New catalytic converter. Less power; more noise.

Installed a Magnaflow catalytic converter on my 1997 Toyota Tacoma 2.7L W59 4x4 earlier today.

The OEM catalytic converter was in great shape. I replaced it because the rest of the exhaust is brand new so - why not?

The exhaust system since then is way louder now. My truck sounds like a “ricer” now. And acceleration doesn’t seem as lively as before.

Afterwards, I replaced my Denso alternator with a rebuilt high amperage alternator, as well as my battery, starter, and alternator cables with beefy 1/0 gauge wire after that repair. I used that as an opportunity to reset the ECU.

The (ostensible) issue, however, persists.

I checked for exhaust leaks using all of the techniques I know about: shop vac, duct tape, and soapy water; shop rag (plugging the exhaust), duct tape, and soapy water while engine idles; feeling for exhaust leaks with my hands (with muffler both plugged and unplugged with a rag and duct tape); plugging the muffler with a rag while engine idles and listening for leaks. I have not found any leaks whatsoever.

I know that aftermarket catalytic converters can be noisy. However, power loss in terms of acceleration - that just seems wrong. What am I not grasping here? Are my symptoms to be expected with a new cat?

Curious to hear your thoughts, fellas.

P.S. I will be sharing a knowledge dump post soon concerning my approach to the Big 7 battery cable upgrade.

 

Spark plugs are tight? Is the tail pipe aimed down or out the side?

 

I can check. Coincidentally, I ordered a new spark plug socket yesterday. However, I have been riding on the same plugs for about 5K miles without issue.

 

My #3 was an oomph, not even and ugga loose and what a difference. Tight plugs matter

 

Just how are you measuring this loss of acceleration??

Magnaflow cats are sold on the idea of being more free flow. More flow more noise.

Did you by chance buy a knock off so many strange things being sold these days.

 

I doubt it. I purchased the catalytic converter from LC Engineering. Everything looked legitimate to me.

I tend to drive along the same routes with similar operating conditions, e.g. air intake temperature, coolant temperature, etc. It is not hard for me to notice anecdotally if performance has waned.

I will continue monitoring over the next couple of weeks.

 

These days one never knows where people might purchase things .

Just changing the Cat caused that much difference?

Very interesting that this problem did not cause any codes to trip if you had a poor connection plugging things back together.

looking forward to see how this plays out.

 

Not to be the master of the obvious, but when you say, “the rest of the exhaust is brand new” does that include a new muffler?

 

I changed the headers, middle pipe, and muffler weeks ago. I changed the cat, however, yesterday. I see where your question is going but it’s not that, friend, lol.

 

Sorry had to ask, lol.

You seem very astute. We get a wide range of knowledge bases asking questions here.

 

For whatever it’s worth, make sure the spark plugs are tight.

 

Did you also replace all the sensors? Are they all working correctly/correctly installed?

Almost sounds like you are not getting any feedback from the O2 sensors.

 

Yes. The upstream and downstream O2 sensors are both fine. They were replaced when the exhaust was upgraded weeks ago. I could use a voltage meter to know with absolute certainty but I think it’s fair to say that the ECU would bark by now.

Assuming there is not an exhaust leak, I guess the real question here is - can a new catalytic converter really change the sound of an exhaust system so dramatically? And is it possible that a new catalytic converter can diminish performance (acceleration) at least in the first hundred miles or so?

 

You’ve driven for 3 minutes not allowing the throttle to close then idled for 3 minutes and repeat 3x to reset the system? I think that’s how it’s done.

 

You talked about a headers back replacement. Assuming it’s all like for like, there should be no change. But if you’ve opened it up, it’s possible the motor doesn’t have the same back pressure. I think you’re gonna need to look at fuel performance by putting it on a dyno maybe pull the injectors and look at them. Clean the MAF too.

 

The Magnaflow catalytic converter did not come with any instructions whatsoever. I was a little surprised by that actually. Anyway, I didn't follow any break-in protocols. I just let the engine idle for a little while and boarded onto the highway. It was fairly obvious the ECU was trying to understand the new catalytic converter. The acceleration was odd. When I finally got home, that's when I went through the process of updating my battery cables and alternator which, like I mentioned earlier, gave me a chance to reset the ECU. The weaker acceleration issues persisted; however, that seems to be improving, which I talk more about below.

I am supercharging the truck in roughly one month. I cleaned the fuel injectors about six months ago but perhaps that job will give me a chance to clean them again. I have a 5 gallon ultrasonic cleaning device so that should be no issue. I won't be able to flow-test them, though. Regarding the MAF, however, I cleaned that last weekend after cleaning my K&N filter.

I have been driving the truck around. It is performing better. While the acceleration isn't as great as it used to be, everything else seems great.

I am going to continue monitoring performance but, fellas, I think this thread might have been reactionary on my part. In all likelihood, my ECU is figuring out this new catalytic converter. It is probably no more or less complicated than that. If I didn't find any exhaust leaks using several techniques then there probably are none to be found. I think the noise is the natural consequence of an aftermarket catalytic converter. I am surprised that a catalytic converter would cause such a dramatic change in tone, though. Anyway, like I said, I will keep an eye on things to be sure.

 

To close the loop on this discussion, here is a photo of some vital metrics while test driving last night. These metrics are from driving about 6 miles total around town.

 

Maybe unplug the battery for a bit and do the procedure

 

I’d put the original cat back on, or straight pipe it

 

I am going to monitor performance for the next couple of weeks before making any decisions but that isn't a bad idea.