Hello, that pulse for 15 seconds and then nothing is the ECM intentionally shutting down that fuel injector because the ECM (engine computer) is seeing a cylinder misfire and it's shutting the fuel injector down to protect the Catalytic Converter from any damage caused by raw fuel going down the exhaust. If you have good spark out of that spark plug for the number 4 cylinder, then you may have a compression issue. Possibly a sticking intake or exhaust valve. Or a worn camshaft lobe. Further diagnostics are needed. Are you getting any cylinder misfire codes? or circuit codes for that injector?
Doing a cranking compression test might reveal a problem, if you use an oscilloscope for diagnostics, doing a relative compression test will show all the cylinders in a parade pattern and might show low compression on that cylinder.
One other thing, if you are checking the fuel injector with it unplugged and losing pulse, that might be why. If there is current monitoring on that fuel injector and it's not plugged in it might flag a circuit issue and shut down the injector also.
Images (Click to make bigger)
Thursday, February 9th, 2023 AT 10:27 AM