Main fuel relay problem?
Thread Starter
Honda-Tech Member
Joined: Jul 2010
Posts: 8
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From: Humboldt, KS
Main fuel relay problem?
Yesterday i go to start my car and it wont start. The clicking noise that occures when the s3 light flashes also is not as loud. So i figure it must be the main fuel relay b/c isnt that what that noise is? Anyways the car started for me a few hours later, usally when it wont start the s3 light will flash over and over which i heard was tranny problems as well. Overall thet is a bug in this car that im getting TIRED of and im going to try replacing the mfr, my main question, is the mfr also refered to as the main relay? I dont want to buy a part that does not need replaced lol. any advice would help out ALOT. Thanks
Old Fart
Joined: May 2004
Posts: 26,173
Likes: 18
From: kelowna, bc, canada
Re: Main fuel relay problem?
The PGM-FI Main Relay, [main relay, main fuel relay, MFR] is actually two relays in one, the fuel pump power relay and the fuel injector power relay, the injector relay also supplies power to a few engine valve/solenoids and one of the powers to the ECU/ECM.
If the PGM-FI Main Relay is working you will hear two "clicks", when you turn on the ign. switch to run, [not start] the "clicks" are very close together so they may sound like one click, the CEL will turn on and you will hear the fuel pump prime for a few sec., you will then hear a 3rd "click", the fuel pump will stop priming and the CEL will go out, this is the fuel pump relay turning off, the ECU/ECM will turn the fuel pump relay back on as soon as you start cranking the engine to start.
The injector relay is on as long as the ign. switch is in run or start, you can test it by turning on the ign, switch and testing for power at the injectors.
If you do not hear the fuel pump prime when you turn the ign. switch to run, give the PGM-FI Main Relay a "tap" or two, if fuel pump starts priming, repair or replace the PGM-FI Main Relay... http://www.tegger.com/hondafaq/mainrelay.html if tapping the relay does not work, do the same at the fuel pump, no access cover on a G2 so you will have to tap hard on floor pan under rear seat, or on the gas tank itself, if fuel pump primes when tapped, replace the fuel pump, [sorry no fix].
If you do hear the fuel pump prime but engine still does not start, [o not turn off the ign.] test for power at the injectors, [wire that is the same color on all 4 injectors].
Until you find the problem, get used to turning the ign. switch to run, [not start] and listen for the fuel pump priming, if it primes but engine does not start, test for power at the injectors, it is also a good idea to remove the knee bolster trim, [under dash trim] for easy access to relay, [for "tapping" test] same goes with back seat bottom, [for fuel pump "tapping" test.
For test equipment all you need is a 12V test light, [$2-$3 at most auto supply stores]. 94
If the PGM-FI Main Relay is working you will hear two "clicks", when you turn on the ign. switch to run, [not start] the "clicks" are very close together so they may sound like one click, the CEL will turn on and you will hear the fuel pump prime for a few sec., you will then hear a 3rd "click", the fuel pump will stop priming and the CEL will go out, this is the fuel pump relay turning off, the ECU/ECM will turn the fuel pump relay back on as soon as you start cranking the engine to start.
The injector relay is on as long as the ign. switch is in run or start, you can test it by turning on the ign, switch and testing for power at the injectors.
If you do not hear the fuel pump prime when you turn the ign. switch to run, give the PGM-FI Main Relay a "tap" or two, if fuel pump starts priming, repair or replace the PGM-FI Main Relay... http://www.tegger.com/hondafaq/mainrelay.html if tapping the relay does not work, do the same at the fuel pump, no access cover on a G2 so you will have to tap hard on floor pan under rear seat, or on the gas tank itself, if fuel pump primes when tapped, replace the fuel pump, [sorry no fix].
If you do hear the fuel pump prime but engine still does not start, [o not turn off the ign.] test for power at the injectors, [wire that is the same color on all 4 injectors].
Until you find the problem, get used to turning the ign. switch to run, [not start] and listen for the fuel pump priming, if it primes but engine does not start, test for power at the injectors, it is also a good idea to remove the knee bolster trim, [under dash trim] for easy access to relay, [for "tapping" test] same goes with back seat bottom, [for fuel pump "tapping" test.
