Ok, so what we have is a 2.33 built motor with gt 30/40 turbo running 30 psi, walbro 255 fuel pump with fuel pressure reg, brand new coil packs 5k miles ago.


Had PFR7B plugs and the misfire when the engine was built and what happens is during the first 3 gears of acceleration starting at 7k rmp i'd get a big jolt like i hit a rev limiter and a bang from the exhaust.

The plugs later were abandoned for NGK BR8EIX (grade 8 0.7mm gap) and that fixed the problem for awhile, but when the weather turned cold (below 10c outside) i'd get the same jolt but only in third gear . On warm days it drives perfect with no probs.

Driving to the garage today everything was fine and didnt have a single misfire

Well since i didnt want to leave it at that i've decided to chang the plugs anyway for DENSO ik01-24 racing plugs, grade 8 with 0.44mm since they sounded like a nice spec. And well, after changing the plugs, i now get that dreaded misfire in all 3 first gears again!

Obviously the next step is to change the coil packs, but since it is just so damn expensive and they have only been on for 5k miles - is there anything else i should look at ?

Cheers

 

Oh yeah, it only happens when you really push it, i.e at full 30psi of boost. When you give it 2/3 throttle it revs fine to 8k rpm.

And full throttle in 4th 5th and 6th is as smooth as baby's bottom. Not even a hint of anything.

 

can anyone hazard a guess ? Or shall i replace the coil pack next?

 

A fellow enthusiast and friend of mine has passed the 450 mark and has i think a very similar if not the same problem? We have tried everything from the MAF sensor to fuelling but still to no avail. He was recommended a re map which would apparently iron out the problem but these obviously dont come cheap so definitely try to trace the problem to plugs or coils beforehand

 

Plugs are only minor important...A spark is a spark when there is fuel and air.
Missfires are to do with the supply to the plugs or just general tunning. After all the electrical...which you can test at a pinch...there is only mixture to figure

 

The other thing i was thinking about were injectors - Wouldnt it produce the same effect if there isnt enough fuel flow to the cylinders ? But then again, why wouldnt it hesitate in every gear in that scenario?

And my car has been mapped twice now, but i didnt notice the problem untill just recently because remapping is done in higher gears.

 

it could be a plug if it is breaking down after all why would they be routinely changed on servicing if they do not cause problems?

in my opinion plug change first as it easiest option if still no good start looking at other stuff

 

boost leek or a split hose , just a guess