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Rough Idle and hesitation

 
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Thu Jul 06, 2017 6:19 pm    Post subject: Rough Idle and hesitation Reply with quote

I'll start off with a back story. I have a 97 Pathfinder with 188K miles and for the past 6 months or so, I've had a hesitation under load between 2000 and 3000 RPM. The hesitation wasn't severe but definite power loss. It feels like I'm letting off the accelerator and pressing it back on gently. After plugs, wires, cap, rotor and fuel filter the symptoms lessened but still there. Couple weeks ago I was planning on a road trip but had decided to turn back 10 miles into the trip after the highway hesitation turned into what feels like a misfire. After a couple more days of driving around town, I now have a rough idle and at times the engine will stall completely at a stop. While the engine was cold yesterday morning and this morning, I was getting white/blue smoke and smelled of raw fuel and after a quick hard test drive with barely diluted seafoam in the tank, I was getting more of a black/blue smoke and raw fuel smell at a rough idle.

I have no check engine light and nothing apparent under the hood. I have yet to do a full inspection for vacuum leaks. I took the EGR valve off and sprayed it down with brake clean but nothing more since I'm not too familiar with how the valve works. All hoses on the valves are attached and in good shape. I've researched distributors are usually the issue with my symptoms.

Any and all advice would be greatly appreciated. Thank you
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smj999smj
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Joined: 22 Jan 2012
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Location: Prospect, VA

PostPosted: Thu Jul 06, 2017 9:35 pm    Post subject: Reply with quote

Distributors can do this and are very common on VG engines. I would also make sure the vacuum hose didn't come off of the fuel pressure regulator and would test the fuel pressure. I would also check he front oxygen sensors and clean the EGI grounds and contact point where they are mounted to the upper intake plenum.
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2006 Pathfinder LE VQ40DE AWD, Nitto Dura Grappler P265/65R17, aftermarket radiator, Airlift 1000's, Bilstein HD rear shocks
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Sun Jul 09, 2017 6:17 pm    Post subject: Reply with quote

Thank you for the help smj999smj. I replaced the distributor as well as clean the contacts on the intake and I still have the same symptoms. At times, it runs just fine and others it's wanting to stall and heavy hesitation under no load from 1500 to 2200 rpm. I haven't located the regulator yet but that's my next step as well as check for fuel pressure. I believe the regulator is behind the intake near the firewall? Couple friends of mine are leaning towards an air/fuel issue which makes sense.

How do I go about checking if the O2 sensor is faulty or is that something you just replace? Haven't done much with O2 sensors.
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smj999smj
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PostPosted: Mon Jul 10, 2017 1:20 am    Post subject: Reply with quote

Yes, regulator is at the back of the engine at the end of the fuel rail and near the firewall of the engine compartment.
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Mon Jul 10, 2017 5:26 pm    Post subject: Reply with quote

I found the regulator and the vacuum hose is attached and in good shape. Nissan sure did make it not easy to get to. Looks like you have to pull the intake to replace it? Anyway, I'm trying to track down a pressure tester to test my fuel system and from what I researched, it looks like 35 PSI is what is called for?
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smj999smj
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PostPosted: Mon Jul 10, 2017 10:26 pm    Post subject: Reply with quote

Yes, 34-36 psi regulated and around 45 psi static pressure is normal. The upper intake plenum needs to be removed in order to replace it.
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Thu Sep 14, 2017 4:01 pm    Post subject: Reply with quote

I finally got a hold of a fuel pressure tester and tested the system and it appears the fuel system is all good. Pressure at idle is around 35 and with a pinched return line, the pressure would jump up to near 70. Tested vacuum on the regulator and that is all working properly.

smj999smj you had mentioned O2 sensors and checking them. How do I go about testing the sensors?
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smj999smj
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PostPosted: Fri Sep 15, 2017 9:39 am    Post subject: Reply with quote

You would need a scan tool that can graph their signals to do it properly. With that, you could also graph the TPS signal, as well. It sounds like the regulator is working fine. It would be nice if we could get a reading of each of the spark patterns with an oscilloscope but that's typically a piece of shop equipment and it's getting harder to find auto techs that know how to read them!
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Sun Sep 17, 2017 1:21 pm    Post subject: Reply with quote

Unfortunately I don't know anyone with a scan tool that will graph signals. I can get a hold of a scope though as well as a user who can use the tool. I think I'm just gonna pull the plug and replace both pre-cat sensors. Found a good deal online.
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smj999smj
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PostPosted: Sun Sep 17, 2017 4:49 pm    Post subject: Reply with quote

I recommend NTK and Denso oxygen sensors, only. Other brands are sometimes a gamble as to how well they work or how long they last. Also, avoid "universal" sensors that require you to splice into the original sensor's harness and use the old sensor's connector; they can give you problems, as well.
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Sun Sep 17, 2017 6:38 pm    Post subject: Reply with quote

I was able to find "direct fit" sensors that come with the correct connectors that were fairly inexpensive. The brand I bought was APW, I've never heard of the brand but I'm going to give them a try and see.
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smj999smj
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PostPosted: Sun Sep 17, 2017 11:51 pm    Post subject: Reply with quote

I've heard of them. APW is short for "Auto Parts Warehouse" and they've been around since the early '70's. I don't think they actually make any auto parts, rather, they purchase them from other companies and resell them under their brand name. They might be okay, but, I don't use them, personally.
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Mon Sep 18, 2017 3:57 pm    Post subject: Reply with quote

They should ( 2 upstream sensors) should be here by Thursday. We'll see if they make any difference for me. I'm feeling optimistic about the sensors being the issue. Fingers crossed. I'll be going on a camping trip this weekend so it will be a good test.

Thank you for all your help smj. I'll post an update after the weekend.
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Wed Sep 20, 2017 7:15 pm    Post subject: Reply with quote

My O2 sensors came in a day early, replaced them (both upstream) and took her for a quick test drive. She's definitely running smoother but seems like I should have more power. It did stall on me once I got home, parked and let the engine idle. I'll know more when I go on my camping trip this weekend.



Here's what they look like. A bit charred but not sure if that means anything. They also look original.
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Merrix



Joined: 19 Jan 2017
Posts: 12

PostPosted: Mon Feb 12, 2018 10:12 am    Post subject: Reply with quote

I'm revisiting this page as I'm still having the same issues with my idle and stalling. I've recently replaced my fuel pump and still having the same issues. Could my issues be a faulty EGR valve?
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