Jump to content
SAU Community

Recommended Posts

Okay. I’ve had this RB25 in the car for a while. I did the conversion myself but Ive done many others with success. The car runs like a champ, doesnt miss a beat and starts fine. No codes come up on the ECU and I have plugged in the Nissan consult and everything seems fine. Timing is good, TPS is good and I have even gone thro every sensor diagnosis procedure listed in the factory Nissan service manual.

Now the car sounds fine driving like a normal person but when your foot gets heavy and you want to go fast it just sounds like the exhaust is plugged up or something. I have normal power in low RPM but when I get up to 4000RPM it just feels held back. The engine sounds fine but you can tell by the exhaust note that’s is just not right.

I had a RB30 in the car before and it sorta felt like it had the same problem. I didn’t think much of it though as I was swapping in the RB25 so I could sell the car but thinking it was the same problem as the previous engine I thought it could be something wrong with the cars components like intercooler, exhaust and fuel system. So I unbolted the exhaust and took it for a rip and was still slow. I checked fuel pressure, changed the filter and upgraded to a high flow pump and still slow. Then I took the intercooler out and tested it and cleaned it out with cleaner and still slow. I have took apart the entire engine harness and pretty much rebuilt it. I did find a bad ground for the o2,TPS and AAC so fixed that but still the car is still slow.

I have done a basic tune up as well like plugs, packed the coils, fluids ect. I have also took the intake off the turbo to see if my turbo was still moving freely and seems just fine though one thing I haven’t checked was if the exhaust blades are still on the turbo but I still build boost like normal so didn’t think that was necessary. I have ign timing set right at 15 deg. Another thing that isn’t hooked up is the neutral switch to the ECU. Is this a problem??? I have done other rb26 conversions without neutral signals in race cars and they were fine with factory rom tuned ecu’s

This problem is going to be retarded, I know. Something really simple but I am running out of ideas. If you guys can think of anything I can check over please let me know. Any tips are appreciated. ;)

Edited by RB30 Ceffy
Link to comment
https://www.sau.com.au/forums/topic/184352-slow-rb25-need-help-please/
Share on other sites

Slow is relative.

Now you've spent quite some time and still feel it is running weak at higher rpm and load, you should really have little problem buying 30mins of dyno time. It should provide some additional insight as to whether it really is running weak, or if you need to be reassessing what is slow or not.

Well I guess I have to hope you can take my word on this one. I personally dont need dyno time to tell me its a slow car and down on HP. A factory rb20 can eat this alive right now :( Ive done over a duzon other rb25 conversions and this one just doesnt cut it unfortunatly. But I see where your coming from. Dyno sheet would help me see where the problem might be coming from. If all is bad I might have to consider this but I dont see how I should be able to fix this in the shop. Thanks!

what about the diff ratio ?

what gearbox are you using?

remember rb25's in skylines had 4.11:1 and 4.39:1

in australia people make the mistake of putting the rb25 into the VL Commodore with the stock 3.45 ratio or whatever it is and wonder why its slow as hell but it will go up to 200ks an hour in third gear.

check your ratio's!!!

i'm having the exact same problem. everything runs right but the power is not as what an RB25DET is supposed to provide... boost reads nearly 1 bar on the boost meter but feels like RB25DE.

if Guilt-Toy is right, then i might have to change to a stock RB25 rear diff as i'm running stock Z31 300ZXT auto rear diff, 200kmh @ nearly 6500rpm @ 5th gear...

Car is a A31 Cefiro. Diff is a factory A31 unit. 4.11:1 diff and RB25 trans. The gearing is as normal as any other factory nissan.

I have changed the factory fuel pump with a nismo unit to see if that was my problem about a month ago. Pressure is fine and all lines are normal. Changed the filter aswell. Still the same after all this.

Ignition is fine, coils are mint, 180 and 1 deg signals from CAS is good. Timing is fine.

I have tried to advance the timing 5 deg and still slow. I tried to boost the thing to 1 bar and still slow.

;):(:):(

Edited by RB30 Ceffy
i'm having the exact same problem. everything runs right but the power is not as what an RB25DET is supposed to provide... boost reads nearly 1 bar on the boost meter but feels like RB25DE.

if Guilt-Toy is right, then i might have to change to a stock RB25 rear diff as i'm running stock Z31 300ZXT auto rear diff, 200kmh @ nearly 6500rpm @ 5th gear...

That diff ratio seems short and it will make the car feel faster because it will be accelerating quickly.

Car is a A31 Cefiro. Diff is a factory A31 unit. 4.11:1 diff and RB25 trans. The gearing is as normal as any other factory nissan.

I have changed the factory fuel pump with a nismo unit to see if that was my problem about a month ago. Pressure is fine and all lines are normal. Changed the filter aswell. Still the same after all this.

Ignition is fine, coils are mint, 180 and 1 deg signals from CAS is good. Timing is fine.

I have tried to advance the timing 5 deg and still slow. I tried to boost the thing to 1 bar and still slow.

