Clearing Up This Boost/airflow Cut Issue

[Finny]

I have seen MANY threads on this forum about this but I am still disagreeing with what I read.

I see alot of people saying I hit boost cut at ~12psi etc.

and the reply is that its R&R (richern and retard) from pinging or missfire or something because of too much boost and not infact a boost cut.

I beg to differ... I think that it is an air flow cut from hitting a certain amount of air flow or falling off the fuel maps.

I have my *air flow cut* down to an exact art. I know the exact ammount of boost it requires to hit it. Its at about 10.5psi with my fmic and I can adjust my boost controller one setting less and it stops... now no one can say that a difference of about 0.3psi will stop pinging or missfire which will cause R&R to set in.

I previously thought my air flow cut was R&R but then today I was driving with a friend of mine who has an RB30/RB25 Hybrid and he said its definatly not R&R and actually pointed out when my car was hitting R&R which resulted in a slight loss of power but not a cut as such. The cut I get is very drematic its like a complete cut of injectors for about a whole second and then its fine untill it hits that exact ammount of air flow again then it cuts for a whole second. Just like a rev limiter which runs off fuel cut in commodores etc. exept the cut is much longer.

I would really like some one to clear this up because I am not going to take R&R as an answer this is a definate cut not a result of the car richening and retarding. The tacho drops rapidly with a compleate cut of all power then after about a second every thing is restored to normal.

Also is there a way of removing this with out a replacement ECU, I am thinking of putting GTR injectors in and tuning my SAFC to suit which would then allow more airflow before the cut because the SAFC would be tricking the ecu and telling it that its getting less air flow than it really is.

Edited August 5, 2007 by Finny

[R34GTFOUR]

I have seen MANY threads on this forum about this but I am still disagreeing with what I read.

I see alot of people saying I hit boost cut at ~12psi etc.

and the reply is that its R&R (richern and retard) from pinging or missfire or something because of too much boost and not infact a boost cut.

I beg to differ... I think that it is an air flow cut from hitting a certain amount of air flow or falling off the fuel maps.

I have my *air flow cut* down to an exact art. I know the exact ammount of boost it requires to hit it. Its at about 10.5psi with my fmic and I can adjust my boost controller one setting less and it stops... now no one can say that a difference of about 0.3psi will stop pinging or missfire which will cause R&R to set in.

I previously thought my air flow cut was R&R but then today I was driving with a friend of mine who has an RB30/RB25 Hybrid and he said its definatly not R&R and actually pointed out when my car was hitting R&R which resulted in a slight loss of power but not a cut as such. The cut I get is very drematic its like a complete cut of injectors for about a whole second and then its fine untill it hits that exact ammount of air flow again then it cuts for a whole second. Just like a rev limiter which runs off fuel cut in commodores etc. exept the cut is much longer.

I would really like some one to clear this up because I am not going to take R&R as an answer this is a definate cut not a result of the car richening and retarding. The tacho drops rapidly with a compleate cut of all power then after about a second every thing is restored to normal.

Also is there a way of removing this with out a replacement ECU, I am thinking of putting GTR injectors in and tuning my SAFC to suit which would then allow more airflow before the cut because the SAFC would be tricking the ecu and telling it that its getting less air flow than it really is.

what gauge are you using to determine that your at 10psi? its not uncommon for gauges to be out 1-2 psi. I have an autometer gauge and it has a 1psi difference to my handcontroller's reading. So using that same logic your boost reading that causes your trouble turns from 10.5psi to 11.5psi which is close to hitting boost cut.

That 12psi cut is approx, my bros skyline can run 1bar all day with out hitting cut and he has everything still connected but then you hear people having trouble over 10psi.

The easiest way to find out if its hitting cut is by plugging the vaccum hose that goes to the map sensor the measures boost (its the same sensor that your interior boost gauge works off, so when you disconnect it your interior gauge wont work), then wind the boost up to 12psi and see what happens. If it runs fine, all that was happening before was a plain and simple boost cut, but if it still misses then i would look at spark plug gap, coils, then maybe even start measuring fuel pressure.

Edited August 5, 2007 by R34GTFOUR

[mad082]

you are getting rich and retard. there are just too many people who have read about it and never experienced it to know what it actually feels like. i had this with my 33. it is like someone turning the key off then back on.

as for injectors, i'm pretty sure the gtr injectors are top feed and r33 ones are side feed so they won't fit.

[TTT]

I was under the impression that if your ECU "richens up the fuel mixture" and "retards timing" to prevent damage, then you would lose performance and possibly feel a little doughy when right up the revs.

what he is describing is very similar to the issue I had with my S14 and my R32 GTS4.

my AFM plug connection in the S14 was a little frayed. and when I had to go to a pod from an air box due to FMIC, I hadn't mounted the pod securely for the 2 weeks.

and if I was accelerating and hit a crack in the road (parramatta rd in sydney) it would completely CUT all forward acceleration for a second then come back.

almost puts your head through the windscreen.

my R32 GTS4 on the other hand was a similar thing but it would do the same thing as it came on boost.

the problem with that one was a dirty AFM "AND" the soldering on the AFM was cracked and would move a little with movements while driving.

NOT R&R.

it is some form of cut due to the AFM.

wether it is cutting because it is faulty or maxed out I don't know in your case.

why not rule it out.

take it off, spray it with electrical contact cleaner, also take the top of it off and resolder the joints.

seal it back up, put it back on the car and go for a drive.

soldering iron and solder can be bought for $20 from tandy.

they will probably have electrical contact cleaner too for another $10.

Kmart, bunnings or any $2 shop will have auto sealant silicon (it's like regular silicon but it is BLACK) for about $5. comes in a toothpaste type tube.

