Bad acceleration

[QuestMan]

A few weeks ago I got a strange issue with my Nissan quest. It became difficult to start when the engine is hot. It feels like you are starting to engine with the almost fully discharged battery. With time new symptoms added. The first of them is a crackling noise at high RPM when you are moving uphill or need to accelerate. I also have two error codes, the first one is Evap very small leak and the second one is P2A00. With time that crackling sound shifted to lower RPMs and my van started to accelerate very slowly. The engine growls but sounds rude and doesn't show the required acceleration. I tried to investigate this problem and found an interesting moment: when I hold RPMs at the same level (3000-3500) after 10-12 sec the car starts to move with slight jerks. I need help on what side to move to find a solution to this issue. The fuel consumption also increased to 15.2 mpg from 16.2 mpg.
p.s. When the gear is in P mode, the engine easily increases RPMs to 5000-6000 without any scary sounds. The problem is observed only when driving.

Thank you

[VStar650CL]

P2A00 by itself is almost always either a bad A/F sensor (front O2), an exhaust leak near the A/F, or a bad fuel injector. In this case it's your rear bank (b1). Unfortunately the code doesn't tell you whether the sensor output is shifted lean or rich, but you can stream that for yourself. The A/F sensors are widebands with a 1.5V nominal voltage, so they function very simply, above 1.5V is lean and below is rich. They'll generally read high until the engine warms up, but once warm, both banks should behave very similarly. Yours probably won't, if it reads constantly rich then chances are you have a leaky injector, if it reads constantly lean or near 0V then chances are it's a bum sensor. If it reads more or less correctly then the ECM is probably flagging it for slow response, so check for exhaust leaks or an out-of-spec rear O2.

[QuestMan]

Thank you for your reply. The graph for both b1 and b2 sensors are listed below.

[QuestMan]

B1 is blue

[VStar650CL]

It's hard to tell anything from that without also seeing either throttle position or RPM, but bank1 looks to be over-responding slightly rich and not spiking as high lean, so that might be an injector issue or a slow sensor. It does make an exhaust leak unlikely.

[QuestMan]

Just curiosity. How can I prove the bad sensor or leaking injector? what will happen if I turn off the oxygen sensor? Will I continue to see all symptoms?
I had other possible reasons and bad fuel pump also may match with them (bad start when the engine is hot and jerks at high RPMs) or an incorrect coolant temperature sensor or Intake air temperature sensor (the air looks too hot).

[QuestMan]

[VStar650CL]

I'm not sure there's a definitive way to prove it, but if you look closely there are parts of the graph at low speeds where the b2 sensor is tracking much closer to the engine speed than b1. My best guess is that's what the ECM is flagging, that the b1 sensor response is laggy at drop- and part-throttle. That isn't really what you'd expect from a leaky injector. How do your STFT's look, is b1 significantly richer (more positive) than b2? If they're about equal then I'd say definitely try a sensor first.

[VStar650CL]

Come to think of it, do you have a freeze frame for the code? That should show the A/F voltages, STFT's, and injector p/w's at the moment the ECM flagged the failure. That could tell us a lot.

[QuestMan]

Unfortunately, my OBD doesn't have STFT or LTFT indicators, but it has others. Could you see them? I tried to select the same region. Unfortunately, the app doesn't allow to increase the font...

[VStar650CL]

STFT and A/F-alpha are the same thing. Yours is pretty equal on both banks, so I'd say it's likely your b1 sensor is simply dying of old age.

[QuestMan]

Thank you

[QuestMan]

Hi

I am ready to give up with this car.
I replaced today the oxygen sensor, started the engine and it was working perfectly, even smoother than before.
I drove ~20 miles and got a new error code P0171. And the problem again with bank 1 side 1. (((

What is that? bad oxygen sensor or a new issue?

[VStar650CL]

Looks to me like it's the wrong sensor. Nissan uses two types, 1.5V bias and 2.2V bias. The 1.5V type uses a much stronger pullup source, so if you install a 2.2V type, the pullup overpowers the sensor and you read way lean. Your new b1 sensor is reading near 3V and the ECM has run out of enrichment, STFT and LTFT are both at the +25% maximum. That's when P0171 gets thrown, when the ECM hits the limits. If you're sure the sensor is right then it may not be sealing, an air leak right at the sensor body will also cause very lean readings.

