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R&r Cut....i Think

Nismo_God

By Nismo_God,
in Engines & Forced Induction

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Nismo_God Veteran

Nismo_God

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Hi All,

I have been experiencing power cut when under load in gears 3-5 low revs.....starts to boost then cuts out.....new coils fixed my miss but still got cut.

I have a SAFC, shouldnt this fix any R&R cut???

can a SAFC reset itself?

or will its reset if my car battery goes flat or disconnected or alarm is immobilised???

Can any let me know how to check to see it SAFC has returned to factory settings.

Thanks!!!

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jeffworld2 Veteran

jeffworld2

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does it miss at all or just go slower? could just be coils

safc will only help r&r i its set up to do so. rich and retard is the ecus way of protecting the engine from what it deems excessive airflow, and an safc works by bending the airflow meter signal.

If you tuned it to be a bit leaner it would be bending the afm voltage away from the r&r limit, but potentially leaning out the engine in the midrange is a bad idea.

could even be beneficial to remove the safc if you still have stock turbo

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Nismo_God Veteran

Nismo_God

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def not coils as just replaced them....not missing.....it completely cuts out...

stock turbo....but safc should help rather then hinder tho....more boost and power then stock, therefore need to tune ratios to match.....

thoughts???

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Nismo_God Veteran

Nismo_God

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yeah thats the road i thought i had to go down....

but just got it tuned 2 months ago and was fine....then all of a sudden it started missing and cutting out.....replaced coils and fixed the miss....

thought safc would hold its tune for more then 2 months....

what can cause a safc to reset?

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**RB2530** Proficient

**RB2530**

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What has probably happened is that you had the SAFC tuned such that it was lowering the afm voltage at 4000rpm 'just enough' to get under the 'airflow cut' threshold....(IMO the airflow cut doesn't act until engine rpm reaches 4000rpm. If air flow voltage exceeds the 'airflow cut' threshold at 4000 rpm, ignition is cut straight away...the threshold increase with engine rpm up to about 5500rpm).

The afm is temperature compensated but only inherently so it is not perfectly independant of temp. You would have had the SAFC tuned to get the afm voltage under the 'airflow cut' threshold a couple of months ago when the weather was cooler. Now that the weather is warmer, air density and humidity are different, it may be that you are hitting the 'airflow cut threshold' again. You may have been only missing the airflow cut threshold by a few mV before.

Plus the overall efficiency of your engine will change with temp as well...

BTW this is not R&R. IMO R&R is triggered by excessive knock...it doesn't cause engine to cut completely..

Anyway I would say get your SAFC retuned to suit warmer weather or lower your boost just a touch...

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**RB2530** Proficient

**RB2530**

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Except warmer weather reduces the air flow/density for a given boost.

Yep that is true...I was referring more to the accuracy of the afm with respect to temperature...ie it's output is x volts per unit mass of air flowing through it...in theory the afm is temperature compensated because it relies on transfer of heat put into the air by the heater element to the receiving element. It could be that as the air temp into the afm increases, it over-estimates the velocity of the air....not by much mind you, and probably not enough to make any real difference to the engine tune overall, but enough to trigger air flow cut if you are already so close it...Also the electronics of the afm are analogue right up to the ECU and would also be effected by temperature...once again not by much but maybe just enough to trigger air flow cut...

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Nismo_God Veteran

Nismo_God

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thanks for your help guys....

i havent had this before....i had a different 33, exact same car...making exact same power...same mods except for the safc.....would this problem be because the safc tune is making the car get close to the airflow cut which in contrast to no safc the airflows are not altered and not close to airflow cut?

or am just way off???

also what gains are made from safc? just fuel economy or power gains? and if so to what extent.....because i dont pay for fuel so not an issue....and if i have to wind down boost then the marginal loss of untuned car.

also what if i get the tuner to do a very emissions friendly tune, would it improve my situation....as in reduced airflow.

cheers guys....new to this so appreciate your help!!

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Nismo_God Veteran

Nismo_God

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safc was tuned 2 months ago...

is there anyway to fix the problem? or is it just something i need to put up with....drop boost...

what happens if i want a bigger turbo and make more power? say a hiflow for example....what would i have to do to resolve issue.

ultimately i would like to fix the problem....

thanks!!

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**RB2530** Proficient

**RB2530**

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safc was tuned 2 months ago...

is there anyway to fix the problem? or is it just something i need to put up with....drop boost...

what happens if i want a bigger turbo and make more power? say a hiflow for example....what would i have to do to resolve issue.

ultimately i would like to fix the problem....

thanks!!

You can do a few things...

1. Drop the boost...My guess is you would not need to drop it that much...This is the safest option and you may not lose that much power...

2. Adjust your afm voltage correction (SAFC) to get underneath the airflow cut. Start at 4000rpm and work up from there...BUT do not do this unless you are checking either AFRs or EGTs at the same time. I would advise you to get a tuner to do this...

3. Change the ECU...Unfortunately you have hit the brick wall in the standard ECU...there is not much you can do...Nissan have put these limitations in the ECU to keep their warranty claims department quiet...All car manufacturers do this..

At this point in time I am going to say start searching the forum because from now on for every answer we give you, you will have two more questions...you will find the answers and learn a lot at the same time..

best of luck...

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