Simplest mod ever

SA_Dave

SA_Dave

Member
Got an annoying lag at low revs then she starts to take off around 3-4K? Only experience is with an auto, but in 2nd at low revs without kicking back my car was slow as. I read about fuel pressure regulators etc and talked to a mechanic who specialises in Mitsis. We decide to take vac hose off the FPR and plug the end with a screw, leaving the hose attached to the inlet manifold (see dead centre of pic).

Well, problem solved, instant guts when you tromp it, often without needing to kick back. I'd be interested to see if this is the same with manual boxes in lower gears at lower rpms. Give it a try guys, 20 sec work to unleash some more potential. Guaranteed not to improve fuel economy, however.
 

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I just tried this on my car, just took the hose off but didn't dare plug the fuel pressure regulator up. Seemed to have the same effect, no flat spot off idle now... how does this work??
 
Interested, but what are the side effects? What does stopping the hose suck do.. just fuel economy?
 
Hugh-CE said:
Interested, but what are the side effects? What does stopping the hose suck do.. just fuel economy?
Click to expand...

I've never come across something like this before... Hmm time to look up how FPR's work... As long as my fuel lines won't burst or something then I may run this
 
I suggest that if you do not understand how this works you do not do it.

Unplugging the vacuum signal to your fuel regulator will increase the fuel pressure and cause it to not regulate itself, particularly and low throttle position.
 
It seems blocking the fuel pressure regulator hose port may be a bad thing, pressure will build up too much and could cause the injectors to fail
 
Hmmm, it doesn't seem to be running rich. I'll check plugs after a little bit. Makes a big difference to how it runs I can tell you. I've been thinking about my lag issue and I read the following ages ago at rpw (http://www.rpw.com.au/index.php?option= ... Itemid=554):
This is the one thing we believe that these vehicles should always have fitted regardless of how little, or much you modify the vehicle. Quite simply the factory vehicle has been tuned for maximum Economy. This has resulted in a flat spot off idle when accelerating hard from a standing start of from a cruise mode situation. The reason for this is Mitsubishi has tuned very lean on the accelerator pump settings, resulting in the lack lustre performance on throttle, but excellent fuel economy.
So only today I talked to a mechanic who worked at Mitsis and he agreed it was an FPR issue and suggested to try the vac hose. I've read a tuning book which suggested one way was to compress the body of the FPR a little to raise fuel pressure but didn't want to try that. I wanted to do something cheap without buying a performance FPR, because a person at a place which suggests this mod told me it wasn't worth doing.
 
It regulates the fuel pressure in the rail...... I would strongly suggest NOT doing this. You're either going to a) increase fuel pressure above what it should be or b) drop fuel pressure.

Btw, anything under 3k yes of course the car is going to lag, you're no were near the power band for these engines. They're a gutless 4cyl what do you expect. They also don't just put regulators in for *poo*s n giggles...
 
MazioBarditore said:
I just tried this on my car, just took the hose off but didn't dare plug the fuel pressure regulator up. Seemed to have the same effect, no flat spot off idle now... how does this work??
Click to expand...
No, don't plug regulator, just Vac hose to inlet manifold.
 
MazioBarditore said:
Hugh-CE said:
Interested, but what are the side effects? What does stopping the hose suck do.. just fuel economy?
Click to expand...

I've never come across something like this before... Hmm time to look up how FPR's work... As long as my fuel lines won't burst or something then I may run this
Click to expand...

check this out http://www.youtube.com/watch?v=Kub3q1-YNZA that was very helpful!



So if fuel isn't going back into the tank, thats where you consumption goes.. but is it bad to have the extra fuel hanging around?
Having the higher fuel pressure is what makes it lag less but will it get too high pressured and bust something? :/
 
Skippy said:
It regulates the fuel pressure in the rail...... I would strongly suggest NOT doing this. You're either going to a) increase fuel pressure above what it should be or b) drop fuel pressure.

Btw, anything under 3k yes of course the car is going to lag, you're no were near the power band for these engines. They're a gutless 4cyl what do you expect. They also don't just put regulators in for s*** n giggles...
Click to expand...
I've thought a lot about this Skippy, and it's not the power band, which cuts in somewhere around 3-4K rpm on mine. It's a definite lag at low revs, which I put down to fuel, or ECU related thing such as timing. And this worked. Surely pressure can't be more than FPR is rated for, so it only matters at low inlet manifold pressure. Once you're cranking then FPR is maxing, right? Furthermore, if I kick back from a higher gear and bring on some torque at higher revs there is no lag but lower revs there is, but you can feel it different from the power band.
 
Hugh-CE said:
MazioBarditore said:
Hugh-CE said:
Interested, but what are the side effects? What does stopping the hose suck do.. just fuel economy?
Click to expand...

I've never come across something like this before... Hmm time to look up how FPR's work... As long as my fuel lines won't burst or something then I may run this
Click to expand...

check this out http://www.youtube.com/watch?v=Kub3q1-YNZA that was very helpful!



So if fuel isn't going back into the tank, thats where you consumption goes.. but is it bad to have the extra fuel hanging around?
Having the higher fuel pressure is what makes it lag less but will it get too high pressured and bust something? :/
Click to expand...

Correct me if I'm wrong, but I'm pretty sure the 4g93 runs a return line back to the tank? 4g94 definitely does

From what I've been reading the higher fuel pressure at lower rpm would be similar to the fuel pressure further up the rpm band, so surely if nothing bursts then it shouldn't cause that at idle? Wouldn't it just run rich at idle?
 
I'd gladly put it back on if someone comes up with a known catastrophic issue from doing this, rather than "it's a bad idea".

On the other hand, if it is bad then is has surely proven that a proper performance FPR would be worth it (or at least that the factory one is lame)?
 
SA_Dave said:
I'd gladly put it back on if someone comes up with a known catastrophic issue from doing this, rather than "it's a bad idea".
Click to expand...

I agree, I will probably research it more before I do it, but if somebody who understands it better than me can explain what bad effects it could have and how that happens then I will take their advice and not do it.
 
You can be our guinea pig mate, we'll wait until something fails and then laugh at you. And if it works, everyone who didn't say not to do it will say "told you so".
 
rigby said:
You can be our guinea pig mate, we'll wait until something fails and then laugh at you. And if it works, everyone who didn't say not to do it will say "told you so".
Click to expand...

Every new venture needs a pioneer ;)
 
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