There is no fuel cut on my car

[talonkid93]

Hi people keep on complaining to me about how they have fuel cut and i dont. my car is running about 20 psi and even when i redline i dont get fuel cut . I was wondering if maybe i have some sort of fuel cut defencer or something i just got the car like 1 month ago.

 

[Gstclipse69]

Whoever is telling you they have fuel cut probably have a boost leak contributing to their fuel cut. Are you still on a 14b running 20psi? I dont see any fuel mods on your profile. If your running 20psi on stock fuel you are LEAN. Do you have a logger so you can somehow look at your o2s?

 

[TurboAnything]

You are ok with the few mods you have you would have to run more boost. When my talons were stock i would see fuel cut at about 22-23 psi.

 

[DGajre777]

Fuel cuts are associated with boost leaks.

 

[talonkid93]

Fuel cuts are associated with boost leaks.

i have a small 16g turbo and a 190L walbro in the car.

 

[TerribleTSi]

do you have an AFC? my friends car stopped hitting fuel cut when we installed his safc2 with out any other mods. ran closed wastegate just to kill the motor but never hit fuel cut. it was cool for about 5 hours then the white smoke came hahaha

 

[DGajre777]

i have a small 16g turbo and a 190L walbro in the car.

Fuel cuts have nothing to do with how small of a fuel pump you have. It has to do with metered air being lost through a boost leak.

 

[Loewen21]

Fuel cuts have nothing to do with how small of a fuel pump you have. It has to do with metered air being lost through a boost leak.

Maybe theres something i don't get but isnt fuel cut when you over run the stock system and it cuts fuel to prevent damage? Like trying to run 25 psi with an untouched fuel system. Theres more to it than just boost leaks.

 

[DGajre777]

Maybe theres something i don't get but isnt fuel cut when you over run the stock system and it cuts fuel to prevent damage?

Yes, that is the intention of fuel cut. But a stock-ish properly operating turbo will not cause fuel cut unless there is a boost leak in the system.

You may be getting confused with fuel pressure regulator over-run caused by installing a big fuel pump like the Walboro 225 or Supra TT 260LPH pump on the stock fuel pressure regulator which causes the car to run like crap at idle or deceleration.

Like trying to run 25 psi with an untouched fuel system. Theres more to it than just boost leaks.

"The simple answer is that because fuel cut is pre-programmed into the ECU, there is no method of disabling it. There are no modifications that can do so, aside from an ECU upgrade that eliminates fuel cut. Upgraded fuel pumps, injectors, and fuel pressure regulators do nothing to avoid or eliminate fuel cut. NOTHING."

VFAQ Site - Visual Frequently Answered Questions



"Chapter 7: DSMs and fuel cut

Turbochargers are positive feedback devices - the faster they spin, the more air they push into the engine. The more air they push into the engine, the more exhaust gases are produced. The more exhaust gases that are produced, and the faster the turbo spins. The faster they spin....

See the problem? The faster they go, the faster they go! Eventually something would have to break. To prevent this situation from occuring at all, turbos have a device on them called a wastegate that limits the turbo speeds to manageable levels. This is a pressure-activated valve that opens at a preset pressure and vents additional intake pressure either to the atmosphere or back into the exhaust stream.

Modern turbo design notwithstanding, it is still very possible for the wastegate on the turbo to malfunction, leading to exactly the ever-faster turbo behavior described above. Recognizing this, the designers of the DSM ECU built a fail-safe limiting mechanism into the DSM ECU modules. And it goes like this:

Should the ECU ever see an intake air mass greater than a certain preset level, it will stop fuel delivery and spark to the engine cylinders. This 'critical mass' depends on air volume, temperature and pressure, as measured by the MAS sensors. The act of the ECU cutting off fuel delivery to the engine is known as the infamous 'fuel cut'.

Why'd they do this?? Well, should the wastegate ever malfunction in such a way as to allow the turbo to spin out of control, the ECU will stop firing the cylinders to save the turbo from exploding. This is not the only method the ECU has to limit the turbo operation, but it is the last and most desperate. The mass air limit at which the ECU will fuel cut was based off of the maximum amount of fuel that the stock fuel pump and injectors could deliver to the engine cylinders.

