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b17 running way to rich

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  • b17 running way to rich

    hey g2ic i have a b17 in my car and arunning a obd0 pr3 ecu the problem im having is it is running way too rich so rich to the point that when driving on the highway at like 3000 rpm the car starts missing i get a check engine light for knock sensor....replaced the knock sensor and CEL still comes on and same condition idk what it could be let me know what you guys think.........fuel pump and fuel filter replaced and plugs replaced condition of plug is black like the night time, due to me using the jdm pr3 ecu i have to run 2 single wire o2 sensors for each pair of runners what i did was run the wire for the second o2 sensor from the ecu and splice it into the 1st o2 sensor to trick it into thinking it has 2 sensors.......i am also running the apexi vafc with no tune just OE setup any type of advice could help thanx

  • #2
    The stock pr3 ecu isn't optimal for that engine. I'd convert to obd1 and get it tuned. Or you could just get it tuned and stay obd0. Tuning will be a couple hundred bucks but after that you'll be good to go assuming everything is functioning properly. Personally I'd pay for the tuning and have the problem solved in a couple hours opposed to spending hours and hours over a period of days or weeks trying to mess with it myself, potentially damaging the engine in the process and requiring a rebuild which would be more than it would have been to just tune the damn thing in the first place. I learned this from experience. Do it right the first time, or be prepared to do it again.
    Track Project DB2 #896
    LeMons Project DA9
    My OG DA9, Wrecked, Stripped, R.I.P

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    • #3
      i think first though, i'd want to run a quick range check of the o2 sensors. you can use a multimeter for this. set it to volts and, with the vehicle running at operating temp, BACK PROBE (<--very important) the o2 sensors. you should get a reading of about 1V or 900mV, then down to about 100mv up and down. o2's usually fail lean, so if it's bad, you'll get a reading that won't go up to 900mV. maybe say 500mV. the ecm sees this low reading (lean) and tries to correct by dumping fuel.
      usually an oscilloscope is best suited for o2 performance testing but for a quick and dirty range check, the DMM will do

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      • #4
        now the only issue with that is you don't know if the o2 is actually failed or if you are in fact running lean. to check that, while probing, fog in a shot of propane through the intake duct. if the o2 still only reads up to anything below 900mV, it's bad. reason i'm suspicious of this is that you were misfiring. running rich usually won't result in a misfire. you never hear of a rich misfire code. engines love running rich. they'll purr like a kitten with excess fuel. you may actually be running lean. the black soot on the plugs could have been caused by the retarded timing of the knock sensor (unburnt fuel).

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        • #5
          Start by grounding out the pin for the knock sensor at the ECU. That will eliminate the MIL light and any ECU corrections that would result from the KS code. Might or might not help. Also, it is VERY possible to develop a misfire from running too rich. Maybe less likely in a Honda but still possible. That said, you would have to run extremely rich to foul a plug(s) due to excessive fueling. The factory P61 tune on my B17 ran so rich at one point that it would occasionally stutter/misfire. Plugs were black as night and 1 or 2 were usually wet. .02

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          • #6
            Have you checked your timing. If the base timing (crankshaft and camshafts) are off it'll run rich. I just went through this with my car. Does it idle rough as well

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            • #7
              currently i have checked timing and they are spot on and i also checked ignition timing and its spot on too i am goin to perform the o2 sensor range test and see what happens from there grounding out the knock sensor is a great suggestion so im goin to try that to......thanx for the help so far keep the suggestions and help comin

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              • #8
                coolant temp switch good? wont run good when it dont know weather the engines warm or cold

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                • #9
                  Originally posted by Sirtef9 View Post
                  coolant temp switch good? wont run good when it dont know weather the engines warm or cold
                  That would be the ECT sensorn not the ECT switch, it just controls the rad fan relay.

                  A bad ECT sensor can result in the engine running rich, but as welfare points out it should not result in a misfire, the engine runs rich everytime you start it when cold, the ECT sensor supplies the ECU/ECM with engine temp., as the engine warms up the ECU/ECM adjusts A/F ratio.

                  The most common symptoms of a bad ECT sensor are, engine runs rich, poor milage, engine starts fine when cold but is harder to start when warm. 94

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                  • #10
                    Update !!!!

                    Well i have the same problems as before i tested the ect sensor and thats fine tested the o2 sensor and it is fine to i grounded out the pin from the ecu for the knock sensor and CEL still comes on for knock sensor......i get the feeling that my ecu is bad because if i grounded out the from the ecu for the knock sensor i should not have gotten a check engine light for it so i removed the ecu and inspected the ecu and found no burn marks on the board or vtec control board.......let me know what yall think

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