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Rb25 Falls Over Past 4500rpm

govich

By govich,
in Engines & Forced Induction

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govich Community Regular

govich

Posted
Posted

Hey guys,

Pictures (1000 words):

http://members.optusnet.com.au/govich/dynos.jpg

Left is the current dyno sheet, right is a year ago.

Words:

I've recently run into this problem where my R33 will make good power to 4500rpm and then just runs out of puff completely. It's a stock RB25 running a stock turbo with the usual mods; intercooler, boost controller, e-manage ultimate, exhaust cam gear, turbo-back exhaust. No power mods were added or removed between those two dyno runs. The AFRs are fine, ignition timing seems fine, it makes the same power to 4500 which leads me to think compression is fine, the cat converter hasn't collapsed (visually the internals look fine) and i can't find any obvious exhaust restrictions.

This leads me to the stock turbo which has started exhibiting a faint whine at all engine speeds (changes pitch with speed) but the thing still builds boost instantly and easily holds 10psi until redline (see dyno graph). From the dyno graph it seems like an airflow issue somewhere and i'm going to start pulling the car apart soon but just wondering if anyone has run into something like this and could save me some time.. The turbo is still my main suspect but i don't really know how to test this other than simple shaft play tests and having a physical look at the thing, short of taking it off and sending it to GCG or similar.

Any comments appreciated. Cheers guys

govich

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https://www.sau.com.au/forums/topic/249534-rb25-falls-over-past-4500rpm/
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govich Community Regular

govich

Posted
  • Author
Posted (edited)
Does the boost drop suddenly, it could be sucking the intake pipe shut.

I replaced the stock flappy pipe with a silicone one from the group buys on here some time ago. Boost holds above 10psi for the whole rev range (see dyno sheet).

Edited by govich
toffy Veteran

toffy

Posted
Posted

how do you know the fuel presure/afr's are fine?. give it a service including fuel filter,air filter,plugs, oxy sensor (on the exhaust , people don't realise these need to be changed every 50,000 klm) , water temp sensor and drain all the fuel out of the tank and get some fresh stuff.

govich Community Regular

govich

Posted
  • Author
Posted (edited)
how do you know the fuel presure/afr's are fine?. give it a service including fuel filter,air filter,plugs, oxy sensor (on the exhaust , people don't realise these need to be changed every 50,000 klm) , water temp sensor and drain all the fuel out of the tank and get some fresh stuff.

I have a 500km old wideband O2 sensor installed which tells me AFRs are fine :laugh: Confirmed by a second dyno sheet from the 158kW run which shows identical AFRs throughout the rev range to the 205kW run a year ago. 11.8 for the last few thousand RPM. Air/fuel filters are <5000kms old and plugs are <2000kms old.

Cheers for the suggestions so far, i'm about to start pulling it apart.

Edited by govich
  • 1 year later...
Conrad 2NR Enthusiast

Conrad 2NR

Posted
Posted
I have a 500km old wideband O2 sensor installed which tells me AFRs are fine :D Confirmed by a second dyno sheet from the 158kW run which shows identical AFRs throughout the rev range to the 205kW run a year ago. 11.8 for the last few thousand RPM. Air/fuel filters are <5000kms old and plugs are <2000kms old.

Cheers for the suggestions so far, i'm about to start pulling it apart.

Ever resolved this problem?

Experiencing the same on a completely stock RB25DET. Didn't do the conversion (into an A31) myself so I'm about to purchase a multimeter to start checking if the fuel pump is receiving the required voltage or if the coilpacks, AFM or TPS are failing.

paulr33 Grand Master

paulr33

Posted
Posted

it could be a few things, when did the problem start? Whats changed since the problem started?

any error lights on the dash? auto or manual ? any hacks / mods done on the car which are bogus (ie mangled safc installs etc)

any diag from the greddy emanage? how is it tuned? does stock ECU give any errors (get consult)

JiN_MaN Veteran

JiN_MaN

Posted
Posted
Ever resolved this problem?

Experiencing the same on a completely stock RB25DET. Didn't do the conversion (into an A31) myself so I'm about to purchase a multimeter to start checking if the fuel pump is receiving the required voltage or if the coilpacks, AFM or TPS are failing.

Fuel filter, had a similar problem on my first silvia,

Conrad 2NR Enthusiast

Conrad 2NR

Posted
Posted
it could be a few things, when did the problem start? Whats changed since the problem started?

any error lights on the dash? auto or manual ? any hacks / mods done on the car which are bogus (ie mangled safc installs etc)

any diag from the greddy emanage? how is it tuned? does stock ECU give any errors (get consult)

This is what happens when people actually use the search :P

I bumped an old thread because I am experiencing similar problems. Dyno'd my car and it barely made anywhere close to what it's supposed to.

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