Sup guys.
Yes, I did it before, and somehow I guess I have to tune my fuel pressure again.
I searched and read all the old post and bookmark I had. and I have no clue why mine is like this.

First of, I tuned my car to really good fuel curve before I rebuild my bottom end engine. but somehow now I got everything back together, my fuel curve is like screwed up!

What I have now is 8.6:1 JE piston with long eagle rods, SFMU, Walbro 255, 310cc injectors, fuel/EGT/Boost/af gauge with datalogger.
I only have OEM o2 sensor. Also I changed from a S16G to Evo 16g. so I try to use the long term fuel trim to tune as well.

And this is annoying me today the most coz I was driving on the highway, for about 50miles, and I cannot even go above 60mph.... wtf. please help guys

First I do this:
I set my idle fuel pressure to around 25.5PSI and static is 36PSI. but my long term fuel trim is always on -23 to -25.
but my EGT goes up HIGH! I cannot even accelerate, and when I go uphill, I have to slow down to 35-40mph.

Second I do is, (after 15 miles driving)
I set my idle fuel pressure to around 22PSI and at 0PSI, I reach to about 33PSI fuel pressure. but my long term fuel trim is always on -23 to -25. my short term fuel trim is bouncing around -8 to 8.

Finally, I go crazy and just set the idle to 29PSI, and static to 40PSI, and still even worst or the same.

WTF! can someone please tell me why?
is it becaues my compression ratio changed? so I have to retune my fuel? or do I have to change my disk and spring? remember I set my fuel correctly before I rebuilt! but now it's all screwed up!!
I haven't boost yet, so no clue why???
Gil

When I ran those size injectors with the SFMU, i need idle fuel pressure to around 22 psi. How much boost are you trying to run? The high EGT issue is most likely being caused by too little ignition timing advance for your setup, not necessarily from too lean. What octane fuel are you using? If its 92 or 93, try some 87 octane(CAREFULLY listen for knock), with boost less than 10 psi. You dont need as much timing with that lower octane, and lower than stock compression ratio pistons. I'd bet you would see EGT's not quite so hot. Remember that the stock ECU's timing maps are programmed for 87 octane fuel, and 9.6:1 compression ratio..even stil, the stock timing map is conservative, which is why when running lower compression, you can get away with more boost/timing on a certain fuel octane.

When running 10 psi on the S16G with 93 octane, and 8.8:1 compression, I had to add about 5-6 degrees of timing to keep EGT's in the normal range(using the Megasquirt), with A/F in the low/mid 12's. Same A/F with the stock ECU doing timing the EGT's would skyrocket up to 1600 degrees.

You really need a wideband o2 sensor to tune properly also...

Originally posted by XtremeRS
When I ran those size injectors with the SFMU, i need idle fuel pressure to around 22 psi. How much boost are you trying to run? The high EGT issue is most likely being caused by too little ignition timing advance for your setup, not necessarily from too lean. What octane fuel are you using? If its 92 or 93, try some 87 octane(CAREFULLY listen for knock), with boost less than 10 psi. You dont need as much timing with that lower octane, and lower than stock compression ratio pistons. I'd bet you would see EGT's not quite so hot. Remember that the stock ECU's timing maps are programmed for 87 octane fuel, and 9.6:1 compression ratio..even stil, the stock timing map is conservative, which is why when running lower compression, you can get away with more boost/timing on a certain fuel octane. When running 10 psi on the S16G with 93 octane, and 8.8:1 compression, I had to add about 5-6 degrees of timing to keep EGT's in the normal range(using the Megasquirt), with A/F in the low/mid 12's. Same A/F with the stock ECU doing timing the EGT's would skyrocket up to 1600 degrees. You really need a wideband o2 sensor to tune properly also...

Thanks for the quick reply.
My engine idle at around 16inHg, don't konw if that makes a different.
I am running 93octane. coz I thought now I turbo charaged my 420A (since last year) I thought I have to run 93 to get away from detonation. so what about the long fuel trim? don't I tune by that as well? it's always stuck at -2x (-20 to -25)
So you saying I just run a lower octane gas then the EGT will go down? but I thought higher octane will give me lower EGT for turbo charged cars or eclipse??

And when you say I have to advance the timing. I have no megasquirt yet. so do I go adjust the timing belt? that's going to be a pain..>????

Please give me more advise.
Thanks alot!

Originally posted by gilee_8
Thanks for the quick reply. My engine idle at around 16inHg, don't konw if that makes a different. I am running 93octane. coz I thought now I turbo charaged my 420A (since last year) I thought I have to run 93 to get away from detonation. so what about the long fuel trim? don't I tune by that as well? it's always stuck at -2x (-20 to -25) So you saying I just run a lower octane gas then the EGT will go down? but I thought higher octane will give me lower EGT for turbo charged cars or eclipse?? And when you say I have to advance the timing. I have no megasquirt yet. so do I go adjust the timing belt? that's going to be a pain..>???? Please give me more advise. Thanks alot!

Long term fuel trim is not that important, and quite frankly, short term is not either, as long as BOTH are not pegged at -25%. 25% negative or positive, is all the ECU can adjust for, so keeping both as close to 0% is the best thing to do. When running larger than stock injectors, it will be very difficult to get the long term fuel trim at a low% number. The short term fuel trim number is what you want to pay attention to, since this is the instantaneous fuel adjustment the ECU is doing. With my 310's, i was able to keep STFT from -5-10%, and my long term trim was usually near or on -25%.

