Running On 5 Cylinders During Startup (occasionally)

[Jezza-gtR]

Its got nothing to do with how fast the motor revs, if it does can you please elaborate?

I did actually mean a combination of they rev quickly / do go to a high rpm. 6-8,000rpm. If an engine is spinning at 7,000rpm the combustion prcocess is and needs to be happening pretty quickly. So a small gap is used when the engine is revving high to acheieve good combustion.

If a large gap (1.0-1.1mm) was used in a turbo application, at those high rpms the spark would be blown out because it has too large of a distance to travel and your engine would run like crap.

[Kujotk]

I did actually mean a combination of they rev quickly / do go to a high rpm. 6-8,000rpm. If an engine is spinning at 7,000rpm the combustion prcocess is and needs to be happening pretty quickly. So a small gap is used when the engine is revving high to acheieve good combustion.

If a large gap (1.0-1.1mm) was used in a turbo application, at those high rpms the spark would be blown out because it has too large of a distance to travel and your engine would run like crap.

Don't burn me because you might find this interesting, and it is the real reason behind the spark plug gap issues.....

I don't doubt that spark gap from 1.1 - 0.8mm makes a difference in an engine, becuase I have experienced it myself in many cars... but it doesn't have anything to do with the distance having further to travel.

spark distance will not make a difference in anything under 120million rpm @ 1mm gap

120km/second

= 120 000 000 mm/second

1mm gap means the same spark can travel 120million times back and forth in one second

120million times / 8000rpm = 15 000 spark chances per every rpm.

So you would agree there is an overkill????

Sorry bout my maths but I thought that was the same reason aswell, further the gap the slower it travels and may cause problems in high rpms....but some wanky engineer proved to me it has nothing to do with the distance the spark has to travel, it is determined about how quickly the car can regenerate a spark.

Say the store value of electricity to creat a spark @ 1.1mm has a value of 1 unit to make the spark.

Then when it creates a spark it's eleectricity store value then drops to 0.5 units, it then has to regenerate from 0.5units back to 1unit to create another spark.

If the gap is shortened it means you now only need 0.8 units of electricity to create a spark instead of 1 unit, basically the regeneration time of electricity to create the spark is reduced, not the spark distance time...

Same out come as what is common accepted knowledge, but the reason behind it is different. If there was a constant supply of electricity to create the spark, then you could in theory have a spark distance of 15meters and still have no problems at 8000rpm.

In the near future this issue of voltage dropping after every spark should be eliminated and spark plug distance and material types will not make any difference. But it is likely that petrol technologies in market share decline will render this breakthrough useless (in cars anyway) as more and more car companies are trying to introduce alternative fuels.

I have re read this and it makes sense to me, but if you can not work out what i mean, the concept is similar to the old school camera flashes... where you would take a photo with the flash on, then you had to wait a second for the battery to give out enough power for the next flash. If you took the pictures very quickly and not letting the battery fully electrify the flash elements, then the flash would be weak or wouldn't work. Basically the flash is the same as the spark....

[Jezza-gtR]

Sorry bout my maths but I thought that was the same reason aswell, further the gap the slower it travels and may cause problems in high rpms....but some wanky engineer proved to me it has nothing to do with the distance the spark has to travel, it is determined about how quickly the car can regenerate a spark.

It's not so much the slower the spark travels it's the fact that there is a larger distance it needs to travel. Also the spark doesn't travel back and foward it just jumps between the contacts. I re-read what you posted twice, I am a bit tired but I can see where you are comming from.

The only thing I dont agree / understand is that the plug doesn't need to recharge. It fires every combustion stroke so its not working for 3 strokes. So I don't know if that is worked into your maths.

[t_revz]

what the engineer told you was correct but can be described differently. during the time between firing the coil is energised, when it needs to fire the power to coil is momentarily cut which creates a large magnetic field which is transferred from primary(coil winding-ignition wiring) into the secondary(coil winding and through spark plug). if the coil isnt powered up long enough before firing due to very high rpm then the magnetism in the coil will be reduced and spark will be weaker. also low voltage will do the same even if it has time to become fully saturated/magnetised

and as for spark plug gap im 99% its due to combustion chamber pressure. electricity cant travel through dense area as easily but i cant remember exactly why anymore if 1.1 works and doesnt miss should be ok but many or most people us slightly lower to ensure correct spark even if its not quite as big.

[Ultimategtr]

I had the same issue, except it would only miss for about 30 secs randomly, esp on a cold day/night. No way it will be the plugs.

Turned out 2 of the springs in the coilpacks were corroded and had white powder coating all over it(This is the bit that sits on top of the plug, on the inside of the coil). I replaced them and its perfect now.

