New stroker with a couple quirks???

[steve76t]

I've just installed a 4.6L stroker in my 2001 TJ and have a little more than 150 miles on it so far. For the most part all is good but I have two issue's. First I'm getting a very occasional stumble at idle when coming to a stop at an intersection or stop light. It's only happened three times for far. However, when it does happen the engine hesitates or stumbles for a second or so, very nearly stalling completely.

Second issue is that I've got a check engine light and error code P0420. I know the code is a cat issue, but the cat should be fine and never had this code ever pop up with the old engine. Anyone experience O2 sensor codes when replacing their stock motors?

[2tKTM]

Car at the shop the other day was throwing a p0420 code, after replacing the cat as per customer request it came back on. We threw a new downstream o2 sensor in and it remedied the problem.

Most likely it's that downstream o2 has taken it's final breath, the p0420 is thrown as a "cat efficiency" code.

[steve76t]

I replaced the downstream O2 sensor behind the front cat & so far no more P0420 code. Only been a couple days of driving to & from work but the code hasn't come back on yet. Got a feeling that it was just a bad sensor.

As for the bobble or hesitation, I haven't had it come up again in over a week now. Maybe it was just my computer learning and adjusting to the new motor?

[2tKTM]

I wouldn't be worried about the hesitation if it isn't still happening. Definitely could be the computer still learning, among other things still settling into place.

After you have the motor broken in good (1000+ miles) you might do a hard reset and do a couple WOT pulls up through third gear to let the computer get a feel for the motor better.

[steve76t]

Got it... Only have about 250 miles on the mill now, but doing a hard reset sounds like a good idea once all is broke in. Thanks!

[Cheromaniac]

As for the bobble or hesitation, I haven't had it come up again in over a week now. Maybe it was just my computer learning and adjusting to the new motor?

Exactly. I've found that it takes at least 100 miles of variable driving for the ECU to complete its adaptive learning.

[steve76t]

well crap... after about a week and 150+ miles my CEL came back on and is giving me the same P0420 code again. Kind of wondering if I may have an exhaust leak, cant find one yet, and not really a bad cat? Anyone actually have a P0420 error come up and actually end up with a bad cat? I'm still running a stock 01 TJ exhaust manifold and maybe that's got a small leak somewhere???

[optmaxx]

Did you use molly rings? I heard that they take a little longer to seat, so I'm wondering if maybe your rings didn't completely seat (which is normal for a new build with low miles), and you might be getting a little bit of blow-by until they seat completely? Just a thought. What type of oil are you using?

[IH 392]

Did you use molly rings? I heard that they take a little longer to seat, so I'm wondering if maybe your rings didn't completely seat (which is normal for a new build with low miles), and you might be getting a little bit of blow-by until they seat completely? Just a thought. What type of oil are you using?

I've always been told the exact opposite, they are seated in before the cam break in is done, now if it had "CHROME" rings in it it would take some time to get them seated.
Synthetic oil will delay the break in.

[Russ Pottenger]

Did you use molly rings? I heard that they take a little longer to seat, so I'm wondering if maybe your rings didn't completely seat (which is normal for a new build with low miles), and you might be getting a little bit of blow-by until they seat completely? Just a thought. What type of oil are you using?

I've always been told the exact opposite, they are seated in before the cam break in is done, now if it had "CHROME" rings in it it would take some time to get them seated.
Synthetic oil will delay the break in.

IH 392,
You are correct.

All rings require break and procedures. Molly rings are typically the easiest and most forgiving.

The more economical molly ring sets utilizes a molly filled cast top ring. When we get into the more expensive premium molly ring sets The top ring is made out of ductile iron in the Molly is attached through a plasma spray. This ring is used in high compression engines or boosted Applications and is less likely for the Molly to flake off under detonation.
These rings generally like a fairly smooth finish, 400 grit.

Chrome rings on the other hand like a much courser finish something like 280 grit and are much harder to break in. Their applications are primarily more desirable in dirty air applications.

[IH 392]

Yep, that's pretty much how I remember it, we used tones of plain rings as most of our builds were for HYSTER forklifts and we were told that the Molly rings weren't compatible with the LP as it was/is a "dry" fuel?, most of the issues were with low compression and retarded timing!, the Clevite rep came to the shop and steered them down the correct path, but I'd been telling them that for three years!??

[steve76t]

Hastings Plasma Molly rings and Joe Gibbs break-in oil. Still have about 125 miles before my needed 500 mile oil change where I'll go to a 10w40 Joe Gibbs oil.

Ring break in and blow by a possible reason for a P0420 error code?

[steve76t]

Hastings Plasma Molly rings and Joe Gibbs break-in oil. Still have about 125 miles before my needed 500 mile oil change where I'll go to a 10w40 Joe Gibbs oil.

Ring break in and blow by a possible reason for a P0420 error code?

[steve76t]

Damn it... I now have about 600 miles on my new motor and still getting the P0420 code. I've replaced sensors, reset the computer a few times, haven't found signs of exhaust or intake leaks, etc. Each time I reset the computer it'll take about 100 miles before the error code comes back on. I'm really trying to find a reason this is going on other it really being the front cat. From what I have found it's extremely rare for the cats in the downpipes to go bad.

[steve76t]

may have fixed by P0420 error code after all. Replaced the new front o2 sensor with another new one & now have nearly 200 miles on it without the code coming back up. Got my fingers crossed