Clogged exhaust

Greetings! I have a Mazda Tribute, 2005, with clogged exhaust systems that make the EGR valves blow up. Definitely due to a problem with the exhaust system, but I can’t find where it is. Any thoughts/suggestions are welcome. Thanks! I’ve replaced one of the catalytic converters and checked the other, but it didn’t help, my next guess is the muffler or the manifold. Engine occasionally misfiring due to a vacuum leak that prevented the intake manifold to provide even oxygen for full combustion. The extra gas when into the exhaust system a burnt up one of the cats and left a clog somewhere in the exhaust system. If is the other cat it’s a $650 part.

I think you need to figure out why so much gas is entering the exhaust system where it melts catalytic converters. One place to check is for a leaking fuel pressure regulator. If the regulator has a leak, extra gas will be drawn into the intake causing a very rich fuel mixture burning up the cats.


Thanks, Tester, will definitely look into that!

Exactly what have you checked and done so far?

A vacuum leak in the intake manifold will not make the engine run rich, it’ll make it run too lean. The manifold is under vacuum and will pull excess air in through a leak. What it can cause, besides erratic operation, is the cylinders to run too hot, much like using a bellows to push more oxygen into a fireplace. The function of the EGR system is to alow a bit of inert exhaust gas to be drawn in to the intake when the engine is under load to prevent the cylinders from running too hot, but it cannot and will not compensate to a manifold leak.

That level of excess heat can cause damage. In addition to causing premature ignition, which can cause mechanical damage within the cylinder…and could be premature enough to send an explosion back to the EGR valve and blow it up…it can cause overheating of the cat converter. The PCV valve’s entire purpose in life is actuallly to prevent backfires through the intake system, like you could get with severe preignition, from igniting the volatile casses contained in the crankcase/valvecover spaces, but it won’t protect the EGR valve.

You might at this point have a plugged exhaust, but I think the true cause of your problems and its manifestations within the engine have yet to be determined. You’re trying to solve the damage rather than the cause. You need to start by going back to the engine and checking compression, checking for proper and smooth vacuum, check valve timing and ignition timng, and try to find what the root cause is and what might have been damaged by it (think burned valves).

As best I can make out this post, that would be my suggestion.

You can remove the oxygen sensors and measure the back-pressure at those points. That should narrow it down…

I have seen double-walled pipe fold in on itself internally and block exhaust flow…I don’t know if they still use double-walled exhaust tubing…

They do in specific spots.My header pipe has double walled curves.

But I still think the root cause is in the engine.

Looks like i have my work cut out for me between looking into the regulator, the engine…Thanks everyone for your incredibly helpful suggestions in locating the root of the problem! Hopefully too much damage hasn’t been created at this point. Thanks again!