Locating misfire

[TheGrimReaper]

Good morning all. Just thought I’d see if I would have some luck getting some answers on here as I’ve been chasing a misfire for a little over 3 months and can’t seem to be able to find the problem. I’ll try my best to include all info on what I’ve done.
My car developed a misfire just after filling the tank and when checked was only in cylinder 8. I went out brought new coils,plugs and leads and switched them over to find that it didn’t change anything. I then opted to check the injecters I swapped 8&7 and then found when starting the car the car developed a misfire in 6,7,8 when put back together. I took it to a mechanics and pressure tested the plugs and found they had a high pressure reading. He checked the plugs,leads and coils again but found that they were working however cylinder 1 plug looked like it wasn’t firing at all. Going to preform a scan today to see if anything has changed since tinkering last night. The last time I tried starting it it passed the system check then once firing I could here the misfire it was so bad that the exhaust was rattling under the car but it wasn’t throwing any codes. It took almost 2-3 minutes of rough idling before it threw a code. Could this be a fuel problem or something gone wrong with something in the block itself. Car runs rough in idle with strong petrol smell from exhaust and just seems to lack acceleration. Once up to speed (60kmh) it feels ok but still off. After ideas on where to go next.
Thanks all who has an input
Car is 2006 Holden Commodore VE SS 265,000km on the clock.

 

[Immortality]

Are you still on the same batch of fuel?


Have you tried unplugging individual injectors whilst idling to see if the miss changes?

Dirty injectors?

 

[TheGrimReaper]

Are you still on the same batch of fuel?


Have you tried unplugging individual injectors whilst idling to see if the miss changes?

Dirty injectors?

I have still got the same fuel as what was put in as I didn’t think it might have been that. When I first scanned it tho back in November it was cylinder 8 only but since moving only two injecters I seemed to have picked up multiple misfires. From my knowledge 6,7,8. I was leading towards injecters but at almost $1000 for the set don’t want to be wrong. If it’s already misfiring would removing the injecters one at a time make it run better or worse and what’s the best way to test them do I unplug and the wiring harness start car test and then repeat for each of them. Would it hurt the block or force more fuel into the other injectors if one is unplugged.
Thanks for the response tho very helpful

 

[Immortality]

As you unplug each injector it will run worse until you find the one that's on the misfiring cylinder and it probably won't change much.

Bad fuel could cause a misfire. Try adding a bottle of octane booster. Sure you put in the right fuel? Could also try some injector cleaner. You can have injectors cleaned/tested. Was this a model that had the injector failure/recall?

Unplugging injectors won't force more fuel into other injectors, fuel pressure is controlled via the fuel pressure regulator.

 

[TheGrimReaper]

As you unplug each injector it will run worse until you find the one that's on the misfiring cylinder and it probably won't change much.

Bad fuel could cause a misfire. Try adding a bottle of octane booster. Sure you put in the right fuel? Could also try some injector cleaner. You can have injectors cleaned/tested. Was this a model that had the injector failure/recall?

Unplugging injectors won't force more fuel into other injectors, fuel pressure is controlled via the fuel pressure regulator.

Thanks for that I’ll be sure to work my way down the injectors today. Am I best to unplug one start car the turn off then work my way down or can I simply have my car running unplug each one till they are all checked. I wasn’t aware that these models had recalls on injectors something else for me to look up. I was thinking it may also be the fuel but apon filling it up I belive the tank was almost on empty so it may have picked up some debris when filled. I think I have already added a bottle of injector cleaner with the boost but doesn’t seemed to have changed much. The car currently just sort of surges Instead of running. Once started the cars misfires but nothing major then as the car warms up and the revs drop to 700-500rpm the car starts to shake violently and after about 1-2 minutes it throws the codes. If I press accelerator and hold revs to 1500-2000 and hold the car is ok still misfires but not as bad as soon as I let go the revs drop not only quickly but almost to 300-400rpm almost conks out then rises and idles at 500-600rpm.