Rb25det+deceleration=backfire+pop+burble

[TTT]

So I've had 2 RB20's and this is the first RB25.

Mods are.

Apexi Cat back

Blitz pod (I think).

all else is stock, bov, boost, pump, regulator, injectors, afm etc etc.

When I am driving along, and back off from the accelerator, if the revs are below say 2700rpm, instead of being a smooth sound and smooth deceleration, I get small popb and burbles from the exhaust.

if it is above this rev, it will be a smooth deceleration/sound all the way down from what ever rev I was at.. lets say 3500, to around 1500rpm, then burble and pop a few before I step on the clutch.

The car idles fine.

doesn't make any difference wether it's hot or cold weather or hot or cold engine.

I am getting 13L/100kms (got 399km and put in 52.3xL) with mixed freeway (100km/h) and suburban stop go traffic.

I don't have black shit all over the rear bumper so it's not running rich.

the Rb20's I've had have never done the above popping.

is it normal in RB25's?

this weekend the car will get new oil/filter and plugs as it's due for it's 5000km service but not sure if this will change anything.

any ideas?

or is it all normal?

[stenve]

bigger exhaust + pod filter = more air flow = messing with the ecu standards maps and in turn the car runs rich to run safe, hence the popping/burbling/etc

only fix i know of is a ecu and tune

eg: safc2 has deceleration air settings that can eliminate reduce this.

thats my understanding of it anyway.

[paulr33]

it will just be an area on the stock map

when you back off from the throttle the afm drops to almost zero load so the load axis drops to P01 and its probably just a bit rich up there near 2000rpm ish

[GeeTR]

Most of the turbo'd Nissan's iv been in have at least a tiny bit of popping and carrying on, on decel.

Id do all the normal shite, like clean AFM, check TPS voltage at idle etc.

[Dale FZ1]

I questioned the same sort of thing happening with mine. I thought it was a rich thing, until using a WB sensor proved otherwise.

A lean mixture due to decel fuel cut will give the result described.

[Haysey]

meh

my old rb20 used to pop so loud it would set off car alarms

this along with blowing flames was awesome...

[chris_r31]

this is what mine does now, burbels an pops off its head.. there is no black stuff on my rear bar..

ah rb20 love..

[neo32]

so it does it at 1500 rpm

i know rb35 have some sort of mix up for fuel at 1500 rpm this to spop car stalling

guys if u want to check this put it in nutral rev to 2500 let it drop back to idle u will see it hesitate around 1500 rpm

[**RB2530**]

bigger exhaust + pod filter = more air flow = messing with the ecu standards maps and in turn the car runs rich to run safe, hence the popping/burbling/etc

only fix i know of is a ecu and tune

eg: safc2 has deceleration air settings that can eliminate reduce this.

thats my understanding of it anyway.

I run a decently sized exhaust, 3ltr displacement with 8.3:1 comp, bigger turbo, pod filter CAI etc etc and the stock ECU runs fine and makes 277rwkw at 12psi with 12.4 AFR....It drives like factory

The good thing about afm ecus is that they measure exactly what they need to know '---air flow---'. So if you do any mods that increase airflow the ECU can adpat to this...They are very much foolproof and adapt to intake / exhaust mods..

Everyone is so quick to write off the stock ECU and go aftermarket when chances are the problem is elsewhere...

I would get a hold of some Nissan consult software and diagnose the problem properly before racing off to for an ECU...

[Cubes]

Mine 'was' popping and farting like nothing else with the rb26 base ignition map.

Partly due to the blocked bov but since having it tuned and pushing more ignition in to the trailing/idle map area's the pop/fart has completely gone.

Upon decel its a hard fuel cut right up until 1100rpm. The stock ecu was the same.

Have you checked the TPS to ensure its adjusted correctly?

As can be seen by the attached pics the rb25/26 base maps run less ignition at less load compared to the 20.

If you flick between the rb20/rb25 airflow curves and maps the light load uses pretty much the same map points. So I consider it a good comparison.

The 26 does use light load slightly lower down the scale but as I use a single afm + a little tweaking I was using the usual load 2-3 on idle and decel with slight throttle input; having bugger all ignition in these values was causing the pop/fart for myself.

I have a std ecu's rb20 and rb25 rom dump some where; they resembled the pfc's base ign. map almost identically.

[RBwhatever]

Hahaha, for once GTST spoke like he is a newb. lol a true moment is sau history

But seriously now, its quite normal. Mine did it when it had the stock ecu and it still does it with the Power FC. Depends what gear your decellerating in as well.

Edited March 27, 2008 by KeyMaker

[RBwhatever]

I run a decently sized exhaust, 3ltr displacement with 8.3:1 comp, bigger turbo, pod filter CAI etc etc and the stock ECU runs fine and makes 277rwkw at 12psi with 12.4 AFR....It drives like factory

The good thing about afm ecus is that they measure exactly what they need to know '---air flow---'. So if you do any mods that increase airflow the ECU can adpat to this...They are very much foolproof and adapt to intake / exhaust mods..

Everyone is so quick to write off the stock ECU and go aftermarket when chances are the problem is elsewhere...

I would get a hold of some Nissan consult software and diagnose the problem properly before racing off to for an ECU...

So like, you've got a RB30det using a standard rb25det ecu and standard rb25det afm?? or have you changed the afm to a z32?

