02 Sensor/Fuel Sensor/Fuel Systems Circuit Operation

[chunkygoat]

I am looking to learn how the O2 sensor, fuel sensor, air intake, fuel injection, and ECU interact with each other. Specifically - the electrical conditions that occur and the function/effect of the ECU on this system. Any insight, advice, or resources available would be greatly appreciated. I am not quite sure where to look for this information.

This may not be the best place to post this, but I figured I'd give a run at the Electrical section of the FZ forum to see if any of our knowledgeable members here have any insight to the operation of this system.

To put my question here into context, I have been having idling issues with my Honda civic. It seems that when idling, or coming to a stop, or even during the shifting of the transmission when RPM's are dropping - my car idles very low: sometimes as low at 420RPMS (just above stalling RPMS). My check engine light throws a few different service codes varying from:

System Running Lean
Low Fuel Rail Bank 1 Pressure
02 Sensor Malfunction

I have narrowed it down to a few different possibilities including: 02 sensor, fuel pump, or the idle air control valve.

In attempt to better understand what is occurring here, I purchased the OBD2 bluetooth sensor and the torque app. I have been closely monitoring the O2 sensor voltages, battery voltage, fuel pressure, as well as readings coming from the fuel sensors.

What I have determined, is that I have zero understanding of the interaction between these sensors, the ECU, and the actual air intake and fuel pump. What I am looking to learn, is the electrical conditions of the sensors during normal operation. Do the voltages of the O2 sensors sit high while little air is flowing - then drop down close to 0 when the airflow to the intake begins to increase?

Same question regarding the readings from the fuel sensors. What are normally operating voltages for the O2 and Fuel sensors? Also, how does the ECU react to these readings?

The best I can tell, is the O2 sensors read somewhere around 8v when stopped. As soon as I begin moving, voltages of the bank 1 and bank 2 sensors drop to between .2 and .8vdc. Is this normal operation? I also noticed a slight deviation between the O2 sensor bank 1 and bank 2 voltages. Is this expected or should they be reading close to similar values?


Any resources that have taught any of you this information would be a great start. If anybody has any in depth knowledge of this circuit or any information related to the analysis of the interaction between these components would be of tremendous help to me.

If there is anything I missed - please feel free to ask.

Thanks in advance for any insight anybody has for me.

-Matt

 

[TownsendsFJR1300]

You should be able to plug it in (for free) at most any parts store for a diagnostics test.

Once connected to their machine, it should show what the likely sensor /issue is.

I know on alot on the older american made cars (Japenese, don't know), the O2 sensor will throw a code...

The idle air control valve tends to carbon up, nothing some carb cleaner can't ususally fix..

 

[Motogiro]

There's also a mass air flow sensor that is in the picture that cause issues. Sensors can range anywhere from Hi/Lo logic state to decyphering radio frequency range signals to error amplification to simple low voltage DC. Although the code hasn't been thrown, TPS?

I needed to know what my old 4 Runner was doing when it was lighting the CEL so I found one of those OBD ll readers and an app for my phone to help me narrow it down. I think I remember it being 24 bucks for the OBD ll reader a 4 bucks for the app.

As always don't discount the simple stuff like vacuum lines and connectors.

 

[FinalImpact]

^^ Sounds like he has an ELM blue tooth and Torque. If you don't have torque pro, pay the $5 bucks and get it.

Voltages from the 02 output are 0 to +0.8, sometimes 1.0V, but there is more behind the scenes than that. Because its a V6 you can compare banks and they should be doing basically the same thing.

You said bank1 and bank2 so I assume V6. The lean code is often times a break in hose. If between the air filter and MAF or MAP sensor there is an accordion flex hose to the Throttle Body, check the hose for cracks. Its the number one cause of lean code as it introduces unmetered air into the engine if cracked. TAKE IT OFF FOR INSPECTION! Sometimes its because of a broken engine mount allowing the engine to move further than it should.

I have Tq Pro and some key ingredients to log would be this:
Engine load, RPM, Throttle position, STFTB1, STFTB2, LTFTB1, LTFTB2, Vehicle Speed, and ignition advance.

With that info we can get a look at what its doing. Its late and I need some shut eye.

