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Strange problem between main relay, main relay harness, and ECU

Discussion in 'Civic and CRX - EF' started by aasarsak, Nov 29, 2008.

  1. aasarsak

    aasarsak New Member

    Likes Received:
    Nov 8, 2008
    I have scoured the internet trying to find a solution to this problem, but I have not been able to find anything. Here is the situation.

    Normally, when I turn the key on just before starting the car with the engine off (KOEO), the CEL comes on for 2 seconds. During the 2 seconds, I can hear the fuel pump priming the fuel lines. After the 2 seconds is up, the light goes off, and the fuel pump shuts off.

    Ever since I installed my new ECU from xenocron.com, my car doesn't do that any more. I followed the troubleshooting steps outlined in the service manual, but I cannot identify the problem.

    Most of the search results I got pointed to the main relay, so I took it out, hooked it up to the battery and checked for continuity between all the prescribed terminals as stated in the service manual. The relay appeared to be fine, but I decided to go ahead and replace it anyway. I replaced the main relay, same problem.

    The next step, according to the service manual, is to check the main relay harness. I placed a jumper wire between the #5 and #7 terminals and switched the KOEO and viola! the CEL came on and the fuel pump started to humm quite well.

    The only other possiblity I can come up with is that the ECU may not be sending the signal to the main relay to prime the fuel line because the car starts and runs extremely well.

    Some things to consider. After I did the OBD1 conversion, I got a CEL code for ELD. I have no idea what that meant, so I replaced the ELD (the black box fuse holder thingy under the hood), but the CEL code for ELD did not go away even though I reset the ECU by disconnecting the negative battery cable. To keep this particular code from being indicated, I went into my engine management software (Neptune RTP) and disabled ELD.

    The car runs fine except that during long freeway trips, the fuel will cut out. I know this is happening because my wideband 02 gauge indicates a sudden lean mixture and I can feel the loss of power. The wierd thing is that if I apply a little more throttle pressure, the car goes back over to rich and accelerates just fine. As soon as I resume constant throttle cruising, the fuel cuts out again.

    I don't know if any of these issues are related, but that is basically what is going on. The fuel cutting out problem during cruise has been going on since before I did the OBD conversion.

    I believe that the ECU is the problem, but I havent been able to find any source of information that explains how to tell if the ECU is sending the signal to prime the fuel lines.

    Any suggestions?

    Even though I think my particular setup is irrelevant to the problem since it seems to be a chassis problem, here it is anyway.

    89 civic si (usdm)
    P28 with Neptune RTP (tuned by Church Automotive: Long Beach, CA)
    Walbro 255LPH fuel pump
    Stock injectors
    B&M FPR
    DRAG T3/T04 turbo kit (FMU & MAP bypass removed)
    Innovate LC-1 Wideband kit
    Last edited: Nov 30, 2008
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