kent-k

i have hooked up the Brockway engineering RacerDataDisplay920 to MY02 that throws an occasional misfire code. the car runs pretty good,not as smooth as MY05, but everyonce in a while stumbles at idle. it doesn't miss anywhere but at idle (or at least that's what i can feel).

the thing is, as i'm looking at the data coming from the ECU, my 02 sensor voltage varies from .035 - .855 at idle! i thought that the voltage is from 0-1 which means that the ECU thinks that my car is going from very lean to very rich, or vice versa.

what is the proper operating range for the sensor and does this mean that my oxygen sensor went bad? or am i looking too deeply into this.

thanks

Wisconsin S2k

the stumbling idle is fairly common and is not really a "problem". it will generally go away within a few days. the ECU sometimes gets "confused", most often due to weather changes.

kent-k

thanks, it was raining really heavy the past few days and the last time it happened it rained as well. it was maybe two months ago. that must be what's going on.

the thing is though, it stumbled enough to throw codes for 301,303,304.

Wisconsin S2k

whoa whoa that's something COMPLETELY different. i missed the first part about the initial throwing a code. totally my mistake.

well, your codes are not likely because of an O2 sensor. Start by checking all of your plugs. Are they tight? What to the tips look like? Did you get a bad tank of gas recently maybe? (you're using premium only i hope) Does the misfire happen randomly in all cylinders? You stated you're getting codes that indicate misfires in cylinders 1, 3, and 4.

kent-k

i changed all of the plugs a little while ago, when it started missing the first time. i also inspected the valvetrain for broken retainers, keepers and springs. i also did a valve adjustment. got a little more power out of that because they were on the loose side of the adjustment. i cleaned the throttle body and bore as well. i also swapped coils and the map sensor from MY05 into the 02. same codes, random and individual cylinder misfires.

then the miss dissappeared for a couple months. then it came back when i used gas, premium of course, from a shell station. that was the same circumstances as the first time it started to miss, gas from shell. so i've just stayed away from shell ever since. then the other day, i fill up at chevron and the next day it starts to miss.

i've got a few tidbits of data that i don't know is relevant/helpful or not:

car has 27000 miles

compression tests says 110-117 for the four cylinders

TPS reads (on the data display) 5%-87%. i have not checked voltage yet.

02 varies from .035-.855 and sometimes higher very quickly, within a second. at startup, the voltage is around 1.125

map sensor says 40kpa at idle and is pretty steady

battery volts 14.4



thanks for the help guys,

kent

Wisconsin S2k

Ouch, only 110-117 on your cylinders? I think that's your issue. You should perform a leak down test. Compression on each cylinder should be at least around 200 or higher (or maybe 185 or higher). That's why you're getting the misfiring codes. You have a leak somewhere and/or in each cylinder.

kent-k

sorry, typo! 210 and above IIRC. i did it a few months ago

Wisconsin S2k

I'll have to look at my helm manual to refresh my memory, but it can also be a bad ECU

S2kracka

This is normal, the o2 sensor is supposed to cycle during closed-loop operation. It will only stay steady during open-loop which is mainly WOT and cold engine.

Slows2k

The primary 02 sensor's operation range is from 0-1 volt, flutcuating rapidly. That sensor output is normal and not a cause for a misfire. Startup output volts is usally in the 1.2-2v range, it can very. as long as it's fluctuating from 0-1V at idle you're fine.