It's always a good idea to run a higher octane fuel with boost, but you have to remember a higher octane fuel will need more ignition timing. Without a full standalone like the Megasquirt, you have no good way to adjust timing accurately, so you have to tune the fuel side pretty rich in order to keep EGT's reasonable. Dont mess with your timing belt, thats not the timing i'm talking about. It's ignition spark timing.

Just keep the 93 octane in there, and tune it rich until your EGT's dont go past 1575 degrees on a long 4th gear pull, and it will be fine..I think i'm giving you too much info that you can't understand :)

Advancing Timing to cure High EGT's? Wow that's the first time I've heard of that, would you mind explaining in detail the concept of that Matt.


Thanks,
Nick

Originally posted by Collente
Advancing Timing to cure High EGT's? Wow that's the first time I've heard of that, would you mind explaining in detail the concept of that Matt. Thanks, Nick

Ignition timing has a LOT to do with exhaust gas temperatures. This is why tuning to an EGT gauge alone, is not the best way to tune.

When in boost, the Air Fuel ratio should remain somewhat of a constant, where typically, most power will be made from 12.0:1, give or take a bit richer/leaner, depending on how much boost you are running. Low boost can get away with slightly leaner, higher boost should be a bit richer.

Ignition timing and fuel octane go hand in hand, as they both need to be adjusted together. Higher octane fuel needs more timing, because of the way it burns, a bit slower for peak cylinder pressures to occur during combustion. Ideally, we want most torque/work applied to the crankshaft at around 14-15 degrees after top dead center. In order to acomplish this, we have to run the proper amount of timing, with a certain boost pressure, and a certain fuel octane. Take note that fuel octane is what really lets us make boosted power! There is only so much boost you can run, with so much timing, with a given fuel octane,and engine compression ratio. Its just the law of physics...

When running boost, and you dont have enough timing to keep most work done on the crank at the 14-15 degrees ATDC, combustion is happening too late, and more heat and lost energy goes out the exhaust valves. Depending on how retarded the timing is, you can have the actual flame burning out the exhaust, which would be hitting your EGT probe. This creates high EGT's. In order to keep more heat in the cylinder, and to ignite the A/F mixture at the "right time", you have to run the appropriate amount of timing.

Just to show how this all works, a case-in-point:

Since I run the Megasquirt, i have complete control of my fuel and ignition, along with a AEM wideband o2 sensor. When i tuned 10 psi, I set the A/F ratio to approx 12.4:1 This is a good A/F at this boost pressure for making good power output, not too lean, not too rich. I set the timing advance to around 22-23 degrees, and on a long 4th gear pull up to redline, EGT's were no more than 1550 degrees and steady, not climbing any more. The engine felt great, and it was making some good clean power, as it is tuned well for that boost pressure.
Now, i switched back to the stock ECU for controlling the ignition, and from my datalogs, ignition timing is roughly around 14-17 degrees under *any* boost pressure. Remember that the stock ECU cannot read boost at all, so it doesnt know whats going on, except that it thinks its at WOT. Now, my EGT's would SKYROCKET up to 1600 degrees at the SAME air/fuel, same boost, same everything except the timing. I could not even get close to running out 4th gear without having to let off the gas. This goes to show that ignition timing advance was too retarded, and combustion was happening too late, with too much heat going out the exhaust.

A too lean A/F can also cause high EGT's, so you have to be careful as well. Tuning is one big balancing act, and you have to get it all right if you want to make safe, good power for your given boost pressure. This is what sucks about using the stock ECU for ignition timing control..Just by lowering the compression ratio by almost a full point, and then running 93 octane fuel, that right there means we need more timing advance at ALL engine pressures/rpm. I'm running about 4-5 more degrees of timing thoughout my spark map on the megasquirt, compared to the stock ECU's timing maps.

Fuel octane lets us make power. Period. Yes, timing needs to be reduced as boost pressure increases, but only to an extent can you get away with this. There is a certain point where you will "run out" of sufficient fuel octane. Some may think that well, if i need 22 degrees of timing at 10 psi, then i can run 25 psi with only like 10 degrees of timing!NOT so! Lets say we do this, and upping the timing any more than 10 degrees causes knock, so we cant go higher, but even at a rich A/F EGTS are through the roof..we have run out of fuel octane to run that boost presure. If you have to pull timing below 15 degrees on these engines under boost, you dont have enough fuel octane for that boost pressure. There just comes a point where if you run too much boost, that more timing causes knock, and less causes too high EGT, then you need more octane.

Lower compression ratio pistons, high octane fuel, proper amounts of timing, and lots of boost is how you make lots of power. Making lots of power on pump gas is tricky. This is where other things come into play to run more boost can help, using pump gas. Water injection, colder intake temperatures, and more efficient turbo's can all help to make more power on pump gas, but ONLY to an extent.

Lets run 114 octane fuel, 28 psi boost, and 22 degrees of timing on a S20g, and i'll bet it makes damn near 500HP. No way could you do that on pump gas, at least not without a much lower compression ratio than our typical "rebuild" of 8.8:1(which really isnt that "low" for boosted eninges). Ok, that was long.

Hey XtremeRS. Thanks alot for the info!
I totally understand it. But of course I am still a little fuzzy about how to tune with megasquirt.
And yes, since I start rebuilding, water injection and megasquirt is on my list. and I ordered water injection already.

So as of now, all I can do is turn my fuel to around 22PSI idle, and leave it?
but I cannot even go above 60mph right now. that's how bad it is..
So you saying, I will not be able to boost at all until I get both my megasquirt and water injection installed?

Please let me know if timing is the ONLY solution right now.
Thanks again.
Gil

And you got points, I have to bookmark this for later uses!