VY V6 misfiring under load - possibly not plugs or leads

[gregp]

Hi all,

My VY V6 is misfiring under load - taking off or accelerating. I had exactly the same problem 4 years ago, and I fixed it by replacing the leads (plugs had been done 4.5 years / 40,000kms ago, so I did the leads which was 4 years / 20,000kms ago). The car's spent quite a bit of time parked up during the past few years, it's only done 20,000kms in the past four years until we started using it again in June this year. It was fine for a few months, but in the past two months has started misfiring when taking off and under acceleration.

4-5 years is probably long enough for plugs or leads on a car doing 20,000kms/year, but I wouldn't think they should be the problem if it's largely not been used. Is that still the most likely candidate? Or could it be coil pack or something else? It seems to be ignition-related as opposed to fuel - I've tried a double dose of injector cleaner and it's made no difference, it feels exactly like an ignition miss like it was last time, which the new leads fixed. The 'miss' is very sharp and pronounced, just like the engine is not firing sometimes. I would have thought a blocked injector would be a bit hesitant / low on power, but not a sharp miss.

Would an OBD2 tool help diagnose it? I've got one kicking around somewhere if I need it but figured this'd be a common issue.

Welcome any thoughts.

Cheers,
Greg

 

[krusing]

Yes to scanning it first,

I’m tipping either/and/or -
Fuel,
Fuel pump
Fuel pump filter,
Plugs,
Plug leads (check the resistance)
Vac leak,
LIM gaskets,
Just to name a few normal items to check/investigate first.

 

[lout]

plugs are supposed to be changed at 40,000km

 

[gregp]

Thanks guys, I'll work through those things.
* The problem's happened over several tanks of fuel so I don't think it's just this batch of fuel.
* The external fuel filter was replaced at 255k. The in-tank filter's never been cleaned to my knowledge (I've had the car since 2006 @ 80,000km)
* Plugs are indeed due; they're NGK BPR6EFS-15 which apparently are 40k service life. I thought I'd bought 80,000km units but it seems not
* Would a vacuum leak cause an issue under load? I would have thought it'd be lumpy under light load when vacuum is at its highest, but this problem shows up under acceleration when there'd be less vacuum
* Is the LIM gasket the same as the 'valley' gasket? I did this at 180,000kms https://forums.justcommodores.com.au/threads/changing-valley-gaskets-what-else.230237/ though it could be due again. I do still get a little bit of sludge under the radiator cap

Cheers

 

[RWD4ever]

Hi all,

My VY V6 is misfiring under load - taking off or accelerating. I had exactly the same problem 4 years ago, and I fixed it by replacing the leads (plugs had been done 4.5 years / 40,000kms ago, so I did the leads which was 4 years / 20,000kms ago). The car's spent quite a bit of time parked up during the past few years, it's only done 20,000kms in the past four years until we started using it again in June this year. It was fine for a few months, but in the past two months has started misfiring when taking off and under acceleration.

4-5 years is probably long enough for plugs or leads on a car doing 20,000kms/year, but I wouldn't think they should be the problem if it's largely not been used. Is that still the most likely candidate? Or could it be coil pack or something else? It seems to be ignition-related as opposed to fuel - I've tried a double dose of injector cleaner and it's made no difference, it feels exactly like an ignition miss like it was last time, which the new leads fixed. The 'miss' is very sharp and pronounced, just like the engine is not firing sometimes. I would have thought a blocked injector would be a bit hesitant / low on power, but not a sharp miss.

Would an OBD2 tool help diagnose it? I've got one kicking around somewhere if I need it but figured this'd be a common issue.

Welcome any thoughts.

Cheers,
Greg

Yes bad DFI coils can do this. When just pottering along, there is enough spark. Under load, more air in the cylinders and higher voltage is needed to fire. If you have a multimeter, measure the resistance across the two terminals on each coil. If one is higher than the others, that is suspect.
OBD2 will not help with Ecotec, unless it is a scan tool that works with ALDL.