Jump to content
SAU Community

Rb25det Slight Missfire And Power Fluctuation

Rezlo

By Rezlo,
in Engines & Forced Induction

 Share

Recommended Posts

Rezlo Community Regular

Rezlo

Posted
Posted (edited)

Bit of back round.

RB25DET S1 perfect compression stock internals

progressive water/Meth injection

750's

Walbro pump (will get changed to an external 044 bosch with surge tank in the next 3 months)

Nismo regulator

PFC w/datalogit

Wide band

greddy intake mani

Q45 maf

Q45 TB

splitfire coils

range 7 NGK iridiums

GT3076R

Plenty of supporting mods

and so on,

All installed in a pretty light S14

At low boost .9 bar it runs loverly, very linear power up to 7500rpm, just a slight stumble at low cruizing speeds even with a perfect AF and timing (changes dont realy make a difference)

at high boost its goes up to 1.5bar nice and fast (before 4500rpm) and pulls well and clean, but when I get to 6800 to 6900rpm it takes off to 7500rpm almost like its got a 150shot of nitrous, Boost stays stable and my AF is remains at 11-1 stable, timing also doesnt change much at all at that RPM to make such a prominent power change, I am seeing FC datalogit knock figures of 11 to 14 (ahh i love Meth injection) and nothing changes there, no other noticible log changes happen, everything looks 100% normal on the ECU, just a massive leap in actual power.

Im thinking that maybe my plugs are gapped a tiny bit to tight, but would like to know if you guys have ever had somthing like this? happen?

Car is also has a bit of a crapy idle, if i recall right my plugs are gapped at around .68 to .7mm which i know is tight, but my previous coils were going belly up so i kept them tight and didnt bother re-gapping when i put the splitfires in.

What you guys recon?

Edited by Rezlo
Rezlo Community Regular

Rezlo

Posted
  • Author
Posted (edited)
get it on a dyno and find out where and when it is happening, Also how old are the plugs?

The power increase comes in at between 6800-6900rpm and holds right threw to 7500rpm red line in any gear at WOT in high boost, it repeats its power increase every time i go up towards red line.

Plugs are about 4000km old.

Finding a good dyno in South Africa is a challange!!!

Edited by Rezlo
Simon-S14 Grand Master

Simon-S14

Posted
Posted

oh, yeah i can imagine it would be!

Get a set of cheap coppers and gap them down to .5 or so mm, chuck them in and run high boost and see if it goes away, if it does, then you've got a prob somewhere in the ignition system. might be an ignitor perhaps?

Rezlo Community Regular

Rezlo

Posted
  • Author
Posted

kinda seems like the opposite, like its to tight.

Im going to go over all the grounds and yank the plugs and check them, and go up in gap and see, im not blowing out spark up top so im going to go up in gap till i just start to blow spark out at high boost & RPM and see if that sorts out mid range,

Im thinking that maybe the top end is right and everything else is a bit off key due to a to tight plug gap.

Anyone else willing to share their plug gap running split fires at 1.4 to 1.5bar on heat range 7's?

Rezlo Community Regular

Rezlo

Posted
  • Author
Posted

Just got it off the dyno, 352wkw and 482nm @6987rpm (both still climbing)

power and tq were just rocketing up, he wouldnt take it into that power surge into the 7000rpm range,

Will regap them tonight and see if i can tell a diff.

Rezlo Community Regular

Rezlo

Posted
  • Author
Posted (edited)

problem solved, my wideband LSU4 sensor is going bad, started taking fuel out of it and it got better and better, taken 15% away from the injector map and its cleared up PERFECTLY, WB still reads 11-1 under boost...

Edited by Rezlo

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Matt Z
      SAU NSW - Archies Flame Grille Meet & Cruise to Kurnell

      By Matt Z · Posted

      Join SAU NSW for a flame-grilled feed & flame-spitting cruise! Sunday 17th August 2025 3:30PM Meeting Archies Flame Grille Sylvania Waters 4:45PM Cruise Departure 5:15PM Arrival at Cape Solander Kurnell Meet Location: Archies Flame Grille Final Destination: Cape Solander Kurnell *Disclaimer* There will be a lead and follow car so no one should get lost. If you would like to attend or bring others along please put your name down and a +1 as numbers will be needed prior! This is NOT a race and we will all be adhering to all road rules. If this is what you want please come to one of our many track days. This is an official SAU:NSW event and will be run under a CAMS permit. One of the things that really sets our club apart is our commitment to being true enthusiasts. When on normal roads we strive to maintain good relations with the authorities as well as the public in general. When attending one of Skylines Australia NSW events please try to: • Be aware of surrounding environment and act accordingly. • Drive courteously on the state’s roads as a true enthusiast should. • Understand how important it is to maintain the good name of SAU NSW and thus, treat others accordingly. • Any misbehavior will not be tolerated and you will be asked to leave.
    • Ozdavroz
      WTAC 2025

      By Ozdavroz · Posted

      Yeah good luck out there! Will be good to see a mighty GTST going harder than the GTRs
    • bcozican
      WTAC 2025

      By bcozican · Posted

      i will be there 😁
    • patrickxdf12
      Squeaking clutch/throw out bearing

      By patrickxdf12 · Posted

      Hello!  i just finished manual swaping my r34 skyline with a r33 rb20de box(RB71C)box  When the car is running it squeaks crazy loud and it was smoking from the gearbox area. The gearbox is fine it was tested. The clutch slave cylinder seems like it doesn't fully releases the clutch. I want to ask if this noise is from the throw out bearing or could it be the clutch assembly or disk att.xFliq87Gzw6kImKBVqDebXkj0fBqymk0JaYeP3_3SlM.mp4
    • RP1421
      S15 Spec R

      By RP1421 · Posted

      A few small updates since the previous post and lessons. I decided to do a little interior light upgrade on the 110. I quite like the iilumo items, even if they're a bit of a premium over other brands. You'll also note the Stedi Fogs, that will go into the S15 fog lights as I needed to match the bulbs since I got the new ones earlier. I hope they fit as the body is quite a bit longer than your normal bulb.  Annoyingly, I managed to trip the fuse, which normally wouldn't be an issue until I located the fuse. I can't say I've ever come across this. I had lucked out that someone nearby had a spare, but oddly enough Toyota dealerships seem to keep this in stock. I ordered some to keep in my stash and as luck would have it, someone else nearby tripped the same fuse so I passed on the favour.  I also did a little service on the 110 ahead of some additional work coming up. It's been annoying that Goleby's stopped carrying this particular HKS filter for the 110, so now I need to keep them on order from Japan. I also took the opportunity to install a bash plate and number plate riser. The plate riser is such a cheap but nice fix to help really tidy up the car. I'm tempted to now also replace my headlights, on this car. Both items were from Project Aero.    I also needed to replace the rear tyres on the 110, and after trying to get it aligned learnt that I need to replace some bushes in the front end, so that's next.  Closing out this update with a nicer picture as always! 
×
×
  • Create New...