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Discussion Starter · #1 ·
I have found some tips... How to remove Fuel Cut
for TX5, MX-6, and Probe GT 2.2L turbo



Due to the number of requests I have received, here is some information on hoe to remove the fuel cut for the Telstar TX5, Mazda MX-6, 626 and Probe GT 2.2L turbo engines.

There are a number of ways to remove it, but first, let me explain the different 'cuts' that the ECU may initiate, and the conditions that cause them

1) 'Overspeed' cut
The 'overspeed' cut has 2 conditions.

RPM > 6300

RPM > 6000 for 5 seconds or longer

If either of these 2 conditions are met, the ECU initiates an ignition cut. Ignition will operate again when revs drop to 5800rpm.

2) Fuel cut
The fuel cut occurs when the ECU detects that the car is using too much fuel. Fuelling is stopped for 2 seconds.

3) 'Overboost' cut
This is the one you may be interested in! In effect, it seems the overboost cut is actually an ignition and/or fuel cut that occurs at approximately 12psi of boost in a standard engine. Technically, 2 signals are monitored by the ECU.

'PIP' signal from ignition (strength, length and frequency of spark) and

Air Flow

Using these 2 signals, the ECU determines the load the engine is under, and a boost cut is activated. This is denoted by a 'beep' from the dash, and total loss of power for about 2 seconds.


There are a number of ways to bypass the fuel cut.

The cheap way, and the expensive (and best!) way.

The cheap way is to alter the Air Box so the ECU cannot detect that the air flow meter is open fully for 3 seconds or more (as this is the condition the ECU uses along with the PIP signal). Therefore, if a modification is made, so the airflow meter vane in the air box cannot quite fully open, then the fuel cut will not occur.

The way to do this, and it has been done by someone with an MX-6 in Canada, is to screw a bolt into the side or the air box behind the vane, so it cannot fully open.
To imagine what I mean, picture the vane inside the air box. under low speed cruising, the air volume and pressure entering the inlet will only force the vane open a small amount (Picture a door in a doorway). Using a potentiometer in the air box, a voltage is sent to the ECU.
With the vane open only a small amount, the voltage will be low. As engine load increases, and more air is sucked in, the vane is forced open more and more, with the voltage rising higher and higher.
As full engine load is reached, the vane may not be open 100% on standard boost. BUT, as boost is raised (via bleed valve or whatever method), MORE load is placed on the engine, and the vane may open FULLY to get the largest amount of air into the engine. The maximum voltage is sent to the ECU that the air flow meter can send. When the ECU receives this max voltage (or voltage above a preset limit near maximum voltage) for 3 seconds or longer, in conjunction with other information from ignition PIP signal, boost cut is activated. This just happens to occur near or at about 12psi. I have seen some cars that can run 12-14psi without hitting boost cut.

You can

1) Place something behind the vane inside the airbox (or put a bolt through the back of the box) to stop it opening fully, thereby lowering the voltage sent to the ECU, never activating boost cut, or

2) Modify the potentiometer, so overall voltage is lower, and it takes MORE boost to reach cut out. Using this method, it is important to somehow modify fuelling if you want to run significantly higher boost levels.

I TAKE NO RESPONSIBILITY IF YOU WANT TO TRY THIS. If not done properly, you could SEVERELY damage the engine. It is recommended that you get this done professionally, and with the use of an air/fuel meter, so detonation will not occur. If you want some more information, then mail me!

Other options :

1) Fuel cut remover

The only place I know that has a fuel cut remover that works is Fueltronics. The cost when I last checked is $250. I am not sure that this is the best solution however. The 'overboost' cut is in place as a safety measure. With this cut removed totally, the ability is there to melt pistons, or put a rod through your block (no, I'm not being crude!).

2) New ECU or chip.

The seemingly best option to me, given the amount of research I have done, and the amount of time I have spent on the phone. To remove or alter (raise) the fuel cut, you also need to take into account the extra fuelling required when running more boost, and also any alterations to be made to timing. New chips vary in price quite a lot, and so do the reputations of the chip making companies depending on who you talk to... I think it's also very important to get a chip custom programmed, as every engine and application may be different. Make sure you do some research into it though.

Note : for the 2.2L 12 valve engine, a new chip involves soldering. The standard ECU has it's main ROM soldered to the circuit board. When getting a new chip fitted, they remove the old one, and place a socket in it's place, allowing you to 'plug in' a new chip (or your old one).

New Computers (Microtech, Autronic, SMC, Fueltronics and so on) or 'in-line' modules, such as Link are a more complicated topic that will be dealt with on my modifications page.
 

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speed limiter?

Thanks for that good info. Question: Is there a top speed fuel or ignition cutoff on the 88-92 mx6turbo?
 
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Discussion Starter · #4 ·
I dont now if there is a speed cut, but im studing that case.

your welcome


Rodrigo Garcia
Sto. Dgo. R.D.
 

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err. there is a speed cut in some of these cars(my car cuts out at 115 mph as do all 88-89 LX/DX in USA) , and there are much easier ways to elimanate. Seriously tho, it is not a good idea to eliminate the speed cut, because unless your car has been properly prepared (especially tires) you risk serious damage to your car. Further more, most public roads are not designed for such speeds(except on the autobahn), so it really isn't safe for you or the other people. Of course, if you want to run on a track, with proper medical aid availible, by all means remove the fuel cut.
There is a good write up about the simplest way to remove the fuel cut
at performanceprobe.com.

Here is a link:
http://www.performanceprobe.com/doityourself/upgrades/speedlimiter22.htm

If you do a search in the 1G forums, you will also find that there is a switch inside the speedometer, the wire to which can be cut (this is the yellow-white wire mention in the link above). This will also remove the speed-limiter.

However the methods I mentioned only remove the speed-limiter. They do not affect the over-rev limiter. It is possible, with a new ecu to remove that, and I believe that the three most widely known replacement ECU's (JayB, AdamTurbo, and ZombieSS) all have some form altered rev-limit, either increased or removed. But frankly, with the F2/F2T heads, it doesn't make sense, because these engines just don't make power after about 5500 rpm, and the rev limit on all of them is 6300, so really it is kinda pointles to remove the rev limiter. Granted a few members with high turbo boost levels are continueing to make power, but they are few and far between.

BTw, the speed cut on the 88-89 GT's, at least in the USA, I think the Canadian cars don't have the speed cut, is 135 mph.
 
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