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Old 12-13-2011, 07:32 PM
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How to modify a stock ECM

let's forget about emission or legal stuff, let's say we are talking off road only here.

How do I modify a stock ECM to run with performance parts installed, say a bigger cam or a turbo for example.

I mean DIY very low price tricks, not buying exotic chips or reflashing proms, things we all can do at home, like installing a variable resistor in place of the IAT sensor to richen the mixture or tampering with the distribuitor holdown to advance the timing, etc, etc.

How do I turn the CEL off (besides removing the bulb) after I removed the catalyst, etc.

please tell us some secrets, and smog cops don't worry, we will never run a modifyed car on the streets.

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Old 12-14-2011, 08:10 AM
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I am not sure what you are looking for, but I'll answer some....maybe not how you want

To run with a larger cam is pretty simple, but can not be properly done with out "chip" or eprom tuning. The ECM looks at several variables to decide fuel delivery and timing control. However, the most important things it uses are the fuel and timing tables which reside in the software. These tables, fixed numbers such as injector flow rate, along with external input from various sensors, feed into an algorithm to control injector dwell time(how long they are open). So, forget throwing in fat injectors with a cam without retuning. Engine temperature, intake air temperature, manifold pressure, and/or manifold flow sensors, and Oxygen sensors are all used in conjuction with these tables to calculate needed fuel. The fuel pulses are timed and adjusted in microseconds through complex algorithms that you can not change in most cases. Some factors can be scaled, but the main tuning is done in the tables.

Timing is very similar to fuel....

So, it is just about impossible to do anything other than minor changes and have favorable results.

With a turbo setup, it changes ALOT. Most factory ECU's are not really even capable unless you want to learn how to program at the machine level. There are some exceptions, but as a rule it will not work right if it was not turbocharged to begin with unless you are an expert programmer or want to pay one. When I did my turbo setup it took close to a year to build, program and tune the EFI. I was a controls engineer at the time so I thought I was well equiped...I was wrong and the learning curve was painful.

If you try to halfway tune it with some kind of "tricking" of the ECM you will end up with a pig that runs right about half of the time and you completely loose the benifits of having EFI. At that point you might as well carb it and be done. It will run better.

Sorry, but EFI is not a little puddle you stick a toe in. If you are gonna dabble, you are gonna get wet. So, either deal with it in factory trim, learn to tune it, or pay someone else to.

Last edited by TurboS10; 12-14-2011 at 08:28 AM.
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Old 12-14-2011, 09:20 AM
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I others words, use a megasquirt or run a carb..!! right?

I have some experiencie with SDEFI systems in 4 cylinder turbocharged engines with good results so megasquirt shouldn't be that difficult, I like the low price of megasquirt, though SDEFI is not very expensive.

http://www.sdsefi.com/

have you used their products or heard about them?
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Old 12-14-2011, 06:59 PM
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read this... http://www.megamanual.com Great write up. It actually gets into the five main circuits (power, clock, serial, input, output) and how they all work together. gets into maf vs. speed density some. Google the difference to get more info on it. I am a huge fan of the DIY efi controller. If you want low buck DIY this is it for you. Go through the MSI, MSII, MSIII, and MSPNP to see what is ideal for you. It will be a lot of hacking and splicing but worth it in the end when you can say I did this. I actually plan on designing my own someday... just cause I can... I wrote a 17 page paper for my senior seminar class for school all about the incorporation of computer controlled fuel injection systems and how the computers manage and modify fuel tables for ideal operating conditions and i get into the difference between open and closed loop operation. I plan on going through the paper and changing it for an engine croud and posting it on our wiki. I am a computer engineering student so I wrote the paper to be easy on the words for my computer friends and not engine gurus.
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Old 12-15-2011, 10:42 AM
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Quote:
Originally Posted by Augusto
I others words, use a megasquirt or run a carb..!! right?

I have some experiencie with SDEFI systems in 4 cylinder turbocharged engines with good results so megasquirt shouldn't be that difficult, I like the low price of megasquirt, though SDEFI is not very expensive.

http://www.sdsefi.com/

have you used their products or heard about them?
Actually, if I do another project I dont know which way I would go. I might try megasquirt, but something like FAST appeals to me alot more after having done a diy project in the past. I dont have the time to deal with all the diy problems and I am usually looking for a faster solution. If I was going really simple like TBI fuel only, then I think megasquirt would be my choice. If it was a turbo setup I'd go with something else most likely.
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Old 03-02-2012, 03:33 AM
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i'm gettin' old

to prove this, when shopping for a new cell phone, i'm looking for one that has rotary dial. i'm 60, and putting a late model 5.7 hemi in my '24 dodge coupe. i'm really glad i found the right aftermarket wiring harness. i can imagine trying to figure out the factory harness. thanks for the tip on the megasquirt setup. from what i understand you mentioned, is that it allows a person to alter/modify the readings that the ecm receives.
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Old 03-02-2012, 07:42 AM
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Lol...