[QuestMan]

I bought a Standard Motor Product Oxygen sensor. I checked the data after the installation of the sensor and it was ~1.5V. 3V were gotten during the driving. Close to the house, it showed 1.5V again, but it was 3V again after an engine restart. I will change B2 and B1 sensors tomorrow. That should allow the exclude or prove the sensor issue.

[QuestMan]

Also have a few photos of the "old" oxygen sensor.

[QuestMan]

I also will be appreciated if you would see some data from the B1 and B2 sensors. I took a small drive again. Looks like the voltage is in the normal range, but LTFT and STFT look abnormal. What do you think about this?

[VStar650CL]

Yes, your earlier frame must have frozen the sensor V at a bad moment. However, the STFT/LTFT mean B1 is only reaching normal V with the injectors wide open, where B2 is running normal enrichment. I doubt that represents a vacuum leak, since you say it runs decent. So that leads back to square one, either the sensor is getting extra oxygen from an exhaust leak, or the sensor is reading abnormally lean and the ECM only thinks the bank is at stoichiometry when it's actually very rich.

[QuestMan]

A small update. I have fixed the issue with the oxygen sensor. It was most probably an air leak near the sensors. Unscrewed it and then screwed and now it shows normal values. Drove 75 miles and no errors.

But, I still have an issue with acceleration. The problem begins around 2000-3000 rpm. It looks like the car accelerates normally (relatively normal) in the range up to 2000 but then does this extremely slowly in the range 2000-3000. Moreover, when I held rpm at the same level (~3000) for 10-15 sec I feel like the car starts to jerk, the engine sounds rude. I still need help with this issue.

[QuestMan]

I am considering a few possible reasons.
1. bad camshaft sensor (or both)
2. bad MAF sensor
3. bad coolant temp sensor
4. fuel pump.
5. clogged cat on the Y-pipe (unfortunately, the car is without two main cats)

At 3000rpm it feels like it doesn't have enough to shift the gear, it tries but can't reach the required rpm level.

[VStar650CL]

That sounds like either a weak fuel pump or a partially-blocked exhaust. It would be very odd behavior for a cam or crank sensor, and the car would be throwing codes if the coolant temp sensor was seriously out of whack. The MAF is possible but unlikely, but you can exclude that by monitoring the volume and seeing if it does anything weird at the point where the engine loses power.

[QuestMan]

Bad news. Today morning I got P2A00 again. The same side... I also see 1-2 misfires in all cylinders...

[QuestMan]

And an extra symptom. The engine can't run more than 4000 rpm

[QuestMan]

I got P0726 today. Looks like it is a part of the problem...

[VStar650CL]

That's weird, P0726 is a derivative code (the TCM isn't getting an engine RPM signal from the ECM) and 99% of the time it's because of a cam sensor issue. It's usually accompanied by P0340/P0345, and it's very odd for it to show up alone or with any other codes. I'm starting to wonder if your ECM isn't wacko.

[QuestMan]

During the last drive that car was crazy. I accelerated extremely slowly and it looked like stuck at 2500 and then 3000 rpm (like it was limited by something). The mil light is off. I will replace camshaft and crankshaft sensors...

[QuestMan]

Update.

Yesterday I removed the third cat. It was clogged. Pieces of one main cats were in front of it and blocked the normal way of exhaust gases. Took a test drive and my van has never been accelerated so fast. Even a small touch of the accelerator throws an odometer in the red zone. No strange sounds, jerks or similar but it sounds like a tank (or even louder). I need to replace this part on the muffler or pipe. Do you know the diameter of the y-pipe? 2.5 in?

[VStar650CL]

There's no monitoring on the rear cat unless it's a Cali car, so straight pipe is fine. Many people use a resonator so it at least looks like there's a cat there. Dunno the diameter, though, you'll need to measure. If you don't have a caliper to get an accurate OD, use a tailor's cloth tape measure to get the circumference and then divide by pi (3.14159).