Why aftermarket computers suck....

[ryan.hess]

Well, I didn't want to take up any more of another thread, so here we are. A while back, I installed a northstar in a fiero. In the interest of getting it running, I purchased a Holley commander aftermarket ECM. Luckily it was used, so I didn't waste too much money, but anyways...

Most aftermarket computers are good at one thing - being semi user friendly. As in, they usually come with a book. This is the single largest downfall of the GM ECM. It has a steep learning curve. If you've never tuned anything before, you have to learn *how* to tune, and where to change values in the ECM. Usually you're limited by talking to people who have been there, done that.

So back to my project. Computer install was straightforward, and I got the thing tuned (after lots of driving and several months). 3 things I immediately noticed.

1) When the engine temperature reached 180, and the fan turned on, there was a chance it would stall. It didn't happen all the time, because usually it could recover from the 400 rpm dip, but about 50% of the time, it would stall. This would only happen if you were sitting at a stoplight or driving slowly when the fan kicked on. Holley recommended raising the timing and fuel in the cells where it tried to stall. Did that, still stalled. "Maybe you need to replace your fan motor". Did that, checked and replaced wiring, and fusible links, still stalled. Holley stumped.

2) When I would cruise to a stop, sometimes it would stall. Add fuel, add timing... Still stalled, Holley stumped.

3) It would stall until it was warmed up. Now this one was interesting. Holley recommends changing the throttle stop screw until your IAC counts are about 20 at idle when it's warm. The problem was it needed more air until it warmed up. So it would idle great when warm, but when it was cold, lookout! Any time you lifted off the throttle, it would try to stall. Backing out of the driveway was FUN! Holley wanted me to raise the idle when it was cold to fix it. Uhh, no. I have an auto. Having it idle at 1200 when cold would mean I'd always have to be on the brakes.

So, now I have a custom programmed GM computer. Idles like a DREAM. No longer stalls when the fan kicks on. No longer stalls when coming to a stop. No longer stalls when cold. As an added bonus, I got rid of the dakota digital speedometer interface, because I could now use the ECM to control the speedometer output. (As a side note, dakota digital's interface sucks. Imagine stopping at a stoplight and seeing your speedo jump to 50mph. That happened ALL the time. It picked up all kinds of noise from the ignition and computer. I tried all the DD suggestions to fix it, including using shielded cable, but nothing worked. Thankfully the GM computer fixed it.)

The problem is, most aftermarket computers are crap. GM spends millions of dollars creating the best computer to control the engine under every possible condition imaginable. Most of that is put into the software development. This is where most lack. In the case of the fan-kick-on-stall, the GM computer compensates for the power draw by opening the IAC a little bit before turning on the fan. Brilliant. In the cruise-to-a-stop-stall, the GM computer *slowly* closes the IAC, by watching the car's speed. The Holley doesn't even have a VSS input. For the cold stall, I have no idea. Better IAC logic I guess.

So, still undecided on what to get? Here's some questions about your computer that you need to ask.

Does it have/can it:

-VSS throttle follower?
-Can it control transmissions?
-open IAC for cooling fan kick-on?
-open IAC for A/C, power steering, or user defined (?)....
-divide VSS pulses by (any number) to output to speedo (if not you need something like the dakota digital, +$80)?
-all that emissions crap (important to have if you have e testing)
-knock sensor?
-associated knock retard vs knock event severity
-Adjustable closed loop AFR (i.e. instead of 14.7:1, can run it lean at idle like 15.2:1 for emissions& gas savings)
-Highway mode AFR, like above when highway speed/low load is detected
-Spark advance correction vs load and coolant temp
-control for 2 fans with seperate on and off temps, adjustable IAC kick up for both, as well as vehicle speed "off" control
-idle over/underspeed spark control (with adjustable spark advance/retard to bring rpm back to desired)

All of these are important. Some more important than others. GM has it all. The Holley has 2. I don't know about Megasquirt, but I suspect it doesn't have them all either, since it was basically put together by a couple hobbyists.

Now don't get me wrong - the aftermarket computers have their place - namely in controlling engines that otherwise couldn't be controlled. I think they also help beginners understand the workings of engine management. All good stuff, but in my opinion, it doesn't belong on a daily driver.

Feel free to flame.

edit - one more MAJOR point that I learned about a little while ago. I was talking with an engineer that designed the northstar. During a wide open throttle run, after 20 seconds, the computer lowers the AFR to 10.5:1. That's right, 10.5:1!!! Anybody who knows a thing or two about tuning knows that's a ridiculously rich mixture! Why is this done? After 20 seconds of wide open, the pistons start to overheat. The extra fuel is introduced to cool the pistons and spark plugs. With out that, the engine would self destruct. These guys run the engines on the dyno at wide open throttle for hours at a time.

IF I had decided to be naughty and made a high speed run on a flat road with the holley, I would have blown my engine. Thank God for GM's engine dyno testing.

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[SappySE107]

I agree with you. Im sure the expensive aftermarket computers will control more variables like the IAC follower and steps to open when the fan kicks on. However, the stock computer does this already so unless you have a 94-95 OBD1.5 flash computer, you are better off learning to tune your OBD1 or get a programmer for OBD2. There are more variables known in the OBD1 computer though so hopefully the OBD2 companies are still working on adding options to their software.

