What's the secret for making fuel pump relay work circuit?

[Henry]

We have our MS2 wired according to the documentation to control a relay for the fuel pump. There is 12+ where it needs to be and the relay energizes with a power probe. The fuel pump runs if we bypass the relay.

However, we can't seem to get the MS2 to drop the relay to ground. Is there a setting in the software that turns the relay control off and on?

[hybrid]

In TunerStudio, you can go into the output test mode (under advanced button) and manually switch the fuel pump on and off.
But the fuel pump should always prime when you first turn the ignition on.

If it's not doing that, something is wrong.

[rickb794]

You should get a priming pulse when the MS is first turned on. Then the pump will come on after the MS sees rpm (gets sync).

If you are not getting a priming pulse the MS might not be turning on. If something pulls down the 5vref it will not turn on.

[Henry]

If we jump the fuel pump relay, the car runs just fine, so the ms2 is working. It looks like there is something going on so that the ms isn't pulling the relay to ground. Where should I start looking?

[kjones6039]

If we jump the fuel pump relay, the car runs just fine, so the ms2 is working. It looks like there is something going on so that the ms isn't pulling the relay to ground. Where should I start looking?

As mentioned above, I would start by using the output test mode........

Ken

[DaveEFI]

To test the hardware side, carefully remove the daughter card and put to one side. Run a temporary wire between pins 31&33 on the socket. This feeds 5v to the pump driver circuit input. Power up MS, and the pump relay should make all the time MS is powered.

[Henry]

I did the 'fuel pump on' thing with no results. I'll do the jump pin 31/33 thing next. Is enabling this circuit something that was an option in the initial build process? If so, we might have not gone that route at that time.

[cmonref]

Henry: if this is the 91 Honda CRX, I can't help you. If it is a Porsche, the fuel pump relay has two stages and requires a little magic with MS circuitry.

[hybrid]

I did the 'fuel pump on' thing with no results. I'll do the jump pin 31/33 thing next. Is enabling this circuit something that was an option in the initial build process? If so, we might have not gone that route at that time.

There is nothing to "enable" for the fuel pump to work. It's an integral part of the ECU and should work no matter what.
Do the tests that have been suggested. If you can get the pump to work by jumpering the pins, then there could be an issue with the daughtercard.
If it doesn't work by jumpering those pins then you have some other hardware or wiring issue.

[rickb794]

cmonref brings up a good point, it may be an external problem. We all assume it is a MS thing and you have tested the external part.

Grounding pin 37 of the DB37 with the key on should activate the fuel pump relay.

[DaveEFI]

Only a straw poll given my limited experience, but a blown ZTX450 (pump relay driver) is the most common fault I've fixed on V3 boards. And I can't hazard a guess as to why.