P0430 code and engine stumbles above 70km/h

[dragondesign]

Hey guys, getting a P0430 code. Normally I wouldn't think the cats are the problem, but I've got a serious oil burning problem. Some details:

- 2005 Pathfinder, 180,000kms (115,000 miles)
- uses 1L of oil every 2000kms driving and has been quite some time. Money is tight and I don't want to do a full rebuild to fix the burning at the moment
- About 3 months ago started gettign P0430. When I clear the code it doesn't come back for about 2,000kms.
- About 3 weeks ago started feeling the engine stumble when accelerating above 70km/h
- Engine idles perfectly, revs normally, and has strong acceleration up to ~70km/h
- When I let off the gas the stumbling stops, but starts again as soon as I apply any amount of throttle
- If at highway speeds of 130km/h or more under acceleration, there is a loud deceleration followed by the engine slowing its self (similar to engine braking in a manual transmission)

Because of the oil burning problem I suspect that I've plugged the driver's side front CAT with carbon. Currently in the process of removing the secondary cats to see if I can see anything plugging the primaries. Have been trying to get the front driver's side cat off at the header, but having a real tough time getting tools in to all the bolts.

I don't want to spend big money on new cats yet because the burning oil will ruin new ones too, so I'm thinking of emptying the front cats to clear the exhaust. This should buy me some time until I can fix or replace the engine.

Before I empty the front cats and destroy $2,000 worth of parts I want to make sure they're the problem. Temperature diagnostics didn't tell me anything but I couldn't get them as warm as they get under load.

Does this sound like the solution to my problem? It feels a lot like a missing spark plug / coil, but I'm not getting any codes. Checked the driver's side bank and the plugs look decent, can't get to the passenger's side without a bunch of work so I'm hoping to save that for when I do a compression test to diagnose the oil problem.

Any ideas? I'm stuck out of town at work until Wednesday and am working on the pathy in the evenings. The exhaust plugging could stop me on the road, a misfire shouldn't, so I'm tempted to "fix" the cats to make sure i'm breathing free. Any ideas?

[smj999smj]

The best way to check for a clogged or restrictive converter is to use an exhaust backpressure tester. With the engine "cold," remove the front O2 sensor and install the tester. Start the engine and the gauge will allow you to measure the backpressure in the exhaust at idle and higher RPMs. The tester will give you instructions. You can pick an inexpensive one up for around $45 like this one:

http://www.walmart.com/ip/SG-Tool-Aid-T ... la&veh=sem

If you are burning oil significantly, it would make sense that the front converters would be getting clogged with oil. If you remove the front converter, you will likely find a baked on residue on the front of the catalyst media. You "might" be able to scrape it off carefully and get the light to turn off. If you gut the front converter, the code will keep resetting until you get a working converter installed between the front and rear O2 sensors. I agree that it doesn't make much sense to install new converters on an engine that is burning oil. Are you sure it's the rings that are failed and not a PCV issue?

[dawgn86]

Maj

Where is the pcv valve located at on my 2006 4.0 engine ?

[smj999smj]

Right side, or "passenger side," valve cover.

[dragondesign]

I replaced the PCV about a year ago. The old one was certainly dirty, but performance didn't improve after replacing it.

Unfortunately I don't have access to a backpressure gauge right now as I'm stuck at work in the middle of nowhere.

I took off both rear cats, all four o2 sensors, and the driver's side front cat. I ran compressed air at 60psi through all four (ran front pass side through the o2 hole) to check the flow and both sides seem comparable. There was a bit of carbon build up on the inlet mesh of the front driver's side, but nothing like I was expecting to see.

I'm kind of at a loss - don't want to gut the front cats if they're not bad (although they will eventually fail due to carbon build-up from the oil). If I do clean them out I'll put o2 extenders on to stop the SES light while I figure out the oil thing.

I'm mostly concerned with fixing the stutter / hesitation - I'll work on the oil thing this summer. If it's not the cats what else could cause it? Everything else I can think of (plugs, coils, fuel pump/filter, o2 sensors) would behave the same when revving the engine or at slow speed wouldn't they?

I need to drive my vehicle home (650kms) on wednesday at noon, so I'm eager to at least try something. So far all I've come up with is to put the front wheels back on and go for a drive (in the spring mud unfortunately) with the exhaust unhooked. If there is no stutter then it has to be exhaust flow or o2 sensors. If the problem persists I can put it all back together. Thoughts?

Any idea how to bench test the o2 sensors with a multimeter?
Any good tips on cleaning carbon off the cats (without removing the debris screens in them)?

[dragondesign]

Also as previously mentioned, the PCV is on the passenger side of the valve cover. It's way back in by the firewall. I managed to get it out without removing more than the engine cover but it was a time consuming pain. Once you pull the hose off of it you'll see the green plastic sticking out about an inch from the firewall.

[dragondesign]

for anyone that is following along...

Put the fender liners and wheels back on this morning and went for a quick test drive with no exhaust connected. I didn't feel any hesitation at high speeds, though it was a gravel road and it was of course loud so I can't be 100% sure. It would seem as though the issue has to be cats, o2 sensors or the muffler.

Made the decision to empty the one front cat that I had taken off, expecting that because I'm burning oil it would be plugged and black on the inside. I broke it all out and to my surprise it's uniformly grey all the way through. They use cotton (or some kind of white fluffy fiber fill that looks exactly like cotton) in between the two honeycomb sandwiches and the cotton was still white. If I hadn't removed the cat myself I'd swear that it was brand new and never used.

Now I need to gut the second one to equalize the pressure of the system, but I feel like i'm going back to the drawing board.

Another interesting fact is that I've had it running about an hour while the exhaust has been disconnected but I haven't seen any oil blow out the exhaust. If it's not leaking anywhere and not burning / passing into the exhaust then where has 15 liters of oil gone in the last year??

[disallow]

are you certain that you are burning the oil and its not leaking somewhere?

[dragondesign]

I looked all in under the engine. There's a bit of a stain around the oil filter but nothing more than typical from changing the filter myself. There are usually marks around the filler cap that make a mess of the area in the valve cover surrounding the coils. Neither of those areas would suggest 1L/1500kms of oil usage. I've got ticking lifters because I let it get too low before I realized there was a problem.

So if it's not leaking then logically the only other option is burning, right? Maybe there is some magical hidden place where oil is getting collected, but by this point (probably 15-20L in the last year - I put on a lot of miles) it has to be pouring out of wherever it might be.

I haven't done a compression test yet but that's next on the agenda once I am content that I'm not going to break down on the highway in Northern Alberta with no cell service. Checked the driver's side plugs (the easy ones to get to ) and they looked pretty good.

Here's a fun question though:

I'm getting the code for a bad bank 2 cat. Bank 2 is supposed to be the side with cylinder 2 of the engine (driver's side). When i look at the shop manual it calls out the driver's side o2 sensor as bank 1. When I pulled the driver's side sensors the other codes I got were also for bank 2. That being said I doubt the pass. side cat will be dirty when I gut it either....

[smj999smj]

Left or driver's side is Bank #2. If the shop manual says it's Bank #1, the manual is wrong.

[dragondesign]

update - gave in and took the pathfinder to the shop when I got back to town. Turns out the problem was due to worn out u-joints. They did a check on the oil leak while it was in there and it turns out that a bunch of valves are passing oil.

Fixed the joints and it sounds and feels great again. At $3,500 to do valves I don't know if it's worthwhile. Might just add oil as required, since there aren't front cats to fail anymore!