Australian Car Repair Issues? Ask an Auto Mechanic for Answers ASAP
Do a exhaust back pressure test a bad catalytic converter could be causing you this misfire .
Then if compression is good and low then using a noid light check the injector wiring harness on
the 4th injector ..Seen injector drivers in the ECM fail and cause this .
Leak down test on Number 4, a bad valve not closing fully also a possibility even though the compression test is showing
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Kind regards Greg.