Civic Code 45

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#11

01-17-2008, 04:53 AM

JimKueneman

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RE: Civic Code 45

Quote:

Thanks for sharing your interesting data. Were the O2 sensor readings above taken only on the drive to work, which didn't throw the CEL. Did you happen to take readings on the way home when the CEL turned ON.

The DVM has been connected and on for the last 3 days. When the CEL comes on the sensors run at 800mV and 700mV fairly steady. Clear it is going into a preprogrammed mode. The exhaust smells quite rich as well. I have been clearing the code within 5 minutes and it jumps right back to the values I wrote before in closed loop.

I have been struggling with the difference between the primary and secondary sensors. The primary reads 100mV higher all the time. SovXietday may be right. If the sensor has shifted up a few hundred millivolts then the ECU will think it is running too rich and lean it out to try in compensate.

I am going to try to load the sensor a bit with a resistor to fake it back down a few hundred millivolts to see if it helps.

Jim

#12

01-17-2008, 08:52 AM

RonJ

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RE: Civic Code 45

Quote:

ORIGINAL: JimKueneman
The DVM has been connected and on for the last 3 days. When the CEL comes on the sensors run at 800mV and 700mV fairly steady. Clear it is going into a preprogrammed mode. The exhaust smells quite rich as well. I have been clearing the code within 5 minutes and it jumps right back to the values I wrote before in closed loop.

I have been struggling with the difference between the primary and secondary sensors. The primary reads 100mV higher all the time. SovXietday may be right. If the sensor has shifted up a few hundred millivolts then the ECU will think it is running too rich and lean it out to try in compensate.

I am going to try to load the sensor a bit with a resistor to fake it back down a few hundred millivolts to see if it helps.

Though I really admire your methodical approach for solving this problem, the outcomes of your tests along with the comments from SovXietday already seem to represent overwhelming evidence favoring the idea of a bad primary O2 sensor. It appears to me that, under specific conditions, your primary O2 sensor stops functioning, causing the ECU to go into the preprogrammed open loop mode that is much less fuel efficient under normal driving conditions. If so, then it may be best to replace the primary O2 sensor rather than try to reduce its voltage output. For a variety of reasons, your resistor method may only work temporarily or not at all.

#13

01-17-2008, 10:04 AM

SovXietday

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Location: Harleysville, PA

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RE: Civic Code 45

Quote:

ORIGINAL: JimKueneman

I have been struggling with the difference between the primary and secondary sensors. The primary reads 100mV higher all the time. SovXietday may be right. If the sensor has shifted up a few hundred millivolts then the ECU will think it is running too rich and lean it out to try in compensate.

No, flip that. The ECU "reads" too much oxygen and thinks it's extremely lean, so it runs extremely rich to compensate which causes your poor cruising drivability and poor gas mileage. However, when you get on it the problem clears up.

Change the primary O2.

#14

01-17-2008, 10:28 AM

mybrokenblinker

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RE: Civic Code 45

wow i've had this problem off and on for a while now, good to hear some info on it...

#15

01-17-2008, 10:51 AM

RonJ

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RE: Civic Code 45

Quote:

ORIGINAL: JimKueneman
If the sensor has shifted up a few hundred millivolts...

Also, the pictures in post 2 describe how to determine whether the primary O2 sensor is producing voltages within the specified range. With a fully warmed engine running at 3000 rpm in neutral/park, the sensor voltage should be 300-600 mV.

#16

01-17-2008, 12:12 PM

JimKueneman

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RE: Civic Code 45

Quote:

Though I really admire your methodical approach for solving this problem,

The danger of mechanic turned electrical engineer

Quote:

Agreed. The resistor was just to prove it without a doubt. I just ordered a new O2 $en$or.

Quote:

That is possible too. This assumes that the sensor is reading low and the system is running in open loop without throwing the CEL. My thought process went that if the CEL light is off then it can't be in open loop and the system is trying to lean out the fuel because the O2 has a DC offset on it causing it to read too rich. The poor fuel mileage comes from the just the fact that the engine is not running optimally and simply not running correctly.

As long as the CEL light can be off and the system be in open loop then I competely agree with what you say.

#17

01-26-2008, 05:27 AM

JimKueneman

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RE: Civic Code 45

Quick update on the problem. Got the O2 sensor yesterday. Went out to install it. Pulled off the shield on the mainfold and guess what.... I found the real problem. The exhaust manifold is cracked right through the hole for the O2 sensor. Guess that explains why it was dumping the fuel to it, looks lean when you are sucking air through the mainfold!

Makes things a bit pricey to put the converter intergal to the manifold..... Any one had any luck welding a cracked manifold?

Jim

#18

02-04-2008, 06:39 AM

JimKueneman

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RE: Civic Code 45

Update 2)

Finally had time to insall the new O2 sensor. Things are looking good. Here is how a good senser should look with a Fluke 77 attached to it.

Decel - 0V (it actually runs a bit negative)
WOT - high 800's to 900mV
Idling in gear. Quickly bouncing between 100mV (or less) to 600mV, Now THAT is a closed loop system that is working
Low speed driving - similar to Idling quickly responding between a few hundred mV and 600mV
Highway speeds under load (i.e. not downhill, needing power to maintain speed). proportional to the speed. with about a 50mV variation. At 60MPH about 700mV at 75MPH about 750mV.

Hope this thread helps give a clue to trouble shooting a sluggish O2 sensor and its symptoms.

Jim

#19

02-04-2008, 07:26 AM

RonJ

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RE: Civic Code 45

Thanks for the interesting update. I'm glad you found the fix. By the way, how did you deal with the cracked exhaust manifold?

#20

02-09-2008, 12:27 PM

JimKueneman

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RE: Civic Code 45

I haven't. I used JB weld for a temp seal just to see if the old O2 was really ok. Did nothing. JB weld is only good for 600F and since the header gets up to 1200F+ it was only a matter of time. I drove it until the JB turned to powder to make sure it was not outgassing and may poison the new O2 sensor.

You need to buy a new cat converter and header at $450. I may just take chance that the leak won't hurt the new O2 and drive it.

Jim