Opinions on these methods to lower knock and IDC's...

Since the last track day, my datalogs haven't been sitting well with me. My IDC's are in the 130's and I had a few counts of knock up to 28! My 02's were reading .94v and .95v. The knock is pretty bad and feels like dropping an anchor behind the car when all the timing is pulled. This was all at 14psi w/ 9b's, BPU'd w/ a hotwired walbro

Since then, I've decided to take action to find possible solutions for this. I've come up with 2 methods, I just need an opinion on which would be more suitable and effective.

1. I bought an alchohol injection kit and was going to install that. This would give me a sure fire way to get the effected results I'm looking for...

2. OR, sell the alchy kit and get an adjustable FPR and bump up my injectors. I'm running a hotwired Walbro w/ the stock FPR, my 360's seem to be pegged with those IDC's. I'm guessing bumping up the fuel pressure to 55psi would net me an extra 12% or so of injector flow.

I'm wondering if my stock FPR is being overran and causing some issues... Some people have told me though at WOT the stock FPR won't cause any ill effects, it's only at idle and open loop you'll have driveability issues (w/ a hotwired walbro), which i haven't seen.

I'm thinking out loud, but opinions on this would help me out...

up your fuel pressure, you don't even need bigger injectors for 14lbs on 9b's

Quote:

---

Originally Posted by dpartinvr4

up your fuel pressure, you don't even need bigger injectors for 14lbs on 9b's

---

That's why I can't figure out why my idc's are so high. All my timing is being pulled and it sucks. 360's should be enough for the power I want.

theres a thread on the "other site" that has a really good right up on what eache injector size is capable of at what psi of fuel pressure. .... i would start with upping your fuel pressure. that should solve your problem.

If it's not going lean, reducing your IDC won't fix the knock issue. And without fuel control of some sort, raising the fuel pressure will cause more problems than you have now...

I'd check for boost leaks that could be causing higher than normal IDC, I'd calculate the REAL IDC mathematically to see if you really have anything to be worried about, then I'd pour the water/meth to it and call it a day...

Quote:

---

Originally Posted by dpartinvr4

theres a thread on the "other site" that has a really good right up on what eache injector size is capable of at what psi of fuel pressure. ....

---

Got a link? I'd like to see that.

Tech: My take on injectors vs. timing control vs. HP with the stock ECU - 3000GT/Stealth International Message Center

Thanks for the helpful input. All parts are on there way for a new FPR set-up. I'm going to hold onto the meth injection for the time being and may play around with that as well. Gonna see just how low we can get these 9b's in the 12's before retiring them.

Quote:

---

Originally Posted by dpartinvr4

up your fuel pressure, you don't even need bigger injectors for 14lbs on 9b's

---

If it's true that you're running only 14psi on 9b's, then you might want to consider that fuel isn't your issue. .94/.95v on NB02 on 9b's shouldn't be knocking (unless of course you modified the stock timing from its' 5*).

What coolant temps are you seeing during normal/wot driving?

FWIW: I have 16Ts, running ~15.5psi with NB02 reading .93/.95v without knock but if I go to even 16psi my NB02 will read .91/.93v and I'll see a max of 5-7 counts of knock for maybe 200rpm then it's gone.

No boost leaks were present other than a slight leak where the injector meets the manifold. I pressure tested and That's been fixed.

I no longer have the datalog but I think my coolant and intake temps were on the safe side. I remember thinking that might be the issue. My AC is deleted so the rad gets tons of fresh air. I also had air deflectors feeding into the engine bay where the ABS module used to sit. It was a fairly cool day as well.

So before the season kicks off, I'll up the fuel pressure and check the base timing. I think you guys are right, it's not a fueling issue, but since I have a hotwired Walbro, I like the idea of having the stability/tuning ability of the AFPR.

As for that link: Awesome thread, are those horsepower to injector estimates flywheel or WHP?

