Why Does It Cut-out?

[Paul SM]

Since installing a Hybrid intercooler as part of an engine rebuild, I find the car cuts out momentarily under normal accelleration just as it reaches 0.75 bar on the boost guage. This doesn't seem to happen if you rev it hard through the gears, then it will go to 0.75 without cutting out but won't go higher. If you try to accellerate from around 2500-3000 revs in 4th or 5th, ie, just cruising and putting the foot down to overtake, then it's a real cow, bouncing back off 0.75 as it cuts out.

With the original intercooler I could run 0.8, even 0.9 bar without any such problem.

I've tried adjusting the boost valve, replaced the blow off valve, the airflow meter, even the ECU, but it still happens. Has anyone experienced (and solved) this problem? I would sure appreciate some advice because it seems to be getting worse.

[Luciano_R33]

im not 100% on this one, but maybe you need to install a fuel cut defender.

ask a few tuning workshops about these fcds, and explain the problems youre having. Might be able to diagnose the problem that way...

[Paul SM]

im not 100% on this one, but maybe you need to install a fuel cut defender.

ask a few tuning workshops about these fcds, and explain the problems youre having. Might be able to diagnose the problem that way...

Thanks for the thought, Luciano. The car's in the workshop today so if they can't figure it out I'll pass on your suggestion...

[pixel8r]

Why get a fuel cut defender when you can get a Apexi SAFC 2nd hand for the same money and it not only can be tuned to remove fuel cut (R&R) it can be tuned to give better performance (and potentially fuel economy) at all revs.

But then why get a SAFC when for a couple hundred more you can get a GReddy E-manage.

Fuel cut is an extension of R&R which is a "safety" fuel map built into the factory ECU. R&R is triggered when the ECU detects too much airflow. It knows nothing about what boost you're running, only the amount of air passing through the Air Flow Meter, which it measures by reading the voltage output from the AFM to the ECU. As I understand it, R&R is triggered when the ECU detects more airflow than it thinks your engine can handle...and fuel cut is just a more extreme form of that, possibly when the airflow exceeds the range of the AFM?

Basically, from what I've read about different FCD products, all the FCD does is monitor the output voltage from the AFM to the ECU and when it reaches a high enough voltage that the ECU will trigger fuel-cut, the FCD will instead "clamp" the voltage to just under that, and thereby preventing fuel-cut.

The only problem with this approach is that the ECU will be reading less airflow and therefore supply less fuel, which is fine for a stock car because they run very rich as you start raising the boost but after a certain point you will risk running lean and damaging (blowing up?) your engine. It will also still run rich up to the point where the FCD cuts in so its not exactly tuning anything and is effectively just allowing you to bypass the engine's over-boost protection and sending your Air/Fuel Ratios up the creek even more.

The better solution is to go for something that can "bend" or "modify" the AFM signal at different RPM points (12 points for the SAFC blue screen with buttons, 16 points for the SAFC2 blue screen with knob). This can be tuned on a dyno to make your car run more efficient, giving an AFR graph thats almost a straight line rather than getting richer and richer as you add boost. You will get enough tuning range from the SAFC to run at least 16psi which is plenty, and possibly more than you should be running with the FCD.

I could be wrong about how the FCD works so please correct me if thats the case, but from what I've read on different manufacturer sites etc. this appears to be how they work.

My advice is to find a tuner who knows how to reliably tune a GReddy E-manage (blue - the cheaper one, unless you can afford the ultimate) on a skyline and buy one of those (~$400 from nengun.com). One of these will give you way better value for money than either a FCD or a SAFC, there is just no comparison.

[Luciano_R33]

do what he says^^

[Paul SM]

Why get a fuel cut defender when you can get a Apexi SAFC 2nd hand for the same money and it not only can be tuned to remove fuel cut (R&R) it can be tuned to give better performance (and potentially fuel economy) at all revs.

But then why get a SAFC when for a couple hundred more you can get a GReddy E-manage.

Fuel cut is an extension of R&R which is a "safety" fuel map built into the factory ECU. R&R is triggered when the ECU detects too much airflow. It knows nothing about what boost you're running, only the amount of air passing through the Air Flow Meter, which it measures by reading the voltage output from the AFM to the ECU. As I understand it, R&R is triggered when the ECU detects more airflow than it thinks your engine can handle...and fuel cut is just a more extreme form of that, possibly when the airflow exceeds the range of the AFM?

Basically, from what I've read about different FCD products, all the FCD does is monitor the output voltage from the AFM to the ECU and when it reaches a high enough voltage that the ECU will trigger fuel-cut, the FCD will instead "clamp" the voltage to just under that, and thereby preventing fuel-cut.

The only problem with this approach is that the ECU will be reading less airflow and therefore supply less fuel, which is fine for a stock car because they run very rich as you start raising the boost but after a certain point you will risk running lean and damaging (blowing up?) your engine. It will also still run rich up to the point where the FCD cuts in so its not exactly tuning anything and is effectively just allowing you to bypass the engine's over-boost protection and a sending your Air/Fuel Ratios up the creek even more.

The better solution is to go for something that can "bend" or "modify" the AFM signal at different RPM points (12 points for the SAFC blue screen with buttons, 16 points for the SAFC2 blue screen with knob). This can be tuned on a dyno to make your car run more efficient, giving an AFR graph thats almost a straight line rather than getting richer and richer as you add boost. You will get enough tuning range from the SAFC to run at least 16psi which is plenty, and possibly more than you should be running with the FCD.

I could be wrong about how the FCD works so please correct me if thats the case, but from what I've read on different manufacturer sites etc. this appears to be how they work.

My advice is to find a tuner who knows how to reliably tune a GReddy E-manage (blue - the cheaper one, unless you can afford the ultimate) on a skyline and buy one of those (~$400 from nengun.com). One of these will give you way better value for money than either a FCD or a SAFC, there is just no comparison.

Hey, thanks heaps for such a comprehensive reply and suggested solution. What gets me is how you blokes know so much technical stuff - makes an old (university educated) fart like me feel totally inadequate!

My workshop guy seemed to have solved the problem by cutting the boost right back to about 0.6 bar on the boost adjusting valve but that was definitely throwing the baby out with the bathwater since the car lost all its sting.

I was so fed up I decided to bite the bullet and get a Power FC like I was advised to do in the first place when planning the aftermarket intercooler. I found a keenly priced one over the weekend being offered by an E-Bayer with a perfect history and hopefully it's now on its way here from South Africa!.

The fun should start once it arrives...

[pixel8r]

Hey, thanks heaps for such a comprehensive reply and suggested solution. What gets me is how you blokes know so much technical stuff - makes an old (university educated) fart like me feel totally inadequate!

My workshop guy seemed to have solved the problem by cutting the boost right back to about 0.6 bar on the boost adjusting valve but that was definitely throwing the baby out with the bathwater since the car lost all its sting.

I was so fed up I decided to bite the bullet and get a Power FC like I was advised to do in the first place when planning the aftermarket intercooler. I found a keenly priced one over the weekend being offered by an E-Bayer with a perfect history and hopefully it's now on its way here from South Africa!.

The fun should start once it arrives...

The powerFC should solve your fuel-cut problems for good

Hope you get a good result from it