.

 

Edited May 20, 2019 by brus brother

[89Ru]

On 5/19/2019 at 9:02 PM, brus brother said:

While you wait for your bore scope to arrive, disconnect then reconnect exhaust components sequentially until the symptoms disappear.

Started with 2nd cat pipe (the rear), easier to just bolt it on and run with it disconnected at the spring flange to the resonator pipe.  This isolates the resonator and both mufflers.  Plus I'm skeptical that if I wrench on the muffler flanges they will fall apart, they look pretty rusty. 

Power definitely decreased compared to running with only the front cat.  

So now I have both the cat pipes connected (new aftermarket front cat and original rear cat) and I'm back to crappy power.  Still haven't ruled out a problems farther downstream, but going to replace the 2nd and only remaining original cat.  Also got a CEL, P0303 and P0304.  Both misfire codes.  Think these are from the flashing CEL yesterday.  What's up with these delayed codes?  My '97 OBW would misfire and flag a code immediately.  Coolant temps didn't run a bit hotter than normal this time but could hear preignition.

[brus brother]

to  be clear,  you ran it with ONLY the new first and original second cat pipes connected (everything beyond the second cat pipe was disconnected) and had the loss of power symptoms?

well that seems to have now isolated a constriction in that second cat

curious why you earlier sensed there was restricted output at the right tail pipe.

where are you getting your parts from? can you link a schematic of your original exhaust system?

cats are expensive little items.

 

Edited May 21, 2019 by brus brother

[89Ru]

10 hours ago, brus brother said:

to  be clear,  you ran it with ONLY the new first and original second cat pipes connected (everything beyond the second cat pipe was disconnected) and had the loss of power symptoms?

well that seems to have now isolated a constriction in that second cat 

Yes, I agree.  Just suspected the R muffler due to a bit less exhaust pressure...maybe exhaust shops have calibrated pressure sensors to measure this stuff and speed up the diagnosis. 

Getting parts from Rock Auto.  2nd cat pipe is around $140.  New cat is arriving Friday. 

On diagram below

#19 Front cat 

#14 Rear cat 

#3 Resonator 

#8 / 9  Mufflers 

Edited May 21, 2019 by 89Ru

[forester2002s]

The knock-sensor 'listens' for pre'-ignition.

Without reading all previous posts, did you replace the knock-sensor? It's a cheap item.

[89Ru]

55 minutes ago, forester2002s said:

The knock-sensor 'listens' for pre'-ignition.

Without reading all previous posts, did you replace the knock-sensor? It's a cheap item.

Not yet but will do if all else fails.  So far all I have replaced is the front cat and both oxygen sensors.  

Edited May 21, 2019 by 89Ru

[heartless]

the muffler thing is a total red herring. it is a "single" exhaust system made to look like a dual. forget about that aspect.

you could eliminate one of those mufflers completely and still have a fully functional exhaust system. the problem is elsewhere.

 

 

[89Ru]

Installed the new aftermarket rear cat.  Ran it without connecting it to the resonator pipe.  Power restored!  Loud!   Now it makes sense compared to how quiet it was when I ran with the restricted rear cat disconnected...it was muffled without any mufflers attached, due to low, restricted flow.  

Hooked up the rest of the exhaust and it runs mostly normal, no codes, power restored.  Stumbled a bit when rolling to a stop, assuming that it hasn't learned how to idle just yet.  

Going to clear the ECU anyway by disconnecting the battery, just to start fresh since its recent history includes operating with restriction.  

So about $750 later we have new aftermarket front and rear cat and both O2 sensors.  Rest of exhaust is original.  

If I had to do this again I would start by disconnecting at the center spring flange and run it with open pipes.  If its not loud enough to annoy the neighbors with the spring flange disconnected there is a restriction somewhere toward the engine.  And then remove pipes one at a time toward the engine.