Very Slight Misfire & Can't Pass Emissions

[hp22]

2003 Jazz with 290k km (180k miles).
Totally Failed at Emissions out of nowhere,

CO & Lambda all good, However CH at 740
After I changed spark plugs which looked totally fine,filters, taking it for a hard spin before the next test the CH was still too high at 240 and failed.

No errors on dash, local service couldn't see anything reported wrong when plugged to computer as well.
Any ideas where to look at and possible causes that could be causing this?

The only other thing that I think of is I started experiencing very very small almost non-noticeable mis-fires a couple year ago at idle and idle that is sometimes more rough than it should be ( all good when driving and there is no power loss or anything like that).

Lately, the exhaust also has started to sound like it's misfiring slightly.
I have had the car for 10years and the slightly weird sounds from the exhaust definitely are not normal.
Basically the exhaust should sound like:

prrrrrrrrrrrrrrrrrrrrrrrrrrrr
instead,it sounds like
prrrrrr puk prrrrrrrrrrrr puk-puk prrrrrrrrrr puk-puk-puk prrrrrrrrrrrr
Here is a video:

So in Short, CH Emissions are way too high, Car very slightly gives out a misfire sound at idle sometimes, exhaust sounds like it shouldn't.

Any ideas?
Thanks.

[Jocko]

I take it you mean HC (Hydrocarbons) which needs to be below 200?

[hp22]

I take it you mean HC (Hydrocarbons) which needs to be below 200?

yup, exactly.

[culzean]

Have you changed all 8 spark plugs, could you have some dodgy ignition coils ?   Try a thicker oil ( 20W/40 or even 50 ) , worn bores and valve guides can cause engine to burn oil, and raise hydrocarbon emissions.  Last but not least, CAT can be failing.  Does the vehicle still do long journeys or short 'down to the shops' trips, the CAT can get partly blocked on shorter trips. Also a whole 500ml bottle of redex in the tank and a long drive  can clean fuel system and injectors. 

[hp22]

Have you changed all 8 spark plugs, could you have some dodgy ignition coils ?   Try a thicker oil ( 20W/40 or even 50 ) , worn bores and valve guides can cause engine to burn oil, and raise hydrocarbon emissions.  Last but not least, CAT can be failing.  Does the vehicle still do long journeys or short 'down to the shops' trips, the CAT can get partly blocked on shorter trips. Also a whole 500ml bottle of redex in the tank and a long drive  can clean fuel system and injectors.

yup changed all 8, no idea about ignition coils, it hasn't thrown out a single error on dash and when scanned nothing came up either.
Redex was on my to-do list. Fairly sure I dumped some thin 5w30 premium oil in it the last time I changed it, guess the oil change  is due soon so probably will try adding a thicker oil for good measure as well.

If it was the CAT, wouldn't all the other Emissions be off? The others are completely fine and good, only the HC was through the roof.

I see some people in other threads has mentioned Dirty EGR valve as a cause of misfires in their jazzes, can something like that also throw off the emissions since EGR it's actually related to emission control?

Edit; I had a can of carb cleaner,took of the EGR and cleaned it, it was kinda dirty with soot and the spring wasn't very springy,after cleaning all the black crud off at least the spring was much better,I don't think it gave any effect to the slight misfire/running rough.

[culzean]

You would notice a dirty /  stuck EGR at low revs as it is like having an air leak in inlet system and engine can cut-out, judder and stall easily, ( generally be a nightmare )  they stick open ( if they stick closed nobody notices as they normally only open north of 3000 revs anyway to let exhaust gasses into inlet and cool the combustion to reduce NOx ).  Try the Redex and the thicker oil first as the cheapest route...

[E27006]

HC too high, can be  un-burnt  petrol in the exhaust gases,  a sparkplug/ignition fault
You have changed all the sparkplugs, so time to look for ignition coil defects
.
The Dsi Jazz has 8 spark plugs and 8 ignition coil lead assemblies. We need to test for a bad coil.
I too  suspect one or more defective ignition coils,  only 7 (or perhaps 6)  sparkplugs are firing.

 Two suggestions to try and identify a defective coil

1)
 pull an ignition lead from a cylinder one at a time , then start the engine,  switch off and then push back the lead if there is no change to the engine sound or running, do the process of pull off / push back on for each lead in turn.

2)
 I would buy two new ignition coils and fit the pair of new coils to cylinder 1 , then 2, then 3 then 4 in turn, testing for better running of the engine after each change.
There is a  thread with a few details of using  non-Honda coils from  Ebay etc,  the non-Honda coils are a lot less money to buy

Link to posts on non-Honda ignition coils:

https://clubjazz.org/forum/index.php?topic=12004.msg81553#msg81553

[Jocko]

Redex do a Pre MOT cleaner. Maybe worth a try.. Autodoc do a range of coil packs at a range of prices.

