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Old 11-11-2017, 07:27 PM   #1
kratemertyl
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Main relay good, but no voltage at pump

Ok so heres how it went down. Car was running great. Got crashed on the driver side while sitting in a parking lot. Car started up just fine and i drove it home. Due to the door not functioning i let it sit for a week or two without driving it. Jumped in it to start it anf would not fire.
Noted that i could not hear the fuel pump prime. Checked pressure at fuel rail and saw i had none.
Checked voltage at fuel pump and found none. Check #2 and #28 fuse, both good. I then assumed main relay went out. Bought new one and replaced.
Same result.
Tested old relay, it tests good.
Jumped wires at main relay connector, yellow and blue(always hot) with yellow(power to fuel pump) and fuel pump kicked on.
Using a test light put clip on the ground pin of the connesctor and the probe on the hot wire. Tested good.
When ignition is turned on the connector shows power at the black and yelloe wire.

I think thats everything.
Im wondering if my alarm has shorted out and is not allowing the car the fire. Just seems odd cause the relay should be getting power from 12 volt constatnt, and ignition source and has a ground.

If i just jump the fuel pump while turning the key it still doesnt fire, im guessing cause maybe the injector resistor boc isnt getting power?

Idk where to go from here.
The car has a hondata piggy back and i guess i need to hook up my computer and play around, but i really havr no idea hoe to operate all that .

Help!
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Old 11-11-2017, 08:21 PM   #2
sonikaccord
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You are missing a very important wire in your diagnosis. What is the GRN/BLK wire showing for voltage?
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Old 11-11-2017, 08:55 PM   #3
kratemertyl
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So interesting,
My volt meter decided it was a good time to break.
So with a test light, if i clip it to a ground and then put the probe on the green and black tracer wire with the ignition onthe fuel pump turns on. But it barely lights up. The black wire with green tracer doesnt show any voltage either
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Old 11-11-2017, 09:06 PM   #4
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That makes sense. The test light is effectively grounding the fuel pump part of the Main Relay. The fact that the pump turns on when when you probe the GRN/BLK wire, leads to the ECU either not turning the pump on or a break in the connection to the ECU.

The BLK/GRN wire is the Starter Signal that tells the ECU to turn on the fuel pump when the key is in start.
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Old 11-11-2017, 09:10 PM   #5
kratemertyl
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So the blk/green is supposed to send a signal to the ecu not the other way around?
I see in the schematic that that blk/green intercepts with something called starter cut relay #1
Not sure what this is
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Old 11-11-2017, 10:18 PM   #6
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Yes. The Blk/GRN wire should have 12V when the key is in start, IIRC.
I would focus on the pump not priming first, as I think that tells us a bit more.

The starter cut relay is for the clutch switch. It shouldn't affect priming.
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Old 11-12-2017, 09:46 AM   #7
kratemertyl
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The black/green does not show any voltage. It does not have any voltage at the pin of the ecu either.
Im thinking i need to look into the ecu. Not sure how to do that though.
Any hondata guru's out there?
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Old 11-12-2017, 11:38 AM   #8
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Did you press the clutch in, then check the voltage on BLK/GRN? The clutch interlock switch provides the 12V to that line.

During the first 2 seconds of ignition on, what do you see on the GRN/BLK wire? It should be 0V when the fuel pump is running or priming, 12V when off.
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Old 11-12-2017, 12:31 PM   #9
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i will check that out tomorrow when I get home. I have the clutch neutral safety switch disabled but I will make sure its doing what it should. I thought if the clutch wasn't pressed in, that the ignition wouldn't turn the car over? and that the fuel pump would still prime
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Old 11-12-2017, 02:44 PM   #10
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That's right. The fuel pump should prime as soon as you turn the ignition to ON, and it should go stop priming at the same time the CEL light goes off. That makes the clutch voltage a secondary issue and the GRN/BLK wire voltage is the primary suspect.

The fact that you can turn the pump on with the test light is a strong indicator that something upstream of the main relay is acting up. It's literally only a wire splice/continuity and and an ECU to check. I'm not too familiar with Hondata. I guess you could turn the fuel pump output on and off from there as well?
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Old 11-12-2017, 06:51 PM   #11
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Im pretty sure u can adjust how long the pump primes and im assuming u can see other stuff regarding the fuel pump. If somebody on here cant walk me through it im gonna call my tuner tomorrow and see if he can help.
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Old 11-13-2017, 10:24 AM   #12
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Might have narrowed it down to ecu
Grn/black shows its an active ground when ingnition is off and when on. Im pretty certain when the key is on this wire is supposed to un ground (excuse terminology) at the ecu. And its not
Is that right?
Or is this a bad wire thats grounding out amd its not supposed too?
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Old 11-13-2017, 06:42 PM   #13
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That's right, the ECU should should "release" the ground for the GRN/BLK wire when the fuel pump is NOT running. When the ECU request that the fuel pump turns on, it grounds this wire and in turn causes the main relay to send power to the fuel pump.

It should read battery voltage when the ignition is on and when the main relay gets power.

To determine if the wire is grounded, disconnect the Main relay and connector A(26 pin connector) from the ecu and check for continuity to ground
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Old 11-13-2017, 10:35 PM   #14
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Will do, went to 3 different stores today trying to find a good multi meter preferably a fluke but was unsuccessful. Gonna try a snap on truck tomorrow.
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Old 11-14-2017, 03:42 PM   #15
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wow, I might be having this very same issue ... subscribing, keep us informed krate ..
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