Fuel Cut ? Ideas?

[iijj]

My S2 RS V has an HKS EVC4 Boost Controller and regularly, whether on low boost (0.55bar) or high (0.8bar), and not every time, it will have what seems like an ECU dictated fuel cut, momentarily but completely cutting power for a half second or more.

It happens when boosting hard or slightly backing off after a foot-flat overtake.

Have done a search about R&R and Fuel cut on Neo engined Nissans and it seems it is a fuel cut. Most solutions presume no aftermarket boost controller so I thought I'd ask what you guys and girls think.

The car was just dyno-tuned 3 weeks ago and has had th'body cleaned, plugs, oil etc. A/F ratios are all good at both high and low boost settings. Don't want to push the turbo or risk detonation at all but would like to leave these power cut moments behind.

Would a Fuel Cut Defender serve its purpose here?

Has anyone fitted the Jaycar FCD Kit ($19.95)? If so, how well did it work?

Anyone selling an HKS one?

Since I am only, according to my boost gauge, around 0.7bar max (10psi), and have a GTR33 cooler setup, I doubt I am endangering either turbo or engine life...

Thoughts?!?

[Tangles]

how far do you want to go with the mods?

fcd (see ebay hks, pop up now and then) would be a solution and that is that; set and forget and drive into the sunset.

or if you want to go further with mods then look into the safc

that way after fuel mods, air mods, exhaust mods, larger afm + turbo etc, youd know that with the safc you can have a nice package and not risk detonation (with an economy tune) nor experience Rich and retard

[_Ryan_]

i would look at this thread: http://www.skylinesaustralia.com/forums/Ja...tro-t61207.html

before buying an SAFC, and if you have a decent budget, look at this one: http://www.skylinesaustralia.com/forums/ma...&hl=emanage

-Ryan

[chook]

I doubt it would be cutting spark at 0.55bar, I would suggest looking at your coil packs, or possibly spark plugs (has this started since they changed your plugs ?) plug gap ? I had similar thing, changed plugs, all fine.

Does it still cut out with all boost OFF, ie ~0.45bar ? also, post this where the skyline boys can read it in maintenance etc, they might have some more ideas...but I wouldnt be trying FCD.

Edited January 6, 2008 by chook

[leetom]

was it doing it before you tuned it (changed plugs)? and wot about the b/c have you just fitted it, was it ok before b/c?

if it only started doing it after tune take it back ( who tuned it,..... if it only started doing it after tune maybe you could pm me and tell me who done it.

hope you get sorted ,

leigh

[pixel8r]

Basically, what Brendan (Tangles) said.

My preference would be the safc since it'll help out with more than just avoiding the "boost cut" (for the sake of something to call it). I believe its based on airflow, rather than boost pressure. R&R can make it really bog down or it can actually cut ignition completely. I've felt both, and can confirm an SAFC will overcome it. However if you're happy with the car running as it is (normally a little bit rich from the factory) then the FCD will be the most cost-effective option.

[Sydneykid]

Let's clear up the fuel cut and lean thing first. If the ecu turns off the injectors, there is no fuel, no fuel means the engine is not running. That is not LEAN combustion, it is NO combustion. The standard ECU also does this on overrunn ALL THE TIME, to save fuel.

If it turned off the ignition you would have raw fuel/air in the exhaust system. When the spark was returned you would get backfiring in the exhaust system which is somewhat bad for the cat. So not something Nissan would do. Hence no ignition cut, but a lot retarding of igniton timing is OK.

What causes the standard ecu to move to R&R mapping and eventually fuel cut, is sensors operating outside their normal range. Simply put, at a certain rpm and throttle position there is a range of voltage that the AFM should be reporting. But you have jacked up the boost, hence increased the airflow. So the ecu is seeing higher AFM voltages than the rpm and throttle position would suggest that it shoudl eb seeing.

A Boost Cut Defencer (in Janglish) is a simple voltage clamp. You set it at a certain voltage maximum and no matter where the AFM voltage goes above that it doesn't get sent to the ecu. The idea being that you work out at what AFM voltage the ecu triggers R&R and/or fuel cut and used the BCD to clamp the voltage at that maximum. The ecu doesn't see too high a voltage and doesn't go R&R and/or fuel cut.

The problem is that the voltage for R&R and/or fuel cut is variable by rpm. For example, 4 volts might trigger it at 5,000 rpm but it might only need 3.8 volts at 3,500 rpm. Where do you set the BCD? If you set it at 4 volts then you are still going to get RR and/or fuel cut at 3,500 rpm. If you set it 3.8 volts then the engine is going to be mightly lean and advanced (in ignition timing) by the time it gets to 5,000 rpm. Think detonation and lots of it.

An SAFC (or DFC or equivalent) is simply a variable BCD, you get to choose the voltage clamp at various rpms. Hence it is a far more suitable solution.

[iijj]

OK... Some great knowledge and some excellent info.

I have had an SAFCII on a previous S1R33 4 Dr I owned and it was great to have that knock reading but it kind of became something I watched and worried about all the time.