Put the AFPR in today and set it to 50psi base and seems like success! I'm now running 16psi with zero signs of knock and timing advanced 20 degrees throughout the pull. My one O2 is stuck at 0.01 volts, the other showed a max of .93v. I think the cold air might be helping me out most of all though, intake temps were only 68F. IDC's at 108%. No more mid throttle knock either.

So far so good, we'll see what happens in the warmer weather.

YOur idc's are still high, and it shows in your timming...

Yeah, still trying to figure out why... Haven't found a timing light to check my timing.

standard timing advance is 30degrees, so 20 is retarded timing. you want your idc's at 82.5%

I was hoping to see closer to those numbers with raised fuel pressure, but no luck. It didn't seem to make that much of a difference other than seeing no knock.

Hotwired walbro, 50psi of fuel pressure and a new fuel filter, should be plenty for what I need... I guess that would just leaves my injectors as the possible problem.

do you have a wideband? what are you afr's? and what are your fuel trims?

Quote:

---

My 02's were reading .94v and .95v.

---

That means nothing.

Seriously guys, reading O2 sensor voltages off narrowband O2 sensors was discredited in like 1998. Temperature sensitivity plus a number of other factors means that 0.94V could be anything from 14.5:1 to 9:1. You categorically, absolutely, positively, Hey Rube! no-foolin' CANNOT use a narrowband O2 sensor to detemine anything other than "rich" or "lean" with the switching point being 14.7:1. That's it. So stop it already, OK?

If you want to know AFR, you need a wideband O2 sensor and the appropriate controller. Full stop.

In the meantime, pull the plugs and have a look and see what they tell you.

I'm not super familliar with the control strategy of the 3S computer, but it is fairly common for knock to trigger both retarded timing and increased fueling. If the car really is knocking, increasing fuel pressure may throw enough fuel into the motor to stop the knock and get out of the knock control extra fuel. In that case, I'd expect to see increased fuel pressure reduce IDC.

But the other thing to consider is that the 3S has no concept of "boost" in the ECU. Instead, it uses "engine load" as a function of percent of MAF flow. When the ECU was mapped, the OEM programmers know which RPM/Load cells correspond to what boost values, and they change the programming strategy accordingly.

It is not unusual for cells in the upper load range to be programmed with maximum injector pulse width. The OEM knows that these cells will never be seen during normal operation, so they represent an "overboost" condition. That means something is wrong, so the strategy is to open up all the taps in an attempt to preserve the engine.

If you improve airflow via turning up the boost, less restrictive exhaust, etc you start seeing these load values during normal operation - but the computer doesn't know this is "normal" - so it dumps fuel in. And changing fuel pressure won't change that.

DG

Quote:

---

Originally Posted by O_ROD

I was hoping to see closer to those numbers with raised fuel pressure, but no luck. It didn't seem to make that much of a difference other than seeing no knock.

Hotwired walbro, 50psi of fuel pressure and a new fuel filter, should be plenty for what I need... I guess that would just leaves my injectors as the possible problem.

---

Quote:

---

Originally Posted by steve68

Why do you think that increased fuel pressure will reduce IDCs?

Steve

---

Pretty sad thread when Steve has to point out the obvious....

Tech: My take on injectors vs. timing control vs. HP with the stock ECU - 3000GT/Stealth International Message Center thats how i know it will.

Quote:

---

Originally Posted by dpartinvr4

Tech: My take on injectors vs. timing control vs. HP with the stock ECU - 3000GT/Stealth International Message Center thats how i know it will.

---

I've probably read that thread 200 times... Show me ANYWHERE in that thread Trevor made that claim.

Increasing fuel pressure increases the flow of the injector, which in turn ALLOWS you to make adjustments with your A/F controller... Would you put larger injectors in without fuel control? What do you think would happen then? Would the IDC's go down?

Agreed.

dpartinvr4, how about you write a summary of the mechanism you think would cause lower IDC through higher fuel pressure. Spell it out for us.

DG

higher fuel pressure means your injector will flow more. if it flows more, it has to be open less time to get the same amount of fuel in the chamber. this means you can get the afr you want with a shorter injector cycle. basically more pressure means more flow which means your injector has to be "on" a shorter time to get the same amount of fuel into the chamber.

