2004 Honda lean condition

I live in Japan and own a 2004 Honda Inspire with just over 100,000 kms. The car manuals are in Japanese so I am having trouble narrowing the problem down. The engine is a j30a V-6. I am currently experiencing a lean condition on both bank 1 and 2 but more promenant on bank 1. I have inspected the pcv valve and conducted a vacuum check to no avail.

Some questions:
My short term fuel trim on both banks never approach 0 and generally stay at about what the long term trim is at. Also, the EQ stays around 1.0. Shouldn't the EQ be above 1.0 due to the lean condition? Is this an indication of a faulty or dirty sensor?

As seen in the data below it looks like the downstream o2 sensors control fuel trim. Am I correct? The upstream sensors are labeled as "air/fuel ratio" sensors when I look up the part numbers and the downstream seem to be standard o2 sensors.

I did view the data at open throttle and it seemed like the sensors went rich then lean upon deceleration and the short term fuel trim good down slightly but not significantly. Lastly, I am not experiencing any noticeable lack of power or idle issues. Thank you for any information you can provide.

Respectfully,
Stumped

C_CNT - 0
FUELSYS1 - CL
FUEL SYS2 - CL
LOAD_PCT(%) - 26.3
ETC(F) - 181
SHRTFT1(%) - 21.9
LONGFT1(%) - 19.3
SHORTFT2(%) - 16.4
LONGFT2(%) - 10.2
MAP(IN/HG) - 7.7
RPM(/MIN) - 658
SPARKADV - 10
IAT(F) - 129
TP(%) - 13.7
O2S - B1S12--B1S12--
O2B1S2(V) - 0.400
SHRTFTB1S2(%) - 24.2
O2B2S2(V) - 0.670
SHRTFTB2S2(%) - 14.3
EQ_RAT11 - 1.002
O2S11(mA) - 0.031
EQ_RAT21 - 1.002
O2S21(mA) - 0.000
TP_R(%) - 2.4

Hey there jrainey1981! I'll take a shot at your questions. :silly:

jrainey1981 wrote: My short term fuel trim on both banks never approach 0 and generally stay at about what the long term trim is at. Also, the EQ stays around 1.0. Shouldn't the EQ be above 1.0 due to the lean condition? Is this an indication of a faulty or dirty sensor?

Equivalence Ratio staying at around 1.0 is a good sign, as this indicates a stoichiometric mixture. The upstream air/fuel ratio sensor readings of nearly 0mA confirm this.

If your lean condition was on one bank only, I'd say maybe you have a bad upstream sensor? But you're lean on both banks, so I'd say we need to search for something common to both banks.

As seen in the data below it looks like the downstream o2 sensors control fuel trim. Am I correct? The upstream sensors are labeled as "air/fuel ratio" sensors when I look up the part numbers and the downstream seem to be standard o2 sensors.

You're looking at these PIDs, right?

I'm not positive about your Japanese market vehicle, but in the US market, these PIDs are misleading at best. Usually they're flat out wrong. :lol: I wouldn't place any value on those PIDs at the moment.

The downstream sensors definitely do have SOME fuel trim control, but it's not my initial first thought. If you want to be certain, you can try disconnecting both downstream sensors and rechecking your trims.

I did view the data at open throttle and it seemed like the sensors went rich then lean upon deceleration...

I take this to be an initial good sign for the fuel delivery and air/fuel ratio sensors.

...and the short term fuel trim good down slightly but not significantly. Lastly, I am not experiencing any noticeable lack of power or idle issues. Thank you for any information you can provide.

Also an initial good sign for the fuel delivery system, IMO.

They don't sell the Inspire in the US, unfortunately. I need you to let us know if this car has a MAF sensor or not. It makes a difference in our list of suspects, and the next easiest test to do.

Thanks for the quick reply Tyler and during the Superbowl no less. A honda inspire is basically a V6 Accord. I think the engine may be a little different because I have a hard time finding information in English.

I will definitely try disconnecting the o2 sensors and reporting the difference.

The other thing that is making the diagnosis more difficult is that the short term fuel trim never goes towards zero...

Thanks again!

The car has a MAP sensor only and sits on the throttle body just after the plate.

...Superbowl? :huh:

Kidding! I'm just not big on football. Maybe I'd watch if the Chiefs made it?

Thanks for confirming the lack of a MAF. Truthfully, having one would have made this diag easier. :silly: The speed density Honda systems very rarely run lean, in my experience.

While you're rechecking data after disconnecting the O2's? Have a look at the MAP PID with the key on but engine off. That'll be the barometric pressure reading, and (should be) equivalent to your altitude above sea level. Mostly checking to see if the MAP is reporting correctly.

Ok, MAP is approx barometric pressure.

I disconnected b2s2 and the short term fuel trim stayed at zero. Got a check engine light and the smell of gas was overwhelming so I shut off the car. Only ran the car for about 1 minute but bank 1 short term fuel trim was already at 9.3. Spark advance was at -7degrees of that helps...

The engine seems to lack fuel severly, on both banks. It's so severe that for that very reason the stft can not get anywhere close to zero.....

Do you have data on other than idling condition? What happens at higher rpm and/or at full load?

How about fuel volume and pressure?
It might be something simple like dirty injectors or fuel filter. Not sure wether your car features an in -line filter....if i does not then the in-tank strainer might be clogged.Could you take an amp reading of the fuel pump?

I have a 2006 Honda Stream We get a lot of Jap imports in New Zealand.
I checked live data in mine the other day and the front oxygen sensor controls fuel trims full time while the rear sensor occasionally makes an adjustment, I imagine if the CAT can't keep up???.
I have seen mention of the "rear sensor takes over if the front sensor fails" but don't know much more on the subject.

@juergen.scholl Unfortunately I purchased a cheap scan reader that doesn't do the neat graphs (hindsight is 20/20) Below is the scan data for idle, 1500rpm, 2500rpm and driving. I looks like the short term fuel trim for bank 2 goes to a more normal number and bank 1 goes down but still stays a little high. I am going to need a little time to procure a fuel pressure gauge to test the fuel.

I have attached the document to process the information a little easier


@Desmond6004 I also believed that was how the O2 sensors worked here too but when I saw the scan tool data I started to question myself. I don't know too much on the subject either...

Thank you for the data! No worries about the graphing - your spreadsheet works perfectly for what we're doing.

Bank one is stubbornly lean! :lol: Bank two gets somewhat better off idle, but not better enough. I'm with Juergen about a possible fuel pressure or clogged injector problem.

Proving it will be difficult without changing parts. If your fuel pressure is good, then you'd need an injector balance tester to find which injectors are flowing less than the others. You'd also have to remove the upper intake to get to the injectors on this engine. It's not hard to do, just inconvenient. :silly:

EDIT: Here's an example of an injector balance test, if you haven't seen it already:

Thanks Tyler. I ordered the items needed to test the fuel pressure and conduct the injector balance test. Hopefully I can finally get some clarity on the situation. I will update the post as soon as I have anything worth posting. Thanks again!