Does anyone know what the standard fuel pressure regulator on a tf (are they all the same) is set at?

I have just installed a fuel pressure gauge on the rail link, it reads 38-39 psi at hot idle is that right? The reg has done 278,000 kilometres .

I have also noticed that when throttle is quickly applied the reg will quickly drop 5-7 psi and and instantly build back up. My theory is to get an adjustable fuel pressure reg, up the pressure so when the throttle is mashed ,the drop in reg pressure is equal to the previous idle pressure.

What is a safe pressure to run?
Have people had much trouble with bleed off? Like is it hard to start the car?

I would be verifying exactly how the pressure should respond for a normal stock regulator, as a very short duration drop in pressure could reasonably be expected due to the way control systems work.

The ECU code has maps for adding extra fuel during acceleration which could be compensating for this response (amongst other effects) if your regulator is working normally.

Also, changing the fuel pressure will affect the ECU's control of fuelling, as higher pressures allow the injectors to deliver more fuel.

Without ECU logging and a wideband oxygen sensor, you'll just be guessing about what happens when you make changes.

I was not thinking of extreme pressures, a few psi, a presumed kick in responsiveness due to the nature of the diaphragm.
The injectors are old and have not been properly ultrasonically cleaned in the past 277,00+ kilometers,surly they are not flowing to spec.
Increased fuel consumption and money is not an issue, as long as there is 0.01 percent increase in performance .
I am just purely theorising.

Do you think it's tunable with just a wideband sensor?

Does anyone know what the standard fuel pressure regulator on a tf (are they all the same) is set at?

I have just installed a fuel pressure gauge on the rail link, it reads 38-39 psi at hot idle is that right? The reg has done 278,000 kilometres .

I have also noticed that when throttle is quickly applied the reg will quickly drop 5-7 psi and and instantly build back up. My theory is to get an adjustable fuel pressure reg, up the pressure so when the throttle is mashed ,the drop in reg pressure is equal to the previous idle pressure.

What is a safe pressure to run?
Have people had much trouble with bleed off? Like is it hard to start the car?

The Magna runs a return fuel system, so there is a pressure regulator which is what creates and holds the pressure. A vacuum hose connected to the regulator lets the pressure in the fuel rail drop when manifold vacuum increases. If you want to check if your pump and regulator are OK, hook up a vacuum gauge. If vacuum increases, fuel pressure should drop, and vice versa.

So your fuel pressure regulator is already adjustable - it's adjusting pressure automatically all the time to compensate for manifold vacuum.

However, if pressure drops for more than a split second when vacuum drops (i.e. when the engine wants fuel), it means either your regulator, pump or fuel filter has a problem. There are some good videos on YouTube for performing fuel pressure tests, but a good test is what they call a "Dead head" test. You need to hotwire the fuel pump to do it (jumper a relay under the bonnet) and then clamp the fuel return line hose. You should see pressures rise to double the regular rail pressure. If it gets nowhere near it, your filter or pump needs replacing.


If your car is suffering from bleed off - i.e. you are seeing fuel pressure rapidly drop to zero after you shut the car off, this could be either your regulator or fuel pump failing - usually the fuel pump.

Here's a video of me doing a fuel pressure test on my motorbike - it has a 36psi stated rail pressure (without vacuum line connected).

http://youtu.be/kKrZLaOdWQQ

Anyway, adjustable fuel pressure regulators are designed to allow you to increase the base rail pressure. More rail pressure means more fuel per squirt so the car would run richer everywhere. Normally you increase the rail pressure for boosted cars so you don't run lean due to higher than atmospheric pressure in the manifold making it harder for the fuel to exit the injector. For example if your fuel rail pressure was 20psi and you had a turbocharger with 20psi of boost, no fuel would come out! That's a silly example of course but it shows you what I mean.

There is always a tradeoff with fuel rail pressure; sometimes its better to install higher-flow injectors because - if I recall - increasing the fuel pressure too high can make it hard to get a good tune for light throttle applications, so in that case a higher flow injector may be a better idea.

I was not thinking of extreme pressures, a few psi, a presumed kick in responsiveness due to the nature of the diaphragm.
The injectors are old and have not been properly ultrasonically cleaned in the past 277,00+ kilometers,surly they are not flowing to spec.
Increased fuel consumption and money is not an issue, as long as there is 0.01 percent increase in performance .