Most common issues;
Busted hoses and vacuum leaks.
Dirty MAF sensor.
Fail ignition - Coil On Plug (COP)s tend to arc over internally.
If its old enough to have Idle Air Control its not Throttle by wire so cleaning the sludge from the IAC valve can really help idle issues.

Also, read the Yamaha blurb on FI. It is not so different than your cage. Same concepts. We can go into more detail later...

 

[FinalImpact]

OK - adding on to what I posted there;

Like our bikes the car has map table the ECU/ECM reads from for baseline information. Its goal is basically to maintain stoichiometric Air Fuel Ratio of 14.7:1 so the catalytic converter operates efficiently.

It does this by sensing all of the inputs to determine the calculated load or amount of work the engine needs to do and how much fuel it needs to do it. So using the throttle position sensor (TPS), engine speed (RPM), ambient temperature and pressure as well as engine Air Inlet Temperature and manifold vacuum, Engine Coolant Temperature (ECT), combined with Mass Air Flow Sensor (MAF), the ECM uses a look up table or map to determine how much fuel, ignition advance and likely valve timing advance to give the engine under various conditions.

The long and short term fuel trims work something like this. Based upon the default fuel map the long term fuel trims work with the table to make corrections based on sensor data to offset the Read Only Memory MAP table. It stores this information and when the conditions are applicable, uses this learned data to determine what adjustments to make for say steady state fueling like at cruise. The short term fuel trims come into play when the nail the throttle and the ECM needs to make instant fuel trim decisions and maintain stoichiometric Air Fuel Ratio. So based upon what the Sensor 1 O2 readings are, the ECM can correct up to +/-20% of the long term fuel trims.

I didn't read these in detail but google "understanding fuel trims"

What are fuel trims all about?
http://www.magnaflow.com/07techtips/TechBulletin/TB80010.pdf

Understanding Fuel Trims - Long Island Catalytic

Post up some actual data and lets see what you have going on.

 

[chunkygoat]

FinalImpact,

You sound to have nailed it on the head here. With the exception that it is a 4 cylinder - everything you have said fits in perfectly with what I have experienced thus far.

I am in fact referring to the ELM OBDII and I have purchased the Torque Pro app (which, I can vouch, is WELL worth the 25 total dollars). Funny you say a cracked hose running from the MAF/MAP to the Throttle Body many times caused by a broken engine mount. Well I had replaced the engine not even 2 years ago. Because the motor we put in was not the same year, the bolt patterns for the motor mounts did not line up perfectly. There is still 1 mount broken mount that I, myself, have not gotten to fix yet.

Thank you much for the detailed operation between the sensors and ECU. I will try to log some information today for the fuel trim short term, fuel trim long term, banks 1 and 2 o2 sensors, throttle position. I will also track a scatter plot of engine load (y) to RPMs (x) if this helps.

I really want to inspect this hose to the throttle body, I think this sounds like a very valid and possible issue caused by the broken motor mounts, which I have had in the past.

Regarding the O2 sensor, I do know that bank 1 is what usually gets the code when the ECU throws the O2 sensor code. Looking at the voltage over a period of time graphed out - bank 1 looks to be sporadic and inconsistent. I see peaks as high as 12v and lows as low as .2v. The graph under test results when graphing O2 bank 1 voltage depicts a very clean looking SIN wave underneath the actual graph, but doesn't explain. It appears they suggest the O2 bank 1 voltage bear some resemblance to a SIN wave?

I will shows some graphs later, and I will preface this with the fact that I have replaced both O2 sensors, so unless something is damaging them which I find to be unlikely - I want to lean (pun?) away from changing the O2 sensors again until it is my last choice.

I will graph some of this information out later today if anybody wants to take quick look and see if they spot something that stands out that I have overlooked.

 

[FinalImpact]

I dont have time to fill in all things but lets clear this up. A V6 for example is bank 1 sensor 1 (ahead of precat ~ 1998 and newer), then bank 1 sensor 2 is after the pre-cat but ahead of the main cat.
Bank 2 sensor 1, bank 2 sensor 2 followed by bank 3 as the main cat.
So your I4 bank 2 is the main cat. What year and model? Does it have dizzi or coil packs? Is it vtech?