When exhaust is plugged?

[Dash01]

'89 535i beater car has partial obstruction in the exhaust, so it won't develop power but idles OK.

At the tailpipes, flow is not consistent between left and right tubes when the engine is revved.

Laser thermometer pointed at exhaust pipes just downstream from the manifolds shows passenger side tube is much cooler than driver side tube, so the passenger side has an obstruction somewhere along the line.

Question: When 535i/M30 exhaust systems have such obstructions, is there a common failure point such as the cat, resonator, muffler, or where?

Is the cat segregated side to side, i.e., does exhaust from one manifold/exhaust pipe get internally mixed inside the cat with exhaust gas from the other pipe, or does that exhaust gas go straight back with no mixing? In other words, does the cat have an internal wall keeping flows separate?

This will help determine whether the car needs a new cat, new resonator/muffler, or whatever.

Could be, my cat is fine, but the resonator or muffler has an obstruction, or vice versa.

Insights, thoughts, or suggestions are much appreciated.

[Binjammin]

The "cat" on a 535 is actually two cats. One of yours is probably broken internally.

[Dash01]

The "cat" on a 535 is actually two cats. One of yours is probably broken internally.


OK, so there's a wall between left and right sides, so exhaust from one manifold goes all the way through the cat without mixing with exhaust from the other manifold?

Is there some simple way to determine if the obstruction is in the cat, or in the pipe(s) or mufflers aft of the cat? The '89 535i is not indicating "check engine" light.

Given dogleg shape, is there any way to see into the cat for blockage, or to gut the cat? (I'd rather not gut it.)

How about cleaning it by soaking in solvent for a few days? I've read that citric acid works well for this, perhaps carb. cleaner, acetone, solvent, etc. works if the ceramic honeycomb is OK.

knowledgeable people (which I'm not) please chime in.

[Binjammin]

Catalytic converters do not clog. They break and the broken pieces plug up the exhaust.

[ross1]

Catalytic converters do not clog. They break and the broken pieces plug up the exhaust.
Yes, they do. The brick can melt into a solid, restrictive mass.

[E38740iMD]

Of if you can't gets filled wit sut or carbon deposits.

[Binjammin]

Yes, they do. The brick can melt into a solid, restrictive mass.


Of if you can't gets filled wit sut or carbon deposits.

Sorry, melting down falls into the broken category, because it can't be unclogged.

More specifically, what I meant was that the idea that cats get clogged with carbon is a fallacy, they don't.

[ross1]

http://www.easterncatalytic.com/wp-content/uploads/2012/01/po420_fig03.jpg (http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=yjCEfoOnJrnqUM&tbnid=TRikBWEnJzCuCM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.easterncatalytic.com%2Feducat ion%2Ftech-tips%2Fthe-misleading-nature-of-the-po42o-code%2F&ei=ROk6U7mUIa2msASxnYH4Bw&bvm=bv.63934634,d.b2I&psig=AFQjCNHRtrv3PEycqSvpyOL8dWlHWE4Q0Q&ust=1396456093433856)

The catalyst brick pictured here is "intact" and obviously would be quite restrictive

[Binjammin]

http://www.easterncatalytic.com/wp-content/uploads/2012/01/po420_fig03.jpg (http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=yjCEfoOnJrnqUM&tbnid=TRikBWEnJzCuCM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.easterncatalytic.com%2Feducat ion%2Ftech-tips%2Fthe-misleading-nature-of-the-po42o-code%2F&ei=ROk6U7mUIa2msASxnYH4Bw&bvm=bv.63934634,d.b2I&psig=AFQjCNHRtrv3PEycqSvpyOL8dWlHWE4Q0Q&ust=1396456093433856)

The catalyst brick pictured here is "intact" and obviously would be quite restrictive

Never once seen that happen in real life. If that were to become "clogged" like that it would eventually overheat and either melt or break anyway.

