P0430 on new cats (after upper engine repair)

[mckpaul]

Hey guys I'll try to keep this brief.

I had a P0305 misfire that I posted on here with several responses, long story short it's fixed, it was a bad exhaust lifter and wiped cam on #5. Got the truck back, runs great, drives great, all is well.



That said, prior to the repair, one of the things I did was replace the y-pipe/cats with a new set from AB Catalytic in Canada, direct fit aftermarket cats (the truck has 129,000 miles and ordering online was less expensive). These were put on about 4 weeks ago, and the truck was driven a limited amount for about 6 days with the bad lifter before dropping it off for the lifter repair.



So, I got the truck back, running great as mentioned, but about 2 days in it threw a P430. Scrolling through the scan tool I noticed the long term fuel trims were both running about -17 to -18 consistently, with little variation between idle, acceleration and cruise. I also noticed in the fuel system screens that the alcohol content was about 39%. I didn't make any changes and took the truck back to the shop. (Meanwhile researched alcohol composition levels). The truck is a flex fuel version but I've never run E85 (commonly sold around here) gas since I bought the truck in November. However, in the last 10 or so fuel fills I've been stopping at about 3/4 tank trying to get the monitors set, and I read where multiple partial fills can cause the alcohol percentage to get confused. He reset the alcohol composition, and it went back down to 3%, and he reported that the fuel trims went back to normal, but he didn't say he performed a fuel trim reset.



I took the truck and after an hour or so the P430 came back, and I noticed the long term trims had gone back to the negative numbers, just not quite as low...maybe -12 or so. The alcohol percent still looked OK after filling the tank, actually came up to about 6% (all the gas sold around here says "May contain up to 10% alcohol), so I cleared the P0430 and executed a fuel trim reset (last night) So far the long term fuel trims appear to be staying normal now (maybe +2-ish) and the short terms fluctuate around -1 or 2 and +1 or 2. Fingers crossed the P430 won't come back.



If I understand correctly, my 2010 Tahoe does not have a physical alcohol percent monitor device, and it does it automatically by crunching numbers after fuel level changes after adding fuel, correct?

I can't imagine one of the brand new cats was damaged with less than a week of driving 6 miles to work, had a misfire and bad lifter but wasn't running terribly. Is there any thing else that could create a P430 I can check for?

I'm not sure if there's anything in the engine top rebuild he could have done wrong that might cause that code, it's running beautifully. Could the cat have gotten maybe a little saturated while it was running rich before catching the high alcohol % and negative trims and maybe with some driving it'll dry out?

I looked at the downstream O2 sensor data, bank 2 did some fluctuation. I swapped the bank 1 & bank 2 downstream sensors trying to eliminate a bad sensor, but no change bank 2 still showed fluctuation.



I've read where exhaust leaks can contribute to P430, and considering the new cats were installed one weekend and then a week later the heads were pulled off, it's possible there could be a small exhaust leak, but if so it's not audible.

 

[kbuskill]

I would drive around for a bit on the highway to get the exhaust up to temperature for an extended period of time... maybe even driving in a lower gear (4th or 5th) for a bit to get the RPMs up and burn out any residual fuel in the cats.

 

[mckpaul]

I think you are correct. Someone directed me to a writeup about converter break-in. In the last three months digging on the net for info on the misfire issue I ran across the break-in and tried to make a mental note in case I ever put new cats, and with all that went on trying to fix the misfire and then finally taking it in to have it repaired, I completely forgot about it. It involves driving 30 minutes at highway speeds, turning it off for one minute, and driving highway speeds again for 10 minutes and turning it off again to break new cats in or they throw that code. It went on to say new cars are programmed to ignore the cat code for a certain amount of time until they get broken in.

I'm going to do the drive cycle after work and hopefully that will solve it.

Thanks for the reply!

 

[swathdiver]

That's right, GM says about 100 miles for theirs. The Magnaflow set I put on threw a code within a few miles and for the rest of the 100 miles was fine. Gas mileage kept improving with time as they broke in.

