I know, the title of the thread already answers the question haha, but bear with me.


It seems in the last several months that the performance of my HHR has been gradually decaying, to the point I am starting to think my catalytic converter may be partially blocked. The only CEL codes I have are an emissions related one that has been on for years, a p0420 (again, leading me to the converter) and a code related to the car not warming up fast enough (my thermostat is a bit odd, it takes a while for the car to get to full operating temp at times).

I thought for sure my converter was clogged, so I performed the "temperature test" on it, using an IR thermometer. Did the test at idle, as well as revving around 2-3k rpms and got the same results, the outlet temps on the converter were higher than the inlet, indicating that the converter should be working properly from what I understand of this test.

The car just really struggles to maintain highway speeds, especially if there is any kind of incline. If you floor it from a stop sign, the car just kind of lazily jumps up to around 3k rpms and will eventually rev up through first gear. Can't even chirp the tires on dry pavement. The car now has around 236,000 miles on it, it is a 2006...it has had some kind of lifter/valvetrain noise on startup for a good long time now, but that never seemed to effect performance in the past.

I admittedly haven't changed the spark plugs in a very long time, but the car starts right up and idles smoothly, no misfiring. Fuel pressure was at 50psi at idle.

I am still not ruling out the converter and want to do more testing on it, this car has made oil disappear for a long time, and I know that it does leak oil, but probably burns some as well, so with the age and mileage it wouldn't be out of the question for the converter to be clogged. Also at highway speeds, it is almost as if the harder you try to push it, the slower it goes. If I floor it at 65, it downshift, but it's almost as if it wont pick up speed, and in some cases it will actually slow down. Maybe a transmission issue? Though it doesn't really seem to be slipping.

Just kind of looking for ideas, as I don't want to just start throwing money at it. Car otherwise seems fine, fuel economy is pretty good. Still getting 28/29 mpg at 65mph according to the DIC. I have tried all the basics that I know to do without getting "serious" so just wondering what ya'll think!

 

P0420 isn't a code to dismiss; it means the cat is not working correctly and is not repairable.
After market cats are available for a lot less than you will spend trying to avoid it. Try eBay.
Get a AC/Delco 131-158 t-stat to clear the P0128. The part number makes a difference.

 

My P0420 code was resolved by replacing the catalytic converter I ordered this one

https://mufflerexpress.ca/products/c...rter-2005-2007
Before you change the cat, run a quart of Marvel Mystery oil for another 500 to 600 miles, it cleared up my oil consumption problem, it was being sucked into the throttle body from the valve cover PCV hose
As for the noise at start up, remove the valve cover and check the timing chain and guides, a loose chain can be catastrophic if the guide fails.

 

Well, I took the leap this morning and removed the section of exhaust containing the catalytic converter.

Upon inspection I could see that there was some clogging. Many of the small holes appeared to be blocked when hit with a flashlight. Of course you can only see the first layer, so I can't say what else was going on.

I was able to find a solution locally, and I will say that the engine seems to be back to normal, or at least much improved. It was holding highway speeds with no problems, where previously it would struggle and downshift. Just seems far more free revving and eager to move. Even happily broke the tires loose at the stop sign down the street haha.

Thanks for the push to get my hands dirty!

 

Glad you are driving it and not cursing it! Enjoy the drive!

 

Now investigate the chain noise at start-up.
It can become a very expensive issue .
It can be a PITA, but remove the cam cover and look.

 

You really need to find the cause of the cat failure and be sure it is fixed. Most likely causes are burning oil or misfiring or getting silicone into the exhaust..

 

Coolant in the exhaust will kill the catalytic converter, as will synthetic oil. If it’s getting sucked into the throttle body from the pcv hose .

 

I would investigate this next, starting with a compression test. No point doing a bunch of other stuff if the motor is just worn out.