o2 sensor

Good evening,

I doubt the issue is the sensors. They are just telling you rich and lean. That fuel mapping is controlled by the ECM.

You should check some thing first.

1. Fuel pressure, Make sure you have correct fuel pressure. Low pressure will cause that reading.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

2. Verify exhaust back pressure. Check the pressure to be sure you do not have a blocked cat converter.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

3. Engine timing. I would check the timing belt to be sure it is not slacked.

https://www.2carpros.com/articles/how-a-timing-belt-works

Roy

Thank you for your response.
i don't have catalytic converter and also don't have any codes storied in ECU.
i have checked fuel pressure before change o2 sensors and it was fine.
Last thing is timing. i think if it was timing it could be permanent not temporary problem because i can acceleration good but a minute later it goes bad again and it repeats.

What was the fuel pressure?

If you do not have cats, then the light should be on unless you have some kind of bypass.

Roy

it was about 50 psi.
I'm using o2 sensor spacer for downstream and there is no problem with that and no check engine light or pending code.
I'm troubling with sluggish acceleration now and its intermittent for example when stop at lights then try to accelerate its good but a while after it goes sluggish like its regain its power and lose it.
i have checked everything but find nothing also replace MAF sensor with new OEM one.
Update:
Today i test it first it goes to close loop very soon i mean when coolant temperature was about 40 degrees.
second i have unplugged both upstream sensors and car accelerate so much better, but i can't believe if my new o2 sensors is defective as well as my previous o2 sensors.
i should mention one more time that there is no check engine light or even pending code in my ECU.

Okay, the down-streams have no effect on the running anyway.

Do the other 2 checks I suggested and let me know.

Roy

Thank you.
You said 3 things include fuel pressure, catalytic converter and timing.
about fuel pressure as i said it was about 50 psi. for catalytic converter i don't have catalytic converter on my car because i removed it. i did timing about 30k kilometers ago and didn't have any problem since.

As i mentioned, today i unplugged my both upstream o2 and see lots of difference in acceleration, but i don't know what's wrong because they are new and also OEM.

When you did that, the ECM went to a default mode or open loop. That is why it ran better.

Like I said in the beginning, the sensors are not the issue.

You have a control issue.

Do you have a scan tool that can read live data on all the sensors?

Roy

i have torque app on my phone and except crankshaft and camshaft sensor i have checked almost all sensors in my car and they are all in good shape i think, but i can record a video from my sensors data if you want,

What are the long term trims on the upstream O2 sensors?

Roy

i have reset my ECU yesterday but before that it was at 0.
sometime i see that it goes to -0.8 and -1.6 (i mean 0.8% rich and 1.6% rich) but never stuck for long time on each one and fluctuates between this 3 percentages.

You do not have a vacuum leak.

I would not dismiss the timing belt either. I would still verify.

Roy

i think if it timing problem it would be permanent problem, but i haven't any noise or idle problem and still i think unplug o2 sensor can't affect timing problem.
what else could be the problem?

Again, I would not assume anything. It still needs to be verified.

Injectors could also be an issue but that should have shown up on the long term trims.

Roy

Then you think it is timing problem?
i have a p0335 code once that occur with a hiccup but after that it never shows again. i have checked crankshaft position sensor after that but it didn't seems bad at all.
this problem makes me crazy for longer than one year.

Seem bad? How did you check it?

Possibilities below.

Roy

It doesn't seem fried or damaged or anything else and its fault code didn't show up again.
i have checked everything i can find in the engine including:
TPS
MAF
Intake air temperature sensor
Coolant temperature sensor
Injectors
Ignition coils
Spark plugs and wires
Fuel pump and filters
But nothing. I mean there was no codes. checked their resistance with dvm or their values and live dates on torque app.
the only thing that didn't work normally was o2 sensors that i changed them.
but one strange thing is my long fuel trim is the same as before o2 sensors change for both banks even after o2 sensors changed and reset ECU.
just one thing changed in car behave
with my previous o2 sensors when i started engine from cold start sluggish acceleration was permanent unless i restart engine after restart engine, that sluggish acceleration was gone completely.
but now it's comes and goes even after restarting engine.

Again, the O2 sensors just send a signal to the ECM for fuel mapping.

They were never the problem. They did there job.

Visual checks of the sensor are not checks. Its actions are what needs to be checked. One of the checks is alignment of the cam and crank pointing directly at the timing belt.

Roy

So the timing checked everything was aligned and right. now what do you think?

Was the belt loose? Was the tensioner tight?

Roy

no the mechanic, checked the belt and tell me nothing is wrong about timing or belt.

Okay, something was missed somewhere.

Let me review.

Roy

thank you for your quick and accurate responses.

You are welcome.

Always glad to help.

Roy

do you think bad ground could cause this situation?

No I am going in the direction of mechanical.

I'm searching every where in last year i can tell i have read almost every forum and topic about sluggish or poor or slow acceleration. but i can't figure it out if it's timing. so why there isn't any rough idle or misfire or engine noise ?

if it's fuel pump why fuel trims are about 0 and why it's intermittent like something regain and lose?

it is my spark plugs.

Timing does not necessarily end with rough running especially if it is off maybe 1 tooth.

Fuel pressure will be seen on long term trims.

Did you check compression?

Roy

Did you respond? I got an email but nothing came up on my message board.

Roy

no i just read your respond now.
i didn't check compression. do you think it could be problem?

It needs to be checked.

Roy

but before that can you help me to check timing mark by myself? because I don't trust the mechanics out there.
do i need to rotate engine?

Once the cover is removed. hand rotate the motor until number 1 is lined up on the crank pulley as in the photo I attached.

Then look at the cam gears that I attached as well. They need to be exact.

Roy

do i have to remove crank pulley to rotate engine? or i will hand rotate crank pulley?

You can hand crank the engine with the pulley attached.

Roy

thanks. if you find anything else please tell me to check that. thank again

You are welcome.

Roy

Do the problem isn't timing either. don't you think an intermittent problem like this could be a sensor related?
because i think mechanical one couldn't be intermittent and when something mechanical damaged it's not working correctly until repair it. could a fuel pump get weak intermittently or a fuel filter get clogged partially? i don't know any more.

Not a sensor at all. It would code when out of its parameter.

Yes to a fuel pump but you would need to monitor the pressure while driving and when the issue happens.

Roy

Okay, i have a spare fuel pump and change it soon. but the question that remain is if it's fuel related why fuel trims are about 0?