whilst doing some work to the right hand side off my car i cleaned and gapped the spark plugs

they are NGK iridiums with about 10k on so not due for changing yet

they where pre gaped to 0.8mm (more like 0.9 in reality)
most people seem recommend smaller gaps around 0.7/ 0.6

my car also runs on gas aswell. whilst running on gas i was geting a couple small misfires at certian points so i re gaped to 0.4 on the drivers side of the engine.
this made it run much better so a couple months latter (yesterday) i did the other side. right hand side.


now cylinder 4 is misfiring all the time. from idle to 5k. 20% or 100% throttle it misfires all the time. engine light flashing the whole thing

what could i have done wrong?

has anyone got any suggestions i can try? i dont have a lot off time and no daylight to be messing around so i thought id ask for some help first

 

The coil-pack could not be put on properly. Best to remove the plug, check it's condition again. refit and make sure its nice and tight.

check the coilpack and it's connection's on the inside are okay

Wouldnt think it be anything other than that considering they were okay beforehand

 

I once had a faulty plug lead, caused by the Subaru technician pulling on the lead, rather than the connector, when changing plugs. Gave a similar effect.

You might also have a faulty plug, try swapping the plugs on one bank.

 

I dont think you can gap iridium plugs, you will just damage them.

 

Indeed gapping can damage the tips - but normally platinums, I guess iridiums probably can suffer too - can't say I looked too hard at the tips to see how precious metal is attached to the electrodes.

Word to the wise; I have actually killed a spark plug just by removing it and refitting it. Not on a scoob - a Kia picanato of all cars...plug was tight, but gave it no thought. It misfired under load afterwards. My guess is the extra torque required to unscrew the plug had caused the body of the plug to flex and create a invisible hairline fracture in the ceramic insulator for the spark energy to leak out (i.e a spark jumping somewhere else, rather than at the tip). By making a gap tigther, you reduce the energy required to make a spark jump a gap.

I normally see this issue with coil-on-plug coil packs. They often contain ceramic as a electrical insulation material whichi s obviously brittle, so they don't take kindly to be being pulled and twisted. The amount of VAGs I get with misfires after a plug change because some DIYer has been too heavy handed with the coilpacks and broke them internally (all four in one case - they were visibly bent! .

I suggest that 0.4 is pretty tight. If having it that tight cured a misfire, I'd say another part of your ignition systm has degraded and is leaking spark energy. Spark always takes teh path of least resistance. If that means jumping though a lead or shorting inside a coilpack instead of a plug, then thats what it'll do - espcially on difficult to ignite fuels like high octane LPG.

BY all means swap components between cylinders (one at a time) to see if the misfire moves. That is usually the easiest/cheapest way to pinpoint the problem.

 

false alarm! i pulled on the connector and it came off. it was on but haddent locked!

thanks for the information though. still very usefull!

as for the curing misfire. yes it did reduce the misfire a little bit going to 0.4 im also squirting in a little petrol to lower the octaine a little and wet the valves.

when it dose misfire mabey once every 3 months ill get a warning light. this alsways shows diffrent cylinders as misfirering. sometimes 3 and 4. sometimes 1 and 4. sometimes 3 and 2 ect. making me think its not a problem on each one


when looking at upgraded coilpacks i found you can increase dwell in the ECU. having done this a little bit it also helped

bad for the coil packs yes. but they are 10 quid each on the WRX!

iv got 4 new coil packs in the post.

 

I had this on our Tribeca also running gas. Tried all sorts of fixes which made no difference. Turned out to be BAD valve seat recession.