scooby46

iTrader: (2)

Hi, i have a 95 sti, ive just put on a decat downpipe. So now its fully de cated after the previous owner removed the middle cat. The problem im getting now is that sometimes in 4th gear and definatly after half throttle in 5th gear the engine jolts violently after hard acceleration. This really isnt a plesent experience because this happens at high speed. Ive spoken to a guy who thinks it may be fuel cut because its overboosting. He also says to cure this problem i need to get a 3 bar map sensor from a newer scooby and put that on, as mine is only a 1 bar sensor. Does this sound right?? And can any1 explain to me what overboosting is, what a map sensor is and what i could do to sort this scary problem! Thanks Leon

scoobz72

A fuel cut occurs as a safety feature to protect your engine! It feels like the car has momentarily cut out, while on full boost. The engine carries on after, but then it re-occurs if you continue to full boost. The short term way of getting around this is not to full boost, but feed in gently. Ideally you may need a fuel cut defender to bypass this. Its a device which can save you a lot of money.
Do you use a boost controller?
If so try turning it down, or if you have a bleed valve setup, try manually reducing boost from this until you achieve a safe boost.
If your car is extensively modded with a bigger turbo, then you can safely run 20psi+ provided the car has been mapped to do so. This is where the fuel cut derives from, the fuel is being starved, so comes in lean, which is not ideal on full boost.

Hope this helps

Justin

scooby46

iTrader: (2)

My car is standard apart from hks induction kit, baileys dump valve asnd s full de cat. If a fuel cut defender is a safety feature then will removing it damage the engine? yes i get the symptoms you describe at the start. i dont have a boost controller, its set at standard boost for a 95 version 2 sti. and it hasnt had a remap. What do you think about adding a 3 bar map sensor??

Tidgy

if its over boosting then needs a professional remap, its there as a defence so if you dick around with the boost without checking the fueling you could blow up your engine.

get a remap and you'll have pweace of mind and the car will go much much better

scooby46

iTrader: (2)

o i forgot to mention - it has a walbro 255lph fuel pump on it now. So if i get it remapped i wont need a 3 bar map sensor??

Tidgy

has it been mapped at all?

if not it needs it, very very quickly or you may end up picking up bits of piston

scooby46

iTrader: (2)

no it hasnt as far as i know. Its running standard boost which is 1 bar on a v2 sti if im right. This prob has only ocurred since fitting the downpipe de cat.

apalmer

iTrader: (8)

Hey

This site gives a useful insight to standard boost cut settings for JDM cars, suggest you fit a dawes device and set the manual boost limit until budget permits a remap:

I think a dawes device retails for around £30 ??

Roojai Subaru Impreza

Glowplug

iTrader: (8)

Do you have a boost guage fitted, what is the boost topping at? I 'think' strictly speaking you should have it remapped but not sure if your ECU can be remapped 'persay' Best plan would be to talk to a pro mapper to get the best from your mods or you could have a look at a ESL board Products
Failing that if £'s are tight then as stated the other post a MBC to reduce the boost until you can get the £'s together, although this i think will be defeating the object of doing the decat Hth

scooby46

iTrader: (2)

It sounds like a remap is needed then. i dont want to cause any damage to the engine so i best take it easy untill i get it done. Can any of you guys fill me in on the 3 bar map sensor - what it is and what it does? thanks

apalmer

iTrader: (8)

Errmm was he talking about a 3 bar FPR, fuel pressure regulator? If so the later models had a 3 bar FPR as standard! Not sure about earlier Imprezas!

MAP sensor as opposed to MAF sensor is a fuel/air ratio device concerned with induction and fuelling

scooby46

iTrader: (2)

He might have ment maf - but im sure he said map. basically he said that my v2 sti only has a 1 bar maf sensor, and to cure the problem i need to get a 3 bar maf sensor off a later impreza which should stop the fuel cut problem. Weather thats true or not i dont know.

Glowplug

iTrader: (8)

I had simlar problem and it was a proper pain in the *** trying to stay below the cut level, it made a pleasurable car into a pig to drive esspecially when overtaking, you will find yourself changing up very quick to beat the fuel cut

scooby46

iTrader: (2)

yeah i know what your saying but my problem is in 4th and 5th gears. I live on the isle of wight so driving at speed in those gears doesnt happen very often. haha

Glowplug

iTrader: (8)

Yeah overboost is more likly in 4th 5th, your on max load in those gears. Isle Of Wight eh, bet you can be heard from one end to the other, do you ever meet yourself coming the other way??

scooby46

iTrader: (2)

haha no its not that small. Ive just come back from donny this weekend and noticed it alot as i opened it up on the motorways.

Tidgy

so your runnign a car that suffers from overboost tyo fuel cut and you wont have it mapped b13?

seems rather dangerous to me

scooby46

iTrader: (2)

Also would it be worth fitting a fuel regulator to my scoob? what are the advantages and disadvantages??

apalmer

iTrader: (8)

Personaly m8 i wouldn't part with any money until you have spoken to a pro mapper, Simon from JGM is super helpful and would more than likely point you in the right direction. www.jollygreenmonster.co.uk

Fuelling is the most important part of the engine, all mods aside...

jd5217

go on, dare you to keep hitting the fuel cut.

Tidgy

pmsl JD,

and FPR isn't needed.

im runnign over 340bhp and don't need one, JD is running over 450 and is the same

jd5217

no, i do have a fuel pressure regulator.


standard fit from manufacturer.

Tidgy

sorry my bad

jd5217

so back to topic in hand?

WRX Blues

I had exactly the same experience with my STi3 - it really ruined ownership until I got it sorted. I had very similar mods, dumpvalve and full de-cat. To cut a long story short I fitted a Blitz DS boost controller set at a peak level below fuel cut (1.25bar from memory). I didn't get a re-map but got it checked on Power Engineering's rollers. Despite it getting a thumbs up I also fitted a knocklink - which proved a pointless excercise because it never got above the first green light . I always ran car on Optimax (no V-Power back then) and a bottle of Millers . Re-map may be your best option but this solution worked safely and I ran her for a good 20k miles before trading in.

Glowplug

iTrader: (8)

Tidgy mate, i dont have fuel cut now , that was down to a bad actuator hose , sits nicely at 1.1 and fuelling is exellent.
Basically it a £2500 15 year old car so,
a. i cant warrent the price of a remap and
b. i wouldnt want to go any higher power or boost wise due to her age.
Different story if it was 10 grands worth of bugeye for example.

You have to weigh these things up, expensive remaps are not always worth it
End of the day if it goes bang i just buy another

Tidgy

supose thats the difference, can you afford to keep throwing away cars?

for the sake of a few hundred quid is it worth the risk?

jayallen

iTrader: (31)

How can these guys have their non mappable ecus remapped?? It will take alot more than a few hundred quid with the advice you are offering more like £600+

Tidgy

if you compare prices, then a the chip plus fitting plus the map, then compare it with sutable substitute, then the price difference is only a few hundred quid between the two.

and iirc early cars can now be mapped dirrect without an additional chip

Tidgy

perhaps i should add, the hardware isn't the issue i have, the same hardware would be used in the way i'd have it done.

its the generic or custom map im talking about