2002 QX4

[osageorange4]

I have a 2002 infiniti QX4 that I am having a issue with. It started about 2 months about. When accelerating from a stop light the engine started misfiring and rattling like it was running out of gas or maybe getting to much gas. I pulled over and shut the engine off. After five minutes I started the engine and it ran like nothing ever happened. Then about 3 weeks later it did it again and I did the same thing and it ran fine again. About three weeks ago it flared up again. This time it ran fine until the rpms reached around 2500 then it would ralttle and loose power. It has gotten to the point that at 2000 rpms it rattles and misfires and I can barely make it up a hill. Any ideas as to what could cause this. I do get a code of P3000 random misfires.

[4xq]

I think I would start by changing the fuel filter and checking fuel pump pressure. It does sound like you are not getting gas, which will cause lean misfires.

There is no schrader valve to attach a fuel pressure gauge to on these - the easiest way to check pressure is back at the fuel filter.

[osageorange4]

Thanks I will start there first and let you know what I find.

[nickelghandi]

I would also try cleaning the mass air flow sensor. It is located along the intake just after the filter. This solved my intermittent hesitating and sputtering issue. You can buy MAF cleaner from parts stores for cheap.

Also could be throttle position sensor or a ton of other things, but start small and easy and work your way up the chain.

[Buzzman]

About three weeks ago it flared up again. This time it ran fine until the rpms reached around 2500 then it would rattle and loose power. It has gotten to the point that at 2000 rpms it rattles and misfires and I can barely make it up a hill. Any ideas as to what could cause this. I do get a code of P3000 random misfires.

If the engine starts to balk at the 2K rpm mark, and won't rev any higher, that usually means it has gone into safe mode, or limp mode.
The truck is sensing a problem, and in order to "save" itself, it will refuse to go over the 2,000 rpm mark.
It is usually accompanied by a SES code.

This happened to me a few weeks ago when my radiator blew, and the engine started to overheat.
It went into limp mode, and pretty much saved my engine.

[osageorange4]

If I just free rev the motor under no load it does not misfire only under load does it have the condition. That is why logic seem to point to lack of fuel. More load more fuel required.

[osageorange4]

Well I changed the fuel filter and checked the fuel pressure. The pressure was good but when I changed the filter the liquid that came out was like gas and dirt mixed together. Kinda black looking. I dont know it that is abnormal. I wonder if that good have made its way to the injectors and clogged some of them

[nickelghandi]

That sounds normal. I just changed mine on Monday and it looked the same way. The liquid came from the side that faces the tank, correct? If so then that is completely normal.
I would now check things like the MAF, the Throttle Position Sensor, and the oil and transmission fluid. I had a lot of issues arise from a bad throttle position sensor. Bucking, reluctance to shift, all kinds of things.

[osageorange4]

Yes the side facing the tank. I took the car to autozone to have them check the codes again. Still the the P3000 random misfires P0037 O2 Sensor bank 1 sensor 2 0159 bank 2 sensor 2. I dont know if the O2 sensor thing is a symptom of the misfires or not. Would the TPS and MAF throw a code if they were bad.

[nickelghandi]

The MAF would throw a code for sure. Usually with The MAF you would see more crippling effects. It sounds like you are in "limp mode" which is what the engine and transmission do to prevent damage if something is wrong. When my TPS was bad, I had a few rough upshifts and then it would go into limp mode and remain in 3rd gear. The TPS might throw a code on its own but I'm not sure, and it could be the cause of your O2 codes if the engine is running too rich or too lean because it isn't detecting the correct throttle position.

[osageorange4]

I still have not figured this issue out. Now when I push the throttle and hold it in a set position the engine will rev a little and go down rev a little and go down. Any ideas

[osageorange4]

I posted a few weeks ago about a ongoing issue that I have been having with a 2002 infiniti qx4 . I have no power going up hills or anytime under load. I can rev the engine all day but under load it rattles and surges. The first time it happened I just shut off the engine and when I started it up five minutes later it was fine. Now it is to the point that if I hit 2000 rpms it rattles and surges. The weird thing is if I start the vehicle when it is cold and take off it will hit 2500 rpms with no issue then will rattle if I attempt it again.

[Rogue One]

Sorry to hear you haven't resolved your problem yet. I noticed you created a second thread for this topic, so I've merged the two. This will cut down on confusion, and duplicate postings.

[4xq]

This still sounds like a fuel issue, but it could be sensor / electrical.

Rev the engine as best as you can, and as it cuts out, spray starting fluid down the snout. If it revs higher and smooths out, recheck fuel pressure with the fuel pressure regulator hose disconnected. Minimum pressure is 43 psi with the hose disconnected, 34 with the hose connected.

If starting fluid does not help, then its probably sensor related.

[osageorange4]

Thanks for the input I will check the fuel pressure today. Let me be more specific about the revving. If I hold the throttle steady the rev fluctuates if I rev it up and down it does fine. I am not sure if you read the whole post but it does throw a few codes. Do you know where I would put the gauge check in to check the pressure

[4xq]

You have to test the fuel pressure back at the fuel filter. There is no schrader valve under the hood to connect to unfortunately. The "rattling" sounds like engine knock you get from lean fuel mixture. So I think checking for a fuel problem is a good idea.

I had a p0159 a couple of years ago - it had no affect on engine preformance. It is the sensor after the CAT that monitors CAT efficiency. Replacing the O2 sensor fixed it. It is kind of hard to thread the new wire and connector up between the firewall and the back of the engine. I used a coat hanger - stuck it down to where I could tape the new connector to it, and pulled it up with the coathanger. The new wire / connector should ensure p0037 gets fixed.

Check Advance Auto if you have one close - you can often find a good coupon on retailmenot which makes their prices pretty decent.

[osageorange4]

Thanks

[osageorange4]

I wasnt able to get the fuel pressure checked today because autozone did not have the right one and there loaner was out. I will get it Monday when it comes back in. I was able to look at one of the O2 sensors though. I pulled the rear bank one and compare it to the other rear bank sensor. The one that the code came from sounded like a baby rattle. The other nothing when I shook it. I am assuming it is broken inside. Both sensors that coded are on the same side of the engine. I wonder if that could be part of the issue. Any thoughts.

[4xq]

P0037 - HO2S Heater Control Circuit Low Bank 1 Sensor 2
P0159 - O2 Sensor Circuit Slow Response Bank 2 Sensor 2

I guess I need to read a little more carefully - I read your post as sensor two on the same bank. My goof there.

You are getting codes from the rear sensors on both banks, your front sensors are not coding.

I'm guessing the "baby rattle" sensor came from bank 1 throwing the p0037 circuit code. I would replace it.

The p0159 code can be several things, one of which is low fuel pressure. Check here: http://www.nissanhelp.com/diy/obd_codes/P0159.html

Have you run some good fuel injector cleaner thru it?

[osageorange4]

So I checked the fuel pressure today and it is at 45 with hose disconnected and 38 with it connected so it seems I am good there. Put some lucas fuel injector cleaner in it today to see if that has any effect. Any more ideas

[osageorange4]

I also just check continuity of all the coil packs and need to see if they are in speck. All the readings are nearly identical. I also looked at the plugs which I replaced when the issue first occurred but my with NGK. I made sure they were gaped at .45 . I got everything back together and when I first drove it it reached 3200 like nobodies business then it started mis firing again. Do I need to get NGK plugs?

[osageorange4]

so the reason for the mis firing again was the fact that 3 plug fowled out. All on the same side of the engine. They were completely covered in black carbon.