Rb25det Running Very Rich Under Full Boost

[stefan-w]

I've got an R33 GTST spec 1, and I'm running into some troubles very recently... hopefully somebody can help me

This is the problem I'm having:

When at full boost in lower revs (up to about 4500rpm), my air/fuel ratio is 10.9... pretty rich already.

But when around 4500-ish rpm, it goes down to 10.0, and the screen blinks (meaning it is running even richer than that 10gr of air per gram of fuel it can display).

This feels like a bit of a flat spot, like the one people seem to have after installing a FMIC (mine is running so rich, I prob. could get away with one).

It's idling just a tiny bit rough, but it has done so since I've bought the car.

I have not changed anything on the car recently that could cause this problem.

This is the speclist (engine wise), most parts are less than 1 year old:

- RB25DET, completely stock engine, m/t

- stock ECU

- stock T28 turbo (ceramic turbine wheel, steel compressor wheel)

- stock after-turbo elbow

- removed carbon cannister

*all else, if not mentioned, stock*

- Bullet Exhaust 3" stainless steel downpipe

- Autobahn88 3" stainless steel testpipe (OE egt sensor installed after trimming some of the thread of from the decat)

- Invidia/RS*R 3" stainless steel catback

- Apex'i pod filter

- NXS Motorsports manual boost controller (set at 10psi firm)

- customised OE spark plug cover (ventilated to keep the coilpacks cooler)

- large capacity fuel filter

- new Gates fuel hoses in engine compartment and fuel tank

- Walbro 255lph in-tank fuel pump

- fuel pump direct 12+ volt feed from battery (loom powers relais, 11,5v max)

- HKS SSQV mkI blow-off valve

- Splitfire coilpacks

- NGK 'Iridium IX' spark plugs, grade 7 with 1.1mm gap (BKR7EIX, changed january or february)

- Apex Performance aluminium radiator and 1.1bar cap

- twin 12" slim fans

- DIF dual fan control unit

- 76°C thermostat

This is what I've tried:

- resoldered the afm's internals

- ECU reset

- air filter cleaned

- replaced most (if not all) vacuum lines and fuel hoses

- checked for leaks in piping after the afm (there were none)

- I always use RON98 fuel

- I've read the 'stop your hesitation' topic here, but it is about running lean, not rich... I could try to check the tps though...

This is what I'd like to know:

What could be the cause of it running só rich?

What can I try to stop it?

And another question, as it might be part of the problem:

When driving on the motorway, my afr is around 12.0-12.4... is that normal?

[paulr33]

what are you using to measure the AFR? is it a wideband gauge and wideband sensor? or normal guage and piggybacking off the ECU 02 signal?

it's the stock ecu, its designed to do that, get a piggyback or standalone ECU and tune it correctly

and the standard turbo isn't T28 and it isn't steel wheel

[j2fast]

I've got an R33 GTST spec 1, and I'm running into some troubles very recently... hopefully somebody can help me

This is the problem I'm having:

When at full boost in lower revs (up to about 4500rpm), my air/fuel ratio is 10.9... pretty rich already.

But when around 4500-ish rpm, it goes down to 10.0, and the screen blinks (meaning it is running even richer than that 10gr of air per gram of fuel it can display).

This feels like a bit of a flat spot, like the one people seem to have after installing a FMIC (mine is running so rich, I prob. could get away with one).

It's idling just a tiny bit rough, but it has done so since I've bought the car.

I have not changed anything on the car recently that could cause this problem.

This is the speclist (engine wise), most parts are less than 1 year old:

- RB25DET, completely stock engine, m/t

- stock ECU

- stock T28 turbo (ceramic turbine wheel, steel compressor wheel)

- stock after-turbo elbow

- removed carbon cannister

*all else, if not mentioned, stock*

- Bullet Exhaust 3" stainless steel downpipe

- Autobahn88 3" stainless steel testpipe (OE egt sensor installed after trimming some of the thread of from the decat)

- Invidia/RS*R 3" stainless steel catback

- Apex'i pod filter

- NXS Motorsports manual boost controller (set at 10psi firm)

- customised OE spark plug cover (ventilated to keep the coilpacks cooler)