Perhaps check that.

[Galois]

the recharging idea is a metaphor.

it comes down to this, higher gap = higher resistance, because air is a really good insulator and the electrons from the spark hate to move through it.

so the coilpack generates a stack of power, but only when it generates enough will it send a spark through the spark plug. it needs to generate less power to cross a smaller gap, which means the coilpack needs less time to generate the power. bad coilpacks do not work as well, so they need a smaller gap.

i haven't read anything anywhere to suggest all turbo cars should have a smaller gap. there's actually a lot of people on these forums saying run the largest gap you can, and with new coilpacks and near standard boost that's usually round 1.1mm. the coilpacks should be able to cross that gap in the turbulent petrol-air mixture without trouble. the more boost makes turbulence higher which leads to even more chaotic pressure patterns which makes the spark less likely to cross the gap, ie the coilpacks aren't generating enough power quickly enough. smaller gap means the spark happens quicker

birds, i sympathise with your iridium problems mate. there's quite a few testimonies in the spark plug thread saying iridiums aren't worth it. a mate of mine recently spend hundreds on his soarer hunting a misfire, he assumed it wouldn't be his 3000km old iridiums and was shocked to find they were stuffed.

a lot of people go with coppers, ngk bkr6es or bcpr6es, and just change them every 5000km. that way the plugs don't have long to foul up, and it's cheap, consistent and monitored (by you checking the plugs every 5000km) power.

i tried bosch fr7dp platinums for about $40 for 6 this time. they're pretty good, platinums for only a few extra dollars was what attracted me.

btw be careful leaving the valley cover off for too long, it keeps the coilpacks cooler but also exposes them to the elements more. and thinnk about it, they're normally very hot under the cover, but with the cover off they're hot at the bottom and cooler at the top, and heat differentials are what leads to the plastic fatigue.

oh yeah, and someone mentioned earlier that the recommended heat rating is 5? in japan it is on average cooler than here, which means our engines are not cooling as efficiently as there, which means they run hotter. also, once you add a cat back exhaust you're allowing the engine to boost more, which will heat the engine up more.

hope you find the problem soon mate

[Birds]

Valley cover is only off for the time that I need to properly diagnose the problem, once I fix it I'll be putting it back on.

I confess to not knowing the science behind electricity and spark plugs but I always thought as long as you weren't misfiring, a bigger gap was better because there was a longer spark (longer distance wise, not longer duration) and therefore better for initiating combustion? Do tell me if this is incorrect. What Kujotk posted up makes complete sense to me though, and I agree with that.

In the end it's just like oils and different viscosity grades / brands...a case of experiment and find out what works for you, because no two situations are going to be the same and you aren't going to cause major damage by experimenting.

[Galois]

I confess to not knowing the science behind electricity and spark plugs but I always thought as long as you weren't misfiring, a bigger gap was better because there was a longer spark (longer distance wise, not longer duration) and therefore better for initiating combustion? Do tell me if this is incorrect. What Kujotk posted up makes complete sense to me though, and I agree with that.

yep, if the spark has to jump further there is more energy behind it, which means more intense combustion at the source

[blk94r33]

Hey. Probally gonna get flamed being a noob, but I know that my car does this occasionally too (GTS not GTS-T though). Had me worried the first time it did it. Other than the obvious miss, does it do anything else odd? Noises etc? First time mine started, opened the bonnet with it running and noticed it had lifter noise, gently gave it a rev and it picked up again and has rarely done it since. Usually after a cold night or after it's been sitting around for a couple days, lifter bleeds down and upsets things.

[Birds]

And I have located the problem...

The problem started to occur more frequently as of late, so I decided I couldn't ignore it any longer. Not good if it's fuel related and I'm detonating my piston everytime it decides to start up on 5 legs and run like that for 10 minutes.

Anyway, I switched coilpacks 1 and 2 around, started the car, and for the first time I was glad it started on 5 cylinders because it gave me a chance for instant diagnosis. I pulled the loom from coilpack 1...she sounded even worse (now running on 4 cylinders)...then I pulled the loom from coilpack 2...nothing happened, just like when it was on cylinder 1. Faulty coil pack! GAHHHH.

Atleast it wasn't a fuel supply issue, coilpack = cheap and easy to replace. Now to see if YJ will stand by their warranty (I'm sure they will from stories I've heard).

Thanks for the ideas guys.

[Galois]

let us know mate, im looking at getting some yellow jackets because of the warranty very soon

[SS8_Gohan]

And I have located the problem...

The problem started to occur more frequently as of late, so I decided I couldn't ignore it any longer. Not good if it's fuel related and I'm detonating my piston everytime it decides to start up on 5 legs and run like that for 10 minutes.

