93 Accord ECM or main relay troubleshooting
07-20-2013, 06:47 AM
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93 Accord ECM or main relay troubleshooting
Hi everyone, I've bee having some issues with my 93 Accord EX cranking but not starting. I think I've got it figured out, but I would love a second opinion and if anyone has answers to a couple specific questions.
I have determined that the Main Relay is not supplying power to the fuel pump. I am able to make the fuel pump run by jumping from 5 to 7 on the connector. I have been through the entire diagnostic procedure in the Honda Service Manual (11-107 to 11-109) and everything checks out, with one interesting abnormality (question 1) that I don't think has anything to do with the issues. The Main Relay bench tests correctly.
The questions:
1. The book says there should be battery voltage at A7 on the ECM for 2 seconds when the ignition is turned on. I get battery voltage but it does not turn off after 2 seconds. What mechanism is supposed to control this 2 seconds?
2. What do A7 and A8 do? These are also listed as FLR1 and FLR2. The way I read it is that they are supposed to provide a ground for terminal 8 of the relay in order to close the relay and provide power to the fuel pump. Does the ECM do anything else with these?
So, my assessment is that the ECM is failing to provide a ground on that circuit. I am able to manually ground terminal 8 from the relay to close the relay and power the fuel pump. I believe that this indicates I need to put in a new ECM.
I've tried to be very detailed with this, but please let me know if I have been incomplete or unclear. Mostly, I am curious if there is something obvious I might have missed or if it sounds like I am on the right track.
Thanks in advance for any help!
Jason
p.s. apologies if this ends up posted twice, I signup up yesterday and posted but it hasn't shown up
I have determined that the Main Relay is not supplying power to the fuel pump. I am able to make the fuel pump run by jumping from 5 to 7 on the connector. I have been through the entire diagnostic procedure in the Honda Service Manual (11-107 to 11-109) and everything checks out, with one interesting abnormality (question 1) that I don't think has anything to do with the issues. The Main Relay bench tests correctly.
The questions:
1. The book says there should be battery voltage at A7 on the ECM for 2 seconds when the ignition is turned on. I get battery voltage but it does not turn off after 2 seconds. What mechanism is supposed to control this 2 seconds?
2. What do A7 and A8 do? These are also listed as FLR1 and FLR2. The way I read it is that they are supposed to provide a ground for terminal 8 of the relay in order to close the relay and provide power to the fuel pump. Does the ECM do anything else with these?
So, my assessment is that the ECM is failing to provide a ground on that circuit. I am able to manually ground terminal 8 from the relay to close the relay and power the fuel pump. I believe that this indicates I need to put in a new ECM.
I've tried to be very detailed with this, but please let me know if I have been incomplete or unclear. Mostly, I am curious if there is something obvious I might have missed or if it sounds like I am on the right track.
Thanks in advance for any help!
Jason
p.s. apologies if this ends up posted twice, I signup up yesterday and posted but it hasn't shown up
08-09-2013, 06:14 PM
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Re: 93 Accord ECM or main relay troubleshooting
Just in case anybody else has the same issues, here are the answers (in a different order):
1. Yes, it was a bad ECM. Got one at the U Pull It and it has run great ever since. I seem to be getting better mileage too, but I can't see how this can be related.
2. Regarding voltage for 2 seconds, I suspect the book has it wrong and that the ECM should provide ground for 2 seconds. Not sure about that, but with new ECM the fuel pump comes on for 2 seconds as expected when ignition is turned to on.
3. A7 and A8 provide a ground just as I thought. They do nothing else. Whatever mechanism in my old ECM that should have provided this ground was not doing so, and the relay would not close.
I hope somebody finds this helpful!
p.s. I think I'll take the wiring connectors and my old ECM connectors and build a test harness. Unless somebody knows where to buy one at a reasonable price.
1. Yes, it was a bad ECM. Got one at the U Pull It and it has run great ever since. I seem to be getting better mileage too, but I can't see how this can be related.
2. Regarding voltage for 2 seconds, I suspect the book has it wrong and that the ECM should provide ground for 2 seconds. Not sure about that, but with new ECM the fuel pump comes on for 2 seconds as expected when ignition is turned to on.
3. A7 and A8 provide a ground just as I thought. They do nothing else. Whatever mechanism in my old ECM that should have provided this ground was not doing so, and the relay would not close.
I hope somebody finds this helpful!
p.s. I think I'll take the wiring connectors and my old ECM connectors and build a test harness. Unless somebody knows where to buy one at a reasonable price.
11-05-2016, 07:20 PM
#3
Re: 93 Accord ECM or main relay troubleshooting
Just in case anybody else has the same issues, here are the answers (in a different order):
1. Yes, it was a bad ECM. Got one at the U Pull It and it has run great ever since. I seem to be getting better mileage too, but I can't see how this can be related.
2. Regarding voltage for 2 seconds, I suspect the book has it wrong and that the ECM should provide ground for 2 seconds. Not sure about that, but with new ECM the fuel pump comes on for 2 seconds as expected when ignition is turned to on.
3. A7 and A8 provide a ground just as I thought. They do nothing else. Whatever mechanism in my old ECM that should have provided this ground was not doing so, and the relay would not close.
I hope somebody finds this helpful!
p.s. I think I'll take the wiring connectors and my old ECM connectors and build a test harness. Unless somebody knows where to buy one at a reasonable price.
1. Yes, it was a bad ECM. Got one at the U Pull It and it has run great ever since. I seem to be getting better mileage too, but I can't see how this can be related.
2. Regarding voltage for 2 seconds, I suspect the book has it wrong and that the ECM should provide ground for 2 seconds. Not sure about that, but with new ECM the fuel pump comes on for 2 seconds as expected when ignition is turned to on.
3. A7 and A8 provide a ground just as I thought. They do nothing else. Whatever mechanism in my old ECM that should have provided this ground was not doing so, and the relay would not close.
I hope somebody finds this helpful!
p.s. I think I'll take the wiring connectors and my old ECM connectors and build a test harness. Unless somebody knows where to buy one at a reasonable price.
i had a similar problem on my 98 and there was water that corroded the fuel pump connector and made the relay buzz and go haywire and check engine was on car wouldn't start. Just also related to this to help.
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