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My '92 CB9 won't start: only 0.7 volts on both A25 and B1 wires at the ECU

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    My '92 CB9 won't start: only 0.7 volts on both A25 and B1 wires at the ECU

    I've been trying to get my 1992 LX wagon (5-speed, 196k miles) to start for more than a month now, and I'm not sure what do to next. Would really rather not have to tow it somewhere and pay to get it fixed, seeing as how I've already invested ("wasted"?) lots of time trying to diagnose and fix it myself... and done most of the parts-swapping I think the average shop would try anyway.

    Hoping one of you highly experienced Honda people out there has an idea of what to try.

    The car just up and quit starting. It went from running/starting 100% of the time to not at all one day in my driveway (it didn't stop while driving and leave me stranded). It always cranks and turns the engine over, the battery is strong, but the CEL never turns off after turning the key to ignition position and I do not hear the fuel pump priming. Doesn't matter if it's hot or cold; the car consistently refuses to start (and the CEL always stays on and the fuel pump never primes).

    I've used these resources to try to determine what the issue is:

    http://techauto.awardspace.com/ecu.html
    http://www.tegger.com/hondafaq/startproblems.html#top

    Here's what I've checked that looks good/normal:
    • Confirmed that all of the relevant underhood and underdash fuses are good
    • Jumpered the diagnostic wire hanging out under the passenger side dash; CEL stays on solid, no blinks/codes
    • Replaced the ignitor; the main relay (twice, in the case the first non-OEM replacement relay I bought was bad); the entire distributor, which replaced the ignitor again; and the ECU
    • Confirmed that the main relay clicks (by feel) when I turn the key to ignition and back off
    • Confirmed that the timing belt isn't snapped
    • Confirmed that the distributor rotor turns when cranking
    • Removed, sanded and cleaned, and applied anti-oxidation contact grease to the multiplexed ground terminal on top of the thermostat housing
    • Checked the connections to the distributor (by unplugging them and reconnecting them... they look totally fine / clean)
    • Confirmed that there's 12v on the big fat black/yellow wire to the coil
    • Confirmed that there's 12v on the black/yellow wire that feeds the fuel injector resistor box
    • Confirmed that the fuel pump itself spins/hums when I apply 12V and ground to its contacts directly (I cut a hole in the unibody of the car to do this)
    • Confirmed that all four of the ground wires at the ECU (A23, A24, A26, and B2) are good


    This is what I've found that is NOT normal:
    • Checked for voltage at the two wires to the fuel pump right after the key has been turned to the ignition position... there is none
    • Checked for spark with the engine cranking... there is none
    • Pulled a spark plug and checked for signs of fuel delivery after the engine has been cranked over... there is no smell of gas, the spark plug tip is bone dry (makes sense, considering there's no voltage at the fuel pump)
    • Checked for voltage at A25, B1, and D1... there's 12 volts at D1 (the feed wire from the battery) but A25 and B1 only show 0.7 volts with the key turned to ignition


    So, the million-dollar question is: What is causing wires A25 and B1 at the ECU to read less than 1V with the key at ignition position, rather than the 12 volts they should be showing?

    The only components left to replace that *might* be the culprit are the coil, the TPS on the throttle body, and the MAP sensor on the throttle body (I normally wouldn't suspect those except that they're shown as potential issues in the first wiring diagram gif below).

    The weird super-low voltage makes me think some wire is shorted, but which one?? And if there were a shorted wire, wouldn't a fuse be blown SOMEWHERE? Again, all of the fuses are good in both fuseboxes. And I mean ALL of them... I've even checked the fuses that don't have anything to do the engine, because I've run out of things I know to check.

    Thanks in advance for the help!

    Images for reference:








    #2
    Have you read for a short yet? I have that that image is flashing and I cant blow it up so I could see which wires go to what.
    Looking at the schematic and from what I can make out it seems all those things feed through the o2 sensor. Have you read for a short on the o2 sensor? I don't know why this would affect the start but that is a pretty easy connector to get too. Just take your multi meter and put it on ohms then put one lead to ground and one lead on the pin and see if you get a reading.
    ~Nick~
    FSAE (F Series Accord Enthusiasts) ..."A dying breed thats taking it to the next level" Lucky #13
    MR Thread:http://www.cb7tuner.com/vbb/showthre...ight=Grumpys93

    Comment


      #3
      Originally posted by Grumpys93 View Post
      Have you read for a short yet? I have that that image is flashing and I cant blow it up so I could see which wires go to what.
      Looking at the schematic and from what I can make out it seems all those things feed through the o2 sensor. Have you read for a short on the o2 sensor? I don't know why this would affect the start but that is a pretty easy connector to get too. Just take your multi meter and put it on ohms then put one lead to ground and one lead on the pin and see if you get a reading.
      Thanks for the rely Grumpys93. You may be onto something, I didn't see how B1 (12V) at the ECU seems to go straight to the O2 sensor.