Get your injectors cleaned and flow matched before you do anything else. If you can't get them within, say, 5% of each other buy a new set.

Newer vehicles often run returnless fuel pressure systems where there is no fuel pressure regulator on the rail, it's just a dead end (no return). These systems control fuel pressure by altering the speed of the fuel pump or by altering the injector pulse width based on the input from a MAP sensor.

This is a somewhat controversial subject for some as they will swear black and blue that an adjustable Fuel pressure Reg will do nothing. Others swear by them and recommend them for all applications! I fall into the middle ground but I will relay my experience and let the punters decide for themselves.

First of all, the factory Mitsubishi Fuel Pressure Reg is 3bar (43.51 psi) pressure at idle and 3.5bar (50.76 psi) under load. All 6g74 and 6g75 engines have this standard type regulator that will add a .5 bar of pressure under load. Also, all 6g74 and 6g75 engines have 275cc fuel injectors (6g74 has 4 holes for spraying and 6g75 has 12 smaller holes).

I have a standard 6g75 motor without any type of ECU tune at this point. The motor is 100% standard and fitted into my AWD TL VRX. I have a SARD Fuel pressure reg installed and these are my results when accelerating from a standing start with the 5 speed auto Tip-Tronic in Drive:

-Stock pressure of 3 bar (43.51 psi) and the engine will rev to 4000rpm and then change gears
-Pressure up to 3.5 bar (50.76 psi) and the engine will rev to 4500rpm and then change gears
-Pressure up to 4 bar (58.02 psi) and the engine will rev to 5000rpm and then change gears
-Pressure up to 4.5 bar (65.27 psi) and the engine will rev to 5500rpm and then change gears
-Pressure up to 5 bar (72.52 psi) and the engine will rev to 5800rpm and then change gears (5800 rpm is the ECU rev limiter kicking)
-Pressure up to 5.5 bar (79.77 psi) and there was no noticeable improvement.

All results above were measured by leaving the car in Drive and merely putting the foot down hard from a standing start.

So does it make a difference? HELL YEAH!!! The car gets to it's defined rev limit faster and the engine feels like it has more torque...especially down low. The mid range is better too and when you're on a high speed run on the freeway and you put the foot down there is a noticeably stronger shove into your seat. While I do not have a dyno, I know someone who has a G force measuring device. We fitted it to my car (you just suction cup it to your windscreen and plug it into your ciggie lighter). There is DEFINITELY a measurable difference in acceleration times and G forces under acceleration. We tried it with a variety of pressure settings and there is a noticeable difference...but there is a limit. You can't just dial it up to any figure and hope for the best. We found with my current set up that a pressure of 4.5 bar is the best for torque and rev improvements and the fuel economy doesn't suffer too much.

All tests were conducted with the 100 RON United fuel that is basically 98 ron fuel with added Ethanol. Similar results were obtained using 98 ron fuel and 95 ron fuel. With 91 ron fuel and there was no benefit beyond 4 bar of fuel pressure.

So there you have it. If you want to go drag racing you can dial it up to about 4.5 to 5 bar and go racing. Want better economy? Adjust it down to 3 bar. Mitsubishi picked 3 bar to give the engines a bit of shove with reasonable fuel economy. Remember they had your everyday punter in mind so they tune things conservatively.

Anyway, Merry Xmas all and drive safe and speed smart!

I have a standard 6g75 motor without any type of ECU tune at this point. The motor is 100% standard and fitted into my AWD TL VRX. I have a SARD Fuel pressure reg installed and these are my results when accelerating from a standing start with the 5 speed auto Tip-Tronic in Drive:

-Stock pressure of 3 bar (43.51 psi) and the engine will rev to 4000rpm and then change gears
-Pressure up to 3.5 bar (50.76 psi) and the engine will rev to 4500rpm and then change gears
-Pressure up to 4 bar (58.02 psi) and the engine will rev to 5000rpm and then change gears
-Pressure up to 4.5 bar (65.27 psi) and the engine will rev to 5500rpm and then change gears
-Pressure up to 5 bar (72.52 psi) and the engine will rev to 5800rpm and then change gears (5800 rpm is the ECU rev limiter kicking)
-Pressure up to 5.5 bar (79.77 psi) and there was no noticeable improvement.

