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boost leak, how i do fix it

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jbl_5star

10+ Year Contributor
150
0
Dec 14, 2009
Puyallup, Washington
once again have developed leaks in the throttle body? how do i fix it?

i rvt'd the gaskets.. its coming from the biss screw and from the vacuum line area...??? any clue on how to fix it without purchasing a new throttle body like last time?
and why do i keep developing the boost leak there? am i over boosting, i shouldnt be its only at 15?
 
If your BISS is leaking, you need to change the o-ring. If it's leaking from the spring or TPS then your shaft seals need replaced. Make sure you use soapy water and look for bubbles. There is no reason for you to need to buy a new TB at all unless it's cracked and un fixable.

Zip tie vacuum hose ends as well and are the ones you have new or old?
 
ok, i took off the vacuum line hoses and found the 3 straight lines (not the misplaced one) have like rvt in them??? is that normal??? or they supposed to be clear??
could that be the prob or the fuel cut ?
 
thats what a frienn told me yesterday.. check the pkugs to see if theyre fouled... gap is supposed to be .028 right?
and i am at 15 get to about wher eit will spool and it cuts if i try to let go and repress the gas pedal it sputters..
 
thats what a frienn told me yesterday.. check the pkugs to see if theyre fouled... gap is supposed to be .028 right?
and i am at 15 get to about wher eit will spool and it cuts if i try to let go and repress the gas pedal it sputters..
 
Correct, gap is .028. Sometimes you need to tighten them up a bit more when you go even higher in the boost (you are not there yet)

And ramsack, its not fuel cut, its more like air cut. Its not the lack of fuel, its the improper mixture of air and gas...the lack of AIR. So it wont iginte because the improper mixture.

If the car "sputters and continues" then it sounds like a spark issue.

Again, fix your boost leaks, tighten all clamps, and then check/replace spark plugs.
 
He has a boost leak, I doubt his sputtering is caused by improper gap, but rather from running too rich. You are on the brink of fuel cut when this happens. I had the same problem when the gasket between the turbo and the j-pipe started leaking. It would sputter and seem like ignition was weak at a certain RPM under boost. I would replace the plugs anyway because they will foul out in no time from running so rich.
 
He has a boost leak, I doubt his sputtering is caused by improper gap, but rather from running too rich. You are on the brink of fuel cut when this happens. I had the same problem when the gasket between the turbo and the j-pipe started leaking. It would sputter and seem like ignition was weak at a certain RPM under boost. I would replace the plugs anyway because they will foul out in no time from running so rich.

I thought fuel cut was caused by the fuel system maxing out and not being able to provide the correct amount of fuel, not too much fuel. I know you say "on the brink of fuel cut", but is it still possible to get fuel cut when you are too rich?
 
Fuel cut is a purely electrical function. When the MAF reads a certain point, the ECU sees this, and stops sending pulses to the fuel injectors. You can have fuel cut and buy a whole fuel system and you will still have fuel cut. The car would be untuned, though. An SAFC would raise the fuel cut point, but also advance timing, which is not good to not have control over timing. If you have a boost leak the MAF is reading that extra air that is just getting blown out into the world, and the ECU sees that, and injects more fuel, and if the boost leak is big enough it can hit fuel cut. Some people can hit fuel cut with just an intake, free flowing exhaust, and sometimes not even need to upgrade the turbo or run more than stock boost. The ECU is blind to fuel modifications.
 
The ECU doesn't care how much fuel the car is getting at WOT... Actually it doesn't even know! The O2 sensor is not used in Open Loop. That's why they call it Open Loop because the data loop with the O2 sensor is "Open". As in, not being utilized.

So with that said. Fuel cut happens because the Maf is stating to the ECU that it is getting too much air for the stock fuel system to support it. That's all the ECU knows. It doesn't know that you have a beefed up pump or injectors or whatever... So you get to a certain airflow and it cuts fuel in an attempt to protect the engine.

When you have a boost leak, the turbo is bringing in enough air to support more pressure/flow than what is actually getting to the engine. The MAF sensor is reading more air than you would normally see at 15psi but it is losing it before your boost guage is picking it up. Therefore, your gauge is reading 15psi but the turbo is supplying and the MAF sensor/ECU is seeing more... Then you get fuel cut...
 
thanks for all you input. the prob was the clogged vac lines, she boosts hard now, but the BOV makes a funny noise< maybe i have clog somewhere in the vac line from the interl wastegate
i have a good idea of why and when it happens i always thought a fuel cut was a safety feature from the maf reading how much air is taking in so it can translate to the ECU on fuel... have the safc piggy back anyways...
i undersatnd that but im not runnin a GM MAF, i have a relocated MAF TRANS... right before the TB elbow... which it wont register the lost of air between intake and it. and safely do a fuel cut, youll just feel it a weaker pull,... ### it see so many lbs of air... wether there is a leak anywhere from intake to before it(look at my pics of my engine bay and you can see)
so if you lose air before it it will register it as normal, but if its after which it was it will register it<

but on the sound of my BOV, is it compressor surging? how do you know?
 
well does anyone know how to identify compressor surge> the vids on youtube i watch have a sound mine BOV sounds funny or do i just need some new VAC line?

nvrmnd it was from cleanin out the vac one of the lines sucked it in to it and it was clogged<><<< ALL SOUND, runs purrfect
 
i am having a similar problem with my 91 tsi. stock fuel system. evo3 16g. maft translator,gm maft, uicp, i am running 10 psi and can hold wot till about 4000 rpm then its like hitting fuel cut. looks like a litlle boost creep to about 12psi but thats it. i was thinking boost leak but i hold steady around 10-12 never falling. no sputtering or hesitation, could the translator be out of tune, i didnt think 10psi was to much on stock fuel system, thanks for any advice:thumb:
 
i dont think so, only thing MAF does is read cc of air. and translates it to the ecu.. only a safety feature so you dont wind up blowing your engine or create huge amounts of knock.

do a boost leak test and spray down the pipes and fittings, (i use windex, but soapy water works too.)

you will also hit fuel cuts and sputters with, too much air or fuel or the lack there of. fouled sparkplugs(running too rich) or with detonation spark, like the gap on sparkplugs, .028
spark plug wires and distributor.

so my guess if your running stock fuel, ie injectors and pump, maybe its reading too much air not enough fuel. but mainly its due to a leak.
 
Tell me how the ECU would know if you change injectors, fuel pump, etc. It doesn't, it's impossible. As I said before you can have a car that hits fuel cut and you can raise fuel pressure, get bigger injectors, or even a bigger fuel pump and the car will hit fuel cut. It's purely based on airflow because all the ECU knows is that you have 450cc injectors, a stock fuel pump, or stock fuel lines. It also doesn't care if you have too little fuel.

http://www.dsmtuners.com/forums/frequently-answered-dsm-questions/186971-what-fuel-cut.html

If you still don't get that then no one can help you understand.
 
i feel ## pain i also seem to get boost leaks almost every week i boost leak test my car. and i am hitting fuel cut but i have a 14b at 17psi. so thats normal for my set up even with my fuel system all done. i just need ecm link
 
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