p0171 code (lean bank 1)

[sternzy]

After researching for a week or so I haven't really found a definitive answer for the p0171 code (lean bank 1).

The actual symptoms of this code are presently rough cold starting. Throttle response seems excellent once it is warmed up, though the idle can be a little rough it is nothing that say a novice would probably even notice.

After looking the car over this past week and learning all the functions of my code scanner and such, I have noticed a few things...

Cat, and o2 sensor monitors are n/a even after an hour of driving. Now I'm guessing the cat monitor being n/a could be directly related to the o2 monitor not being available.

After reviewing the live data on my Actron 9180 I have found that at a flat idle my o2 sensors look like this, through the entire 35 frames or so:

o2s11 - 0.000
o2s12 - 0.240
o2s21 - 0.000
o2s22 - 0.250

11 and 21 do fluctuate when the idle is revved but still lower then spec I believe. Am I understanding this correct in that i have two bad sensors, and two others that are on their way out? It seems to me that an o2 sensor should not read a flat 0.0 even at idle. Out of 34 snap-shots at flat idle those 0.0 numbers did not change at all.

I will do a 2k RPM snapshot tomorrow. I think I have a good idea of what they should be reading now after reading a Nissan PDF. In the mean time I am am curious what you all think about these numbers.

I have cleaned the MAF, and for the data recording it averaged 1.8 - 2.0 throughout the recording at idle. I also cleaned the air filter, and will be getting a new one, along with a new fuel filter tomorrow before I get into buying new o2 sensors.

Two other things I should mention:

First, the air duct on this car is a mess. The air-box containing the filter is fine, other then the dry rotted seal that attaches it to the scoop. Is this air-duct a priority to repair? The entire rest of the engine compartment looks immaculate, but for some reason this intake scoop is a mess.

Second, when reeving the car from under the hood I can hear a suction noise coming from somewhere around the bank one side, though as hard as I tried I couldn't pinpoint where it was coming from. For all I know this could be a normal noise the coming from the intake as more air-flow is being sucked into the system. I did read about a bad intake gasket on these cars though so i thought I would mention it, where I am having a lean condition.

Thank you in advance for any help!

P.S. Is it possible to still buy after market MAF and o2 sensors which are OEM and do not require a dealer ECU reprogram? If so what differentiates the two separate models? Maybe an "a" or a "b" in the part #?

[loystock]

Welcome to NICO.

Do not buy any replacement component yet until you have identified the cause of the problem. P0171 (lean fuel injection system, Bank 1) simply means the air-fuel ratio is too lean that the ECM can no longer compensate due to very large error. It can be caused by air intake/exhaust leak, defective front O2 sensor, bad fuel injectors, low fuel pressure or even a dirty/faulty MAF sensor. But based on you description, this is due to air intake/vacuum leak in Bank 1. You have to check the entire air intake - from filter box all the way to the plenum. You might as well check the exhaust manifold, especially at the joint.

An O2 sensor is not used during cold starting (open loop). The O2 sensor only cuts in (closed loop with ECM) once the engine has warmed up and coolant temp has exceeded 158F/70C. So the cold starting issues is also due to intake leak.

A good O2 sensor should transition from 0.45V (ideal air-fuel mixture of 14.7:1) to >0.6V (Rich AF mix but low O2 level) and <0.35 (Lean AF mix but high O2 level). When there is an air leak, too much O2 is enters the system so there is not enough fuel to consume the oxygen during combustion, resulting into high level of O2 at the exhaust as detected by the O2 sensor, This is the reason why both Bank 1 sensors are showing low voltage levels (lean AF mix, high O2 level).

[sternzy]

Thank you very much for the reply stock.

I think I'm going to just buy all new gaskets from the intake manifold out to the throttle body. Pretty cheap, and I really cant think of any way I can test those area's to see if they are leaking. I did spray visible area's lightly with starter fluid and got nothing, but as you know on this car some area's you just can't check without removing the intake.

I guess I'll check compression first to see if I have any problems under the head, thanks for your help.

P.S. I don't know if it means anything....but with the scoop(duct) removed I can put my hand rite over the air box opening and it has virtually no effect on the engine, unless you rev it, and even then it just slows it down a little. So I'm wondering, where is the air coming from when I block it? Got to be a leak somewhere.

