Misfire driving me spare

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Originally Posted by Julian B

Help folks.

Still the same car here- 2005 V6 petrol D3.
Some time last year I replaced the engine for a major timing chain mishap and it was cheaper to replace than repair. Sourced a lowish km motor from a forum member in NSW.

Now I have a new misfire problem. At idle and with throttle. From cold and hot. It is driveable and intermittent misfiring but I don't like to tempt fate here and not pushing it. Under load it is much more prominrnt

OBD code only for cylinder 5 misfire and occasionally 'misfire in first 1000 revolutions'.

I have changed all plugs and leads, cleaned and checked connections, swapped coils around, and even spent good money on injector cleaning and testing (all 6).
Still the misfire persists.

I am operating on an assumption which I just realised, that the 5th cylinder is at driver side firewall. Can someone confirm this is the correct cylinder?

Alternator is a bit noisy and putting out 30V AC at idle but de-energising this before starting changes nothing and the misfire persists.

I am lost here. I am thinking one of:
- a higher level electrical issue, such as the AC ripple damaging the ECU/PCM
- spark issue with wiring
- incorrect cylinder getting my attention as I have not changed all the coils- need confirmation re layout of cylinders as above
- sticking valve (based on the intermittent misfire) but you'd think this would change as it warmed up
- another mechanical issue, but it runs very quiet

Any help here would be very gratefully received. I have made this a really nice car and it has been treated nicely in my hands and this is making me crazy.

Julian

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Hi Julian, we have been away for a few days but back now. Unfortunately we do not have a petrol MAF at this stage, last 3 vehicles dismantled were diesel. Sorry but I can't throw any light on your problem but it does sound fuel / air related rather than electrical

Regards Erich

The solution came from a scope test of the firing voltages. Plugs were found to be the culprit with very poor dwell on 5 cylinders.
Unbelievable.
At least it runs butter smooth now with new injectors!

Thanks to all contributors. I hope the journey helps my future friends with similar issues.

Quote:

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Originally Posted by Julian B

The solution came from a scope test of the firing voltages. Plugs were found to be the culprit with very poor dwell on 5 cylinders.
Unbelievable.
At least it runs butter smooth now with new injectors!

Thanks to all contributors. I hope the journey helps my future friends with similar issues.

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Great to hear you got it sorted. It was driving me spare also...Thanks for closing the loop.

Glad you sorted it.

You started the post saying you changed the plugs?

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Originally Posted by josh.huber

You started the post saying you changed the plugs?

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Not all plugs are made equal that’s for sure. I’d be keen to know the plug model and spec before and after.

no there not, these engines like everything in the last 15 years no doubt calls for platinum or iridium plugs, theyre not cheap $15 to $20 each, but you can get the ngk $5 versions that do the same job but just not for as long, 20,000ks vs 80,000ks.

the chances of having a dead plug in number 5, then buying 6 new ones , and puting a dead one back in the same hole have gotta be good enough to buy a lottery ticket

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Originally Posted by josh.huber

no there not, these engines like everything in the last 15 years no doubt calls for platinum or iridium plugs, theyre not cheap $15 to $20 each, but you can get the ngk $5 versions that do the same job but just not for as long, 20,000ks vs 80,000ks.

the chances of having a dead plug in number 5, then buying 6 new ones , and puting a dead one back in the same hole have gotta be good enough to buy a lottery ticket

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That’s why I’d like to hear from the OP - did he replace with like for like plugs. I suspect not ...

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Originally Posted by DiscoJeffster

That’s why I’d like to hear from the OP - did he replace with like for like plugs. I suspect not ...

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Fully agree, i once battled to get a Suzuki GSF600 started wirh no luck. Turned out one plug out of 4 was rated 1 step colder than the others, engine would not fire. Swapped all out for new correct grade and started first go ran smooth as silk. Difference was 1 letter or number in the designation, easy to miss if you dont know

When I had a previous misfire fault which turned out to be skipped time on one cam I bought a set of OEM plugs from Land Rover. They were motorcraft units. I installed these and the car was never driven subsequently, just a cheap experiment for me towards confirming a dead engine.
I kept the plugs, even in the original boxes.
I used these to replace the ones in the current engine that was misfiring, and it seems this was a bad move.
This car had a low km engine replacement sourced here on the forum from a regular contributor. Part of the exchange was new plugs and leads and the plugs were OEM also, but lasted less than 10,000km.
Not planning on using these plugs in the longer term. This is a great lesson on plug technology for me and that using OEM is not necessarily better.

I hope this explains the issue, but yes I think hellishly unlucky to get repeat misfire on that cylinder.