Plus, where could I get one, even second hand in NNSW or SEQLD for less than $400 installed??? They're quite expensive... and then you have to have somebody tune it who knows what they're doing...

Could my HKS Supersequential BOV be affecting on boost behaviour??? I've read it somewhere that the Neo doesn't like aftermarket BOV's...

Ta!

[GorGasm]

Ive noticed two things in my RSV.

I have similar mods to you and im running near on .9 bar.

Firstly R&R was excessive above about 0.7-0.8 bar. This is the sluggish feeling from 4-5.5krpm then full speed from there.

The next was a wierd sort of cutout which happens at about 5krpm and only on 1 bar or half throttle on anything more than 0.75bar.

I have installed and SAFC and SITC and have tuned that to get rid of most of the R&R feeling and my A/F ratios are near flat on 12. Problem is that it will get better/worse depending on ambient temperature. The SAFC/SITC do not get rid of the strange cutout/boostcut. A FCD may work here but im thinking about upgrading to a Z32 afm, adjustable FPR and larger turbo and seeing what i can do from there.

The FCD may help you out but i would definately set it up on a dyno.

[pixel8r]

Ive noticed two things in my RSV.

I have similar mods to you and im running near on .9 bar.

Firstly R&R was excessive above about 0.7-0.8 bar. This is the sluggish feeling from 4-5.5krpm then full speed from there.

The next was a wierd sort of cutout which happens at about 5krpm and only on 1 bar or half throttle on anything more than 0.75bar.

I have installed and SAFC and SITC and have tuned that to get rid of most of the R&R feeling and my A/F ratios are near flat on 12. Problem is that it will get better/worse depending on ambient temperature. The SAFC/SITC do not get rid of the strange cutout/boostcut. A FCD may work here but im thinking about upgrading to a Z32 afm, adjustable FPR and larger turbo and seeing what i can do from there.

The FCD may help you out but i would definately set it up on a dyno.

If you think about what the FCD is doing, its the same as running your SAFC on increasingly -ve numbers as you get higher in the revs...if that makes sense...but you wouldn't do that with the SAFC since you'd risk detonation so why do it with the FCD? With the FCD the ecu may reach its clamp setting at just 12psi, but if you have the boost set to 15psi, thats 3psi more, meaning more airflow, and yet the same amount of fuel as it was flowing at 12psi...that just spells trouble.

Also I managed to get past the fuel cut with my safc, just had to tweak the settings a bit. Its just that the SAFC has its limits and you reach those limits the more you up the boost. You may find that replacing the stock AFM with a Z32 or something may give you a bit more range...but sooner or later the SAFC will not be enough.

In this case its time to move up to a more capable ecu such as a emanage or powerfc (or maybe you have other options?). The FCD would only be a step backwards IMO.

[GorGasm]

true, with an safc you could do effectively the same as a FCD. And yeah its only good to a point.

[Sydneykid]

Ive noticed two things in my RSV.

I have similar mods to you and im running near on .9 bar.

Firstly R&R was excessive above about 0.7-0.8 bar. This is the sluggish feeling from 4-5.5krpm then full speed from there.

The next was a wierd sort of cutout which happens at about 5krpm and only on 1 bar or half throttle on anything more than 0.75bar.

I have installed and SAFC and SITC and have tuned that to get rid of most of the R&R feeling and my A/F ratios are near flat on 12. Problem is that it will get better/worse depending on ambient temperature. The SAFC/SITC do not get rid of the strange cutout/boostcut.

You just need more/better tuning. It is not a simple tune, I have never been able to get 12 to 1 AF ratios consistently through the rpm range and get rid of R&R. You have to compromise and try multiple solutions, with the SAFC, the FPR, the SITC and the exhaust cam timing. It's fiddly and time consuming.

A FCD may work here but im thinking about upgrading to a Z32 afm, adjustable FPR and larger turbo and seeing what i can do from there. The FCD may help you out but i would definately set it up on a dyno.

No it won't help, for the reasons explained above.

Cheers

Gary

[GorGasm]

with SITC and SAFC i have got it to be nearly no R&R. It will never be completely gone without lowering the boost or changing ecu but its quite good at the moment.

The SITC would be so much better in this application if it had more resolution, especially around 4000-5000rpm (It only has settings for 4000 and 5600).

After further thinking, yeah the FCD is probably just a waste of time.

[Sydneykid]

with SITC and SAFC i have got it to be nearly no R&R. It will never be completely gone without lowering the boost or changing ecu but its quite good at the moment.

An adjustable exhaust camshaft pulley helps, as does the adjustable fuel pressure regulator. Add a little fuel presure then reduce the AFM voltage, end up back at the same A/F ratios but further away from R&R in the ECU mapping. As I said, it is fiddly and time consuming.

The SITC would be so much better in this application if it had more resolution, especially around 4000-5000rpm (It only has settings for 4000 and 5600).

Too true.

Cheers

Gary