Either way, sounds like you've got either a remapped ecu or an absolutely unheard of freak of nissan nature ecu.

I've never heard of a standard rb25 ecu being able to comfortably handle such mods as a rb30det conversion, bigger turbo, injectors and afm.

If its true that its a standard ecu and its making that kind of power, then your yet to find out the benefits of tuning.

[r33cruiser]

likewise. mine still does it with a tuned pfc. but hardly noticable.

[**RB2530**]

So like, you've got a RB30det using a standard rb25det ecu and standard rb25det afm?? or have you changed the afm to a z32?

Either way, sounds like you've got either a remapped ecu or an absolutely unheard of freak of nissan nature ecu.

I've never heard of a standard rb25 ecu being able to comfortably handle such mods as a rb30det conversion, bigger turbo, injectors and afm.

If its true that its a standard ecu and its making that kind of power, then your yet to find out the benefits of tuning.

Yes RB30DET with VCT head and RB25DET S2 Stock ECU and stock afm. This has been confirmed by Guilt-toy who did the dyno runs...The Z32 will not run properly with stock ECU unless you modify the output voltage to emulate the rb25 afm..Even then you are limited as the ECU has a 5.12v input ceiling....

All I'm gonna say here is work out how things work!! Then you can optimise what you have rather then spending more money...Not sure if you realise but a rule of thumb for estimating HP based on injector size at (90% duty cycle) and assuming reasonably good thermodynamic efficiency at satisfactory AFRs is = injector flow rate divided by 5 multiplied by number of cyclinders...so for stock RB25det injectors at 375cc/min >>>>>>375 /5 x 6 = 450HP...Guess what my 277rwkw is close to???

So based on this I know that all of my supporting mods are working....

As far as the stock ECU is concerned the only bad thing I have come across is the airflow cut...its a pain in the arse and I have done a lot of work around get around this...Most of what I have done is in other threads I have started..so I wont repeat it here...

AND

Yes yes yes I am looking forward to tunable ECU and bigger fuel system because that 277rwkW was made at only 11-12 psi and engine has been built with 20-25psi in mind...I am really ahead because I have built a very efficient setup, made decent power without having to pour shitloads of boost into it yet.. good luck my team!!

[RBwhatever]

Yes RB30DET with VCT head and RB25DET S2 Stock ECU and stock afm. This has been confirmed by Guilt-toy who did the dyno runs...The Z32 will not run properly with stock ECU unless you modify the output voltage to emulate the rb25 afm..Even then you are limited as the ECU has a 5.12v input ceiling....

All I'm gonna say here is work out how things work!! Then you can optimise what you have rather then spending more money...Not sure if you realise but a rule of thumb for estimating HP based on injector size at (90% duty cycle) and assuming reasonably good thermodynamic efficiency at satisfactory AFRs is = injector flow rate divided by 5 multiplied by number of cyclinders...so for stock RB25det injectors at 375cc/min >>>>>>375 /5 x 6 = 450HP...Guess what my 277rwkw is close to???

So based on this I know that all of my supporting mods are working....

As far as the stock ECU is concerned the only bad thing I have come across is the airflow cut...its a pain in the arse and I have done a lot of work around get around this...Most of what I have done is in other threads I have started..so I wont repeat it here...

AND

Yes yes yes I am looking forward to tunable ECU and bigger fuel system because that 277rwkW was made at only 11-12 psi and engine has been built with 20-25psi in mind...I am really ahead because I have built a very efficient setup, made decent power without having to pour shitloads of boost into it yet.. good luck my team!!

Wow, kudos to you sir. Thats a pretty good result from working with what nissan gave gave ya

[Cubes]

RB2530.

What peak z32 afm volts were you seeing?

[Gtrgodzilla67]

So like, you've got a RB30det using a standard rb25det ecu and standard rb25det afm?? or have you changed the afm to a z32?

Either way, sounds like you've got either a remapped ecu or an absolutely unheard of freak of nissan nature ecu.

I've never heard of a standard rb25 ecu being able to comfortably handle such mods as a rb30det conversion, bigger turbo, injectors and afm.

If its true that its a standard ecu and its making that kind of power, then your yet to find out the benefits of tuning.

i can disprove his theory my gtr leaned out with bigger turbos and free flowing exhaust and intake , on standard, afms, it was hitting close to 13.3 on boost. pfc all better, no other mods, nissan ecu suck unless they are remmaped, or different eprom is installed,

my 2 cents from my experience first hand,

[ZENNON]

meh

my old rb20 used to pop so loud it would set off car alarms

this along with blowing flames was awesome...

agreed - my rb20 does it too

(mine also has mods for more air but stock ecu)

[Trust33]

mine does it. using zorst, fuel pump, hi flow filter, pfc, stock injectors etc. imo the car goes just fine and i like the race like pop n burble it emitts on decel. ftw.

[**RB2530**]

RB2530.

What peak z32 afm volts were you seeing?

Please read my post..I am using rb25 afm...No point in using z32 with stock ECU...The limit is actually one within the ECU. The ECU has an A-D convertor that reads the afm voltage and converts it into a number. The largest voltage it can read is 5.12v...So using the z32 is a waste of time with stock rb25 ECU and fuel system...

Both afms run a 0-6v resolution but at full scale the z32 is actually flowing an extra 50%...