So it wasn't curiosity that killed the cat...

DAA

Well-Known Member
I think my misfire issue killed one of the precats. With about 75 miles since first startup on the head R&R, getting two fault codes. One is a P0431. Which could indicate a failed catalytic converter. This motor has two precats, one for cylinders 1-3 and another for 4-6. Got this same P0431 code shortly before tear down. It's for precat bank two where my misfire was. Misfire dumping fuel being one of the most likely causes of a cat going bad.

It could possibly be a bad 02 sensor. Or an exhaust leak. But I'm pretty sure there isn't an exhaust leak and I just replaced all four 02 sensors while I had it all apart and they were so easy to get to (and, like I said, got that code just before tear down, so...). I'll check all the manifold and flange bolts on the exhaust later today, just on GP, but I really don't think there is a leak.

I don't have anything to monitor 02 sensor activity to diagnose further. And even reaching the inlet on the precats to check temperature looks just about impossible. I'll check the temp of the two precats to see if the bank two cat is hotter, maybe that will tell me something. But I think I'm just going to have to get it into a muffler shop with a scan tool that will do some actual diagnostics on it to verify suspicions before throwing parts in. I think 02 sensor activity will show it. But, I think the misfire probably did kill the cat :(.

The other code is unrelated, and potentially much more troubling, a P0016 crank-cam correlation fault. The OPDA is about a year old. Very strange for this code to happen a year after install. And the timing, immediately following a major tear down, well, I don't believe in coincidence in this situation. Most likely suspects are either the OPDA moved, or perhaps gear wear. I pulled the OPDA - the teeth haven't even got shiny yet, gear wear eliminated as a possiblilty... It was not lined up quite as perfectly as it could be. I was stepping on it while climbing around in the engine bay setting the head back on, so maybe I moved it just a tiny bit. But the spec is it has to be lined up within +/- 3.5 degrees. Which is a pretty big window. I don't think it was more than 1 degree from perfect, certainly not more than 2 degrees. Made the tiny adjustment to line it up as perfectly as I could, cleared the code, and crossed my fingers. Timing set wear is the next most likely, but that really doesn't seem probable. I saw very, very little wear on anything while in the motor doing the head. Can anyone think of anything related to a head R&R that could create this issue? Other than possibly moving the OPDA, I can't think of anything. Didn't touch anything to do with timing. If this code comes back, I'm going to have to get the Jeep to someone with much stronger diagnostic skills and the right scan tool.

Ah, well, it all is what it is. It's discouraging, but, just keep working through the issues one at a time and it will all be back to good sooner or later. Hopefully sooner! And, should mention, despite these two codes, it's running great. I'd never suspect there is anything wrong if it weren't throwing the codes.

- DAA
 

gijohn40

too poor to wheel... :(
Location
Layton, Utah
torque pro allows you to look at the o2 sensors... if you want I can run over and plug my obd2 bluetooth connector in and we can look at your o2's it has alot more features as well. and I am just down the street...
 

gijohn40

too poor to wheel... :(
Location
Layton, Utah
also if you need to buy the precat exhaust system I would recommend advance auto parts... I was surprised that they actually had the part in stock and for only $259 where as everyone else wanted over 300 and it was a special order part.
 
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DAA

Well-Known Member
Well that was easy, :D. Right on, thanks John! I had been looking in the wrong place over in PID's (wanting a misfire counter). Graphing is where the 02 sensor data monitoring lives.

Downstream sensor is basically shadowing the upstream. Which, I think means bad cat. I only have a couple hours google research, so as green as it gets, but I think downstream should be showing a fairly constant voltage if the cat is doing what it is supposed to do.

I'll be glad I put new bolts in those flanges when I take them out :D.

- DAA
 

Omgbecki

Well-Known Member
Location
Ogden
I went through a similar issues years ago with my TJ. Changed plugs had the same problem. Changed coil pack. Same problem. Changed exhaust manifold to a banks header. Same problem. Changed all O2 sensors. Same. Finally got a down pipe with precats and my problem went away. Granted this was when the jeep was 3 years old so it was a lot harder and expensive to get the down pipe. Hopefully you just change that out and are golden. On a side note. What is this torque pro and what's so great about it? Is it actually useful or snake oil
 

Hickey

Burn-barrel enthusiast
Supporting Member
I went through a similar issues years ago with my TJ. Changed plugs had the same problem. Changed coil pack. Same problem. Changed exhaust manifold to a banks header. Same problem. Changed all O2 sensors. Same. Finally got a down pipe with precats and my problem went away. Granted this was when the jeep was 3 years old so it was a lot harder and expensive to get the down pipe. Hopefully you just change that out and are golden. On a side note. What is this torque pro and what's so great about it? Is it actually useful or snake oil
Torque pro is an app that uses an OBD II dongle to read your vehicles computer and sensors.
 
