Loss of power after replacing catalytic converters

I just replaced both of my catalytic converters and passed the emissions test. After driving about 350 miles, the check engine light came on again, but went off after 100 miles. The other day, I started the truck, and it made a ruffling noise under the hood. It lasted for five seconds and stopped. When I started to drive the truck, I noticed a loss of power, especially going up hill. Any ideas what this could be?

 

Any check engine light? Scan for codes? Put your engine and cab type in your profile so we can narrow down issues.

 

Loss of power suggests limp mode. What codes are present when you scan?

These trucks are notorious for (1) never having problems with cats, even when there are cat efficiency codes present, it’s rarely ever the cats, and (2) having big problems with aftermarket cats people install to try and save money, then end up spending more money fixing the problems caused by the cheap cats.

The actual problem is typically the O2 sensors sending bad info to the ECU, making it think the cats aren’t working properly, and a bad upstream O2 sensor would cause the exact symptoms (stumbling etc) you are describing.

 

My original cats were both stolen. I welded in two walker cats that had a 5-year warranty.

 

2005 Tundra, extended cab, Four Wheel Drive, 4.7-liter V8 engine,

 

Is check engine light on, or was it on? If yes, what codes?

Got any pics of the welding job on the cats?

Was any of the O2 sensor wiring damaged/cut through when the cats were stolen?

 

Truck information: Code is P0420, Engine type V8, 4.7 liter, Extended cab, SR5, four wheel drive. 2005 Tundra

 

So bank 1/driver's side exhaust.

Given you've replaced the cats recently, I'd be concerned they didn't weld you up seamlessly but the only way to tell would be to smoke or vacuum/pressure test the exhaust.

But when you put the symptoms of stumbling etc. in the picture, knowing your upstream O2 aka "air/fuel ratio" sensors are what tells the truck how much fuel to spray (by reading the exhaust mixture for fuel/air content), it could point to an upstream sensor getting ready to kick the bucket.

This is one of those sensors where you should really buy the OEM brand, or at least Bosch brand, from a reputable source with verified supply chain (i.e. don't order from scAmazon, fleaBay, Temu, WallyMart, Home Depot, etc.), and you can lookup your part numbers at www.densoautoparts.com

You really should replace your O2 sensors in upstream/downstream pairs. They work in tandem with each other to determine cat efficiency, and if the upstream is worn out, the downstream is probably not far behind.

I just looked up your part numbers, and I notice the part numbers are the same left and right, so if you wanted to verify if this is a case of 'bad sensor', you could swap move the upstream sensors with each other and see if the code changes to P0430. But it continues to pop P0420, swap the downstream sensors, and see if it changes to P0430. If it doesn't, then your problem is more likely an exhaust leak, bad mating at the flange, etc.

Here are your part numbers for upstream and downstream, if you just want to parts-cannon it. The reality is, at this age, your sensors are probably tired, so it's not like it can hurt to replace (they've had a good life). I had my first sensor failure at 69,000 original miles, roughly 4-5 years ago, the downstream driver sensor. "It happens".

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Wow, thanks for the detailed explanation. I appreciate it. I will let you know what happens.

 

During the vacuum pressure test, do you place the vacuum hose into the exhaust, ensuring a good seal is formed? You then use a bottle of soapy water and look for bubbles around the weld seams. I have seen this method on a YouTube video, but I was not sure it was legitimate.

 

It's legitimate. We've had people on here do the same. Soapy water, put the vacuum in reverse (blow), spray soapy water around questionable seams.

 

Okay, I will give it a try. Thanks

 

The ruffling noise when starting the truck and the limp mode loss of power could also be explained by SAIS malfunction. Doesn’t match your code though.

 

Thats a weird one.
Of course I've never driven a truck till it needed a new Cadillac converter.
Yes I'm aware I spelled it wrong....
But thats kinda weird.
I guess with all the computer controlled crap on Trucks these days who knows whats going on.

 

Need to run the codes. It actually doesn't sound that different from when I lost the #8 coil last week. Which would have nothing to do with your cats, but could just be a coincidence.

 

Who did the welding? How was the welder ground connected during the work? Any precautions taken to protect the vehicle electronics during welding?

P0420 could be explained away by the aftermarket cat, but the stumbling indicates something else, unless that cat is clogged already.

Upstream O2 sensors are probably tired, but changing cats wouldn’t kill them right off the bat, and I would expect other codes to follow in that case.

P0420 is the only code set? Nothing pending?

 

You could also try buying some exhaust tape, and wrapping the welded joints. See if the codes disappear. That would potentially rule out a bad weld. But if they didn't drop the exhaust out, chances are there 's an opening at the top of the pipe, and that's the root of your issue.