MalibuJack

iTrader: (5)

For the last few months (when I was able to drive my car between the work I was doing, and the rear-end damage that was being repaired)

I discovered my car had what felt like a misfire.. I was stumped, I removed all of the mods except the Air filter, and Exhaust.. The exhaust has been causing the stock boost solenoid to spike at 21psi.. And it runs great..

I was convinced for the longest time it was a bad MAF reading or plugs/ignition miss..

Well, I got the car back recently, and it still is doing it, but I was bored and I hooked up my s-afc and s-avcr again in preparation for running the wiring under the hood to the boost solenoid

I ran out of time and buttoned everything up, but zeroed out the settings on everything since the solenoid and pressure sensor on the EBC was not connected..

I was playing around with the car, an discovered it was surging again.. but this time the car had the AVC-R installed (its installed inline with the injector so I can read injector duty cycle) and guess what I found? When the boost is up around 20psi, the injectors are about 99.9% duty cycle..

Ok, thats bad, and I'm glad I don't do that very often.. but I definitely want to advise people that if their running ABOVE 19psi of boost, your car may not be getting enough fuel, REGARDLESS of your settings and could lead to damage...

If I'm seeing almost 100% duty cycle under load, I can see a possible lean condition if not other possibilities of damage..

Anyway, just a word of warning, since I am aware of many people running 20-21psi of boost without any fuel system upgrades..

Unfortunately, until I get the EBC connected, and relying on the stock solenoid with an aftermarket exhaust, I'm still going to get this happening on occasion until I finish what I started working on. But I wanted others to benefit from my findings..

Speedlimit

Did you read the injector duty cycle when your car was stock? I'm just curious what Mitsi designed. Several tuners have recommended upgrading the fuel pump before upping the boost. I know there have been discussions here on recommended points to upgrade the injectors but I thought it was well beyond your current mods. Maybe not.

Speedlimit...

propellerhead

iTrader: (3)

The more and more I think about it, I think I'm going to stop making any more modifications until I round out my data aquisition systems. Your post only underscores my feelings.

Everyone talks about throwing in a boost gauge or even an EGT gauge but really those don't do squat when it comes to saving your engine from grenading due to a lean running condition. Sure, an EGT gauge will give you a clue, but probably not until it's too late.

I'm going to shop for a WBO2 and some sort of datalogger to measure injector duty cycle and timing. I'm also going to run out and crank back my boost to an honest 19psi...

MalibuJack

iTrader: (5)

The duty cycle with stock boost is around 85%, not much wiggle room in terms of capacity.. Once your at 99%, your at the mercy of your fuel system capacity which means if the factory fuel pump fails, or the pressure for any reason falls, you will get a VERY lean condition as opposed to a marginally lean condition.

Let me add that the observation was made with the car under load.. It seems that the injectors will do "OK" if your running through the gears from a launch.. But when you introduce additional load, at the high load points when the turbo tends to spike, I can see a potential problem...

Al and everyone else who warned about Fuel pumps are definitely correct about upgrading your pump at the least.. this just adds a warning about fuel injectors since extra pressure/volume does nothing if its not getting into the engine.. I think 19psi is probably the highest safe setting. I'm sure more people will analyze the same thing..

The biggest issue with upgrading fuel injectors is getting the injector scaling right otherwise the car will run really rich (even more than when stock) Its tricky to try to do yourself, and you definitely need a flash, piggyback, or some other fuel management to do it. (a flash is probably easiest to do since its done for you..)

And ALWAYS upgrade the fuel pump when you upgrade your injectors..

Speedlimit

All good stuff Malibujack. I think I'm aware of the pitfalls of running the injectors at 100% as they can basically "float" half open as load exceeds capacity. Do you know how your inline gizmo defines duty cycle? Did they include the basis with the documentation?

Speedlimit...

MalibuJack

iTrader: (5)

Yeah, it measures the PWM signal duration, I think its measured by its interval transition (high to next high).. The more time its "high" compared to low is how it gets its percentage.. or at least thats what it seems.

