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A contest! What's causing the missfire?

Duncan

By Duncan,
in General Automotive Discussion

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Duncan Grand Master

Duncan

Posted
Posted

To save having to actually work out what the problem is myself, I thought I'd let all the guru's on here diagnose the problem :D

Symptoms

1) Car runs fine sometimes when flat out

2) Other times it missfires. Missfire can occur from 3000rpm right up to 7,200.

3) Engine check light has now come on three seperate times

The car

1) Is stock except for 9psi boost

2) May have been zooming around a track at the time :)

BTW, does anyone else have pretty rainbow patterns on their fuel rail?

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https://www.sau.com.au/forums/topic/23056-a-contest-whats-causing-the-missfire/
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Silver-Arrowz Grand Master

Silver-Arrowz

Posted
Posted

You bum! Have time to go to EC but no time to get your hands dirty! Pansy boy! :P

Take the plugs out and get some sand paper and lightly sand the top and see if that does the trick. If not then it's not your plugs.

croat Mentor

croat

Posted
Posted

Duncan i have this same problem at the moment. I had new plugs in but changed them 2 days ago anyways to irriduim with .8mm gap. i have exhaust, cooler, boost to 9psi. When i 1st changed the plugs it worked well on 8-9 psi but after a big night cruising last night (gave it a bit!) and i put it up to 10 for a while then it began again... So i lowered boost back to 8 and now it does it non stop. i think its the coilovers, which is apparently a very expensive fix ($1000 and up).. keep me in touch if you hear anything new.

OZ GTR35 Veteran

OZ GTR35

Posted
Posted

Duncan,

Sh!t man it could be any of those things. I personally over the last 4-5 years of owning a Skyline have seen the following cause problems with miss fire on my car.

My spark plugs, they were 10,000km old and drifted past 1.3mm. 1hr and $20 to fix.

My Air Flow meter, loose wire in AFM, 1hr to fix, $300 for a second hand one.

Dirty Inj, bad fuel in country NSW, 1hr work and a bottle of wine to my local workshop to use the ultrasonic cleaner and flow checker.

Coil pack not earthed properly, after changing my spark plugs I did not seat one of my DIY packs correctly. 1hr to fix and a kick in the ass for being stupid.

Reset ECU, the fuzzy logic can some times be a bad thing. 3-4 hours if you are at fatz house, hmmm beer.

Other problems I have seen from other members, fuel pressure / regulator, faulty spark packs, fuel pump. Never fixed em so can’t comment.

Personally start with the plugs as most the other issues produced more than a slight miss fire, it was more go / no go.

Duncan Grand Master

Duncan

Posted
  • Author
Posted

Well, thanks to everyone that's replied, she's at the mechanic today (apparently they know how to open the big lid at the front and do stuff under it to fix things).

Keep voting, we should have an answer tonight.....

BTW, my vote was for alternator since it is intermittent.

TTT Grand Master

TTT

Posted
Posted

it will be spark related.

but because you said it is only sometimes, I will go with the coil packs.

My one started off that way, it would come and go...

at first it was just an occasional hicup, then it would miss for longer, then eventually that particular coilpack completely died.

this makes it easier to find..

bought a second hand one fo $40 problem solved..

the most annoying thing about it being an intermitent thing is that it makes it hard to find which coil pack it is..

B-Man Grand Master

B-Man

Posted
Posted

What ever it is , it must be still in the shop - went in of friday - now Sunday and no indication from Duncan yet.

So, prolly not plugs as that would have been done first, and Duncan would have his car back and have told us what it was.

Or , not.

I stick by my original analysis.

:D

Duncan Grand Master

Duncan

Posted
  • Author
Posted

:oops:

sorry b-man, yeah it is back but not driven yet. I told them your theory and they had a look, apparently all conrods are still within the block (not sure how they can tell tho :confused: )

They checked plugs (apparently they ARE under the bonnet!) and cleaned the AFM....but since it was always intermittent I'm not 100% sure its fixed.

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