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Discussion Starter #1 (Edited)
******* This information is no longer relevant - see this thread
http://www.b15u.com/tuning-engine-m...everything-you-need-know-if-you-want-one.html *********



Interesting read...taken from twofivetuning.com - Courtesy of Pimpsmurf

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MegaSquirt! Oh MegaSquirt! You are so perfect and awsome! Oh Megawait....

Wait....

Perhaps this isn't a perfect solution, but you won't hear this everywhere. Let's get past the hype and featurelists and see just how megasquirt really is when you want to drive the car places other than a racetrack.

MegaSquirt is a lot of things. It's a boost controller, an option controller (fans, meth, etc), and many many other great things. Unfortunately it was intended to be used with a trigger wheel, but can't read our trigger wheel because of the design.

[email protected] spent a long time playing with it and finally came up with this novel idea! He routed the ignition signals for the coilpacks into the megasquirt to signal the ECM so it can kinda tell when to inject fuel. Unfortunately, this is a bad idea. It does give the illusion that it works, but it's really easy to see why it does not work when you start thinking about it.

A Trigger wheel such as this one:


is really pretty! It also has nice trigger points and notice, two missing teeth? How is that different from the average *******? The average ******* doesn't need to tell the difference between TDC and BDC 3000+ times per second. Unfortunately, the trigger-wheel-less input to megasquirt is more like having a trigger wheel with only 4 teeth. 4 teeth that move around with the timing of the stock ECM causing the rpm dataloging to be fruity and inconsistent. It also has the VERY bad secondary effect of never being able to know where the engine is. Because the intake cam also fluctuates along with the timing, AND the megasquirt batch injection has no idea when it is spraying. This is bad!

Sometimes it sprays 1 and 2 when it should. Sometimes it sprays when the valve is already 1/2 open and that cylinder runs lean while the wideband-based EGO corrections start adding fuel to compensate, causing AFR fluctuations and EGO fluctuations causing boost spikes.

This is an incredibly bad thing. Sometimes when I crank my car, Everything is perfect. EGO corrections are right, no boost spikes, no AFR fluctuations. Then I turn off the engine and power down the megasquirt. Crank again and everything is wrong. I'm now completely convinced that this is due to the coil signal input.

My point is: if you are willing to do an external trigger wheel to run the standalone, then megasquirt isn't dangerous. This is not to say it is perfect in everyway for our engine, but it is a lot safer than the hack coil input.

Moving forward, WOW BOOST CONTROL! EPIC!


Boost control on the megasquirt is very very good when you have it set up right. Most people have been using a GM Typhoon solenoid. Some have had failures of the solenoid, which can cause overboosting. Not a good thing. A better quality, faster reacting, less prone to failure, more modern high speed solenoid is the AEM 30-2400 solenoid. Email [email protected] if you would like to get a "compatible" solenoid for much cheaper than the AEM-brand one. His username here is 16g-95gsx You can also use a MAC valve part number: 36A-AAA-JDBA-1BA

I can supply these very cheap (around $30 shipped to contributing members only) and these work the same as the AEM, and may in fact BE the exact same thing AEM uses. It's certainly more than enough for Megasquirt's boost control.

Meth Control: for a few dollars in parts, you can add several output relay controls to megasquirt. With these you can run meth injection, fans, or even an EZ-Bake oven in the trunk. Very nice.

Now for fueling... oh noes! A snag!

Megasquirt has batch fueling. This is no big deal for a 4 banger, but it means that some of the fuel is going to sit in the hot ass manifold for longer than some of the other fuel, so it will vaporize more and unfortunately, burn better. It's no big deal, but pushing the knock limit should be done with extra care as 1/2 of your cylinders will be more prone to knocking.

The version most people running megasquirt 1 on the QR25DE is the MS-Extra Hires code. It is a fork of the original codebase which includes high resolution injection control, allowing much larger injectors while still keeping idle ok. This code has a fairly low resolution, 2d fuel map, or "VE Table". The VE Table is only 12x12! If you keep 9 of those for vacuum, as our engine tends not to scale as well in vacuum as it does in boost, then you only have 3 cells to use for a fuel map, and anything between them will simply be averaged. This leads to unsteady AFRs as when you tune, you have to tune every area to your target, leaving the spaces between, in some cases to end up rich. Certainly not ideal, but it works fairly well. Even if you had a 100x100 fuel table you would have (albiet, far less) AFR fluctuation. You may remember having tuned the stock ECM with a SAFC. When you got your air/fuel or "ne" points in the right places, you could nail down a solid AFR line all the way across the board for wide open throttle. With a "boost SAFC" hack you can even eliminate rich spots as you go through partial boost. With megasquirt, perfect tuning is simply not possible. Nissan got around this issue with the use of the Siemens ECM. It's 32 bit processor (4 times the bandwidth of the megasquirt's 8 bit processor) which runs at roughly 7 times the speed of the megasquirt 2 CPU, does realtime physics and chemistry calculations to determine timing. This is one of the many reasons why it has been so hard to crack by the aftermarket ECM industry, and why uprev can charge so much for the hundreds of hours of R&D in their product. It doesn't look at rpm and airflow from the MAF and just pick a timing number out of a chart as megasquirt does, it actually takes the airflow into account, along with rpm, throttle position, narrowband data, coolant and intake air temp, and many other things, then determines the correct amount of angle to add to the intake cam, the correct amount of fuel to add to the air, and with all of this taken into account, it attempts to spark at the exact time needed to build peak cylinder pressure at 12 degrees after TDC. This is amazing shit. It dwarfs megasquirt in all respects and the ONLY reason tuning is needed for boost is the stock ECM does not respond well to boost. With larger injectors installed (to have enough fuel for that boost) it dumps way too much fuel. Some have used stock injectors with low boost and found a decent tune by trial and error, and this is certainly possible, but for those of us seeking higher levels of performance, this isn't an option.

