Odd misfire

I've covered a couple of thousand miles in my 2006 Jimny now and have an issue which annoys me.
One of those issues where I don't know how to pin down the cause without changing lots of parts in the hope it fixes it but which could prove expensive for a simple fix.

Almost every time I drive the vehicle it suffers from a misfire which happens once for anywhere from a second to approx. three seconds.
It only happens after driving for 10 mins or so, not when stone cold. It will not happen again no matter how far I drive and will not happen the same day if parked up for a few hours and then driven.
My ODB reader is showing no faults.

Does anyone have any suggestions as the the most likely candidate for this. I would have thought that anything breaking down, plugs, sensors etc. would not be so specific as to happen at a similar time and then not again during a drive. Gear, speed etc have no bearing. It does not matter if I am going uphill, have a half empty fuel tank etc..

I assume it is going to be something electrical, but as I say replacing sensors willy nilly can get expensive. It otherwise drives fine.

Cheers in advance.

Coil packs tend to go and most often the rear one due to it getting the most heat that over time is bad for electronics. Mine did not make a fault code. Sensors like cam and crank will also make these errors. Mine only with a warm engine, but most often misfired for longer time like half a minute so I switched the car off to let it cool down.
I bought an ebay coilpack after testing a bit with coil packs from other suzukis I had lying around. Have had this error on my Swift as well and changing them back and forth to find the broken one, I am actually not sure wich ones my cars got now.
Baleno 99, Jimny 05 and Swift 07 all the same it seems. If you can borrow a coil off someones working car, it is a swift test and fix.

Without any fault codes it’s not going to be easy to find and since it only happens once that makes it very difficult.

One thought, does it happen when the thermostat opens, that might be about 10 mins in? Not sure what that might cause, but looking for something common.

How good is your battery, that first start knocks a lot out of it and often doesn’t start to recover until several minutes in?

After that I would check the plugs and coils, just pull them and inspect, then check everything else, air filter, throttle body, etc.

Not sure if cylinder head gasket could cause this problem, BT the plugs will tell you.

Hope that helps.

Robin

Funny you should mention the thermostat opening as that did occur to me the last time it did it. I will have to monitor more closely.

Its the fact it only happens basically once a journey that has me baffled. A very short window for testing!!!

That would suggest the coils as they fail from heat at the point where it is the warmest is my idea and experience.

When you get the misfire do you get a Check Engine Light flash on the dash board?

I would visually inspect the coil packs and plugs.

Check the coil packs for cracks or other odd marks, clean them first and use a magnifying glass at varying light angles. My other car had a misfire and I had looked at all six coil packs before I spotted a crack on the last one, when I checked the others, all six showed some sort of crack in them, most were probably OK, but I changed them anyway.

I am not sure if you can measure the primary resistance on a Jimny coil pack, but if you can this is worth a check.

Check the plugs for colour and any damage to the central insulator. If you have a head gasket gone and a water leak, one plug will be washed clean. I am only thinking this if the problem occurs when the thermostat opens and lets a lot of water round the engine.

The thermostat might be a red herring if it was doing it last summer when it was hot. When it has been running for a while what is the max temperature you get up to?

CAM sensors are known to play up when hot.

If it is not spark related (weak spark or at the wrong time), it might be fuel. You don't have some strange fuel flow issue (blocked filter) or possibly an injector?

No check engine light.

Only owned it since September(ish) last year. Temp gauge never goes up past half way, regardless of weather.

If heat was the issue (and I'm not saying it isn't) why only a short misfire then nothing. Something failing due to heat would surely continue to fail??

Anyway I will try and check everything mentioned.and see if I can find any clues.

Thanks

My coils where out like 10-30 seconds so your misfire is way shorter than what I had. No Idea why they are out so "little" but if they cut and the engine runs on two or three then there is less current going thru. But if it was the coils one would think they would not cool down so fast.
Could be a limp mode or something inside them, Coil fails does not show on the ECU diagnostics.

Well finally got 5 mins to start investigating.

Swapped out the plugs (iridium and all looking the same) for a set of standard NGKs.
Coil packs look very clean, and identical in condition. No damage I could see.
Air filter was replaced only a few hundred miles ago, along with oil change.

Anyway. Short drive and the issue is still there.
It does not happen until the temp gauge gets around the mid way mark where it then stays.

I'll try and get a coil pack to swap in next.

Other thing to mention is it starts on the button every time and runs fine up to the mysterious misfire.
Has to be heat related I think ....

Okay so got a coil pack and swapped out the rear one as suggested by @yakusa
That was two days and two drives ago and so far no misfire.

Fingers crossed it was that simple a fix ...

Well today's trip was not so uneventful.
Seemed to get past the usual misfire spot but a few miles further on misfired like a devil for much longer. Like minutes. Narrow road with no opportunity to stop. When I did stop it cleared and was fine until I reached my destination a few miles on.
Swapped the new coil pack for the old one and six hours later made the return journey. This time it started misfiring around the usual time but again for much longer.
So more swapping to be done.... ☹️

Put the new coil pack in place of the front one this time, that was a few days ago, and so far so good .... real test will be Monday when I have a longer more important journey to make!!