Fuel cuts happen when the ECU sees the boost level too high and cuts the fuel to stop it increasing any further.
This can happen when some of the restrictions in the standard car are removed e.g. aftermarket exhaust, induction kit or removing the infamous boost solenoid grommet.
It is quite a dramatic measure but the preset level varies between Evolutions, with the VI seeming to have the most conservative settings, an increase of 0.2-0.3 bar over 'standard' max boost seems to be enough to induce fuel cuts in a VI.
Chunky has hit the nail on the head but to elaborate slightly further here is the extract from my FAQ's which will be added to this site soon:
Fuel Cuts Cars affected:
Evo 4-7 (possibly earlier Evo's) Symptom:
A very sudden de-acceleration due to the fuel being cut to the injectors, similar to your foot slipping off the accelerator except it will recover almost immediately. It occurs when coming on maximum boost i.e. while accelerating hard (common at roughly 4000rpm in 2nd, 3rd or 4th gear but possible at other rpm). Also it is more common if the outside air temperature is cold. Problem and cure:
Fuel Cuts are the Engine Management's way of stopping over boost. Instead of detecting the actual boost pressure the ECU (Electronic Control Unit) uses information from the Air Flow meter and the Outside Air Pressure sensor to work out the boost pressure. The ECU will cut the fuel at a minimum of roughly 1.3 bar boost pressure (18.8 PSI) on the Evo 6 but the actual cut point is dependant on air pressure and air density at the time.
Fuel cuts can occur after fitting an upgraded aftermarket induction kit and/or exhaust. The increased airflow created by these parts is enough for boost levels to increase. It is also possible for fuel cuts to occur due to a faulty Wastegate Actuator (see elsewhere).
The cure for fuel cuts depends on what is causing it. If you have just fitted any upgraded parts then the boost level can be dropped fairly easily by a manual alteration to the Boost Control system. This procedure will not be covered here as it is open to abuse that could result in engine failure and should not even be considered without suitable measurement of Boost levels and knowledge of the system. If you are having problems with fuel cuts then consult a qualified garage/mechanic that knows about Evos. Approximate cost of repair:
Depends on the fault.
A new Wastegate Actuator is approximately £200 inclusive (plus fitting approx. 1 hour).
Adjusting the boost level will take 30 minutes with no parts required.
I would say that it happens to all Evo 1 to 6 and probably and amp; as it happen on my 1800RS when the solanoid (spelling shet) got stuck open. This caused peak boost to reach 1.5 bar!, did know what it was at first as didnt have boost gauage. Now have boost controller and everything is OK, apart from HKS which has let in aload of dust, the pipe from the turbo to the fitler is full of ****, going to have to wash it out to night, having to use RAM air filter as a tempoary measure until sorted.
I am not sure exactly when I will get it finished although it is probably 50% complete. I am also not sure when it will be implemented on this site. There are a few additions and changes in the pipeline for the whole MLR site ready for 2002 and hopefully it will be included in that.
The information I have of the faults is either from the forum, directly from people via email or from the trade. I have only listed 'faults' and 'quirks' on the FAQ's that are experienced by more than one person otherwise it would be huge! After all it is 'Frequently Asked Questions', a lot of people have experienced fuel cuts due to aftermarket exhausts etc. , 3 or 4 due to a rusted Wastegate Actuator and I have only heard of you with the problem with the Boost solenoid. There are a few other reasons why Fuel Cuts can happen but I have never heard of them occuring so I don't list them. If other people have had trouble with a faulty Boost Solenoid causing Fuel Cuts then let me know and I will include it as a possible problem area.
You have brought one thing to my attention though, I forgot to mention about the 1800RS/GSR and the Lancer 2000 Turbo! (I said 'probably earlier Evo's' as the cars affected). I must remember to change Evo's to Evo's/Lancer's.
As a general note my FAQ's will be bias towards the later Evo's (4 onwards) as very little is written on here about the earlier cars. I have already contacted Tony Crossley about adding some stuff in about the earlier cars so hopefully it will be more comprehensive. The last thing I want really is for the FAQ's to be purely for the later Evo's but as with most things you only really take an interest in the model you own yourself (in my case the E6).
Wasnt having ago at the FAQ, just saying that my car had the same problem, just passing on information on the question posted by chris. Never expected there to be a load of information about 1800s as there must be only 10 in the country if that. Theirs shed loads of Evo 6s around now, even have them in Hull, so must be going down hill fast
Sorry, I did realise you weren't having a go, I was just trying to say if it is a well known problem then it will be included. Is it a well known problem with the 1800RS/GSR's? As I said I have no idea really about the common problems with the earlier cars so any input is much appreciated.
Surely there has got to more than about 10 1800RS/GSR 4x4's in the country? There must be triple figures at least? There is another one for sale this week in Autotrader (Thames Valley) and I am sure there has been at least another 2 or 3 in the past couple of months. Great Q car in my opinion even if it does say Mitsubishi on it
You can fit a fuel cut defencer (FCD) to raise the fuel cut threshold,
but these units must be used with extreme care; FCD's simply fool
the ECU into thinking that boost levels are lower than they really by scaling
the output from turbo pressure sensor; whilst this allows for more boost,
the big downside is the ECU will also reduce the amount of fuel added to
the mixture, on a car such as the evo where the stock fuel pump is
marginal on modified cars, you will run lean very quickly. When fitting
an HKS FCD to bypass fuel cut on my evo5 (had fitted full exhaust and induction),
when I hooked up an ultra wide band lamda sensor, mixture was so
lean, if driven hard the we'd have destroyed the engine very quickly.
We fudged this by fitting a high flow fuel pump.
Be careful http://www.lancerregister.com/graphics/Wilk.gif border|EQU| 0 align|EQU| middle >
By the way, hitting fuel cut is not kind to your engine at all, if you
do hit fuel cut, get it looked at by a professional.
Best way to bypass fuel cut is with an aftermarket ECU or piggyback
ECU such as an HKS Fcon -they either raise fuel cut or remove it completely.
I know of 7
me, chunky, richards, mechells, pauls, a white RS near southampton and a bloke who phoned me up to tell me he was selling his after a week cause its not what I expected , dont know what he was on, think he knows shorty
Never seen another one apart from the ones above. How many are members of the club. Saying that I have seen 8, one was for sale in auto trader a while back, advertised as an Evo 3!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Still want to put Proton badges on it, but it always puts a smile on my face, just like my girlfriend when she.........................................