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DAA

Well-Known Member
So new Magnaflow precats are in. I had Ray's in Bountiful do it. I'm just way low on time to mess with stuff this week and I hate any kind of exhaust work. They got me the parts a little bit cheaper than I could find them online, charged me $180 in labor, came out about $150 more than doing it myself. They did a nicer job on the joint than I could have crawling around underneath it in my garage, nice straight tight joint, tack welding it before clamping it.

Turns out, both precats were TOAST, too. The bank two, the one I knew was bad, was completely broken up with big loose chunks that very easily could have and likely were causing intermittent restriction. Actually, probably explains something that happened about a month ago. Hit a big bump and the motor immediately started stumbling badly. Had me thinking electrical and chasing down grounds and such for an afternoon. It went away on it's own though. Might also explain why it ran a whole heckuva lot worse after the top end cleaner treatment, maybe. But the other one, bank one, was also partially broken up and in bad shape - explains the irregular and very intermittent holiday I observed the downstream 02 sensor making on that bank - which had me somewhat perplexed. So, they needed replacement, badly, and it's done now. Hooked up Torque again just now, just to see and both downstream 02's are nice and regular with no holidays at all.

As a bonus, it's actually running even a tiny bit cooler still than it has been since the valve job - and it was already running a tiny bit cooler just from doing the valve job. It's running two full needle widths cooler now than it was a couple weeks ago. That can't be bad.

Just have to see where things go from here. One thing at a time. Feels like progress though.

- DAA
 

gijohn40

too poor to wheel... :(
Location
Layton, Utah
good to hear... I replaced my precats about 3 yrs ago and when I did the inter honeycombs where all gone... they were just straight pipes so to say.. and guess what... I never replaced the downstream cat. I have heard that if the cat is clogged it will cause overheating. I have have problems with my temps while on the freeway but when I get off the new upgraded fan really cools it down fast.
 

frieed

Jeepless in Draper
Supporting Member
Location
Draper, UT
Interesting that it runs cooler. That means the thermostat was wide open and the coolant temp was governed entirely by the cooling ability of the radiator and heat output of the motor. Open-loop as the engineers would say.
 

DAA

Well-Known Member
After observing how slowly a thermostat actually opens and closes in a pan on the stove, and seeing how quickly the engine temp will blow past normal and get too hot when it is closed, while just idling in the shade in my garage, I can't imagine that the thermostat could ever actually close while the engine has any load on it at all in ambient temps fit for human life.

- DAA
 

frieed

Jeepless in Draper
Supporting Member
Location
Draper, UT
They're not like a switch, open or closed, but rather a variable valve so at any normal operating temp it will be partway open. If temps rise and stay high long term, the valve should be all the way open and you're left with how fast the rad. can dissipate heat. Short spikes will happen since the valve is slow to move.
 

DAA

Well-Known Member
Yeah but after actually watching it work and seeing how fast temps go up, I think in practice it's a variable valve that never varies.

- DAA
 

DAA

Well-Known Member
Ain't that the truth... Doesn't help that the miles on mine have almost all been hard miles. It has been living a Jeep's life, for sure.

After going through this exercise, I think monitoring 02s could give you a pretty good clue how healthy your precats are. I really had no reason to think bank one was bad. And it DID look a LOT better than bank two, in the 02 voltage. But it had a little bit of jumpiness and this irregular dip way down to .2 it would take every so often, like an irregular heart beat on the graph. It kinda bugged me, but it looked so much better than bank two did, I just kinda shrugged it off. I had bank two as my reference for what a bad one looked like and it looked quite a bit better than that.

With the brand new precats, I now see that it was really telling me it was bad. And bank two was telling me it was beyond bad, there ain't no cat action whatsoever going on here anymore.

I think the downstream 02s ought to be pretty darn regular on a healthy cat. Mine are now. And, have put just over a hundred miles on it with the new ones, haven't thrown a code yet. That crank-cam correlation hasn't happened again either. Maybe I did move it a tiny bit while climbing around on it and that's all it was. Hope so.

Thinking I'm going to go put about a thousand miles on it this weekend, get way in the heck out in the lonely stuff where nobody ever goes, see what happens.

- DAA
 

DAA

Well-Known Member
Put 900-something miles on it over the weekend. 300 of it dirt. Jeep ran wonderfully well! Few pics, a couple of lunch spots and a couple of camps.

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20180922_Camping-5.jpg


Have plans to do the same thing the next two weekends in a row, different areas of course. But lots of dirt.

- DAA
 
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