The Most Elusive Rb Misfire Issue Ever

[Lithium]

Hi all,

I am fully running out of ideas for a very annoying ongoing issue I have with my Skyline. The symptoms are that it has a serious misfire/hesitation which only rears its head when the car has been warmed up and driven for a while, and is mainly in effect between 2500-3500rpm at any load level - straight cruise or at full load. The car will cruise fine at 2000rpm, or at 4000rpm+ (even wide open throttle above 4krpm is perfectly fine) - but in between gets very iffy.

Does anyone have any ideas on what it could be?

Information on the setup:

- R33 GTS25t with the original RB25DET, compression test a couple months or so ago gave +/- 5psi across all 6

- Runs a upgraded (Garrett GT3076R) turbo on 1bar of boost

- Running a GTS Link plugin ECU (MAP sensor, no AFM)

- Has stock inlet and exhaust manifolds

- Has been dyno tuned, and on the road aside from when the miss happens mixtures seem sensible - though the uncombusted air I assume would be responsible for the lean spike on the LM2 when it happens

- Runs a wasted spark ignition system using GM/Holden Commodore VN V6 coils and a Link 3channel ignition amplifier with NGK "BCP" heat range 6 plugs gapped to .8mm

Things we have tried to diagnose this issue so far:

- Changed Spark plugs

- Changed coil packs

- Changed ignition leads

- Changed exhaust manifold

- Done a road test with wideband to check mixtures

All of the above things resulted in no change whatsoever.

Thats all I can think of that might paint a picture of whats going on, any input would be greatly appreciated - feel free to ask any further questions... I am at a wits end with this now, its unlike anything I've seen before and makes the car very hard to enjoy.

Cheers,

Dan.

[shy_s6]

pull the plugs out and gap them down to .6 - .65 try that and let me know how you go, contcact clean all leads plugs while its apart

[MBS206]

When did you put the VN V6 coils in?

These are known for failing, even new coils. Are you able to get the ECU to run on the factory ignitor with splitfire coil packs?

[Lithium]

pull the plugs out and gap them down to .6 - .65 try that and let me know how you go, contcact clean all leads plugs while its apart

We went one better and replaced the leads and plugs and no change. I haven't gapped the plugs further down as I believe replacing the plugs, and the fact that the missfire is not load dependant suggests to me the plugs are completely innocent. There is no ignition break down under full power above 4000rpm, which is where the plugs have to work the hardest to jump the gap - yet at 2500rpm at minimal throttle it misses. It makes the whole thing that little bit more confounding.

[Lithium]

When did you put the VN V6 coils in?

These are known for failing, even new coils. Are you able to get the ECU to run on the factory ignitor with splitfire coil packs?

Put the VN coils in about a year ago, and tried another set this weekend just passed. I have a Series 2, there is no factory ignitor and I'm hesitant to spent ~$1kNZ to buy a set of coils when it may not even be a weak spark issue. I am however hoping to borrow a set of coils and an ignitor(s) to see what happens then.

[gotRICE?]

Lith! Why didnt you say so. You can use mine if you want to?

"Real Name" will give a rediculous hint.

Edited December 16, 2008 by gotRICE?

[Lithium]

Lith! Why didnt you say so. You can use mine if you want to?

"Real Name" will give a rediculous hint.

Cheers man, might have to hit you up on that

PS, I have known for ages you were you... if nothing else the diving whale and fascination with VTEC gave it away

[r33_racer]

carbon or stainless leads?

How good is the wiring for these coil packs?

[SLEEPR85]

Currently having this same problem with my car so will be interested to know the outcome!

[gotRICE?]

Cheers man, might have to hit you up on that

PS, I have known for ages you were you... if nothing else the diving whale and fascination with VTEC gave it away

Fair call.

Well if your around in the weekend, feel free to hit me up and we can swap em out and see what happens.

[Adriano]

You really need to know if it is an ignition problem or fuel. Can you put a scope on the ignition system, does it do it free revving it to 3000 rpm?

