Loud noise under acceleration and reduced power ?

Thank you everyone.

The problem apparently Was that the catalytic convertor was plugged up. Weird that there was no sign of exhaust leakage underneath - and it wasn’t really an 'exhaust noise' type sound. It really sounded most like a wide open carburetor sucking in air.

As I said; I found the downpipe flange joint is held together with springs. And thinking back over what happened with me - I now think that the design intent Is to relieve excess exhaust pressure (say; in the event of a clogged cat. <g>) Because thinking back; what I heard as a 'rattle' under hard acceleration, especially up a hill, was actually excess pressure being relieved out the manifold/headpipe flange.

No one local had the OEM catalytic converter assembly in stock. It's a welded assembly from the exhaust manifold flange thru the cat, thru what I guess is a small resonator (looks like a cat without a heat shield), and then to a flange just ahead of the (really large) muffler. So first I got 18" of exhaust pipe, a coupling - modeled after the after-market cat. that they did Did have in stock.

Back here with that stuff I soon found that the cat. assembly cannot be removed or installed UNLESS you pull the transmission crossmember. WTH? <g> Even weirder is that what I was calling the catalytic convertor on the truck - the thing with the stainless steel heat shield - was hollow: nothing inside it. And had always been hollow - just an empty widget. So what the hell is That for?

And the “resonator" on the truck - plain steel; no heat shield - was filled with catalytic-stuff. <g>

Some of the catalytic stuff was broken on the inlet side - I don’t think I was rough with it but maybe I was: I can tell you that I was pretty angry and somewhat violent when I discovered that you have to pull the transmission’s rear mount off to get the catalytic convertor assembly off the goddamned truck. Instead I sawed the exhaust pipe an inch behind the not-a catalytic-converter thing to remove the OEM assembly from the truck - to avoid removing the crossmember. <g> And I found that a piece of un-bell-ed 2 1/2" exhaust tubing is exactly the right size to sleeve the metric OEM exhaust pipe. Although this required careful filing to make it all slide-fit together. This fits so tight that I didn’t bother adding clamps. I used a piece of 1" thin wall steel tubing - think: EMT conduit - and a 2 lb. cutting hammer - to bash a 2 1/2" hole through the center of whatever is in catalytic converters. Now the truck runs much stronger, makes no whacky noises, and is only the tiniest bit louder than before. The Check Engine light is on but what can you do?

BTW: When I got the new 'donut' for the exhaust manifold (it's actually a steel tube header under a sheetmetal cover) to headpipe joint flange I realized that the old donut gasket was about 50% eroded away. I am imagining as a result of the exhaust gases blasting out there at the 'pressure relief point' since who knows when. Hell; maybe for as long as I’ve owned the truck. <g>

Later today I will wail the shit out of the little bastard on the highway - but so far I am calling it a success. I'll fill up and recheck the MPG too. Which had been steadily easing downward for a few years - really ever since I got the truck.

Thanks for all your help guys!

 

This is a good idea. I would also check the entire intake tract as well. My truck just threw a CEL for the secondary air injection pump and it is louder on startup but I haven't felt any differences while driving. Waiting for the part to change it out. Good luck!

 

2007 5 lug Tacoma 2.7 auto 2WD 175K miles.

You all were right all along.
I cut the cat out which improved it somewhat.
I later replaced the front pipe w/ cat which improved it a bit more.
Then I replaced the rest of the exhaust system / muffler - which improved it even more.
Then I replaced the LT235/75R15 tires with LT215/70R15 tires - which were a Serious Bastard to find! - and even more improvement was had.
Now it's quicker and faster than ever before and and gets better mileage.

Thanks!

PHM
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