Resolved Misfire In R34 Gtt - Rb25det Neo

[V28VX37]

Hi all,

I recently got an R34 GTT and had a niggling misfire problem with the RB25DET Neo. Once warmed up the engine did an occasional shudder on idle and also sometimes felt bit sluggish and seemed to hesitate when accelerating in higher revs. After a couple of weeks of sleuth work this is now resolved, thank goodness.

I trawled through heaps of existing SAU threads for advice:

• How To Fix Missfire Problem, D.I.Y.
  
• Rough Idle R34 Rb25det Neo Engine, On my S2 Stagea
  
• Misfire/stutter At Idle/low Revs (neo Rb25det).. Have Searched, Tested/replaced everything I can think of
  
• Mysterious Shudder/hesitation Please Help!, R33 GTSt
  
• Missfire 4.5k-5.5k Revs
  
• Missfire Boost@4500-5500 RPM - The Answer! (for me at least!)
  

Here's a list of various things we tried:

• Check ECU for fault codes
  
• Remove engine cover and valley cover and clean underneath
  
• Inspect and tape up coil packs
  
• Replace spark plugs (mine had 2-year old NGK PFR6A-11 platinums which I replaced with NGK BCPR6E-11's on stock 1.1mm gaps)
  
• Change fuel (fill up) several times (BP Ultimate 98)
  
• Reset ECU several times
  
• Conduct data logging using Nissan DataScan
  
• Visually inspect air box, air filter and AFM
  
• Re-gap spark plugs down to 0.7-0.8mm
  
• Change engine oil and filter (Motul 4100)
  
• Fit new genuine Nissan O2 sensor
  

However it wasn't until the clever chaps at Chasers re-checked the fault codes (after the car had stalled on idle all by itself, it's an auto) and chucked the car on the dyno that the root cause revealed itself. The Crank Angle Sensor (fortunately) threw and error code and on closer inspection the trigger wheel was found in physical contact with the optical sensor! The CAS was prompty rebuilt using parts from another unit.

The guys also concluded that whilst externally fine the stock coil packs are starting to get weak and they re-gapped the plugs down further to 0.5mm as a temporary solution until I get a new set of coils.

Due to the coils the idle is still a bit choppy intermittently but the car now pulls smooth all through the rev range and has its full power back. It returned a nice round 150 rwkw on the dyno, which I think is spot on for a stock GTT.

Unrelated to the misfire, the original O2 sensor was stuffed too and replacing it has improved fuel economy straight away. I got my OEM replacement from Kudos Motorsports.

Lastly, the only things I can think of that we didn't try:

• Test coil pack harness with multimeter for faulty wiring
  
• Replace coil packs one by one to identify faulty one(s)
  
• Check fuel filter
  

I hope this helps someone else diagnose and solve the misfire issues. Big hat tip to Chasers for helping me out on this!

Cheers

[Shazza24]

Gee guess i got lucky as i had a minor idle problem (R33 S2 Man) and changing the plugs fixed it! However i suppose any car coil packs that have done 90,000+ or 10+ years probably need to be changed. The CAS needing to be rebuilt is a good one, handy to know that though!

[V28VX37]

Here's what a stuffed Crank Angle Sensor looks like on the dyno (black = stuffed, green = fixed):

[V28VX37]

The guys also concluded that whilst externally fine the stock coil packs are starting to get weak and they re-gapped the plugs down further to 0.5mm as a temporary solution until I get a new set of coils.

An update on that pesky little misfire on idle that I had for the past couple of months.

I bought and tried 2 cheap sets of second hand OEM coil packs, on each occasion I thought they helped at first, but really don't even bother. OEM coil packs aren pulled out for a reason.

The car also started throwing the classic TCS+slip+engine light combo, too (ignition circuit).

As the penultime try I cleaned up the AAC valve just to confirm it wasn't that. Affirmative.

So I finally bit the bullet and replaced the original coils with brand new Yellow Jackets and put in a fresh set of BCPR6E-11's gapped to 0.9mm.

The misfire on idle IS GONE. About friggin time too!!

[REEMER_31]

Good man for posting this up, Mine seems to be suffering similar fate, intermittent spluttering on and off, espeically when planting it,

[V28VX37]

Yeah mate check your CAS, it can really stuff things up at higher RPM.

[V28VX37]

Yeah well the misfire is back, has been for a while, mostly on idle. The car hiccups when sitting at the lights. High RPM is better (although not perfect) so I don't think it's CAS related.

Is it even possible to make an RB25 run smoothly without misfire?? I mean 100%, not 99% or 95%? This is silly, I never ever had misfire issues in my modded LS1...

I am starting to wonder whether I need new coil packs, again. As far as I can tell the options are:

1. OEM. I have had 3 second hand OEM sets, never worked 100%. New ones are pricey. Not keen.
2. Aftermarket. Currently running Yellow Jackets that were bought new. I can't imagine there being much difference between brands around the $500 mark?
3. Top shelf aftermarket. Something like the Ignition Projects ones: http://ignitionprojects.com/catalog/ip-coil/nissan/skyline-nissan-ip-coil - Is anyone running these? Dino reported good results with I-P on Speedhunters - http://www.speedhunters.com/2014/10/a-spark-of-efficiency-project-gtr/ . Hellishly expensive though.
4. LS1/LS2 coils conversion. Something like this: http://www.mojoperf.com/drupal/node/21 - unfortunately not available for the NEO.

I'm starting to lean towards the LS coils, kind of over the RB ones... Any recommendations??

Or maybe it's not the coils, who knows with these things

[tridentt150v]

If you tried coils of all different types etc like you have..............and it didn't permanently fix the problem then why would you keep thinking its coils??? my guess si you are disturbing the problem when you did this and thats what fixed it temporarily.

Try other things, get your injectors checked!!

Also next time it misfired pull coils or leads off one at a time and see if it makes a difference - difference = coil OK, no difference then that cylinder is the one to look at If no difference irrespective of cylinder then the problem is not an injector/coil/spark plug..

Clean your MAF.

Check your fuel pressure for regulator agnd/or pump.

Change ECU's do a swap.

Check your coil loom/wiring, check all the connections, pull on your wires and see if they are still solid and fixed/cripped to the connectors etc

Get a compression test both a warm and a cold one and check the results [should be stuff on the www telling you how to use the info]

Start trying to isolate the problem, if you can get it down by process of elimination you will win.

My RB33 idles and runs smooth as, plus doesn't miss a beat really and I have 300rwkw and a WMI system etc etc etc the RB motor is not the problem [unless you have a motor issue].