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Rb20 Cuts Out Near 1 Bar

pipster11

By pipster11,
in Engines & Forced Induction

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pipster11 Grand Master

pipster11

Posted
Posted

hey guys

thought i'd post this up

basically i have a 32 running an rb25 turbo with rb20 actuator (not sure which series r33 it is tho)

also has fmic and 3 maybe 3.5 inch cat back with a gutted cat (i didnt gut it so not confirmed that it does)

the actuator is running off a pressure source on the hot pipe about 20cm from the turbo outlet

it also has a digital boost guage built into the turbo timer and an alarm is set for 0.9 bar

problem i am having is that it doesn't come onto boost very hard and there is a very noticable flat spot between 4000rpm and 5500rpm

once it passes this rpm point it pulls fantastically untill i hear the beep from the boost guage and a split second later it hits what i would say is boost cut as it looses all power and makes crazy noises

my questions are, what could be causing it? how can i fix it? and what could be causing it to do this?

mechanically i'm pretty good and i've now got another car to drive so i can take things apart to insect if need me

help me guys as its really anonying!

Thanks,

Tom

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cainer33 Explorer

cainer33

Posted
Posted

Did I not read somewhere else (correct me if i'm wrong) that if the knock sensor detects detonation, it retards the engine quite a bit.

Maybe.. just maybe, your a/f ratio is leaning out at 4000rpm and the ECU is retarding the ignition to save the engine, hence the loss of power and flat spot.

Having said that, my GTST had that issue when the plug gaps were at 1.1mm and 4 of 6 new coil packs fitted. When i fitted the last 2 packs and regapped to 0.8mm it went away.

FordyR31 Mentor

FordyR31

Posted
Posted (edited)

If u have a stock ECU ur probably getting ur furl cut from the AFM at 1 bar. RB25DET ecu's sometimes dont like to run over 10psi but the R32 ECU's seem to be a little more leniant. RB20DET actuator is a psi actuator so if there r no manual or electronic boost controllers thats what it should be running.

As for ur RB25 turbo. It won't come on hard, it's a Nissan factory RB25 turbo. It will come on a little later than stock and add to ur top end on the RB20 but isnt the sort of turbo to give u that power kick. The flat spot is a common thing with the RB20-25 ecu's. Its usually petty smooth with a completely standard setup but once u start to upgrade things on the factory map like ur turbo, FMIC etc it emphasises it all. If u look at a lot of dyno sheets of RB20's with stock ecu, RB25/VG30 turbo, zorst, pod and FMIC for example u will see the graph start to climb from maybe 3000rpm, then flatten out a bit at around 4000 maybe, then climb again. Its just how it goes. They are approximate figures for example mind u.

My mates R32 with a hi flow R33 turbo and supporting mods with stock RB20 ecu running 15psi hi about 170rwkw until the engine died coz it was pinging all the time over 10psi lol... Ping power sucks!

Get it on a dyno and have a look at what its doing but anything over 12psi isnt good for ur engine on a factory tune or ur turbo.

Edited by FordyR31
pipster11 Grand Master

pipster11

Posted
  • Author
Posted

ok

thanks guys

i know its no where near ideal but i'll put freddy flinstones safc on there and someone locally said that the may be able to lend me an autronic wideband lambada that they have set up to do the tuning on old v12 jags :merli:

will set it up and see what the afr's are sitting on atm and give them a little play

just quicky, and this is gonna sound really bad, but what afr should i be aiming for?

FordyR31 Mentor

FordyR31

Posted
Posted

12's... On a dyno sheet for turbo RB's usually in boost u want ur AFR's to be in the 12's. A SAFC could do the trick, just depends if ur fuel pump and afm etc r up to putting enough fuel in for the 15psi and turbo u want to run. Some may say yeah its fine others may have had issues.

pipster11 Grand Master

pipster11

Posted
  • Author
Posted

cool thanks

fuel system should be ok (may need to rewire using a relay, will use the amp wiring thats already there :))

i cant see any probs with maxing out the afm as it peaks at about 0.9bar = 14psi max

FordyR31 Mentor

FordyR31

Posted
Posted

I had had mates in the R31 club use a SAFC on an old RB20DET redtop ECCS with the likes of a VG30 turbo or other upgrade turbo's running 14-15 pounds no worries with AFR's or any boost/fuel cuts. Always good if its street tuned by u or someone u know to have a dyno run to make sure and be safe I guess

pipster11 Grand Master

pipster11

Posted
  • Author
Posted

well the coils aren't that old, they are jjr ones but looked to be in good condition last time i checked (but i didn't take them out of the mounts)

and there is no boost controller, just the rb20 actuator running straight off a boost source from the hot pipe

pipster11 Grand Master

pipster11

Posted
  • Author
Posted

pu the safc on today

turned the %'s down in the midrange a tiny bit (~6%) and seems to have moved the flat spot i had

will be getting it tuned asap and test to see if it still cuts out up high then

30detkiwi Contributor

30detkiwi

Posted
Posted
pu the safc on today

turned the %'s down in the midrange a tiny bit (~6%) and seems to have moved the flat spot i had

will be getting it tuned asap and test to see if it still cuts out up high then

take the negative lead off hold foot on break 4 20sec,then reconnect,this resets the ecu back to it last mapping.

also check the knock sensors to make sure the plugs are on and wires haven't de tatched.

try fully advancing the cas (cam angel sensor clockwise) seems to make some unknown problems go away :down:

pipster11 Grand Master

pipster11

Posted
  • Author
Posted
take the negative lead off hold foot on break 4 20sec,then reconnect,this resets the ecu back to it last mapping.

also check the knock sensors to make sure the plugs are on and wires haven't de tatched.

try fully advancing the cas (cam angel sensor clockwise) seems to make some unknown problems go away :banana:

one thing i actually have forgotten to do

do u have a pic or diagram of where they are?

will advance the cas again too

and had the -'ve off while i was soldering so ecu is re-set

think its just nearing ractory limits and its starting to pull timing as it comes onto boost

30detkiwi Contributor

30detkiwi

Posted
Posted
one thing i actually have forgotten to do

do u have a pic or diagram of where they are?

will advance the cas again too

and had the -'ve off while i was soldering so ecu is re-set

think its just nearing ractory limits and its starting to pull timing as it comes onto boost

yea your startn ta enter the next level,

the knock sensor sub loom is traceable from the firewall end of the plenum.

look in between 5 & 6 injectors and you'll see a square grey plug.

follow that under the plenum it will go to 2 plugs,1 between cylinders 123 & the other 456 has 1 to,

they are a squeeze plug & flamin mongrely ass to get off sumtimes

pipster11 Grand Master

pipster11

Posted
  • Author
Posted

had a look today

found the front one and its all good

gave up/forgot with the back one

seems to be going well now tho, i've heard the beep beep of 0.85 bar a few times and gone past it and no cut yet :(

possibly it getting into the upper end of the stock ecu map i think

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