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Discussion Starter · #1 · (Edited)
I think my final gremlin is coming near the end. I think maybe my 1st pre-cats may be bad but I am not 100% certain. I get no codes for my long-term O2 Sensors (Post sensors) but the LT fuel trim is always 9-15% (used to be 25%). The pre and post O2 sensors voltage signal displays seem to track each other somewhat. When I use my code reader to measure fuel system, it says something is preventing system "A" and "B" from going into closed loop. The front O2s are new and the back O2s seem to test ok. The temperature is correct too. Not sure what is going on but I will soon take her to a Nissan mechanic in hopes he can figure out what is happening.

Fixed vacuum leaks, cleaned, tuned and adjusted everything to the best of my knowledge. I was just curious if anyone has ever had this issue or heard of such a thing. It sure has me scratching my head.

Rainwood
 

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Year and mileage would help, also any codes? The new O2 sensors OEM or aftermarket? What did you clean, tune, and adjust?
 

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Discussion Starter · #3 ·
Sorry about that. It is a 2003 3.3L frontier w/ 125K. The front two sensors are Bosh. Most parts as I needed were Beck and Arnley. I removed the upper and lower intake manifolds to replace the knock sensor and after doing this, I decided to relocate it. While every thing was off I cleaned pretty good and replace all hoses under upper intake manifold. Cleaned egr and throttle body. I have adjusted the fast idle and throttle body linkage (not the idle air control valve ( cleaned that too). Repaied numerous vacuum leaks and the technical bulletin on the grounding issue. Timing belt and water pump was also replaced. The grounding issue lead me down many rabbit holes and I ended up replacing some things that probably did not need replacing. But it's done now. That is about all I can think of. After the grounding repair, MAF and ignition and coil along with vacuum repairs it steadily has improved. But it's not 100%. It also sometimes is slow to shift into 3rd gear and at a stop light it sometimes drops idle down to like 600 rpm and sputters a little. I was thinking the cats are partially clogged and builds up back pressure at low speeds and idle. I just need a second opinion and someone that probably knows what they are really doing take a look. Sorry for the novel but it has been a journey for sure. I'll be a happy man when she is purring like a kitten :)

Thanks, Rainwood
 
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