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Chris (aka-Moose)
Chris (aka-Moose), Technician
Category: Car
Satisfied Customers: 47668
Experience:  16 years of experience
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Isuzu Trooper LS: I am at a loss here. 94 isuzu trooper, replaced

Customer Question

I am at a loss here. 94 isuzu trooper, replaced engine due to broken timing belt, oil consumption, etc. Went to start engine, will only run if spraying into throttle body, dies if not. Checked for injector pulse with noid light. None of the injector plugs show a pulse which leads me away from the ecm. Swapped wiring harness from original motor, still no start. The only thing I dont have is original crank sensor, but if the crank sensor was bad I wouldnt have spark either, correct?
Submitted: 4 years ago.
Category: Car
Expert:  Chris (aka-Moose) replied 4 years ago.

Hello, I'm Chris. Thanks for visiting Just Answer.


I am sorry you have had to wait so long for the first contact. Sometimes this happens when the question you ask is not detailed enough or its just hard to address online. Many have viewed your post, but have decided to pass.

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Customer: replied 4 years ago.

Yes still need help. The only way I can get the car to run is to spray it with carb cleaner. All the forums I have read say try to spray with carb cleaner to see if it runs, but dont say anything about where to go from there if it does run. I have spark and I have fuel pressure to the rail. I checked injector pulse with a noid lighjt and I get nothing which mean my injectors arent firing. Ive read that the crank sensor could be bad but I also found that the crank sensor tells the coils to fire as well so if i have spark that should mean my crank sensor is working. The car was running fine before I swapped the motor.

Expert:  Chris (aka-Moose) replied 4 years ago.
Turn the key on and off and feel the ECM Main relay to see if it is clicking. If the relay is not clicking, remove it and test for power on 2 pins with the key on. If your missing a power, verify the engine fuse under the dash is good and the ECM fuse under the hood. If the relay is operating then verify all ECM powers and grounds are good. If the relay is getting power but not clicking then see if your getting a ground on any of the other terminals at the relay. If that's also good but still no click, then replace the relay. The ECM needs to receive a square wave RPM signal from the ignition module in order to fire the injectors and turn on the fuel pump relay. If all else is testing good, check for this square wave signal on the Yellow/Red wire while cranking the engine. If there is no signal, the ignition module may be faulty.
Customer: replied 4 years ago.

Can I get a wiring diagram that shows that

Customer: replied 4 years ago.

Okay checked ecm fuses and relay and fuel pump relay all have power where they should and click when the key is turned on. I tried putting a different ignition control module in with no success. Any ideas?

Expert:  Chris (aka-Moose) replied 4 years ago.

Are you getting a rpm signal?


Customer: replied 4 years ago.

can I check that with a voltmeter? Also it shows an external resistor on the wiring diagram for the control circuit of the injectors, does it show where thats at? Just thinking if I left that unplugged?

Expert:  Chris (aka-Moose) replied 4 years ago.

None of my diagrams show the resistor location. An analog volt meter can check fr a square wave signal.