Quote:

---

Originally Posted by dpartinvr4

higher fuel pressure means your injector will flow more. if it flows more, it has to be open less time to get the same amount of fuel in the chamber. this means you can get the afr you want with a shorter injector cycle. basically more pressure means more flow which means your injector has to be "on" a shorter time to get the same amount of fuel into the chamber.

---

I disagree with none of that... I still haven't heard anyone explain how or why the OP expected his IDC's to drop when he raised his fuel pressure.

if you read what I just said, why wouldn't they?

Quote:

---

Originally Posted by dpartinvr4

if you read what I just said, why wouldn't they?

---

Because the ECU has no clue that you raised the fuel pressure... I ask again, would you expect the ECU to magically self adjust if you installed bigger injectors?

The only thing that will happen by increasing the fuel pressure, is the ECU sill leave the IDC's exactly the same, and you will consequently inject a lot more fuel...

Not quite following you Real... raised fuel pressure is going to cause the injectors to act "larger" which will cause them to stay open for a shorter period of time to inject the same amount of fuel. IDC is the percentage of time the injector is on throughout its entire cycle.

What Dpartin is saying makes complete sense. My IDC's vary when I change my fuel pressure.

Quote:

---

Originally Posted by RealMcCoy

Because the ECU has no clue that you raised the fuel pressure... I ask again, would you expect the ECU to magically self adjust if you installed bigger injectors?

The only thing that will happen by increasing the fuel pressure, is the ECU sill leave the IDC's exactly the same, and you will consequently inject a lot more fuel...

---

Doesn't the ECU adjust fuel based on fuel trims and O2 readings? If the higher fuel pressure increased fuel flow, wouldn't the ECU adjust the IDC's because of the increased richness in the fuel mixture?

no, but your ECU reads your air fuel ratio, and will realize that it has to keep the injectors open alot less to maintain 14.7, and for WOT, you have the safc to adjust things so that you can tweak the afr to where you want., and I know this from personal experience.

hmm... found this interesting quote on another car forum.

Quote:

---

The stock ECU mapping does maintain closed loop fueling even under part throttle acceleration up to about 4000 RPM, if I recall correctly. So as Tim points out, it isn't just at idle and constant RPM.

I think the key point to make is that the injector duty cycle is controlled by the ECU and is not *directly* a function of fuel pressure or AFR. What IDC to use at any given moment is calculated by the ECU using lookup maps, learned trim data, the MAF sensor, and in closed loop, the O2 sensor. Once the ECU determines the current state of things and has calulcated how long to open the injector for, it opens the injector. Fuel pressure is not accounted for by those lookups and thus changing fuel pressure has no direct effect on ECU IDC calculations, and thus no direct effect on the actual IDC.

Now, in closed loop, the ECU does reference the O2 sensor to see if the IDC it is using is generating the desired AFR. If it isn't, the ECU will adjust the fuel trims which then causes the calculated IDC to change. This only happens in closed loop, so an increase in fuel pressure can indirectly alter IDC in closed loop. However, the IDC would go down if the fuel pressure increased (due to overrun or whatever) since the ECU would see the rich condition and determine that the fuel injectors shouldn't stay open as long. So in closed loop, if we have fuel overrun, then the ECU will ultimately reduce IDC. And in reducing the IDC, removing the rich condition (where rich is simply richer than target, the target itself might be considered rich too).

In open loop, the ECU is not reading the O2 sensor and therefore does not realize that it is running rich (due to FPR overrun increasing pressure for example). Since the ECU does not know it is running rich, it will not alter IDC. So here we have the engine running rich and the IDC remaining the same.

---

It makes more sense to me now.

Aeromotive FPR + Install pieces - Page 4 - Subaru Impreza WRX STI Forums: IWSTI.com

Quote:

---

Originally Posted by x2xtreme360

Doesn't the ECU adjust fuel based on fuel trims and O2 readings? If the higher fuel pressure increased fuel flow, wouldn't the ECU adjust the IDC's because of the increased richness in the fuel mixture?

