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post #1 of (permalink) Old 09-02-2006, 08:32 PM Thread Starter
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Relay not working

I have a MegaSquirt EFI with a relay board. The relay board has three relays on it one for mail power, one for the fuel pump and one for the fast idle. I am having a problem with the fuel pump relay. On the board are sockets for the relays. When I have the relay out of the fuel pump socket I get +12v on 30 and 86. When the fuel pump should be active I get a ground on 85 and +12v across 85 and 86. When I put the relay in the socket I only get +4v across 85 and 86 and the relay does not work. Anyone have any idea what could be causing this? I have tried several relays so I think I can rule out the relay itself.
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post #2 of (permalink) Old 09-02-2006, 09:29 PM
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Re: Relay not working

Pin 30 supplies voltage from the supply to the fuel pump when the relay is enabled.

Pin 86 supplies voltage from the ECM to enable the relay. If the relay is not closing, it's because of one of a couple of problems:<ul type="square">[*]Pin 85 is NOT grounded well, perhaps a floating ground[*]The supply voltage from (FP1, 2 RAW) the ECM is not enough to enable the relay. That's a bad ECM (or internal part).[/list]However the 12 volts to enable the relay is weak... Those are the places I'd look.






Last edited by LEVE; 03-24-2009 at 07:43 PM.
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post #3 of (permalink) Old 09-02-2006, 10:38 PM Thread Starter
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Re: Relay not working

It seems to be a ground problem. When I connect a chassy ground to 85 the relay closes and the pump runs. Any idea how to test the ground comeing from the MS?
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post #4 of (permalink) Old 09-02-2006, 10:46 PM
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Re: Relay not working

First test the pin from the relay socket to ground to make sure it really is ground. Then if it is good, the problem lies in the ECM or the wiring on the RELAY PCB. I'd apply 12 volts to the input of the Relay Board feed to the relay to make sure it does work. Then it removes the Relay Board out of the equation.
Make up this test probe, and use it:




In fact, I'd make one for every relay and install it on a PCB display on the dash. I may just do that for the Howell, so I can eliminate problems on the fly, and see what's working and what's not working.

Which Megasquirt module did you build?
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post #5 of (permalink) Old 09-02-2006, 11:17 PM Thread Starter
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Re: Relay not working

I tested the relay socket (85) to ground and it is a real ground. I even bypassed the relay board wireing by junpering a wire from the db37 to the relay socket directly and it still does not work. I can run a wire from a chassy ground (jeep frame) to the relay pin 85 and the pump starts running. I also tested the cable from the MS to the relay board and that checks out as well. I am now convinced that the problem is with the MS.

I have a MS v2.2 with the MSII processor.
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post #6 of (permalink) Old 09-02-2006, 11:53 PM
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Re: Relay not working

Have you watched the LED's on the circuit board to see if they're lighting up?
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post #7 of (permalink) Old 09-03-2006, 10:08 AM Thread Starter
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Re: Relay not working

[ QUOTE ]
Have you watched the LED's on the circuit board to see if they're lighting up?

[/ QUOTE ]

Not sure what you mean here. Are you talking about making a test probe and checking the ground on the relay board? If you are, no I have not yet. I have tested already it with a meter and don't see the value in using the test probe. If you are talking about the LEDs on a stimulator then yes the fuel pump LED lights up like it should.
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post #8 of (permalink) Old 09-03-2006, 10:35 AM
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Re: Relay not working

My guess here is that the output circuit feeding the voltage to the Relay board is bad.

Is this: http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf the schematic of the system you're using?

There is value to using the simulator. However, if there is a power drop, then the relay can't be energized correctly. I'd double check by crossing inputs, say from the fuel pump to another relay input to see what's happening.

Another question. Does the relay engage? If the relay is enabling, then the ECM is doing it's job. The next thing to see is where the voltage to the pump is coming from, and why it's low.

Troubleshooting this is a lot of going back and forth, trying to figure out the logic of the circuit and how it could fail and still have voltage. It still smacks of a ground problem.
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post #9 of (permalink) Old 09-03-2006, 10:56 AM Thread Starter
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Re: Relay not working

[ QUOTE ]
My guess here is that the output circuit feeding the voltage to the Relay board is bad.

[/ QUOTE ]

The output circuit does not supply voltage to the relay only a ground. The relay board has a direct connection to the battery and a switched connection to the ignition that supplys the voltage. There is the main relay that uses the switched voltage to power the main relay. When the main relay is active it supplies voltage to the other relays like the fuel pump relay. The ECM only supplys a ground to the relay. When the ECM want the fuel pump on it grounds the relay activating it.

[ QUOTE ]
Is this: http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf the schematic of the system you're using?

[/ QUOTE ]

Yes it is.

[ QUOTE ]
Another question. Does the relay engage? If the relay is enabling, then the ECM is doing it's job. The next thing to see is where the voltage to the pump is coming from, and why it's low.

[/ QUOTE ]

The ECM is definatly supplying a ground when it is supposed to but it does not activate the relay. I do not believe it is a low voltage but rather a bad ground. I can activate the relay by running a wire from a ground directly to the relay. So a direct chassy ground activates the relay and the ground from the ECM does not.
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post #10 of (permalink) Old 09-04-2006, 06:08 PM Thread Starter
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Re: Relay not working

I decided to pull the MSII processor and put the MSI back in. Loaded the lates code to it and evrything work great. Looks like my MSII is bad, I wasn't planning on controlling the ignition right now anyways so I guess I will leave it as is.
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