All results above were measured by leaving the car in Drive and merely putting the foot down hard from a standing start.
Interesting.

Based on what I currently understand of the Magna ECU shift patterns, I'm not sure that you were getting the TPS to the point at which the ECU considers the throttle to be wide open (a TPS value of 78%). If you were, all the shifts would have been at the same revs, as WOT upshifts appear to be purely speed controlled.

There is no rev limiter function in the transmission code, but the apparent 5800rpm shift limit derives directly from the speed at which WOT upshifts are triggered.

Even when my TJ AWD was stock, from a standing start at WOT all upshifts were at the nominal 5800rpm. I've logged my TPS at 80-81% at WOT.

Hey WytWun,

I'm just relaying my experience. My car has the 380 motor AND a 3.0 V6 stall converter. The converter spins up to 2400rpm compared to 1500rpm for the 3.5 V6 converter.

Perhaps that also has some factor. Remember, the standard factory reg is conservative and a little more juice seems to be appreciated by the motor!

Have a Good Xmas everyone!

Just a small thread mine. Does anyone else have any experiences with an aftermarket fpr?

Bump for gains?

Anyone still paying notice to this thread I want to add my most recent experience with my Sard Adjustable Fuel Pressure Reg ( FPR). First a bit of background. My car is a TL AWD with a 380 motor shoehorned under the bonnet. I noticed torque and kw improvements with my Sard FPR so I concluded that with more fuel there is better performance therefore more fuel = more power etc.

Well, I have recently had my 380 tuned to 98 ron fuel by Merlin of Sydney (David Hinde 0419140226-thouroughly recommend his expertise). The engine was tuned with the factory 3 bar fuel pressure reg. We did the tune on top of Mt Baw Baw as there was a Tarmac Rally under way and David is in demand for Legnums, Evos and WRX's. He does the odd Magna. Anyway, my tune was done hot footing it up a mountain under the most severe level of load an engine be exposed to and David flashed the ecu and fine tuned it taking it to the limits until there was no knock/pinging at all. Previously I had never heard any pinging.

So I drove it with the factory FPR for a week and thought "now let's see if there is a gain with more fuel pressure". Well, the car did not like the extra fuel pressure at all. There was a loss of torque and it took longer to rev through the range with no noticeable gains in the mid to upper rev range. The low down torque was poor. I drove it with the Sard FPR for a couple of days and noticed it was pinging it's head off under mild load. I tested for this by driving with all the windows open going up a hill with the tippy locked in 3rd with the foot down. The sound was awful so I began dialing the fuel pressure back until it stopped pinging at...3.25 bar! Close enough to factory specs to not worry about the .25 difference. So I took off the Sard FPR and now have it running the stock reg and it's awesome. Running better than it ever has as it's been a couple of weeks so now the ecu is settling in to it's new parameters. Also, the weather here in Melbourne is cooling so now there is even more power on tap!

Why, pre-tune did it run better with more fuel? David suggested it is due to the timing difference of the ecu for its original 3.5V6. The standard motor before the 380 is the 3.5 that runs milder cams and lower compression (9:1). The ecu thinks there is a 3.5 engine despite the 380 engine change and is still running the baseline timing for a 3.5 which he showed me on his laptop is advanced far more than what a 3.8V6 with 10:1 compression can comfortably handle. Most people probably wouldn't notice or care but we are not most people! The extra fuel was being gobbled up but not efficiently and was having a cooling effect that suppressed the knock that was there but barely audible unless one was wearing the 'sonic headset' to hear for knock. So long story short get your car tuned properly for 98ron or even talk to David to run E85 ethanol. E10 is rubbish but E85 will run like a dream but you have to go 30% bigger on the injectors and then have it tuned for E85 exclusively. Not practical ATM.

So there you have people. With the right tune I now have more kw and torque on tap than ever before.

Cheers,
G-Man

Thanks for the info!

Hey Dreggzy, hope it is helpful info. Merlin is the Man in the Sydney area and knows Steve Knight very well. They are both in demand in the Evo/WRX scene where peope are racing there cars.

Thanks for the info!

Yeah I know all about Merlin. He is an evo tuning legend.