      You can see that OEM ECU wiring diagram much better here (use the magnifying glass function): http://www.manualslib.com/manual/464...age=266#manual

      Are you saying to read resistance at the ECU for the O2 sensor? Which would be wire D14, according to the diagram?

      I might just try unplugging the O2 sensor, to see if that affects A25 and B1... if those wires then go completely dead (i.e., I get 0 volts instead of 0.7 volts).

      Comment


        #4
        Originally posted by CB9 View Post
        I might just try unplugging the O2 sensor, to see if that affects A25 and B1... if those wires then go completely dead (i.e., I get 0 volts instead of 0.7 volts).
        I tried unplugging the O2 sensor... no change. A25 and B1 still show .7 volts.

        So then I tried unplugging every wire connector that was accessible under the hood and plugged into an engine-control sensor, one at a time—the throttle position sensor, the MAP sensor, the water temp sensor, the IACV.

        Oddly, unplugging these sensors didn't change the voltage reading at A25 and B1, with the exception of the IACV... unplugging that made A25 and B1 go to zero volts.

        Comment


          #5
          trace the yellow wire all the way between ecu and main relay. you have high resistance some where. poke the wire at the main relay and check for voltage. if you have 12v out of relay, overlay the wire and see if itll start. do the same for B1.
          COUPE K24

          Comment


            #6
            If that doesn't work. Have you swapped out the injector resistor?

            Did you check for 12vs at A9 as well as A7? The green/black wire.
            Also have you taken a look on the back side of the fuse box for any corrosion? One of the wires on the back of the fuse box may be shorting out or corroded. Or check the grommet around the firewall where the wires feed into.

            Also can you read A21 and A22. That is where pins A25 and B1 connect to the igniter. It's just odd there isn't much before those two pins.

            Silly question, this cb9 wasn't convert from auto to manual was it?

            Something keeps drawing me towards the pump or the ignitor. I know you said you replaced that but that is a high failure item as well and if it's not grounded that could be your issue
            Last edited by Grumpys93; 07-28-2016, 10:08 PM.
            ~Nick~
            FSAE (F Series Accord Enthusiasts) ..."A dying breed thats taking it to the next level" Lucky #13
            MR Thread:http://www.cb7tuner.com/vbb/showthre...ight=Grumpys93

            Comment


              #7
              I don't have my diagrams and notes at hand, but I pretty much know the whole wiring schematics in my head as I've assembled my own harness a few times. You should note that the fuel pump only gets fuel for the first second the ECU is powered on. Once the engine is running does the ECU then keep the power on.
              '93 H22A 5SPD SE - MRT - DIY-Turbo Sizing

              Comment


                #8
                Thanks for the continued help and ideas guys.

                Originally posted by Grumpys93 View Post
                If that doesn't work. Have you swapped out the injector resistor?
                If you mean the resistor box (under the hood, cast aluminum housing with short heatsink fins across the top, driver's side shock tower), no, I haven't... researching online seemed to indicate that it very, very rarely fails.

                Originally posted by Grumpys93 View Post
                Did you check for 12vs at A9 as well as A7? The green/black wire.
                No I did not; I will today if I have a chance.

                Originally posted by Grumpys93 View Post
                Also have you taken a look on the back side of the fuse box for any corrosion? One of the wires on the back of the fuse box may be shorting out or corroded. Or check the grommet around the firewall where the wires feed into.
                I didn't remove the underhood fusebox to inspect the bottom of it directly; I can do that. But, I should mention that I'm in Colorado, where it's very dry most of the time, and wire corrosion is extremely rare (unless it's a flood damage car). It is not unheard of for wires to get damaged by mice chewing them though, in certain areas...

                Originally posted by Grumpys93 View Post
                Also can you read A21 and A22. That is where pins A25 and B1 connect to the igniter. It's just odd there isn't much before those two pins.
                What should A21 and A22 read? 12V as well?

                Originally posted by Grumpys93 View Post
                Silly question, this cb9 wasn't convert from auto to manual was it?
                Not a silly question, as the vast majority of these cars are auto, but no; it came from the factory as a manual.

                Originally posted by Grumpys93 View Post
                Something keeps drawing me towards the pump or the ignitor. I know you said you replaced that but that is a high failure item as well and if it's not grounded that could be your issue
                Would a bad ignitor cause the fuel pump not to prime though? It's possible there's more than one thing wrong, but IMO unlikely... logically, there should be just ONE thing that suddenly went south, as like I said, the car was running fine one day (and has been for over a decade) and then the next it absolutely refused to start ever again.

                I cut a hole in the unibody to access the fuel pump without dropping the tank; by applying 12V power and ground directly to the contact points on top of the pump, it whirs and spins...

                Comment


                  #9
                  With everything said and done trying another ECU wouldn't hurt here.

                  Comment


                    #10
                    Originally posted by Raf99 View Post
                    With everything said and done trying another ECU wouldn't hurt here.
                    I already tried a different ECU. No change at all—same weird 0.7 voltage on A25 and B1, CEL stays on, fuel pump doesn't prime.

                    Comment

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