R33 gtst Slight missfire on idle... Spark plug gap suspect

[Ty1]

Hey guys, ive done some reading up on this but want to get other peoples opinions on changing spark plug gap and whether it will affect my tune. So far i've checked coil packs and replaced with brand new splitfires, new ignition module a few years ago, new fuel pump and injectors, New z32 afm, all vaccum hoses replaced as well as headgasket and intake and exhaust manifold gaskets with genuine nissan items. Tps and aac valve are both relatively new as well. Car is tuned on e85 running a power fc. Made 408rwhp on stock motor and pulls hard with no missfires or hesitation. The only time it does miss is on idle and seems to splutter a bit under 2500rpm. Its only a very slight miss like a cylinder dropping sound but is more noticeable when warmed up. Im running ngk bcpr7es plugs gapped at 0.8 but was wanting to see if 0.9 gap would iron out any idle miss im having and not massively affect my tune. Cheers guys

[GTSBoy]

Changing plugs/gaps will not affect tune.

Stumble on idle is usually a vacuum leak.

[tridentt150v]

^^^ as per GTSBoy says, That gap is only needed when you're boosting.  At idle or just above, it won't matter.  Generally at idle you could have just about any gap in the 1.2 to 0.8mm range and it wouldn't matter.

See if it still happens with your A/C turned off.

[Sinista32]

You've done a fair bit of replacing stuff

my 2c - Check 02 sensor/s (only happens at idle) and

get your tune looked at on the PFC.

[Ty1]

Cheers for the input so far guys. So with the a/c switched on there is literally no miss! It idles at 1000rpm but the miss comes back when its switched off. Once the car is at operating temp it idles at around 850-880rpm. I also noticed when i unplug the o2 sensor the miss goes away completely but the afr's drop to around 13 on idle instead of sitting on around 14.7 which i imagine is normal as it was tuned with the o2 sensor. Does this mean theres an issue with my o2 sensor or possibly the wiring?

[GTSBoy]

O2 sensors get old and slow.  The heaters also stop working and they don't then work when cold (ie at idle).

[89CAL]

It might be too lean on idle. RB's usually like a little more fuel at idle the stoich

[iruvyouskyrine]

Missfire on idle? That's just called 'having any RB engine'

[Ty1]

Missfire on idle? That's just called 'having any RB engine'

Thats what the tuner said too lol he couldnt pick up any faults with anything but surely it cant be normal. It sounds shit on idle! Slight miss every few seconds rather than idling super smooth like it did before. Oh well i might just have to live with it then

[Ty1]

O2 sensors get old and slow.  The heaters also stop working and they don't then work when cold (ie at idle).

O2 sensor was also replaced not too long ago with a genuine nissan sensor as previous one was getting on.

[Ty1]

Just an update guys...had a mate of mine double check the gap on my plugs and turns out it was only around 0.5mm! Pretty pissed off as a reputable tuner gapped them for me too! Anyway they're now gapped to 0.8mm and no more miss what so ever and the car obviously feels smoother too. So...yes, spark plug gap can affect a cars idle lol

[tridentt150v]

At 0.5mm yes it would.  Glad you found the issue and it was cost neutral.

 

PS...Tuner shoulda gone to specsavers!!!!!  mistaking 0.5 for 0.8 lmao

[niZmO_Man]

I wouldn't call someone that doesn't know the difference between 0.5mm and 0.8mm spark plug gap a reputable tuner. Did they have a reason for the small gap?

[Ty1]

I wouldn't call someone that doesn't know the difference between 0.5mm and 0.8mm spark plug gap a reputable tuner. Did they have a reason for the small gap?

He didn't mention anything to me about the small gap. He told me he was originally going to gap them down to 0.8mm. The plugs really shouldnt of needed much adjusting anyway as the bcpr7es come pre gapped at 0.8mm. He was also trying to say the miss was a 'skyline' thing lol the car feels great to drive but now im a bit skeptical on the tune if he cant even gap plugs.

[niZmO_Man]

15 hours ago, Ty1 said:

but now im a bit skeptical on the tune if he cant even gap plugs

Yeah I'd be too. It's strange when people say "reputable tuner", where did they get the reputation from? Instagram/Facebook or here on SAU? Or did they start off good and then got lazy/sloppy/dodgy (reminds me of a certain welder)?

[Ty1]

Yeah I'd be too. It's strange when people say "reputable tuner", where did they get the reputation from? Instagram/Facebook or here on SAU? Or did they start off good and then got lazy/sloppy/dodgy (reminds me of a certain welder)?

I totally agree with you! The tuner did look after me though during the whole process and didnt charge me for a couple of dyno runs as we were diagnosing issues. And from what i could tell, he was a very honest, upfront guy. A mate of mine recommended him and a few of the boys on sau have had good results too. Im not too familiar with the pfc hand controller but is there a way i can view the fuel map/settings and post a pic on here so someone might be able to tell me if it looks like a decent tune?

[Ben C34]

Keep in mind it probably wast the turner who gapped the plugs, could have been a different guy so not really fair to blame one guy

[niZmO_Man]

On 28/04/2018 at 7:52 PM, Ben C34 said:

Keep in mind it probably wast the turner who gapped the plugs, could have been a different guy so not really fair to blame one guy

Yes sorry, I meant to finish off my previous post with this but I got distracted and hit the post button too early.