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Discussion Starter #1
This car just won't stop causing me headaches. After rebuilding the engine I surely thought my troubles would finally be over. I am beginning to wonder if they ever will be over. After 50-75 miles on the rebuilt engine, the CEL came on and is reading a P2A00 code. I know it isn't my 02 sensors as they are all new. I bought new catalytic converters but the one that is also the manifold has a bent flange that bolts up to the head. I sanded it as flat as I could until the belt broke on my large sander. I checked and the specs said a certain space was ok. I sanded ti closer than that. I think my problem is the exhaust gasket is two layers of steel instead of a fiber gasket.

All that said, I am at the point of trying to bypass the 02 sensors. I am so tired of fooling with this car it is unreal. I know about the spacers but there is no room for them on this car, the wires of the lower sensors are so close to the fans now I am afraid they one day they will get into the fans. Does anyone know of a way to fix this mess? What do fellows do that use headers instead of the upstream converters?

I just had another thought, my fans have never come on, it has never ran hot but the fans should have come on by now. Any suggestions?
 

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Air/ vacuum/ exhaust leak some where, bypassing the sensors won't net you anything as ther sensors are precat, maybe the post cat but I'm sure that coffee is for pre cat.

Generic question but did you do the throttle body and maf relearn?
 

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Discussion Starter #3
I wasn't aware that I needed to relearn the MAF, since it fired up and ran perfect. One thing that concerned me when the check engine light first came on, the battery light stayed on for a minute or two, then went out.

If there is a leak, it has to be the exhaust. I will take the manifold back off and grind that flange perfectly flat and see if that does any good. There are no codes pending.
 

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Is your upstream O2 sensor brand new from box? I had the p2a00 on one of my cars and it drove me crazy. In the end it turned out to be the brand new O2 sensor from the local parts store. Once I put in and OEM O2 sensor the problem went away.
 

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Discussion Starter #5
I had this problem before I rebuilt the engine, I tried to flatten the flange on the exhaust manifold and according to specs, I had it within range of tolerance. I bought the upstream 02 sensor when I got that code last time. When it spit the same code I took the 02 sensor back and got another one. These are brand name 02 sensors, not the cheap ones.


I appreciate your suggestion, thank you.
 

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Would using a steel and fiber manifold gaskets help seal the flange? I believe some have done that before.
 

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Discussion Starter #7
That is a great thought, that may well solve my problems. Nothing ventured, nothing gained. I really appreciate your response. Using an additional fiber gasket would sure be easier than sanding the fool out of the flange, thanks again.

Jim
 

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I am reading that sometimes the rear O2 can cause this code. I see that sometimes in some other makes. I think if the rear is stuck it will conflict with the front a/f sensor and cause it to stay rich/lean from the second O2's false reading. You have to see with a scanner what the rear O2 is doing. It may be stuck lean or lazy. You must be sure there is no significant exhaust leak. It should be audible. If you replaced the front a/f with a good ntk or oem, then assume its good.
 

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Discussion Starter #9
Sus Spec, I tested all four 02 sensors and they all passed. Now that you mentioned it, I did hear an exhaust leak when I first fire the car up, but don't hear it now. I bought another exhaust gasket today, I will add that to the steel one and see if that works.

Something I also noticed is my oil pressure is pretty low when at idle. The oil pump is new so I know the pressure is ok, maybe it is guage.
 

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Im sorry for what car is this? 4 O2's for your pathfinder? Still nissan should be the same.

I'm also reading that you should clear the self learn control with a scanner. Thinking disconnecting the battery will do that but dont know for sure. I guess thats a reset for a/f ratio. Another quick check is to clean the maf, with maf cleaner only!

still think the exhaust leak has a big part to do with it.
 

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Im sorry for what car is this? 4 O2's for your pathfinder? Still nissan should be the same.

I'm also reading that you should clear the self learn control with a scanner. Thinking disconnecting the battery will do that but dont know for sure. I guess thats a reset for a/f ratio. Another quick check is to clean the maf, with maf cleaner only!

still think the exhaust leak has a big part to do with it.
He just rebuilt a 2nd gen QR for his b16. So yea those have 4.
 

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Discussion Starter #13
I put a fiber and metal exhaust gasket in addition to the steel gasket I put on when rebuilding the engine. I also changed the oil and filter today even though it had less than 100 miles on the rebuild. I didn't want to take a chance of metal particles in the oil. I will change the oil again in 500 miles. We drove around for a while today and so far it hasn't spit another code but it could any moment.

The MAF is new, I put it on when I first got the car 6 months ago. Who ever owned it before me put a K&N air filter in and used way way too much oil on the filter and it fouled the MAF.

After rebuilding the engine it still stumbles a little. The only thing left is the injectors. If it turns out to be an intake leak the intake has got to be cracked.

I am curious how to preform a smoke test on the exhaust, I know how on the intake but haven't heard of testing the exhaust that way.
 

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Thanks for clearing up the car, sorry didnt see that.

Remove an O2 or just put it in the tail pipe and block off as much as possible. Should be able to see any crack is the exhaust mark with carbon trails too.
 

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Discussion Starter #15
Thanks for clearing up the car, sorry didnt see that.

Remove an O2 or just put it in the tail pipe and block off as much as possible. Should be able to see any crack is the exhaust mark with carbon trails too.
I'll be dog gone, I would have never thought about doing a smoke test on the exhaust, that is a new one on me, thanks ever so much, that is some good information, I appreciate it. I need to make a smoke machine. Thanks again Sus Spec

When I get the SE R Spec V straightened out, I need to put another master cylinder on and find the major oil leak on our Pathfinder. Compared to this car, that should be a snap.
 

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Discussion Starter #16
We drove the SE R for a good ways today and it did ok except it has gone back to stumbling after it warms up. When it is cool it runs great, has a lot of pep and power but after it gets up to operating temps it stumbles and jerks a little especially going up a hill. It did this before I rebuilt the engine. I replaced all the catalytic converters, all the 02 sensors. MAF, the temp sensor and I am sure there are other things. I had the injectors professionally cleaned also. Could bad injectors cause this? I am at my wits end trying to figure this out. So far no new codes but that could change any minute. Any suggestions? Would a ECM that is for an SE R Spec V with an Altima engine be the cause?
 

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To me a problem like this which presents itself after a warmup period is usually either an air leak or a fuel bubble/vaporization in the line somewhere. Check all your hose clamps and flange joints for tightness and hoses for cracks.
 
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