[loystock]

If you could take the air scoop out, then you should be able to remove the air intake. A screw driver, 10mm socket, and a ratchet drive are all you need to get it out. Undo the 4 clips of the air filter box, disconnect the MAF sensor (push release tab until it clicks), disconnect 3 rubber tubes then loosen the clamp to the Throttle Body. You may have to remove bolts and a bracket in order to pull out the air intake. Then you can inspect air intake, the rubber tubes, air filter box and even the throttle body-plate. Gaskets are used on the IACV and the TB coupling to the intake manifold. With the air intake removed, you can also check other components and the intake plenum and connections for any sign of leak.

[sternzy]

I took air induction all apart and reassembled it making sure everything was secure. After doing so I took the vehicle for a 20 minute ride and no light came on. Today I started it up and warmed it up to operating temperature, still no light (yet), nor a pending light.

However, the car still has cold starting issues. You start it once, it starts rite up, then slowly sputters out and dies. Start it a second time and it slowly sputters, and will eventually pick back up and run fine. I am assuming once the o2 sensors heat up and take over the idle procedure the vehicle then runs well.

This leads me to believe ether the TPS, or the IACV is defective or dirty. There is a loud whirring noise that happens briefly when you first start the car, which sounds like it is coming from the area of the throttle body, could ether of these items be making this noise and indicate a fault in one or the other?

[loystock]

The IACV is operated by a stepper motor with driver (power transistor) inside the ECU. It's just downstream of the throttle body, near firewall. A defective (shorted) stepper motor can kill your ECU. Better check the resistance, @ 30 ohm per winding I am not exactly sure about pin assignment - 2-1, 2-3, 5-4 and 5-6 is what I remember. There is an IACV servicing procedure available in the FAQ 'sticky - lost of info there.

[sternzy]

I pulled the IACV out of the housing and tested it according to the haynes manual. All tests returned 20ohms. Doesn't look like you can tell much from them, but I took a couple of pictures. There does seem to be some carbon buildup.




So I'm wondering if 20 ohms is within spec, or if it's possible my ohm meter is off by 10 ohms? I heard they can be fairly inaccurate, but off by 1/3 seems a bit much.

P.S. Haynes manual calls for 30ohms between all listed prongs to be checked.

[loystock]

It should be 30 ohms. Get/borrow another tester if you have doubts. Over time, carbon builds up on the IACV so cleaning is recommended.

[sternzy]

After putting it back together, and also cleaning out the the TB (what I could reach), and letting it sit over night with the negative terminal detached the car is now running terrible.

I tried the following procedures and could not get the cel to blink or anything after about 30 tries:
http://www.technosquareinc.com/350reset.htm

I uploaded a video of what the whirring noise sounds like that I was talking about. You can hear it starting with the second start attempt. As you can see the car is having a horrible time :p

[youtube]http://www.youtube.com/watch?v=uX7ZVkHlJbI[/youtube]

Rite now I have both the negative and positive battery terminals disconnected while I check to see if Napa can test the IACV for me if i take it down.

What seems sort of ironic here is the more I clean, the worse it runs

Thanks again for all your help ^.^

[sternzy]

Replaced the MAF sensor today because after inspecting it I noticed there was no wire on the side of it. Car runs 100% better now (so far).

Took it for a 20 minute drive, no codes or pending codes. All thats left is the three remaining monitors to complete.

Oxogen Sensor Monitor
Catalyst Monitor
EVAP sys monitor

Even if just one of these complete I can get it inspected. Hopefully these items just take awhile to complete 8)

[loystock]

I hope the problem is fixed. We focused on other areas since you mentioned that you cleaned the MAF and took voltage measurements. Your origianl voltage reading was higher than normal at Idle but approximates the voltage at 2500 RPM.

If you want to complete the SRT (System Readiness Test) and set all parameters to READY STATE, you have to do the following:
-Start the car and run at Idle for @ 2 mins (ECU goes in close loop mode once engine warms up).
-Take it to the highway and drive at steady speed of 53-60 MPH for 10 mins or more. I know it's difficult as I usually drive over 75 MPH on a highway. I think you can go up to 65 MPH.
-Take it back to city streets and drive at 30-35 MPH with at least 5 COMPLETE STOP and GO for 6 mins or more.
-Go back to the highway and drive at 53-60 MPH for at least 3 mins.
-The actions above should complete the SRT or at the very least leave you with 2 parameters in NOT READY status which is acceptable in most states, provided the CEL is off, and of course the emission levels are good.
BTW, drive the car for a while (do several WOT but you don't have to overspeed) before taking it for inspection. A bottle of Redline SI-1 Fuel Injector System Cleaner may also help.
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