 

[mckpaul]

Well....the light is back. I tried a couple of converter break-in procedures, one was simply let the engine warm up for 5 minutes, then hold it at 2500rpm for 2 minutes. The other was the one above with 30 minutes on the highway etc. I performed both, the short one at startup before leaving the parking lot and the long one after .When I got off work (here in the Houston area) I had to drive for about 45 minutes of stop and go traffic to get out on a freeway where I could drive 30 minutes uninterrupted, but once I did I was able to drive about 70mph for 30 minutes, turned it off for one minute, turned around and did the same for 15 minutes, then had almost an hour of mixed driving getting home. I clocked about 150 miles overall on the overall trip. So the cats should be burned in by now. I was pleased coming home since I had no light thinking I was done... and the darn thing came on again I the neighborhood. On the upside, I have 164 miles on this full tank of gas, granted some are highway miles, but I still have 5/8 of a tank, may get 200 on the top half of the tank. That's more like my old '03 Tahoe used to do. The bottom half of the tank goes down faster, but the gas mileage is definitely back up. With the bad lifter it had gone down to about 7 miles per gallon.

At this point I'm suspecting a leak before the cat. The driver side (bank 1 that seems to be OK) has a flat plate type flange gasket, but the passenger side has a donut. A new donut was used when the cats were installed, but a week later the heads were pulled. I guess it's possible the guy pulled the exhaust manifold completely out and then re-used the donut, or may have just left the manifold attached to the cat and worked the head out since the exhaust manifold fasteners are bolts not studs, and made the donut leak. You'd think the head gasket set would have come with a new donut and he installed it, but who knows. Either way, I think I'm going to replace the donut, (which I know will involve breaking the driver side loose too and replacing that gasket) and while it's pulled down I'm hoping to have enough room to snake my gooseneck camera down and take a peek at the media. I think it's pretty unlikely, but I guess its possible that driving it for a week after the new cats were installed while I still had the bad lifter it could have been throwing off some extra carbon and got the new cat dirty. But, I only live 6 miles from work, all neighborhoods, never got on the freeway for more than 5 minutes after installing the cats to see if it made a difference. And besides that, the bad lifter was on Bank 1, the opposite side of this code for an inefficient cat. I may go as far as replacing the exhaust manifold to head gasket as well. If I do that I'm sure I'll be able to just look down into the cat to see if it looks like it got trashed.

Most of my life, for our 'second car', also known as the one I drive, I've bought used but nice and clean vehicles, usually with high mileage understanding that it's a roll of the dice, and understanding I'd just have to fix whatever happened. I've bought many cars that way and overall I've done OK. I'm starting to think this is the karma truck. patiently waiting until I'm 60 years old and then deciding to drag my butt through the dirt. I'm quite sure I saw a smirk on her grill last night as I closed the garage.

 

[swathdiver]

Ok, so P305 refers to cylinder #5 on the left bank (driver's side) of cylinders. P0430 refers to the Bank 2 (passenger side) catalytic converter. You fixed the motor and replaced both cats, right?

What kind of cats (brand/PN#) did you replace the originals with? New things can be bad.

You need an advanced scan tool to see what's going on with them and the O2 sensors and to perform some basic tests of the various systems that can affect the health of the catalytic converters. Do you know anyone with a Tech2?

 

[mckpaul]

Hey James,

Yes. Chased the P305 for about 3 months, driver side. Towards the end I purchase an AB Catalytic #41842 direct fit y-pipe with cats from Calnorth Auto Parts in Ontario Canada. They are connected somehow to AB Catalytic also in Canada. Where it would normally be a true y-pipe, for less expensive shipping for online orders, the modify it in production slightly and sell it in two pieces with a slip joint in the cross section of the Y. Fits in a box that way and actually a little easier to install. While I still had the misfire, this was installed one week prior to the repair. I drove it on the freeway about 10 minutes to see if it helped the throttle response at all, and then drove it to work all week for 5 days, about 6 miles through neighborhoods each way. I dropped it off that Friday. I wondered if the cat may have gotten dirty in that one week but as you pointed out, the misfire was on the other bank.

Side note, I was going to install the y-pipe/cats myself but rounded off one of the rusted bolts, so I just took it to a muffler shop and had them install it, along with the new gaskets. They also welded the slip joint.

That week it was on the truck prior to repair, it never generated the P0430 code, only had the P0305 when I dropped it off.

So the repair involved new cam and lifters, so all new gaskets, including exhaust manifold gaskets. What I don't know is if he separated the manifolds from the y-pipe or worked around them. Seems like it would have been to crowded to leave them on the y-pipe.

