Jump to content
SAU Community

Recommended Posts

Before anyone asks, yes i've done the usual searches but I couldnt find anything definitive :10_wink:
 

Background: Stock Rb25det NEO. standard intake, exhaust, boost and ecu.
Engine shuddering or hitting fuel cut whenever WOT and high boost (bucking like a mechanical bull), other than that, it ran fine. boosted down low ok, seems to run smooth(ish). didnt run rich, was getting on average about 450k's per tank
Replaced spark plugs with NGK coppers (1.1mm). Car then had absolutely no torque down low, would backfire constantly when cold or after WOT (which was necessary to get the friggin thing to move) and wouldn't rev over 5000rpm. It felt like it hit Rich and Retard. No codes were thrown

I noticed that the boost gauge was reading a little high after the plug change, and found a vacuum line from the charcoal canister had frayed and cracked causing a vacuum leak. Replaced this and boost reading went back to normal.

I then replaced the Airflow sensor (2nd hand from wreckers), Coilpacks (splitfires), Coilpack lead (Genuine) and Sparkplugs (NGK BKR6EIX-11).
This made a HUGE difference. the old coilpacks were likely from the factory and were just producing a weak spark.
Reset the ECU, still ran rich when cold (but not as rich), low-down torque came back but still cant rev over 5000rpm (feels like the engine just goes back to the R&R state)
It does backfire a little when cold or after WOT (more like a few pops instead of a full blown backfire). Still no codes thrown

Does the ECU lock out the top 2000 RPM when its 'learning'? or is it something else?

What should I be looking at next?
O2 Sensor?
Replace/check all Vacuum and Intake lines?
Cam angle sensor?

Really running out of ideas here

Link to comment
https://www.sau.com.au/forums/topic/473845-rb25det-neo-not-revving-past-5k/
Share on other sites

  • 3 months later...

So this saga is still going on.
Taken it to two separate mechanics, both said that it 'seems' fine.. (despite the fact it cant even get close to the rev limiter in 2nd) 

Ran a boost leak test using my puny ryobi tyre inflator, it held 5psi for about 20 seconds which appears to be ok.. it seems that there's something else going on.
I've plugged in the consult cable and engine temps appear normal as far as i can tell.

Also appears that i'm running .75 bar of boost now (up from .5).
I changed the vac lines to and from the turbo and solenoid hoping that it was just a leaking line that was throwing everything off, still no joy (hiss/whistle noise cant be located with soap and water on any of the couplers)

I'm starting to think now, no power past a certain rev range + hiss/whistle noise + higher boost..  could it be an exhaust leak? or am i just reading too much into this?

Edited by lench
  • 7 months later...

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


  • Similar Content

  • Latest Posts

    • I saw you mention this earlier and it raised a red flag, but I couldn't believe it was real. Yes, the vacuum signal should vary. It is the one and only load signal from the engine to the ECU, and it MUST vary. It is either not connected or is badly f**ked up in some way.
    • @Haggerty you still haven't answered my question.  Many things you are saying do not make sense for someone who can tune, yet I would not expect someone who cannot tune to be playing with the things in the ECU that you are.  This process would be a lot quicker to figure out if we can remove user error from the equation. 
    • If as it's stalling, the fuel pressure rises, it's saying there's less vacuum in the intake manifold. This is pretty typical of an engine that is slowing down.   While typically is agree it sounds fuel related, it really sounds fuel/air mixture related. Since the whole system has been refurbished, including injectors, pump, etc, it's likely we've altered how well the system is delivering fuel. If someone before you has messed with the IACV because it needed fiddling with as the fuel system was dieing out, we need to readjust it back. Getting things back to factory spec everywhere, is what's going to help the entire system. So if it idles at 400rpm with no IACV, that needs raising. Getting factory air flow back to normal will help us get everything back in spec, and likely help chase down any other issues. Back on IACV, if the base idle (no IACV plugged in) is too far out, it's a lot harder for the ECU to control idle. The IACV duty cycle causes non linear variations in reality. When I've tuned the idle valves in the past, you need to keep it in a relatively narrow window on aftermarket ecus to stop them doing wild dances. It also means if your base idle is too low, the valve needs to open too much, and then the smallest % change ends up being a huge variation.
    • I guess one thing that might be wrong is the manifold pressure.  It is a constant -5.9 and never moves even under 100% throttle and load.  I would expect it to atleast go to 0 correct?  It's doing this with the OEM MAP as well as the ECU vacuum sensor. When trying to tune the base map under load the crosshairs only climb vertically with RPM, but always in the -5.9 column.
    • AHHHH gotchaa, I'll do that once I am home again. I tried doing the harness with the multimeter but it seems the car needed a jump, there was no power when it was in the "ON" position. Not sure if I should use car battery jump starter or if its because the stuff that has been disconnect the car just does send power.
×
×
  • Create New...