Help - Cat or something else? Or both?

[gtdan]

OK, have a 2002 T4R SR5 sport with roughly 148K miles. I've had it for a year and roughly 16K miles. Just returned from a road trip to Colorado and barely made it back. Need to figure out what is going on with it.

Symptoms:
It has thrown a p0420 code twice, but hasn't done it in weeks. Didn't throw any codes on the recent 2000 mile trip back to Atlanta from Colorado.

MPG has reduced significantly (sub 10 mpg on the highway coming home!). This has been gradually happening it appears. It coincided with upgrades (tires/rack/front bumper/RTT) so I didn't attribute it to engine problems at first.

Power is GONE. At first it was just struggling to maintain highway speeds. Didn't like being above 60mph. Now, its worse. I barely made it through the mountain passes near Chattanooga. I was dropping to speeds where truckers were passing me going uphill. Couldn't maintain 40mph on some hills. This started to happen on all inclines, not just significant ones. Notice that overdrive gear makes it way worse and I just drop speed. Had to keep it in 4th.

Getting a weird surging/thrusting between 2100-2700 or so RPM.

Sounds like an exhaust leak somewhere too, as there is a raspy/air noise.

My current theory is an exhaust leak causing a feedback loop to the ECU which is causing a downward spiral in air/fuel mix over time.

I'm at a bit of a loss though, as I can't go replacing everything (and exhaust/cat isn't a cheap one to start with).

Any ideas? Anyone been through this before? Thanks.

Dan

 

[gtdan]

Update: Just turned it on and crawled under (thank you lift!). There is a definite leak in the exhaust piping between the 2 cats. Since this would put the leak after the upstream sensor and before the downstream sensor, I could see this being a good part of the problem.

 

[curryT4R]

Update: Just turned it on and crawled under (thank you lift!). There is a definite leak in the exhaust piping between the 2 cats. Since this would put the leak after the upstream sensor and before the downstream sensor, I could see this being a good part of the problem.

I think you've definitely got a good starting point. The downstream sensor is not reading the correct amount of air/fuel mixture. If the downstream sensor is reading too much air due to the leak, it is probably dumping fuel into the cylinders causing your bad MPG, and it's too much fuel for the actual amount of air being read by the MAF.

I would certainly start by fixing the exhaust leak, disconnect the battery for a few minutes to more or less reset the fuel trims, then reconnect it and see how it drives after that.

 

[19963.4lsr5]

Is the hole look like its from rust or its split open?

That hole will allow the exhaust reversion to suck air in and may make its way to the pre-cat sensor that controls the air fuel ratio.

The post cat O2 just looks at the efficacy of the Cat and on some vehicles will also control the target AF during warmup.

You last cat may be clogged and the heat from and overly rich mixture may have caused the pipe to split if it's not rusted through.

The question is how did the hole get there.....if you fix the hole and it still runs like crap I think one of your cats is clogged or melted.


Sent from my iPhone using Tapatalk

 

[gtdan]

So the cat was clogged. Had found another leak in the flange just before the cat. Was pretty much shooting hot exhaust straight up to the floorboard (explains the ridiculously hot passenger floorboard).

Had the cats replaced and hole fixed and she's back to normal again. It's nice to be able to drive up a hill without dropping to 20mph.

 

[Pieszeckipower]

So the cat was clogged. Had found another leak in the flange just before the cat. Was pretty much shooting hot exhaust straight up to the floorboard (explains the ridiculously hot passenger floorboard).

Had the cats replaced and hole fixed and she's back to normal again. It's nice to be able to drive up a hill without dropping to 20mph.

Hello from Chattanooga! Sorry your experience with our mountains left you frustrated, but glad you were able to figure out what your problem was. :yo:

 

[sakoluvr]

Did you go with factory cats or aftermarket?