Mercury 200 not firing injectors

[ShadowFlier]

What's the best way to test(if possible) a Promax 225 ecu to see if it's in good order? I just finished rebuilding a 200 ff block motor with a a17 promax ecu. The motor will not run, VST is getting fuel and the plugs are sparking but the injectors are not firing.

[Motv18]

Check the wires if fresh install easy to miss a ground or plug.

their ground switched so the computer has to be grounded good.
That’s also why so many people test the battery through the hot wire and recommend disconnecting the battery a lot.

noid lights work well. Oscilloscope are nice

if the plugs were left off long enough might clean them. They can oxidize.

[billybob]

I would reccommend taking to a MERC dealer with the old style EFI tester. That tester will actually tell you alot. You,ll be able to hear inj,s firing, and will tell you if all wiring is good. Probe purple wire on harness, to see if ECM is even turning on. That is keyed power to ECM.

[ShadowFlier]

I figured out the problem. The injector harness was bad. I bypassed the ecm power wire(purple) and ran it off of the ignition switch and it fired right up.

[billybob]

That is not the first time I have heard of that.

[H2Okie]

Are you talking about the 16 pin plug in connectors between the engine wiring harness and the ECU having a bad connection or does the purple wire have an "open" in the engine wiring harness somewhere . That purple engine harness wire is only about 18 - 24 " long between the terminal it's mounted on (under the starter solenoid )and the #7 socket contact in the plug in connector . What does the #7 male pin look like going to the ECU?

[ShadowFlier]

That purple wire somewhere in the harness must've been pinched or cut. It was on the terminal block in the correct location connected to the purple wire coming out of the engine harness. I spliced a wire from the purple wire of the engine harness right where it comes out of the plug to the purple wire right before the injector harness/ecu plug and it had power. I traced the purple wire through the engine harness and it appeared to be in good shape so that leaves me to believe that it is disconnected somewhere in the injector harness.