I don't have a Tech2, I have a Foxwell NT520. It is bidirectional, won't do everything a Tech2 will do, but will do graphs on the small screen. As soon as I got the truck back I immediately looked for misfire counts and there were none, but I noticed the long term trims were both about -16, and the fuel composition had somehow worked it's way up to 39%. It had an oil leak so I took it back. He fixed the leak and reset the fuel composition and fuel trims. I have since filled the tank and now the composition reads about 2% and the long term fuel trims are about +2 both banks.

I graphed O2 on both banks. (All sensors were replaced about 3 months back) Bank 1 shows a nice fluctuation on sensor 1 and sensor 2 is pretty much steady. However Bank 2 shows nice fluctuation on sensor 1 and sensor 2 is fluctuating as well, not as fast but not steady. I swapped the bank 1 and bank 2 sensor 2's to see if anything changed, but same result, bank 1 looks good, bank 2 indicates deficient cat.

Considering the whole scenario, I think there's a greater chance of an exhaust leak either on the manifold or donut gasket on bank 2 than a bad cat since a lot of work has been done. I have read where aftermarket cats can sometimes not be accepted by the vehicle, but at the moment I don't think that's the case. At least I hope it's not. All it'll cost is some gaskets and time to check it out. Hopefully now that the y-pipe and manifold bolts have all recently been removed I shouldn't have any problems getting them out.

 

[swathdiver]

Check for the leaks but I think you have a faulty new cat. You've done a great job and eliminated all but one possibility. If that doesn't fix it, it's the cat. Did you save the old ones? You can sell them to the scrap man and offset some of the cost.

Where did you find that set? I thought I did thorough research before replacing mine and never came across that one. I went with Magnaflow which was quite a bit more than Walker but the quality of the bends and tubing was important to me.

 

[mckpaul]

I found that set in an ebay search. You know how part numbers go, several sellers use the same number maybe adding a couple of letters before or after, so once I got the 41842 number I googled that which eventually lead me to the AB Catalytic that builds it. They had a search by make and model on their site and I verified the part number fit my vehicle, even had that engine choice drop down where I selected the vin code 0 engine that mentioned Flex fuel in the description (as opposed to the other vin code 3) They are made with stainless steel walls, actually looked almost identical to the OEM set, wondered for a moment if they might be the source provider for the trucks made in Canada. They seemed to be pretty decent but I was a little leary about the $300 price tag. I called the guy at Calnorth and talked to him (that's how I found out it would be shipped in two pieces with a slip joint, that would have been a bit of a surprise when it arrived) and he said they actually sold on ebay pretty much at cost just to compete.

I was thinking I'd save my old ones just in case, but since I took it to a muffler shop and didn't say anything, when I walked out to see how it was going he had already cut the old set out with a sawzall, it made it easier to get to the nut I had rounded (which he did get out so I didn't complain) I let them keep the old cut up set, didn't think about selling for scrap.

I ordered new gaskets, also ordered a new set of manifold gaskets. I could probably talk the repair shop into installing the new cat gaskets, but I think I'd like to pull the manifold on that side anyway and check for cracks, and if I do it'll be easy to look directly into the new cat at the media. I doubt he'd go as far as to pull the manifold without charging me, and I'm not 100% sold on the guy he had do the job. I'm not a purist that torques every bolt, and as a mechanic there's a line in the sand you draw on what to torque exactly to spec and what you think just tight is OK on. That's one of the problems I have with taking my vehicle to a shop, you don't know what got torqued and what got just tightened. I say that because I had already changed the intake manifold gaskets and actually put a new intake as well, so I knew the bolts weren't supposed to be reused and requested they use new ones. I also knew the spec on that plastic manifold was 44 inch pounds on the first pass, 89 inch pounds on the second pass. I went back to check after the second pass just in case and they all still clicked. When I got the truck back from repair, just for grins I put the torque wrench set at 89 inch pounds on the intake bolts, and some clicked, some I had to turn as much as 1 1/2 turns to get to 89 and click. So I'm pretty sure he didn't take the time to torque the intake properly, or he didn't follow the sequence. So I'm not 100% sure he torqued the exhaust manifold evenly. If I can get the y-bolt nuts loose I'm just going to do it myself including the manifold gaskets.

I know I'm grasping at straws, and just hoping it's a leak, but I have to eliminate that from the possibilities before calling it a bad cat. I'm going to look at the welding on the cat flange and O2 sensor ports closely too.

 

[gpracer1]

Drive it then hit both cats with IR temp gun and see if the bad side cat is lit at the roughly the same temp.