[Lithium]

You really need to know if it is an ignition problem or fuel. Can you put a scope on the ignition system, does it do it free revving it to 3000 rpm?

I don't have a scope I can unfortunately, though the Ignition module has 3 LEDs - one for each channel, and lights up each time it gets a signal.... will have to try it out and see what happens.

Stupidly enough I haven't tried to free rev it and specifically pay attention though conceivable it may rev through so quick its not noticeable. I actually tried racing it a couple of weekends ago at the drags, and I tried launching at around 6000rpm and don't recall it fluffing until the tyres hooked then the revs dropped to the evil area then got all shitty.

[jay1]

check coil packs for sure had similar problem

[Adriano]

Try just holding the revs at 3000

[Adriano]

If it is an ignition missfire, then it would show up as lean mixtures when the fluffyness occurs

[Lithium]

Cheers Adriano, the car is an hour away from where I am so I have to wait till I have a chance to get to it to try it out though I can't believe I hadn't tried that so far. The O2 sensor registered lean spikes when it happened, though if it was fuel related it would also show lean spikes- if not caused by a lean miss aye?

[MBS206]

Cheers Adriano, the car is an hour away from where I am so I have to wait till I have a chance to get to it to try it out though I can't believe I hadn't tried that so far. The O2 sensor registered lean spikes when it happened, though if it was fuel related it would also show lean spikes- if not caused by a lean miss aye?

If the car miss fires, it will show lean.

No matter really.

If plugs foul. It miss fires. Excessive oxy left.

If boost blows out spark. Miss fires, excessive oxy left.

Ignition system fails. Miss fires. Excessive oxy left.

No matter what, a miss fire will register lean. There WILL be excessive oxygen left.

[Lithium]

If the car miss fires, it will show lean.

No matter really.

If plugs foul. It miss fires. Excessive oxy left.

If boost blows out spark. Miss fires, excessive oxy left.

Ignition system fails. Miss fires. Excessive oxy left.

No matter what, a miss fire will register lean. There WILL be excessive oxygen left.

Yeah thats what I thought too, I was just wondering if Adriano knew something I didn't - have been a learning n00b with these things long enough to know that no matter how much you think you know you know that suddenly a whole new thing can show up and prove you don't really know exactly whats going on it there haha

Edited December 16, 2008 by Lithium

[MBS206]

Once the car is warmed up, as you bring the revs up, does it slowly lean out, and then start miss firing in that range?

Or does it get really rich and then start miss firing?

I'm wondering if there's an issue in the tune.

When did it start to occur, and what was the last thing you did to the car BEFORE it started misbehaving, and how long before it started miss behaving did you do it?

I also looked at this thread, but don't think it'll help you http://www.skylinesaustralia.com/forums/Rb...rk-t215013.html

[Lithium]

Once the car is warmed up, as you bring the revs up, does it slowly lean out, and then start miss firing in that range?

Or does it get really rich and then start miss firing?

When did it start to occur, and what was the last thing you did to the car BEFORE it started misbehaving, and how long before it started miss behaving did you do it?

Cheers A comment in that thread stands out and refers to something we'd planned to try in the next couple of days - which is checking or "improving" the earths - haven't ruled out that there might be a dodge or insufficient one somewhere and the more I think about it the more I could imagine this problem coming from one.

I should have elaborated when I said we went out and checked the mixtures... the tune was one of the top suspects despite the fact the car had been driving fine on that tune for over a year, so we went out with the wideband to watch such things. The airfuel ratios are all normal everywhere until the misfire event happens, there is no gradual leaning out or going silly rich - it just suddenly misfires. The map also looks completely sensible, if you view the 3d representation of the map there are no stand out holes in the map which don't follow the normal "terrain" which would indicate there could be a trouble area.

The problem basically came out of nowhere. It had been driving fine for a while with no changes to the car before it developed. Going to also replace the fuel filter and then this weekend hopefully try some factory R33 coils/ignitors and see what that does, my faith in the wasted spark ignition setup is waning as I've had other misfire related issues with it too.

Edited December 16, 2008 by Lithium