How do I know if my ecm is bad?

You're jumping the gun bro..... check the fuel pump fuse/relay first then have someone listen to the pump back by the tank and listen for operation. If the pump is getting power but still doesn't run then you need to drop the tank and replace the pump. If you still feel that the ECM is the problem then check the injector circuit by using a NOID light or analog multimeter set on the 5V range and notice if the injector drivers are sending a continuous pulse to the injectors .....if their not working then check the ECM fuse/relay and go from there neighbor. The injector drivers are located inside the ECM and are a pretty good indicator of ECM condition if the ECM is getting power.

Should also be a fuse for the ECM its self, 10 amp in the fuse box, cant remember how it was labeled. Whitelightning

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They call it ECM also, but I believe it's the only one that is red in color, and it's also the only 10 amp.

HDS

So now what....

Cory

If I remember correctly, my 87 S-10 Blazer had two wires feeding the ecm, one was battery voltage, one was from the ignition switch. there have been problems with ignition switches on GM Vehicles. Other than that I don't know what else to suggest other than a good volt meter, and a wiring diagram, check powers , and all grounds. Swapping ECMs gets expensive if its not the problem.

Whitelightning

There is a module in the distributor that can cause starting problems. Had a bad one in a 89 S15 that was intermittent. Was a real PITA to find. Sometimes it would start, sometimes not. No fuel and no spark was the symptom.

Got a now one. Problem solved.

No it's not - find a buddy with a known working one.

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-- GMC Gremlin