It's very possible and pretty easy to get it to crank (if you have ever tuned a megasquirt, you know this can be a real accomplishment) and certainly possible, although much harder, to tune acceleration enrichments to keep the car from having lean misfires everytime you get on the throttle. What is not possible is preventing lean misfires while doing engine braking. You see, when the stock ECM fuel control (and it's fuel cut) is taken away, it can no longer cut fuel at the exact same time as it is adding a TON of timing while you use the engine to brake the car. If you have misconfigured or disabled (because it's hard to tune) the "Overrun" stuff, then megasquirt won't cut fuel at all while engine breaking, and the electronic TB makes it hard to get it working to begin with. You will also hear a bunch of backfire sounds and see your AFR gauge go completely nuts while this happens. Yeah, that is probably lean misfires and possibly low-load detonation. 40 degrees BTDC can do that to an engine. no matter how much fuel I forced megasquirt to dump, it couldn't stop the misfires with 499cc injectors.


Now on to the REALLY bad shit that megasquirt does in a fuel-only configuration, and how to stop it.

With megasquirt controlling the fuel, the stock ECM is unhappy. It feels impotent and powerless to stop itself from doing things it did not think possible. Namely, it is constantly maxing out it's fuel trims. Resetting the learned fuel trims by either pulling the MAF cable while the engine is running (basically, a really bad idea) or using a tool such as uprev's Cipher (uprev.com) doesn't do much. Perhaps it will keep the timing from getting WAY out of hand and keep you from throwing a CEL code when the ECU finally gives up trying to correct the fuel, but it won't stop the timing adjustments made in real time when the corrections go a little fruity. At the very least, you should tack on the price of a cipher to the megasquirt when you buy one so you can monitor and datalog these things as I have.

A solution to this problem, which will throw a permanent CEL is going open loop. You can remove the o2 sensors but we currently do not know how this effects timing or the intake cam timing we have. I will datalog this when I'm done with the many projects on my to-do list at this point. It's more than likely that the stock ECU pulls timing because it's unsure if it's running lean or not and doesn't want to misfire, or it could possibly keep the timing as it expects but become more sensitive to knock... or not. Who knows?

Another real issue is the wideband-based fuel corrections. The LC1's voltage output is very jumpy to begin with. Not to mention EGO corrections in megasquirt are weak to say the least and can't scale with rpm as they should.


The SAFC2 is a GREAT option for us however. It has knock monitoring, and has been used to tune many engines. The E-Manage Ultimate is also a decent solution. The instructions are kind of weak, but for someone with experience with wiring the ECM harness, it is not that bad and very similar to the SAFC. It also has knock monitoring and datalogging as well as the ability to increase the redline. Unfortunately, megasquirt seems to be BAD at controlling the redline. Mostly because of the issues I spoke about at the begining of this post. It cuts fuel, but it's rpm input is faulty, which has caused people to overrev the engine. Not to mention that if you hit the clutch before getting completely off of the gas, the engine will rev even higher if the boost cut fails.

A 3" housing from z1performance (you want the one for the 350z, which fits perfectly. it's a direct bolt on.) can both increase the boost you can run with a SAFC tune as well as help idle with larger injectors (less fuel trim timing adjustments in the ECM.) It supposably runs 10psi with only 5% adjustments on the MAF voltage and large injectors! It can also run very high boost levels, as username from MySpecV has gotten up to 20psi with just a SAFC and 3" housing. It also may adjust the fuel enrichments as it basically injects more fuel than it thinks that it should while in closed loop. Perhaps it will throw a code eventually, but none has been reported. I will also datalog how it effects timing when I install the one I've had here for weeks!


I am tired and ready to watch some TV so this is all for now. I hope this all absorbs since some people seem to be in denial about just how megasquirt's fuel only configuration could be doing to your engine without your knowlege. It's more than spark and fuel with the QR25, and it's more than AFR to tell if your tune is right.

-JNY
 

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ok so what is the best option for my 03 im going to get a built motor and want to run upwards of 18lbs, im at 15 now,
what is the safest, easiest way to tune this, can i still use my NEO and reflashed ECU
this is my one spot of confusion for turning up the boost levels so any help is appreciated
 

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best way to make power reliably is going standalone but it all depends on your knowledge about tuning cars and/or if you are willing/want to learn
 

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il have to look into that
 

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see i just want something more then the NEO for when i go up with boost, and injector size, i was looking a t the emanage, but dont know a whole lot on the ecu stuff
\also i know my ECU is flashed for 700cc injectors, how do i change that when i run 1000s
 
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