Oh yeah, I never even pointed out "overrunning" the injectors when they float at near maximum duty cycle.. But since I am experiencing a lean condition, I don't think I'm getting more fuel than the injectors can handle.. I think both the injectors and pump are sized pretty closely to their capacity in relation to eachother.

Another thing to point out, I discovered the fuel pump has a low/high relay and an ECU output that triggers it.. It reduces noise at idle, and raises pressure at higher engine loads..

lil'evil_evo

iTrader: (17)

bump for good thread and I had a quick question. How much would a fuel pump help out with the stock injector duty cycle?

MalibuJack

iTrader: (5)

Wow.. nothing like resurrecting an old thread.. My setup is nowhere near similar to what I was running at the time this was posted..

Fuel pump does very little to help the injector duty.. However it does increase the fuel volume and therefore increases the amount of fuel injected at the same duty. However it really only helps at higher RPM since at lower duty cycles, you won't see much of a difference.

It seems to help people who have high duty cycles that are sustained for some time, where fuel volume may drop off for one reason or another (pump overheating or some other issue) Plus you wouldn't be overcompensating for lost capacity by increasing injector duty higher than necessary (The reflash guys sometimes see this on the dyno when their trying to get a consistent tune after several runs)

lil'evil_evo

iTrader: (17)

Thanks MalibuJack that's what I wanted to know

BushBurninEvo

iTrader: (8)

what's your setting on the avc-r. I want it to hold 20psi.

rt turbo

iTrader: (4)

i can vouch for this. with the stock fuel set-up and a pump, 21 psi would feel like 19 psi... not much power increase because the injectors are maxed out and i was probably pulling timing. i put 880s , fuel rail, and fpr and there is all of a sudden a HUGE difference in power from 21 psi to 19. plus the torque band is much improved. the stock injectors will not handle much more than stock boost.

GREDDY

iTrader: (8)

Man, I started a thread a couple of weeks back about my tuner recommending me to upgrade my fuel system and alot of people didnt think it was the right route.
I have 3" turboback, mbc, safcii and injen intake with upper intercooler piping kit. Dyno'd 332+awhp/336+awtq catless on 91 oct on Dynojet. My tuner said the next route is to upgrade the fuel pump, Agency fuel rail and 720cc Greddy injectors. They said it would put me somewhere about 350-360awhp/tq. I thought this was strange since no one usually goes this route but after this thread, I am going to work very closely with my tuner and sort out the correct upgrading route. Let's try to keep this thread open. I would like to hear from Buschur or AMS or other tuners.

gunzo

iTrader: (2)

Jack, you'll hit the limits of your injectors when you up the boost with stock ECU .. reason being it runs too rich .. when you start leaning it out (be it AFC or something else), you'll see that the duty cycles come down again .. with 560cc's you shouldn't have any issues up to around 380Fly hp .. IF everything is tuned correctly ..

In case you guys don't measure fuel press, at only 1.3bar (19psi) at 7500rpms, with stock fuel pump, your fuel pressure is already dropping .. and in order to correct for that, your ECU actually increases the squirting time (so to speak) ..

Think somebody explained this voodoo **** sometime back ..

Ted B

iTrader: (6)

Good point. If a very rich WOT A/F is programmed, the injectors will reach the limits of their capacity, but no lean condition will be evident. This illustrates why injector duty data alone does not tell enough about what is really happening. To get an accurate idea of when the injectors reach their absolute endpoint, one also needs wide band A/F data to show that the desired A/F could not be maintained at 100% duty.

propellerhead

iTrader: (3)

It's commonly accepted knowledge that pintel type injectors will go semi-static at ~85% IDC and disc type injectors go static at ~90% IDC. As I understand it, in a semi-static condition the injector flows at 50% of it's rated capacity. Of course the injector goes semi-static at the very worst of times: at wide open throttle, at full boost and at or near redline. When one of your injectors goes static under those conditions, sooner or later... BOOM! Why risk it to "save" $500?