[kprofthestrs]

so unless you have a 94-95 OBD1.5 flash computer, you are better off learning to tune your OBD1 or get a programmer for OBD2. .

what difference does the 94-95 obd 1.5 have that the ob1- obd2 doesn't?
last i knew it was a 20% or so learning curve. am i wrong. is that what you are refering to?

[bszopi]

Its the fact the the OBD1.5 cars basically have no option of tuning. Either you pull the PROM, edit the code, reflash and reinstall (OBD1) or you get your handheld/laptop and edit parameters via the diagnostics port (OBD2). OBD1.5 has neither of these options, therefore no way to tune...

[korbendallas68]

This summer, there's a all you can carry sale at the u-pull-it. I'm going to stock up on some old ODB1 ECU's... If somebody else hasn't gotten them out of the cars yet...

The cut off for ODB1 was 1993 right? Cause there is a lot of older 3.1's in the yard most of the time, and quite a few 3100's.

I've got a bunch of 94 and 95 3100's ECU's laying around and a 3400 GAGT one too... Too bad I can't use them.

Oh ya. I still have that write-up you sent me for PCM-downgrading (Ben or Brad, can't remember who...)

I'm kinda hoping to get a PCM setup, or even just a file, for the xx~95 3400-swapped cars.

[SappySE107]

What year is your 3400 grand am computer?

[korbendallas68]

2000

Hmm. It's got a ton of numbers on the label.

Here's a Hardware Number: 09357440

[sharkey]

well, im not an expert on the megasquirt yet, but here is what i know

-VSS throttle follower? - no
-Can it control transmissions? - once the gpio board is done, yes
-open IAC for cooling fan kick-on? - no, some done use an iac with it
-open IAC for A/C, power steering, or user defined - see above
-divide VSS pulses by (any number) to output to speedo- no, but a simple speed buffer can be built
-all that emissions crap (important to have if you have e testing)- gpio board will do that
-knock sensor- yes, just data logging so far, next firmware revision will change it for spark retard.
-associated knock retard vs knock event severity- see above
-Adjustable closed loop AFR (i.e. instead of 14.7:1, can run it lean at idle like 15.2:1 for emissions& gas savings)- yes
-Highway mode AFR, like above when highway speed/low load is detected- depends on your tuning
-Spark advance correction vs load and coolant temp - yes
-control for 2 fans with seperate on and off temps, adjustable IAC kick up for both, as well as vehicle speed "off" control- will run 2 fans
-idle over/underspeed spark control (with adjustable spark advance/retard to bring rpm back to desired) - dunno

megasquirt doesnt do it all, but once the gpio board comes out, it will do anything you want it to, include turn on an easy bake oven (as ststed on the megasquirt website). it is still in the development stages, but the best part is all the old stuff is upgradable.

the holley ecu has been around for many years, depending on the version you had, it may have been from the mid 90s, when stand alone efi was pretty rare and pretty crude. they have made leaps and bounds sisnce then. and holley isnt the best stand alone, its actualy down on my list. haltech, fast xfi, accell dfi, sds, megasquirt, aem all make stand alone ecu's. dont base all your views on stand alone soley on your experiance with the holley.

the reason im going stand alone is cause its so much more simple to tune, and datalogging is so much nicer, and there are programs that you open your data into, it makes corrections for you. id much rather spend 10-15 minutes on my laptop between rounds instead of 30+ with a stock ecm and an emulator.

how bout we make a list of what stand alone can do that stock cant. im gonna go off what i know with the megasquirt.

-controll high amounts of boost
-controll nitrous
-2 step
-soft touch rev limiters
-tractiong controll through retarding timing
-run a shift light
-have the ability to data log anything (megasquirt gpio board will have inputs for anything you want to log, egt, 2nd o2, oil pressure, fuel pressure, ect)
-simple to tune
-controll 2nd set of injectors
-controll any injectors, high or low impediance.

thats all i can think of right now, im sure ill come up with more.

[kprofthestrs]

-control nitrous
-2 step
-soft touch rev limiters
-tractiong controll through retarding timing
-run a shift light

i've got all that on my msd digital dis-4. it doesn't control nitrous but it does have a built in step retard for nitrous application. with 2 stage rev limiter, a tach adapter feature and a built in ignition kill.

but thats just my thought.

[sharkey]

you can always add ignition things to do that, but with the megasquirt you dont need to, its all built in a fully tunable. the nitrous portion allows a second set of tables so timing can be retarded and additional fuel will be added when the nitrous is armed. it can also turn the nitrous on and off at specific rpm settings. also, the dis 4 wont retard the timing when it detects the tires are spinning. with the megasquirt you can rogram it for a specific rpm/second rise, if it accelerates quicker, it will think your spinning (and if you program it right, the only way it will accelerate quicker is if they are), retard the timing, and possibly engauge the rev limmiter. of you can wire it with a simple curuit that will compare front wheel speed to rear wheel speed, and detect it that way.