1999 Isuzu Rodeo 3.2L engine has no fuel signal

Car wiring question


I am an ATS member and my son’s 1999 Isuzu Rodeo won’t start. I checked the fuel signal using the noid light tester and it was not blinking. I have a crank sensor code which made me replace the sensor but that did not help either. I then replaced the computer thinking that was the culprit and still the same…no signal to the injectors! I am losing my money and sanity here please help!

Vehicle wiring advice

Always go to the basics before buying any parts for your engine. The way this system works, when the computer (ecm) works, it gets its power from the main relay thru the relay’s red white wire, which goes to the ecm B+ pin terminal. That main relay also houses the fuel pump relay, which feeds 12 volt to the fuel pump thru red wire when you turn the key on. However, looking at the wiring diagram, the ecm powers also the coil plugs (a combination of the spark plug and ignition coil) thru ecm pin F4 then individually grounding them.

To check the ecm, always go to the basics. Check the ecm power supply from the main relay at pin B+ during cranking. There must be 12volts there. Also, the reference pins at the ecm terminals must have 5 volts and double check against those reference volts at the input sensors such as the tps, coolant and map sensor. Failure to have those 5volts reference shows that the ecm has failed.


Reference voltage can fail also if the ground pins at the ecm shows more than 0.250 volt with key on. These ground pins are C7, C8 and C9. Any pins showing more than 0.250 volt shows there is a short in the wire, sensor or any output loads.

When working with any electrical component, disconnect the battery negative terminal.

Whenever working under the dash panel, do not touch the yellow-taped wiring harness to avoid accidental deployment of the air bag which will activate even with the battery disconnected. Remember: you do this service at your own risk.

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