For test equipment all you need is a 12V test light, [$2-$3 at most auto supply stores]. 94
Thread Starter
Honda-Tech Member
Joined: Jul 2010
Posts: 8
Likes: 0
From: Humboldt, KS
Re: Main fuel relay problem?
The PGM-FI Main Relay, [main relay, main fuel relay, MFR] is actually two relays in one, the fuel pump power relay and the fuel injector power relay, the injector relay also supplies power to a few engine valve/solenoids and one of the powers to the ECU/ECM.
If the PGM-FI Main Relay is working you will hear two "clicks", when you turn on the ign. switch to run, [not start] the "clicks" are very close together so they may sound like one click, the CEL will turn on and you will hear the fuel pump prime for a few sec., you will then hear a 3rd "click", the fuel pump will stop priming and the CEL will go out, this is the fuel pump relay turning off, the ECU/ECM will turn the fuel pump relay back on as soon as you start cranking the engine to start.
The injector relay is on as long as the ign. switch is in run or start, you can test it by turning on the ign, switch and testing for power at the injectors.
If you do not hear the fuel pump prime when you turn the ign. switch to run, give the PGM-FI Main Relay a "tap" or two, if fuel pump starts priming, repair or replace the PGM-FI Main Relay... http://www.tegger.com/hondafaq/mainrelay.html if tapping the relay does not work, do the same at the fuel pump, no access cover on a G2 so you will have to tap hard on floor pan under rear seat, or on the gas tank itself, if fuel pump primes when tapped, replace the fuel pump, [sorry no fix].
If you do hear the fuel pump prime but engine still does not start, [o not turn off the ign.] test for power at the injectors, [wire that is the same color on all 4 injectors].
Until you find the problem, get used to turning the ign. switch to run, [not start] and listen for the fuel pump priming, if it primes but engine does not start, test for power at the injectors, it is also a good idea to remove the knee bolster trim, [under dash trim] for easy access to relay, [for "tapping" test] same goes with back seat bottom, [for fuel pump "tapping" test.
For test equipment all you need is a 12V test light, [$2-$3 at most auto supply stores]. 94
If the PGM-FI Main Relay is working you will hear two "clicks", when you turn on the ign. switch to run, [not start] the "clicks" are very close together so they may sound like one click, the CEL will turn on and you will hear the fuel pump prime for a few sec., you will then hear a 3rd "click", the fuel pump will stop priming and the CEL will go out, this is the fuel pump relay turning off, the ECU/ECM will turn the fuel pump relay back on as soon as you start cranking the engine to start.
The injector relay is on as long as the ign. switch is in run or start, you can test it by turning on the ign, switch and testing for power at the injectors.
If you do not hear the fuel pump prime when you turn the ign. switch to run, give the PGM-FI Main Relay a "tap" or two, if fuel pump starts priming, repair or replace the PGM-FI Main Relay... http://www.tegger.com/hondafaq/mainrelay.html if tapping the relay does not work, do the same at the fuel pump, no access cover on a G2 so you will have to tap hard on floor pan under rear seat, or on the gas tank itself, if fuel pump primes when tapped, replace the fuel pump, [sorry no fix].
If you do hear the fuel pump prime but engine still does not start, [o not turn off the ign.] test for power at the injectors, [wire that is the same color on all 4 injectors].
Until you find the problem, get used to turning the ign. switch to run, [not start] and listen for the fuel pump priming, if it primes but engine does not start, test for power at the injectors, it is also a good idea to remove the knee bolster trim, [under dash trim] for easy access to relay, [for "tapping" test] same goes with back seat bottom, [for fuel pump "tapping" test.
For test equipment all you need is a 12V test light, [$2-$3 at most auto supply stores]. 94
The only click i hear is when i turn the key to the start position, the s3 light blinks then i hear a click and it shuts off, and normally the car starts. randomly, i will hear no click and the s3 will keep blinking and ya.. i wont even waste my time starting it bc if it does start it will run like its in 3rd the whole time. but the other day i got the combo, it would make that clicking when i turn it to start,(not as loud of a click) and wouldnt start. several trys and then the s3 keeps blinking so im thinking i may have MFR and tranny solenoid problems? idk but your info helps man thanks.
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