- large capacity fuel filter

- new Gates fuel hoses in engine compartment and fuel tank

- Walbro 255lph in-tank fuel pump

- fuel pump direct 12+ volt feed from battery (loom powers relais, 11,5v max)

- HKS SSQV mkI blow-off valve

- Splitfire coilpacks

- NGK 'Iridium IX' spark plugs, grade 7 with 1.1mm gap (BKR7EIX, changed january or february)

- Apex Performance aluminium radiator and 1.1bar cap

- twin 12" slim fans

- DIF dual fan control unit

- 76°C thermostat

This is what I've tried:

- resoldered the afm's internals

- ECU reset

- air filter cleaned

- replaced most (if not all) vacuum lines and fuel hoses

- checked for leaks in piping after the afm (there were none)

- I always use RON98 fuel

- I've read the 'stop your hesitation' topic here, but it is about running lean, not rich... I could try to check the tps though...

This is what I'd like to know:

What could be the cause of it running só rich?

What can I try to stop it?

And another question, as it might be part of the problem:

When driving on the motorway, my afr is around 12.0-12.4... is that normal?

hey, just would like to know if your fuel lines are bigger than stock? but the fuel mods you have seems to bump ur fuel pressure up. do you have a FPR? if not get one and turn it down a bit.

[paulr33]

no dont bother with the fuel pressure reg, it's not required

your AFR's are mega rich as it's the stock ECU trying to run as rich as possible on full load (it's designed to) and cruise around 12 AFR

[stefan-w]

what are you using to measure the AFR? is it a wideband gauge and wideband sensor? or normal guage and piggybacking off the ECU 02 signal?

it's the stock ecu, its designed to do that, get a piggyback or standalone ECU and tune it correctly

and the standard turbo isn't T28 and it isn't steel wheel

I have a Prosport wideband controller set with a Bosch LSU 4.9 sensor.

This is the set I have; http://prosportgauges.com/wideband-air-fuel-ratio-kit.aspx

No n00bie stuff like getting afr from a narrowband here

And I've read this multiple times before on different forums; the stock RB25DET turbo is a T28 with journal bearings, a water jacket, a ceramic turbine wheel and a steel compressor wheel... spec2 is the same but has has a teflon comp. wheel afaik.

Not right then?

no dont bother with the fuel pressure reg, it's not required

your AFR's are mega rich as it's the stock ECU trying to run as rich as possible on full load (it's designed to) and cruise around 12 AFR

12 afr is crazy... should be at least 14 to 1, best would be 14.7 to 1, and I'm not even daring to talk about lean burn tech because tuning is not my specialty.

No wonder stock Skylines make a full tank of petrol last for 300km or so.

Enough for the off-topic hehe

'As rich as possible', I don't know about that... I was told afr should be around 11.5 to 12.0 under full boost, so 10.9 is rich... my cylinder walls must have a mirror polish by now (bore wash), even though it doesn't use a drop of oil.

It used to just sit at 10.9 at full boost, wich is rich, but it didn't dump in fuel like it does now.

What I don't get is why it does that... any idea?

hey, just would like to know if your fuel lines are bigger than stock? but the fuel mods you have seems to bump ur fuel pressure up. do you have a FPR? if not get one and turn it down a bit.

No, they're 8mm, wich is stock.

The fpr is also stock, so even when I ad two more fuel pumps, my fuel pressure would still the same.

[zebra]

what boost are you running?

standard 33 ECUs run megga rich as Paul said...more so when running higher than standard boost.

Maybe pull some boost out of it, but 10:1 is about normal for a 33 gtst

[**RB2530**]

Check your fuel pressure....

Double check with a search but should be around 45psi with vac/boost signal removed...

[stefan-w]

what boost are you running?

standard 33 ECUs run megga rich as Paul said...more so when running higher than standard boost.

Maybe pull some boost out of it, but 10:1 is about normal for a 33 gtst

I've set the boost controller at 10psi firm... stock is 8psi?

[Takoon]

Hello from Germany,

I have the same problem since some days. My car was mapped 2 months ago and was running fine. Now it is going rich when boost comes up. The wideband-AFR (AEM) shows the ratio about 10 and there is no power any more. From the beginning to the (under) half throttle position the AFR is normal.