---

WOT operation is a programed in map. Unless you modify it with some type of fuel control it's not going to change.

Quote:

---

Originally Posted by dpartinvr4

, you have the safc to adjust things so that you can tweak the afr to where you want., and I know this from personal experience.

---

I believe here is where the problem is... You jumped into this making that asumption, but never stated so. What is the OP using for fuel control?

Quote:

---

The ECU cannot CANNOT directly change the Injector Duty Cycle (IDC) based off of fuel pressure changes. Simple as that. In order to do so, the ECU would need an input for fuel pressure. It does not have this (I know that you know all of this G, just stating it for others http://www.iwsti.com/forums/images/smilies/wink.gif ). Thus, the ECU can only INdirectly change the IDC based on fuel pressure changes. How does this happen? The increased fuel pressure results in increased fuel delivery to the engine. The ECU sees the rich condition via the oxygen sensor. The ECU then applies long term fuel trims (LTFTs). The LTFTs result in a decrease in Injector Pulse Width (IPW). The decrease in IPW mean less IDC. This is true for closed loop operation. This can also be true for open loop operation so long as the ECU has spent enough time in the higher load areas to apply a correction there (which doesn't happen much when you remove the delays).

---

Long Term Fuel Trims....

Quote:

---

Originally Posted by dpartinvr4

Long Term Fuel Trims....

---

Only work in closed loop... They mean jack at WOT.

Quote:

---

Originally Posted by RealMcCoy

Only work in closed loop... They mean jack at WOT.

---

Quote:

---

This can also be true for open loop operation so long as the ECU has spent enough time in the higher load areas to apply a correction there.

---

did you read it?

Quote:

---

Originally Posted by dpartinvr4

did you read it?

---

Yea.. And it might even be accurate for an OBDII Subaru... If I'm not mistaken, this thread is about a 1st gen 3S.

I still want to know his fuel trims, and his AFR.

dang guys... The stock ECU pays no attention to your o2 sensors at WOT, that's why the o2 trim goes to 100. You could run 9:1 or 18:1 (please note this is just a ludicrous example, do not run these afrs, mmm'kay?) at WOT and the ecu would not step in until knock is encountered.

ANYTHING that causes the injector flow to be larger will just make the car run rich at WOT and not effect IDCs at all.. During closed loop operation if there is enough room to trim you may still be at 14.7:1 and consequentaly your IDCs WILL lower, but only because you are in closed loop.

Edit:

Additionally any air flow modifying device used to compensate for larger injectors or higher base fuel pressure can obviously affect IDCs because when adjusted the ecu sees less airflow, therefore injects less fuel.

Quote:

---

Originally Posted by Forest Gump

dang guys... The stock ECU pays no attention to your o2 sensors at WOT, that's why the o2 trim goes to 100. You could run 9:1 or 18:1 (please note this is just a ludicrous example, do not run these afrs, mmm'kay?) at WOT and the ecu would not step in until knock is encountered.

ANYTHING that causes the injector flow to be larger will just make the car run rich at WOT and not effect IDCs at all.. During closed loop operation if there is enough room to trim you may still be at 14.7:1 and consequentaly your IDCs WILL lower, but only because you are in closed loop.

---

yes, but his IDC's are above 100% which is the ECU trying to reduce his knock by ritchening up the mixture, so to get back to even 100% IDC at WOT, if he turns his pressure up, it will help to reduce his knock, so his ecu won't start dumping fuel in when it does absolutely nothing IDC>100%

Quote:

---

Originally Posted by dpartinvr4

yes, but his IDC's are above 100% which is the ECU trying to reduce his knock by ritchening up the mixture, so to get back to even 100% IDC at WOT, if he turns his pressure up, it will help to reduce his knock, so his ecu won't start dumping fuel in when it does absolutely nothing IDC>100%

---

loggers report IDCs WAY too high. If you are actually at 100% IDC you hit fuel cut.