Misfire when cold on 2006 Jazz 1.4i SDI CVT

[Uncle E]

1) Car starts very well with no missing

2) a few seconds after the cold start routine as it moves to cold idle it starts missing

3) random missing for a long time under idle or varied throttle positions. Not cylinder specific missing.

4) when engine reaches approx 82C the missing stops and engine runs very well.

Engine runs well on EITHER bank of spark plugs when warm or starting.

[Jocko]

Welcome. What do you mean "Engine runs well on EITHER bank of spark plugs when warm or starting."
Both banks operate simultaneously. With a misfire on a DSi engine, it is usually rear plugs need replaced or a rear coil breaking down due to infrequent servicing of rear plugs.

[culzean]

Any misfire on an I-DSi twin spark always suspect the rear plugs - they often do not get replaced even by garages - the front ones are so easy to see and people think that is it,  don't even realise the engine is a twin spark and has 8 plugs.  Some people on here have taken rear plugs our and seen massive gaps of 2mm+ because the plugs not replaced from when car was new.  If the plug gaps get too wide they often cause coils to fail,  but replacing plugs is the cheapest option to carry out before anything more costly like replacing coil packs.   As Jocko says the rear plugs fire at almost the same time as front ones,  but during load and higher engine speeds the difference in spark timing between front and rear can alter i-DSi is intelligent Dual sequential ignition..

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[Jocko]

By simultaneously I mean you cannot run one set or the other. As culzean says they fire to give the largest flame front.

[Uncle E]

Hi Culzean & Jacko,
Thanks for your replies. The car was serviced by the local agents ( Cape Town South Africa) in December with new plugs and one rear coil ( second replacement of a rear coil) but the misfire was still there. I have had all eight plugs (and coils) out, they are clearly new with correct gaps. My son-in-law (electronics eng) and I, having researched as far as possible, tried starting up, then pulling off coil connectors one by one, both front and rear. That didn't show any one cylinder. Then we tried disconnecting all rear and start, no difference. Start with all front disconnected and no change. the car starts and idles/revs exactly the same in all situations.
When it starts from cold it fires smoothly then settles to a misfire which is similar to a carburetor motor "hunting" on a lean setting.
Son-in-law, Craig, has the gadget that plugs into the car's brain and was able to establish that the misfire goes when engine temp reaches approx 82C.In other words at running temperature.

[Jocko]

Did Craig check to see if there were any error codes, using his device (assume it plugged into the OBD II port)?
It could possibly be low fuel pressure, due to a dirty fuel filter. Also worth cleaning the EGR valve.
I am surprised that the Engine Management light has never come on.

[Uncle E]

Thanks Jocko.
Craig needs to load additional software, but will check further.
I only have an engine malfunction light which has never come on apart from at start-up, then off.
I've seen a lot of posts elsewhere on the EGR valve which I will have a go at cleaning.
We are currently on strict lock-down here and so no access to garages and motor supplies at the moment.
Will check for error codes. Once at running temp it's fine so I would be surprised if it's fuel pressure.

[Jocko]

Another thing to look for is an air leak at the inlet manifold area. Possibly one of the multifarious small rubber hoses. Air drawing in at the inlet can cause a misfire

[madasafish]

When it idles is teh engine quiet or is there any tappet noise?

I ask because if one  (or more) cylinder's tappet clearances have closed up - you may get a misfire. As the engine warms up, the gap increases . If the engine idles very quietly with minimal tappet noise, that is  a potential cause..  If mielage is over 80k, and gaps have never been checked.....

[Jocko]

As the engine warms up, the gap increases .

In my experience gaps decrease as the engine warms up.

[Uncle E]

It's almost bedtime here. There is some tappet noise until the motor is at temp, then it's quiet.
I'll be looking at the EGR tomorrow. 😴

[Uncle E]

Bolts on EGR valve are extremely tight so a bit of penetrating, a bit of tapping. Some more oil and leave to soak. I'm afraid of stripping or breaking. I'll be in touch when there's progress.