OK guys, I have a 2000 Chevy Blazer 4wd - 4dr. 180k miles on it, but have owned it since 120k, for about 6 years. Ever since I have owned it, the engine runs very loud, and the Blazer feels a bit underpowered (Almost like it's choked). I do not have another Blazer to drive to compare it to, but I know it's louder than any other blazer I have heard on the road. And it's not an exhaust issue (holes or leaks, had Firestone check it), and as far as I know it's a factory exhaust.

Here's the thing, when I go Wide open throttle, and the engine gets into the 4k+ range, the whole tone of the exhaust changes, it gets deeper and quieter, much quieter. It will hold this tone at part throttle, wide open throttle, etc. for maybe 10-15 minutes and then it slowly reverts back to the loud underpowered feel, especially if I bring the car back to stop or idle.

The torque converter locking doesn't change the noise level at all, only going WOT seems to cure it temporarily.

History - It used to have a few AIR system codes. They have all gone away once I replaced the check valves at the manifolds and the rubber hoses.

Currently there are no other check engine lights, but I do get a recurring one from time to time that is for a slow vac leak in the EVAP system. It hasn't bothered me enough to get a smoke test at a garage.

My theory - A clogged, or partially clogged catalytic converter. Could this be consistent with what I'm experiencing? Again, as far as i know, this is a bone stock exhaust system.

I'm open to other opinions, as I do not want to spend $200-$300 for a shop to replace the cats only to have it do nothing. I'd rather spend that money towards tires/alignment (replacing front suspension/steering) where I really need it.

Thanks for any opinions

 

In the early stages of failure, a restricted catalytic converter will cause a lack of power at higher engine loads. Usually not so noticeable at lower speeds, and sound level doesn't change.

Have you checked the driver side motor mount? If the mount is worn badly or broken, or the rubber is deteriorated, engine noise and vibration can transfer directly to the frame. When you accelerate, engine torque lifts the engine off of the mount and the noise stops.

 

I will look into the motor mount. I have never had to identify a broken one before, so I will search the forums to see how to diagnose it.

Ya know, I usually drive this thing all around town and I have no issue with the torque in stop and go. However, this truck is a dog when trying to pass people on the highway. Even though I did not have a CEL showing, I decided to hook up my scanner tonight to see if anything was pending. Sure enough, a P0420 code was pending. Grr.

My plan is to drive this car with my family to the Jersey shore in July. It's made the trip every two years as it's always been the biggest vehicle we own and has a hitch so we can take our bikes on the rack. I need to prioritize the repairs on this car. It's only worth about $2k, and my wife is in my ear about getting a bigger vehicle (Mini-van or Tahoe size) due to the family now growing to 5 people (which the blazer isn't really great for due to needing two child car seats).

The blazer now needs a full front steering overhaul, tires, and following alignment. I can feel the blazer wander all over the road while I hold the steering wheel straight, and there's a ton of slop in the steering. Compared to my wifes '15 Buick Encore, it's night and day. I know I will never get it that tight again, but I need it better than it is now.

 

Another question. I see there are two cats on my blazer, first a small one, then a normal size one just down the pipe. Judging by all the booger welds, looks like one (the big one) or both have been replaced at one point.

I've had plenty of cars, and most have only had one cat, is this first cat needed, and should I replace it? I haven't seen any smaller cats for sale that look like the one I have.

 

The 4.3L is not the cleanest burning engine, (by a long shot) and it needs all of the help it can get to pass Federal emission requirements for a given year. 98 only had one converter. 99 through 02 have 3 converters AND secondary air systems to supply the converters with more oxygen. Converters are rated to handle up to a certain cubic inch engine, so if the secondary air system is working properly, you should be able to use just one, (larger capacity) converter. A competent and reliable muffler shop should be able to supply and install the correct converter.

Best to check exhaust system backpressure first, that will tell instantly if the system is restricted.

 

Well the new cat certainly cleaned up the codes, but did not help with engine sound or power. Turns out, that was the fault or a faulty fan clutch that was very stubborn about disengaging.