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Bad Cats - Catalytic Converter Questions

emcauliff
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emcauliff Member

emcauliff

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I pulled the cats off my 1998 Boxster with the intentions of cleaning them to see if I could get my CEL to clear. Upon removal, one of them is shot. Can I take it to a muffler shop and have them put new cats on, or do I need to order Boxster specific cats for it? Doing a google search, MagnaFlow keeps coming up and the price point is very intriguing. Im not concerned about losing or gaining a little performance, more so just want to get the check engine light to go away. Also, if taking it to a muffler shop is plausible, would it hurt anything to run it 10-15 miles with no cats, just open headers? If I remember right, the computer will go to a default setting for the O2 sensors if they are disconnected.

Thanks in advance for any input!

Eric

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emcauliff Member

emcauliff

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Thanks for the offer flying penguin, I bought some off ebay before I saw you post. I replaced the cats, now Im getting P 1117 and P1121. My OBDII scanner shows no activity on sensor 2 bank 1, the other three fluctuate appropriately (I guess). I find it strange that both sensors after the cats are showing error. Perhaps they are both damaged from being subjected to less than ideal operating conditions due to the bad cats? Should I just replace the inactive O2 sensor? I have cleaned my MAF. The car seems run great, but Im trying to sell it, and the CEL isn't helping.

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JFP in PA Member

JFP in PA

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Thanks for the offer flying penguin, I bought some off ebay before I saw you post. I replaced the cats, now Im getting P 1117 and P1121. My OBDII scanner shows no activity on sensor 2 bank 1, the other three fluctuate appropriately (I guess). I find it strange that both sensors after the cats are showing error. Perhaps they are both damaged from being subjected to less than ideal operating conditions due to the bad cats? Should I just replace the inactive O2 sensor? I have cleaned my MAF. The car seems run great, but Im trying to sell it, and the CEL isn't helping.

P1117 and 1121 are both heater circuit faults for the sensors, and it is odd that you are getting them on both sides after doing related work. Check the resistance on both sensors by pulling the connector and measuring the resistance between pins 1 and 2 on each; you should see 1.8-2.5 ohms. If you don't, the sensor heaters are bad; but if you do, you have a wiring connection issue.

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Ahsai Member

Ahsai

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While you're doing the test John suggested, you can also test the car harness side of bank 1 sensor 2 (the inactive one) to see if you get ~0.4v between pins 3 and 4 with key on engine off. If you don't, you have a wiring issue. If you do, most likely the sensor is gone but if you want to be 100% sure, you can hit the tip with a propane torch for a minute or two and see if you get 0-1v reading between pins 3 and 4 of the sensor.

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emcauliff Member

emcauliff

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Spot on guys! I tested for voltage on the car side first and that checked out. I then took a hard look at the connections and they had obvious electrolysis, so I cleaned them up with some 1000 grit sandpaper, put it all back together and viola, no more CEL. Now Im having some hard starts. Feels like maybe a wrong gas cap? I have to crank and crank and then it slowly catches. Other times it fires right up. I will be digging into this little mystery next. Once it starts, it runs great, which I find weird.

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emcauliff Member

emcauliff

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Does the camshaft sensor have the same symptoms? How can I tell if its the camshaft sensor or the crankshaft sensor? None of the local parts stores have crankshaft sensors, a camshaft sensor is available, which leads me to believe the camshaft sensor is a more common repair?

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JFP in PA Member

JFP in PA

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Does the camshaft sensor have the same symptoms? How can I tell if its the camshaft sensor or the crankshaft sensor? None of the local parts stores have crankshaft sensors, a camshaft sensor is available, which leads me to believe the camshaft sensor is a more common repair?

Actually, it often the other way around. There are more camshaft sensors than crank position sensors in these cars, which is why the aftermarket stock them. Besides which, a failing cam position sensor would throw codes, while a failing crank position sensor rarely does, it just shuts off the fuel pump because it thinks the engine is not turning over. Test the crank sensor.

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JFP in PA Member

JFP in PA

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John, that file applies for Boxsters as well (the file is for Cayenne)?

They are very similar in terms of how to test the sensor, but some of the other info is Cayenne specific. Just about all CPS sensors are simple Hall Effect units, so they work the same.

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Ahsai Member

Ahsai

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John, that file applies for Boxsters as well (the file is for Cayenne)?

They are very similar in terms of how to test the sensor, but some of the other info is Cayenne specific. Just about all CPS sensors are simple Hall Effect units, so they work the same.

Cool. Downloaded for future reference. Thanks! :)

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