Catalytic convertor on a 2015 gas 2500hd

Propane, Butane, LPG, GPL, C3H8, C4H10
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Dan350
Posts: 50
Joined: Fri Dec 05, 2014 8:26 pm

Catalytic convertor on a 2015 gas 2500hd

Post by Dan350 » Tue Feb 13, 2018 1:18 pm

Friends, I have a prinns system on a 2015 silverado 2500hd 6 liter vortec. Lately it has been getting very lousy fuel mileage and occasionally I get a p0420 code with the engine light on in the dashboard. Being the mechanical genius that I am, I erase the code and hope the problem disappears (just like I hope the Montreal Canadiens win the Stanley cup!). Anyways, the code means that there is a “catalyst low efficiency on bank 1” About a year ago I had to overhaul my cylinder heads because of a burnt valve and I upgraded to propane compatable valves and seats. Prior to this, I had a misfire on bank 1 code pop up which was due to that valve not seating properly. Could this condition have cause the cat/cons to go bad? If gasoline (on start-up) and propane made their way past the exhaust valve un-burnt could it cause the cat/cons to go bad? I know it could probably be an o2 sensor but everyone tells me it’s more likely bad cats. Also,last fall my propane guy got a bad batch of propane from Sarnia causing my system to shut off and/or run poorly. It turns out someone filled a storage tank that had “heavy oil residues” in it. It took a long while to figure out what had happened and I went through several tanks before we could put a finger on what the problem was. Could this have led to the cats going bad? I pull a 30 foot gooseneck trailer 5 days a week. I’m used to about 30L/100km of propane consumption and lately I have been using 37+
Thanks!

C3H8
Posts: 1010
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Catalytic convertor on a 2015 gas 2500hd

Post by C3H8 » Fri Feb 16, 2018 1:49 pm

The post cat 02 sensor measures cat efficiency. The ECU compares the pre-cat O2 with the post-cat reading expecting to see a variation in the readings. If it see a wide variation is signals a problem. Misfires are a cats worst enemy. Your loss of mileage is probably due to the cat becoming plugged. You can verify this easily with a pressure test. This is done by attaching a pressure gauge capable of 0 to 10 or 15 pound range. Either drill a hole in the exhaust and install a fitting to attach the gauge or remove the pre-cat 02 and using an adaptor attach the pressure gauge there. Most muffler shops have the 02 adaptors. A new cat will be at or close to 0 PSI back pressure at idle and also very low at 2500 RPM. A pressure up to 1.5 PSI is considered acceptable. Anything over 1.5 psi generally means the cat is toast and causing significant flow restriction resulting in power loss and economy issues. Any time misfires are detected they should be addressed as soon as possible. The results vary but the aftermarket cats cost less than the OEM cats. Typically they work just as well as the OEM's but some people have claimed differently.

Dan350
Posts: 50
Joined: Fri Dec 05, 2014 8:26 pm

Re: Catalytic convertor on a 2015 gas 2500hd

Post by Dan350 » Fri Feb 16, 2018 5:05 pm

Thanks for your insight, i’ll give that pressure test a try and I’ll let you know. Maybe i’ll use a cheap boost gauge.

Dan350
Posts: 50
Joined: Fri Dec 05, 2014 8:26 pm

Re: Catalytic convertor on a 2015 gas 2500hd

Post by Dan350 » Sat Mar 03, 2018 1:44 pm

The dealer wanted 1600$ for the cats. I ended buying a used one (25000km) for my local LKQ dismantler for 200$. After having it installed, i immediately noticed that my truck’s power had been restored. The check engine light hasn’t gone on and yesterday I did a round trip to quebec city which is about 550km with a 15000 lb load on my 6000lb trailer and I averaged 35l/100 km on propane with a 4000lb return load which is what i expected. I haul heavy loads like this maybe 1-2 times a year, i usually average 7-8000lbs. Anyways, for now the problem seems to be solved. Thanks.

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