[666DAN]

R34's are better

>5.1v on the AFM.....cut!!!

>4.8v on the boost sensor....cut!!!

2-pronged approach required for them, Z32 and a proper voltage clamp on the boost sensor works a treat.

[mad082]

NOT R&R.

it is some form of cut due to the AFM.

wether it is cutting because it is faulty or maxed out I don't know in your case.

that is rich and retard. the ecu reads a load point at that rpm that it either doesn't have mapping for, or is in what it classes as unsafe so it dumps in a heap of fuel and retards the timing. i know of other members on this forum that have had it happen. and it only happens once the air flow increases. and i can happen at low rpm but then if you go up in the rpm a bit and stab it it won't do it.

i used to be able to get it to do it at the same rpm every time on all sorts of roads.

[TTT]

well rich and retard sounds like a retarded term to describe a complete "CUT" situation.

if your car runs rich, it uses more fuel and doesn't feel as resposive.

if the timing is retarded then it is a similar feeling.

so are you telling me that if you were on a dyno, accelerating and the power figure goes up, A:F ratio starts to come out of closed loop, goes down towards, 12:1, 11:1 etc, then when you are at max torque and you hit your inappropriately named "R&R", then the car would "CUT" and the AFM line on the dyno graph would all of a sudden flat line at 10:1 like a dead persons heart rate monitor?

I just think that R&R is not the correct term to describe the complete BRUTAL shutdown that happens.

[mad082]

I just think that R&R is not the correct term to describe the complete BRUTAL shutdown that happens.

i don't think it is the right name for what happens either. that's why i just normally refer to it as boost cut.

[Finny]

I Totally agree.. This is not a result of richening and retarding. If that where to happend the car would richern and splutter and blow smoke atleast before it was too rich to fire.

This fully cuts the injectors like no fuel what so ever instantly cut. No engine noise nothing for a whole second.

I have an autometer guage!!!

This is a boost/airflow cut I am not sure if its triggered by the air flow meter reaching a certain ammount of air flow or the pressure sensor. I assume its the air flow sensor because early in the morning when its cold it cuts earlier like before 10psi and when its all warmed up and warm intercooler I can get about 11psi.

This is definatly not R&R I have experienced R&R when I had to put lower octane fuel in my car and all it did was lowered my power by a notisable ammount for a minute or so after the car stoped pinging but nothing like the cut I am getting.

I will have to get my digital camera out and record this cut effect.

[mad082]

This is definatly not R&R I have experienced R&R when I had to put lower octane fuel in my car and all it did was lowered my power by a notisable ammount for a minute or so after the car stoped pinging but nothing like the cut I am getting.

that is the knock sensors doing their job. as far as i know they just reatrd the timing, not add more fuel.

but what you are getting isn't boost pressure related as such. since you can have it happen at 3000rpm but then keep your foot into it and not have it happen at 5000rpm on the same boost, so it is still based off the afm. even if you disconnect the factory map sensor (that control the factory gauge) it will still do it.

[Finny]

Yes I think this is an Air flow cut... maybe because it doesn't have fuel maps to handle that much air flow or somfin and spazzes out and cuts or it may just be an air flow cut set on the ecu.

When I get off my arse and wire in my SAFC I will ne able to better diagnose this as I will be able to see at what % of air flow it cuts at etc.

[TTT]

whatever the f**k you want to call it.

to resolve it, you need more resolution and tuning.

PFC + Z32 AFM + tuning = problem solved.

I should have been a mathamcmatics teacher.

[mad082]

pfc alone would solve the problem. z32 isn't necessary.

[R33silverS2]

Yeh its def not r&r. I have experienced the same thing on my car aswell. As people would know with r&r there is a loss of power but you can still hear the car spool and see the revs go up. However with this cut, it feels like the engine turns off or the inmjectors 'cut' out in a violent way that makes you almost fly forward like the brakes have been applied cos only ever seemed to happen at wot. I bought myself another airflow meter still a stock s2 one but i have not experienced this problem since putting in the new afm. It was wierd as it would occur only on real cold nights at wot - so therefore you would conclude an overboosting issue, however the boost wasn't even high when it would do it as in it would 'cut out' at about 9psi. Also seemed to be quite intermittant as well. So it seemed to me atleast to be air flow related rather than a set boost level. i.e 12 psi etc.

[R33silverS2]

pfc alone would solve the problem. z32 isn't necessary.

Thats prob true, however new afm seems to have fixed mine up (for now anyways). Fingers crossed it stays that way.

[TTT]

it's been said before..

if you take your AFm off, remove the black sealant on the top, remove the black cap, re-solder the afm wires that are in there, seal it back up and plug it all back in, it will be like new.

as long as the wire element in the AFm is also clean.

so clean, re-solder it, new AFM

[GTAAAH]

Yer like GTST said my old car was hitting what i was guessing was R&R, turned out the AFM was shagged from running too high boost (bad manual tap with + and - reversed = infinite boost)

z32 = fixed

[Rolls]

My 31 with a redtop rb20det used to get a complete fuel cut for 2 seconds in cold weather, would happen around ~4k on full boost, didn't matter what throttle you were using. Had it remaped as it was running off the scale (~9:1) rich on full boost, anyway since its been leaned out to 12:1 it no longer gets the fuel cut. It also got rid of an awful rich misfire around ~5.5k

[Finny]

Have a guess what it was

I installed my SAFCII and found a bloody fuel cut defender that the idiot previous owner had installed. both that and the boost controller was brought from autobarn so I assume the guys at autobarn where like you need a FCD if you are going to get a boost controller otherwise your car will fuel cut... idiots..

Any way removed it and the car is perfect runs fine now.