Anyway, I switched coilpacks 1 and 2 around, started the car, and for the first time I was glad it started on 5 cylinders because it gave me a chance for instant diagnosis. I pulled the loom from coilpack 1...she sounded even worse (now running on 4 cylinders)...then I pulled the loom from coilpack 2...nothing happened, just like when it was on cylinder 1. Faulty coil pack! GAHHHH.

Atleast it wasn't a fuel supply issue, coilpack = cheap and easy to replace. Now to see if YJ will stand by their warranty (I'm sure they will from stories I've heard).

Thanks for the ideas guys.

that's why i harp on about Splitfires dude!! they're not that much more expensive either - just get some blues ones in there and be done with it

[Birds]

Haha I knew I'd hear it from you Daniel

At the time of purchase I'd heard stories about faulty units from 3 or 4 manufacturers including Splitfire and JJR, so I thought it was pretty lucky dip as far as getting a bad batch. And my friend never had issues with his YJs so I thought bugger spending another two hunj on Splitfires...I'm still pretty happy cause I know YJ won't let me down with their aftermarket support and their product has been great up until now. Wonder what might have caused the fault though? Makes me wonder if the rest will be okay too.

[siksII]

Good to hear you finally narrowed it down although it took so long!!! Im really lazy when it comes to fixing stuff like that but I think we have found someone thats just as bad or even worse

I have had spitfires in my car for about 3-4 years now.. no problems with them. Back when I bought mine there was only two choices - Splitfire or Nissan.

[Birds]

Hahaha yes I am very lazy. It's amazing when you fix something though, makes you realise you should have done it sooner and that it wasn't time consuming at all. It's the "starting" on something that is the pain in the ass.

Performance-Wise are sending out a replacement coilpack as we speak, I didn't even have to send my faulty one first...top marks

[Galois]

just ordering mine now birds, 6th cylinder here we come!!!

[kjb_r33]

Most of you were partially correct about the reasoning behind closing up the spark gap.

High combustion pressures does mean more resistance across the gap. This will obviously as stated earlier require more energy to get across the gap.

From here is were most went wrong. It doesnt leave some power over for the next fire, it doesnt make the next spark build quicker.

Dwell is the time the coil is turned on, and has to be long enough to reach full coil saturation. This means the the full power the coil can deliver.

Obviously as engine revs go up we have less time to achieve this, so our ignition system has what we call dwell extension. At higher RPM the coil is turned on EARLIER, which means the dwell is longer (cant be turned off later as when coil is turned off it fires, this would affect timing).

Most coils with dwell extension (ALL since contact points went) will always reach full coil saturation. This means that if our coil can create 50,000 volts at idle, it will do it at 7000 rpm as well. Now, larger gaps, or high resistance in the leads, HIGHER compression pressures and leaner mixtures is going to use MORE of that 50kv to get the gap to ionise, that is, become conductive, so the spark can jump the gap. We have 50kv there, but we want to use the least amount possible.

The reason for this, is that whatever is NOT used to jump the gap, keeps the spark burning for a longer period of time. More ionisation voltage means LESS spark duration, or time the spark is actually there. The longer the better because the air fuel mix is moving due to turbulance, the longer the spark is there the better the fuel is ignited.

im bored, having a sickie lol

Questions?

[Birds]

Yup, usually I can get my head around concepts that are new to me but I struggled with that (I'm also sick today so that might not help). In summation, smaller or bigger gap is better for which application?

just ordering mine now birds, 6th cylinder here we come!!!

Haha I didn't know you were running on 5?

Can't wait to start my car without wondering if she'll start on 5 or 6

I wonder what the problem with the coilpack was...and why it would suddenly come good after 15 minutes of driving.

[kjb_r33]

Yup, usually I can get my head around concepts that are new to me but I struggled with that (I'm also sick today so that might not help). In summation, smaller or bigger gap is better for which application?

Haha I didn't know you were running on 5?

Can't wait to start my car without wondering if she'll start on 5 or 6

I wonder what the problem with the coilpack was...and why it would suddenly come good after 15 minutes of driving.

Smaller leaves more energy for longer spark duration, but it lack and spark area. Larger gives a bigger sparking area but has a shorter duration.

Like most things its a trade off, need to find a happy medium. Higher boost, especially with standard coil packs it would seem that around the .8mm gap works.

The coil would start working with temp as heat makes things expand, a broken internal wire for instance doesnt touch cold, get some heat in and now it contacts.

[Birds]

Makes sense to me, I thought it was something to do with heat making it work again. Something is definnitely loose inside it either way, as I did have the problem happen to me just once after the car had started on 6 cylinders and was already warmed up.

Cheers.