[E38740iMD]

http://www.easterncatalytic.com/wp-content/uploads/2012/01/po420_fig03.jpg (http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=yjCEfoOnJrnqUM&tbnid=TRikBWEnJzCuCM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.easterncatalytic.com%2Feducat ion%2Ftech-tips%2Fthe-misleading-nature-of-the-po42o-code%2F&ei=ROk6U7mUIa2msASxnYH4Bw&bvm=bv.63934634,d.b2I&psig=AFQjCNHRtrv3PEycqSvpyOL8dWlHWE4Q0Q&ust=1396456093433856)

The catalyst brick pictured here is "intact" and obviously would be quite restrictive

Mine exactly looked like this when i removed mine. I was loosing power in the upper rpms :(

But now im good

- - - Updated - - -


Never once seen that happen in real life. If that were to become "clogged" like that it would eventually overheat and either melt or break anyway.

I need to figure out why it actually happened because it must be still occuring.i have no cat now if it still pumping out deposits then the prius community will get there shovels and pitch forks...

[Binjammin]

Mine exactly looked like this when i removed mine. I was loosing power in the upper rpms :(

But now im good

- - - Updated - - -



I need to figure out why it actually happened because it must be still occuring.i have no cat now if it still pumping out deposits then the prius community will get there shovels and pitch forks...

It really almost always happens from something to do with not maintaining the car. Misfires, rich or lean running, smacking the exhaust on something... those will all do it right quick.

[E38740iMD]

When i got the car it had pillow stuffing in the factory airbox. I was like ....DF! :confused. And who knows how long it was in there. So if definetly clogged my air filter causing car to run rich. Right now i have a faulty Maf. (I think) would be a good time to get a miller maf (if only it was a bit cheaper imo)

[Binjammin]

When i got the car it had pillow stuffing in the factory airbox. I was like ....DF! :confused. And who knows how long it was in there. So if definetly clogged my air filter causing car to run rich. Right now i have a faulty Maf. (I think) would be a good time to get a miller maf (if only it was a bit cheaper imo)

Shouldn't have run that rich... remember, the MAF measures how much air is going in, if you plug it up, less air gets in. The o2 sensor will also provide fine tuning for that.

[cdnalpina]

I had a 'catalyst overheat' message on a J-spec 750il highline (E32) I owned as I was driving it back home from Vancouver. Power was reduced and the car performed erratically. I stopped at a muffler shop on the way home and they used an infrared temperature reader. They read the temp before and after each cat - one side it was consistent, the other side it was hotter after the cat than before the cat. So, that was a sign, he said, of the cat being plugged or having failed internally and chunks obstructing the exhaust flow. When I got home I had the cats cut out and sure enough the bad one was annd broken inside and causing restriction.

So try that, car needs to be running and at operating temperature to get a true view of what is going on temperature wise. Or take it to an exhaust shop, they may be able to do this (and perhaps other tests) for you.

[TheStigg]

There are diagnostic ports (item 2) on each exhaust manifold, for inserting a pressure gauge. A normal reading should be 3 psi or less @ 2000 rpm

http://www.nmia.com/~dgnrg/ex_manifold.jpg

You will likely strip the threads taking it out, so be prepared to tap it to the next size over with a new bolt. I once had a Ford truck with a 351 Windsor that was running rich and caused a complete meltdown of the cat over the course of 100 miles on the highway, to the point that it lost nearly all power. After it cooled off, I could see a solidified grey molten ooze squeezing out between the manifolds and the heads.

[Binjammin]

There are diagnostic ports (item 2) on each exhaust manifold, for inserting a pressure gauge. A normal reading should be 3 psi or less @ 2000 rpm

http://www.nmia.com/~dgnrg/ex_manifold.jpg

You will likely strip the threads taking it out, so be prepared to tap it to the next size over with a new bolt. I once had a Ford truck with a 351 Windsor that was running rich and caused a complete meltdown of the cat over the course of 100 miles on the highway, to the point that it lost nearly all power. After it cooled off, I could see a solidified grey molten ooze squeezing out between the manifolds and the heads.

I've tried to take a few of those out, and I would swear they were cast just LOOKING like a bolt, but I've never been able to remove one, not even with heat.