;):(:D:(

Take your CAT out and check it. maybe its blocked? do you have any air leaks in the piping when on boost? maybe it only leaks on boost ?

have you put it on the dyno and checked the air fuel ratio ? i would be doing this after checking the turbo and cat

cat is fine.Dont need cat's where Im from :P

But ya. I guess I will dyno it and see what I can come up with. I dont have any boost leaks. All pipeing is fine and pressure tested it just a couple weeks ago to make sure. Didnt leak to 80PSI so thats good :D

Im going to book a dyno run maybe later this week if I have time. I was thinking along the same line as you acsplit. It feels like it pulls timing up top. Thats what made me think I had a sensor on the fritz but Ive checked it all and nothing comes up on the consult. I also thaught that the 25 would need the factory boost control solenoid. So I tried to plug that back in and with it not in and still ran the same either way. Confuses me lots but im all out of ideas. I'll get the dyno sheet up as soon as I get er done but for now keep shooting off ideas guys. Thanks!!!!!

hey mate i know this may sound way off track but it may help, u say its higher up in the rpm coul dit possibly be the vct on the rb25 not switching over to give it more or less timing ect? im dnt no a great deal about this stuff but am slowly learning and thought that this may be your problem. hope it helps

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

    • 1994 Series 3 R32 GTR. Freshly built as the perfect weekender. Has many brand new Nissan OEM pieces (some you can no longer source). Last serviced (April 2024) at V Spec Performance, Melbourne, Australia. Feel free to DM me if any questions. Asking price: $190,000 AUD.  Engine RB26DETT Original 05U block Factory R32 crankshaft CP 86.5mm forged pistons Spool forged rods Factory cylinder head – rebuilt Factory valve train Factory camshafts Factory inlet manifold Factory throttle body Garrett dash -5 turbos Custom intercooler piping with Plazmaman clamps Plazamaman 100mm race intercooler Turbosmart BOV Tomei fuel rail 660cc injectors Goodridge 9000 series fuel lines with crimped fittings Stainless steel front pipes Tomei titanium exhaust with stainless steel cat converter Spit fire coils Powder coated rocket covers New Nissan coil pack emblem badge Fully repainted engine bay in Factory Black Refurbished ABS unit New Nissan brake master cylinder New Nissan brake lines New Nissan clutch master cylinder New Nissan washer bottles Custom catch can (powder coated with Goodridge lines) Steering rack rebuilt New Nissan power steering lines New Nissan AC lines A/C compressor refurbished AC condenser refurbished HPI radiator and new thermos fanes New radiator fans NOTE: All nuts, bolts, fixings new or zinc coated Driveline Factory 5 speed gear box rebuilt Xtreme twin plate clutch Stainless steel clutch line Rebuilt factory transfer case Custom one-piece tail shaft Rebuilt factory front diff Rebuilt factory rear diff Suspension HICAS deleted Bilstein dampers IKEYA formular front and rear arms and tie rod ends New bushes wherever possible Whiteline anti roll bars (underneath car only) Brakes Brembo F50 front callipers – 4 piston AP racing 380*32 front rotors, J Hook design Custom floating hat and calliper mounts Brembo 4 piston rear callipers PFC pads Stainless steel braided brake lines Body New Factory Black paint job Ceramic coated exterior panels New Nissan aluminium bonnet (super rare) New Nissan headlights (super rare) New Nissan indicators New Nissan front bar New Nissan front lower lip New Nissan head light and bonnet seals New Nissan windscreen cowling New Nissan wiper arms and wiper blades New aftermarket windscreen New Nissan windscreen seal New Nissan front doors window surrounds and seals New Nissan rear quarter windows (must replace for proper paint job) New Nissan rear window surrounds and seals New Nissan side skirts New Nissan boot badges New Nismo rear bonnet lip New Nissan guard liners Interior New Nissan lens cover over cluster New Nissan gear boot shift New Nissan gear knob New Nismo steering wheel New Nismo floor mats New Billet Handbrake lever New Nissan OEM pocket facia to replace radio Underbody Original stone guard removed and new stone guard coating applied Powder coated front and rear cross members Fuel lines painted to match factory colours Fuel tank removed, cleaned, repainted and refitted All nuts and fixings cleaned, repaired and zinc plated Wheels Rays/Volk racing TE37 18 x 10.5 + 15 in Bronze Yokahama A050 265 x 35 x 18                         
    • @Supernanoyour car has ended up in my hands and I was wondering if there has been any work done to the motor?  
    • Sigh... yeah OEM mount rear battery, very R33, very demure, very mindful.
    • Would need a substantial current draw in the car to make a bunch of sparks. Obvs to now test resistance to ground of the car's B+ lead. If there's a short there, you'll see it. Only likely place for that, as you suspect is alternator. But there is also the possibility that rats have had a chew on some insulation. Shitbox has the battery in the boot, yeah? Plenty of cable to attack.
    • Oh, I thought of that too... I disconnected the battery and hooked up the leads direct to the car without the battery in place. Sparks... I suspect the following: Alternator has decided to kill itself Starter has decided to kill itself I'll recharge the battery, then unplug both, and go from there. The above might take 6 months - however I did buy a Victron 15 AMP trickle charger, apparently it's better than CTEK? Amazon, delivery by tonight. https://www.amazon.com.au/Victron-Battery-Charger-15-Amp-waterproof/dp/B07P4LMMMD?ref_=ast_sto_dp    
×
×
  • Create New...