Is This The Boost/fuel Cut?

[Konrad]

Hi,

Just today i got intstalled a set of splitfire coils and NGK iriway iridium plugs. Now once i get above 9psi/3000ish rpm the car misfires badly, like totally cuts out for a split second, then runs fine again, but still wont let me rev the car, is this the fuel cut i've heard about??

Before installing the coilpacks i was running 12psi fine with no problems like this.

What is the boost point where the fuel cut kicks in?? i've read quite a few conflicting posts where some say anything above 8psi have been affected, others run 12+psi fine. ..

Any help would be appreciated

Cheers.

[chrissso]

Hey mate,

Are the plugs in properly? - reseat.

Are the plugs the correct heat range? - std is 5. 6 and 7 should also be ok.

Are the plugs gapped to 0.8mm - std plugs are 1.1mm, regapped to 0.8mm makes a sturdier spark.

It could be running rich. - ECU adds more fuel than fuel needed running more boost. This can cause misfire. - Need aftermarket ECU or piggy back cumputer and tune.

It could be running lean. -fuel pump not supplying enough fuel to the engine, causing it to ping and the ecu hears this by microphones and cuts/retards the ignition. - need a fuel pump, common in early 33's

Its a 94 GTST which usually has a boost cut around 12 psi, so MOST probably not it..

[MKDR33]

Does the engine violently cut out then go again? if so, it sounds like a fuel cut. I heard this is because ur afm detects too much air being sucked in and authorizes the ecu to cut the fuel. i get this with anything over 16psi.. also, i have 2 boost controllers, an electronic one and a turbosmart manual valve. when i use the turbosmart one, it cuts out at around 13-14psi, when i use the electronic one it cuts out at around 16psi. not sure why this is..

To fix the fuel cut problem either get another ecu (Power FC) or Fuel Cut Defencer..

Ive also heard, replacing the stock afm with a z32 helps aswell..

[Konrad]

Thanks for the quick replys lads

-I imagine plugs would be seated fine (didn't do it myself tho) and heat range 7 i believe. Car revs fine up until the point it cuts out (if that makes sense).

-Would have thought car would run leaner now that it has a better spark (new plugs, decent coils) not richer, but running leaner could be a possiblity- no audible knock but doesn't mean it isn't there..... Tune has not been changed or anything like that. Just the plugs and coils were done. Dont imagine that these changes alone would be enough to make it run safe (on my last dyno run a couple of months ago) to dangerously lean unless my fuel pump died all of a sudden.

-Definatley describe it as 'violently' cutting out, its not a blip in the rev range, the car comes on boost, then just cuts out for a second, then runs fine again, then cuts out again...

I'm thinking fuel cut as if i keep my foot down the time it cuts out is always the same. ie. it revs...then cuts....wait 5 secs, cuts out for second again,..wait 5 secs, cuts out again etc...

Seems wierd that its happening at such low boost tho, where does the ecu get its boost signal?? (some small hoses were replaced with silicone ones in the process, was wondering if these would cause it aswell).

Tomorrow i'll make sure theres no disconnected hoses, plus i'll do a ecu reset and wind my bleed valve back to the lowest setting.

[chrissso]

Have you got an AFR graph from the dyno? What boost on the dyno?

It's getting to winter now and cold air is more dense and this will effect things as well.

[Konrad]

Last dyno run (see attached)

Running 10-11psi, r34 gtt cooler, exhaust and pod.

I know what you mean about colder air from winter conditions but i drove the car 80km to work at 5:30 this morning, it was fine, after doing the work on it and driving it home around 4pm i noticed the problem so doubt it's got much to do with the temps.

[chrissso]

From your graph, I'd' say that its running to rich. That AFR of 11 can be put up to a 12 by piggyback or ECU and you'll get more power as well.

IMO cold weather makes skylines run even richer and then you get misfire. Is your engine the original 94model? Some of the newer rb25dets have a lower boost cut.

Anyway - still think that it's just running to rich.

[Rhinorebel]

Isaac, I went through almost the same mod path you are doing, and had the same problems. As soon as you raise the boost and start to push the ecu, save for a good replacement. As you know, I went for the Haltech E11V2 and it is worth every cent!! Any problems are easily diagnosed via laptop and changed easily as well. Lots more fuel mapping points than the Power FC too so it is a smooth power curve!! The strangest result was that the car has 40 more rwkw but is 3 decibels quieter!!

[Konrad]

I think i need to clarify something here. I was running 12psi BEFORE the plugs and coils were swapped over,

ie: 2 days ago boost gauge = say 11psi no misfire/fuel cut symptoms

now: 9psi = the problems. The only way i can get the car to boost to 12psi is if i stab the throttle for a sec or so then lift right off, it builds boost then drops off again. If i'm say on a freeway onramp and gradually squeeze the throttle it gets to a certain rpm/boost (around 3000rpm and 9psi ish ) then its like someone shuts off the ignition alltogether (definatley feels like more than one cylinder if its just a plain old misfire).

Anyone got ideas???

[chrissso]

Yeah, it's not boost cut.

Well, heat range 7 is getting a little cold, should be OK, but may have something to do with it. You will run rich in winter. And do you have the full code for the sparkplugs?

[shanef]

she's farked mate, definately needs a rebuild...

BUT seriously, ive got no idea

kthxbi

[The Dan]

What's the part number for the coil packs?

[Konrad]

Dan- SF - DIS001. They are the right part no for my car.

Anyway problem is fixed, turned out to be a leak in the inlet pipe before the throttle body, so at anything above mild boost it was obviously blowing open and loosing boost.

All fixed now. thanks to all who posted