I have the idea, that the intake pipes are leaky, maybe where the bov is fixed on (GREDDY Type S) - but have to check. Will check the fuel pressure regulator too..

cheers

vik

[paulr33]

get a piggyback or standalone, run 12psi and youll make more average power everywhere, get better fuel economy and it will overall be heaps quicker

you'll need a bigger intercooler as well

[R31Nismoid]

Mate it's just the stock ECU doing what it does - protecting the motor. Nice and simple really.

You are hitting the limits of the stock ECU where it goes into R&R mode (Rich & Retard) which causes the AFR's to become ridiculously rich.

Having a ATMO BOV is doing you no favours either. They are well known to cause overfuelling.

Get a proper ECU/tune and problem solved.

Also check the fuel pressure as others have stated, but i doubt the factory reg has failed because if it did you would have massive clouds of fuel behind the car when giving it a good boot. I know thats certainly what mine did when the fuel reg spat the dummy

[stefan-w]

Hello from Germany,

I have the same problem since some days. My car was mapped 2 months ago and was running fine. Now it is going rich when boost comes up. The wideband-AFR (AEM) shows the ratio about 10 and there is no power any more. From the beginning to the (under) half throttle position the AFR is normal.

I have the idea, that the intake pipes are leaky, maybe where the bov is fixed on (GREDDY Type S) - but have to check. Will check the fuel pressure regulator too..

cheers

vik

Your car actually loses loads of power?

Mine doesn't feel like that, it's notable, but it just keeps going on.

get a piggyback or standalone, run 12psi and youll make more average power everywhere, get better fuel economy and it will overall be heaps quicker

you'll need a bigger intercooler as well

True, and I've tried fitting one, but a large intercooler doesn't fit between the side markers in my front bumper (stock Type M)

Mate it's just the stock ECU doing what it does - protecting the motor. Nice and simple really.

You are hitting the limits of the stock ECU where it goes into R&R mode (Rich & Retard) which causes the AFR's to become ridiculously rich.

Having a ATMO BOV is doing you no favours either. They are well known to cause overfuelling.

Get a proper ECU/tune and problem solved.

Also check the fuel pressure as others have stated, but i doubt the factory reg has failed because if it did you would have massive clouds of fuel behind the car when giving it a good boot. I know thats certainly what mine did when the fuel reg spat the dummy

I've replaced the HKS bov with the stock recirc valve and pipe, but it didn't make any difference (other than it didn't seem to be as responsive, nor spool as quick as with the HKS).

I do need another EMS, I agree... but I'll just turn the boost down for now, to 8psi, and see what it does to the afr.

I was thinking about getting a Link or Vipec plug-n-play ECU, but I'd also like to sell the car (I'd really like a GTR), so it would be best for my wallet to leave it as is as much as possible, but I don't want to sell a 'faulty' car.

[R31Nismoid]

It's not faulty though - sounds like it is doing exactly what it's designed for

[stefan-w]

In other words, I'm probably running too much boost?

That would be an easy fix... and a woeful one as well haha

[HEKT1K]

for reference, my car on stock boost was hitting ~10.7 from 5000rpm onwards (although it was a fair bit leaner before that point, ~12.0)

don't think you have a great deal to worry about

[stefan-w]

I was talking about the 'fix your hesitation' topic before... just realized it's on GTRcanada.com, not here... so here is a link to what I meant;

http://forums.gtrcanada.com/gts-tech/t-fix...tion-26010.html

HEKT1K;

10.7 is hella rich already, too rich and the excess gas washes away the oilfilm from the hone... thus polishing it, causing blow by and oil consumption.

[Takoon]

Hello,

my problem is solved. It was the BOV. It was completely screwed in. Now it is more open and the car is running normal.

Cheers

vik

[Don Dada]

Thats normal for a stock ecu to dump shit loads of fuel to protect the motor.

If u turn down the boost it wouldn't be that bad.... but what the hell!!!...... its ok once its not hitting r&r

I actually put on an adj reg on there to drop the fuel pressure along with an safc2 and it was much better

As for it being rich at idle that would be your o2 sensor