[hp22]

Changed to Fresh thicker oil & Dumped in a bottle of redex (btw I'm very aware it's snake oil so not putting much hopes on it...although It possibly helped my other car in past to stop stalling).
Drove 50km..not seeing any immediate engine performance/sound change, I do realise redex takes longer than that, so will keep a look..


How exactly do you identify a defective coil by removing one at a time while still running the engine?
Can you only unplug the lead for it while keeping the coil in without actually physically unscrewing and pulling out the coil?

I very much remember it was an absolute pain to remove the rear ones when I was changing spark plugs.

Also after you unplug/remove the coil , what exactly do you need to look/listen at?
Won't the car simply start to run much worse even if you only remove 1 coil?
If I got it right, you should start removing coils and see for which coil once removed the car continues running the same as it was before?
 - as in , if it was dead/not working it wouldn't affect the performance either way since it wasn't working?

[hp22]

Or could this be the procedure to test?

Start the car
Unplug the leads  for both front/rear coils for cylinder 1 (without physically removing coils).
The car would then start to run worse I guess since it would be running on 3 cylinders only?
Then Plug in for example the front coil for cylinder 1 and listen if it starts to sound better?
If it does, pull out the plugs for the front coil so again both coils are disconnected for cylinder 1.
Then Plugin in the Rear coil for cylinder 1 and listen if it starts to sound better?
If it does..that means that both coils for cylinder 1 are good?

Move to Cylinder 2 and continue repeating the process till all coils in all 4 cylinders are tested until you come accross one that if plugging it back in ,no improvements happen in engine sound/running?

[E27006]

Or could this be the procedure to test?

Start the car
Unplug the leads  for both front/rear coils for cylinder 1 (without physically removing coils).
The car would then start to run worse I guess since it would be running on 3 cylinders only?
Then Plug in for example the front coil for cylinder 1 and listen if it starts to sound better?
If it does, pull out the plugs for the front coil so again both coils are disconnected for cylinder 1.
Then Plugin in the Rear coil for cylinder 1 and listen if it starts to sound better?
If it does..that means that both coils for cylinder 1 are good?

Move to Cylinder 2 and continue repeating the process till all coils in all 4 cylinders are tested until you come accross one that if plugging it back in ,no improvements happen in engine sound/running?

Pulling the leads with the engine running will probably give you a painful electric sting as the HV discharges through your hand and arm,  but I agree with your principle, you are looking for the dead / dying coil, isolating the dead / ineffective coil   the engine running will not change, whereas isolating a good coil  should  cause the engine to run a lot worse 

How the Dsi system operates:

https://enginetechnologies.wordpress.com/2014/03/23/honda-idsi-engine-technology/

[Westy36]

Just a thought, but perhaps E10 has upset the car a bit. Perhaps try some super u/l 97RON?

[hp22]

Or could this be the procedure to test?

Start the car
Unplug the leads  for both front/rear coils for cylinder 1 (without physically removing coils).
The car would then start to run worse I guess since it would be running on 3 cylinders only?
Then Plug in for example the front coil for cylinder 1 and listen if it starts to sound better?
If it does, pull out the plugs for the front coil so again both coils are disconnected for cylinder 1.
Then Plugin in the Rear coil for cylinder 1 and listen if it starts to sound better?
If it does..that means that both coils for cylinder 1 are good?

Move to Cylinder 2 and continue repeating the process till all coils in all 4 cylinders are tested until you come accross one that if plugging it back in ,no improvements happen in engine sound/running?

Pulling the leads with the engine running will probably give you a painful electric sting as the HV discharges through your hand and arm,  but I agree with your principle, you are looking for the dead / dying coil, isolating the dead / ineffective coil   the engine running will not change, whereas isolating a good coil  should  cause the engine to run a lot worse 

How the Dsi system operates:

https://enginetechnologies.wordpress.com/2014/03/23/honda-idsi-engine-technology/

hmm.. are you sure it would shock you?
I saw someone on Youtube doing just that on the Jazz.

(very hard to understand what he is saying..)

Yes.. Coil packs create extreme jolts of energy,however those plugs are just 12v power supplies to them?

[Jocko]

Just a thought, but perhaps E10 has upset the car a bit. Perhaps try some super u/l 97RON?

E10 is due to be phased in from September the 1st. Pumps say E10 are actually E5 until then.

[E27006]

Now I understand,  in the youtube video, the ECU to coil plug is being "pulled" this is safe for the "puller" the voltage is less than 12V,   I referred in my post to to pulling the coil assembly from the spark plug, with no-where-to-go the HV spark would discharge  to the easiest path, the fingers and hand of the "puller"
y