Actually, the megasquirt replaces the stock ECU. However, I do not know if the megasquirt has enough "horsepower" to run COP ignition and sequential fire injection. I just have not looked at it lately.

I can also tell you that if you dont understand the factory wiring, you will not be able to do the megasquirt. If you dont want to get on the steep learning curve required it might be in your best interest to have a rod shop do the wiring and tuning on the engine. It might not cost you any more to pay a knowledgable EFI tech than it would to buy, build and attemp to tune an aftermarket ECU.
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Old 03-02-2012, 09:05 AM
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Quote:
Originally Posted by emwolb
to prove this, when shopping for a new cell phone, i'm looking for one that has rotary dial.
LOL LOL... this would be sooo cool
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Old 03-02-2012, 09:08 AM
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http://globetribune.info/wp-content/...yCellPhone.jpg
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Old 03-02-2012, 05:59 PM
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Well it won't help with a rotary cell phone but you can do all the megasquirt does with JY GM parts. Still need a laptop, TunerPro tuning software is $30. and all definitions are free and will do 100's of cars, cable is about $50. Burner $85 and a newer EEPROM and adapter $40. from Moates.
http://www.moates.net/ when done you still have equiptment to do other cars with another adapter and chip.

GM EFI systems are very well supported!

JY ECM is cheap and several will run stock $58 mask from GM that came on turbo cars with 2 bar MAP sensor for boost. Or others that did not have boost can still run an enhanced version called/at Code59.org
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Old 03-23-2012, 04:25 PM
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I can only answer one if your questions. After you remive the cat you use spark plug antifoulers to space the o2 sensor from the exhaust slightly. It tricks it into thinking the cat has slowed the flow of exhaust and cooled it down
You may have to use different combos of different lengths but it will work.
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Old 03-27-2012, 07:36 AM
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The anti fouler trick is only needed if you are running OBDII computers, anything before 96 is OBDI and only uses a pre cat O 2 sensor that you really want to work correctly.
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Old 04-01-2012, 08:48 AM
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Quote:
Originally Posted by bigdog7373
I can only answer one if your questions. After you remive the cat you use spark plug antifoulers to space the o2 sensor from the exhaust slightly. It tricks it into thinking the cat has slowed the flow of exhaust and cooled it down
You may have to use different combos of different lengths but it will work.

The O2 sensors aren't looking for cooler or slowed down exaughst. What the pcm is basically doing is comparing the waveform of the upsteram sensor to the downstream sensor. It wantrs to see a big difference, sort of like this:




you can do this using a resistor in the sensor signal line, just know
that will take some trial to get the right value, as you are working with a generated voltage of less than 1 volt.
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Old 04-01-2012, 01:26 PM
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but.. if the o2 sensors are placed away from the exhaust stream they will generate less voltage, same effect as using a resistor in the line...

i would say it will work, not becuase of the slowed down gasses or something but just becuase they will show the ecm a lower voltage reading, therefore the difference it was looking for.

not sure though if the ecm wants a lower or a higher voltage reading from the after cat sensors, it may be necesary to install the spacers in the front O2 sensors... maybe?
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Old 05-22-2012, 03:01 PM
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Quote:
Originally Posted by Augusto
let's forget about emission or legal stuff, let's say we are talking off road only here.

How do I modify a stock ECM to run with performance parts installed, say a bigger cam or a turbo for example.

I mean DIY very low price tricks, not buying exotic chips or reflashing proms, things we all can do at home, like installing a variable resistor in place of the IAT sensor to richen the mixture or tampering with the distribuitor holdown to advance the timing, etc, etc.

How do I turn the CEL off (besides removing the bulb) after I removed the catalyst, etc.

please tell us some secrets, and smog cops don't worry, we will never run a modifyed car on the streets.
It depends on what vehicle you are talking about but I am a firm believer in using EFI Live. You can do just about anything you want to with this program and not have to install any "chips". Yeah, it costs a little but if you plan on keeping the car and have the time to fiddle with it, EFI Live is the program of choice. Once you learn it, you'll love it. You can read about it at http://www.efilive.com
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