Unfortunately, those owners who purposefully modify their engines to provide greater power are deliberately forcing more air through their engines in order to produce more power. Recognizing the limitations of the stock fuel delivery system, serious modders usually upgrade the fuel pump and/or injectors in order to provide enough fuel capacity for the hopped-up engine.

However, the fuel cut limit, based on the stock fuel system, is pre-programmed into the ECU and cannot be changed. There is no method by which the ECU can be made aware of the improvements made to the fuel system, so it will blithely cease fuel delivery once the mass air intake reaches a predetermined level regardless of how much fuel capacity is really available. This characteristic of the DSM ECUs, while understandable, has been a source of nearly endless frustration for power-hungry owners.

There are solutions to this problem. Aside from reprogramming the ECU (which is sometimes possible) to eliminate the fuel cut, all of these solutions utilize the same basic principle - fool the ECU into believing there is less air entering the engine than, in fact, there is. This is often accomplished by altering one or more of the input signals sent to the ECU by the various air measurement sensors present in the MAS.

For example, a volume of air at higher temperature contains a smaller mass of air than an equivalent volume at lower temperature. The ECU determines the intake air temperature from a sensor in the MAS. Electrically altering this signal can make the ECU read a higher air temperature than actually exists. Based on this erroneous temperature, the ECU will calculate the mass air intake as being less than the actual amount.

Even expensive fuel control systems utilize this technique to keep the ECU from activating fuel cut. These systems, however, often intercept more than one ECU signal, and can provide their own monitoring equipment to allow the operator to properly observe the condition of the operating engine. This allows the owner to 'fine-tune' the car to achieve the desired characteristics while keeping the engine safe from harm.

Obviously, doing this type of modification is a relatively dangerous process. By changing the ECU inputs, the operator runs the risk of altering both open and closed-loop ECU operation to the point where the engine does not receive enough fuel. As always, it is up to the operator to monitor the engine operation to ensure that a damaging situation does not occur."

The Essential Primer on the Diamond-Star Engine Control Units - Chapter 7

 

[Nvisabl]

Fuel cuts have nothing to do with how small of a fuel pump you have. It has to do with metered air being lost through a boost leak.

Fuel cut as I know it has nothing to do with a boost leak though a leak can cause it. Fuel cut is when you over run what the MAF is able to count 1g is something like 1600nz ish. 2g 's are in the 2400hz area.


DJ
my CSM moves 2406hz on a stock 350,000 mile 4g61t motor w/ a 60-1 @ 26psi

 

[DGajre777]

Fuel cut as I know it has nothing to do with a boost leak though a leak can cause it.

Playing with words, are we?

Let me rephrase - Fuel cut has nothing to do with how small of a fuel pump you have or a maxed out fuel system. It can be caused by metered air being lost through a boost leak. It can also be caused by a malfunctioning wastegate actuator on a turbo.

 

[Nvisabl]

Playing with words, are we?

Let me rephrase - Fuel cut has nothing to do with how small of a fuel pump you have or a maxed out fuel system. It can be caused by metered air being lost through a boost leak. It can also be caused by a malfunctioning wastegate actuator on a turbo.

A leak does not in of itself cause fuel cut it has to do with maxing out the MAF. Fuel cut can happen without a boost leak. Not playing with words explaining what fuel cut is. He may not hit fuel cut because his tune is so poor that even @ 20psi he isn't moving enough air to hit fuel cut or better yet he has a leak after the MAf but before the turbo (ie. old days before 2gs AL Blaha modified 1g MAf, we went 12.49@110mph on a small 16g Stock appearing {think dsm shootout} on a 1g MAf old school 5 knob afc.) Log showed 1400hz we were bypassing lots of air to stay out of fuel cut.
Waste gate actuator again can cause fuel cut but it isn't why there is fuel cut.
DJ