I have a 99 Accord EX 4 cyl 38,200 miles. Just have it turn up. It's getting less than 16/20 mpg local/ highway, very poor gas mileage. No check engine light comes on. I have it connect to an OBDII computer to read senor readings. Both O2 sensors are constant getting ~ 0.85V readings when idle or driving, which are very high. A few times I seem 0.2V or 0.3V, which lead me to believe the O2 sensors are good. If I am not mistaken, this means the gas/air mixture is too rich. I suspect the ECU is bad. I reset it a few times using the OBDII software, but didn't help. Does anyone else have similar problem? Any advise are welcome.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by zman1618 &raquo;</TD></TR><TR><TD CLASS="quote">I have a 99 Accord EX 4 cyl 38,200 miles. Just have it turn up. It's getting less than 16/20 mpg local/ highway, very poor gas mileage. No check engine light comes on. I have it connect to an OBDII computer to read senor readings. Both O2 sensors are constant getting ~ 0.85V readings when idle or driving, which are very high. A few times I seem 0.2V or 0.3V, which lead me to believe the O2 sensors are good. If I am not mistaken, this means the gas/air mixture is too rich. I suspect the ECU is bad. I reset it a few times using the OBDII software, but didn't help. Does anyone else have similar problem? Any advise are welcome.</TD></TR></TABLE>
Sounds like it's running rich to me too. What temp or voltage does your scantool show on the ECT sensor?

 

I have a tested and new o2 sensor for sale btw, sorry to post jack

 

The Scantool show sensor readings during cold start (actual air temp NYC ~50F): air intake temp 51F, O2 sensor 1 ~ 0.76V, O2 sensor 1 ~ 0.6V, ~1200 rpm, fuel trim ~-5%. What's ECT? No ECT readings from my scantool software.
After 5 minutes of warm up: air intake temp 58F, ~750 rpm, O2 sensor 1 ~ 0.80V, O2 sensor 1 ~ 0.7V,fuel trim ~-5%. When O2 sensors are reporting high ~ 0.8 - 0.9V, it means the sensors are working fine. I notice that the fuel trim reading is always more than -4%, does it mean the ECU is able to control trim fuel, is this normal?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by zman1618 &raquo;</TD></TR><TR><TD CLASS="quote">What's ECT? No ECT readings from my scantool software.
</TD></TR></TABLE>
Engine coolant temp. Does it show MAP voltage?

 

there might be simpler solutions too, such as dirty plugs, underinflated tires, and so on. You sound like you know what you're talking about so I'm guessing you've already checked all of these but i thought i'd throw out some suggestions anyways

 

Thanks for explaining ECT. The ECT temp reading from changes cold 58F up to warm 170F. There is no MAP voltage reading on my Scantool software. I am trying to a better SCANTOOL software. I am using the hareware and software from http://www.scantool.net. Does anyone know a better software?

 

I think it still could be o2 sensor at port #1. Mine went out at 60k. This was way too early. I have a 98 accord 4-cyl. with 120k. Also, the cat. converter went out around 75k. But what puzzles me is the check engine light should have gone off.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by iam7head &raquo;</TD></TR><TR><TD CLASS="quote">I have a tested and new o2 sensor for sale btw, sorry to post jack</TD></TR></TABLE>

It's this oem, for the primary or secondary, how much?


Modified by zman1618 at 7:11 PM 3/31/2004

 

Hi,

How do your spark plugs look? Sooty? That is a good indication that it is running rich, also, you might try checking your exhaust pipe by wiping it clean with a cloth and then driving around a bit, and rechecking if it is getting coated with soot.

I think if we drive it like that for too long, the CAT might give up... So it is a serious problem..

 

I compared O2 sensors reading from my car and my friend's. My car stays at .7V or higher, but my friends jumping up and down from .01V to .8V. There is some thing wrong with my car's fuel management system, just don't know which part and how much?

 

If I am guessing right, the CEL should come on if the value in closed loop stays above .45 V for more than 3 minutes. It is an indication that the sensor is sluggish. What instrument are you measuring the voltage with? If it is fluctuating too fast, you will not be able to get it on a cheap digital multimeter.

 

I used OBDII connector from scantool.net. All readings are seem to be acuate.

 

if you figure out the problem please post how you fixed it, i have a similar gas mileage problem with my obd1 5th gen accord... everything is fine, just gas mileage is shitty... sorry to jack..

 

what do you mean by all readings seem accurate? Are they within specs?

 

And what all do you need to get the readings? What connector did you buy from scantools. net and did you hook it up to your PC? how much did it cost?

 

http://www.scantool.net/support/?_a=knowledgebase read their knowledgebase.

 

After I put a front new O2 sensor into the car. It caused a MIL: OBDII code P1167. P1167 Air/Fuel Ratio (A/F) Sensor (Sensor 1) Heater System Malfunction
P1167 Heated Oxygen Sensor Sensor1 (Primary LAF HO2S) Heater System Malfunction
Does any one know which part is extactly wrong and how to fix? TIA.
Why is the old O2 does not cause a MIL? It is very confusing.