What If? $8D (1227727 ECM) for TBI

**RobertISaar** · 08-11-2012

this, along with some of the limp-home stuff, i think are the last real mysteries to some of the popular ECMs.

i need a scope. :D i mean, i can watch the 3X pulses and the resulting EST and injector outputs at low RPM on my bench via LEDs, but it would be nice to see it at speeds faster than my eyes can deal with.

**1project2many** · 08-11-2012

Well, old lab scopes can be had for short money on Ebay but there's inexpensive software that will allow you to use the sound card as a scope as well. You might be able to locate a trial or demo copy and use equipoment you already have to get started. Come to think of it, you can "record" a signal obtained through a mike or line input then analyze it with wave editing software.

**RobertISaar** · 08-11-2012

i've actually considered doing that before, i just need to make sure i have all of my level-matching stuff in order, i really don't want to kill the audio output on my laptop. from a guess, i'd say i have a stereo mic input, which would allow me to watch the 3X and either injector or EST pulses at the same time, then open the resulting file in audacity, since it allows for some really fine magnification of whatever part of an audio track to see the waveform.

48KHz should be far beyond the range i'll need too.

**Six_Shooter** · 08-12-2012

I have one of these, it works decently, powered by USB and is portable.

http://www.vellemanusa.com/products/view/?id=522377

**1project2many** · 08-12-2012

48KHz should be far beyond the range i'll need too.

lol... unless you're trying to watch a 48x crank signal at speed above 60k rev/minute you should be ok.

**RobertISaar** · 08-12-2012

Originally Posted by Six_Shooter

I have one of these, it works decently, powered by USB and is portable.

http://www.vellemanusa.com/products/view/?id=522377

as much as i like the idea, i don't want to spend $300+ on something that i wouldn't use anywhere near enough to make it worth that.

Originally Posted by 1project2many

lol... unless you're trying to watch a 48x crank signal at speed above 60k rev/minute you should be ok.

yeah, i'm pretty sure ~9000 RPM with a 4X signal would be all i would get up to for automotive stuff..... unless i start playing with high frequency MAFs, in which case ~12KHz would be the ceiling there.

**EagleMark** · 08-12-2012

If your ready to do some testing I will lend you my Osiliscope.

**RobertISaar** · 08-12-2012

i'm not the one that needs it.

that and i'm not sure what target ECM we're trying to mess with ATM, the 7727 or the 7808?

actually, this last page has me all turned around, what exactly is the current issue we're trying to solve?

**JeepsAndGuns** · 08-12-2012

Ok, so I'm thinking. If we need 2 injector drivers to "properly" run a tbi, and the 7727 only has 1 driver, then why are we still trying? Unless we can run a tbi with only 1 driver and pulse both injectors at the same time. I guess one thing we need to find out, is it putting out the correct pulse for the tbi injectors whenit has the bits changed to tbi?

Also, if this 8708 has two drivers and is also weatherproof, why are we not trying to use it? Could it be used with a tbi 4727 (or simillar) memcal?

**RobertISaar** · 08-12-2012

the 8708 was only ever used in Q4 W-bodies.... which were made in 90 and 91 and extremely rare at that.

if i had to guess..... i'd say that due to it's similarity to the 7727(it's actually a little closer to the 16149396 due to the 8708 having the extra RAM that the 9396 had), it MIGHT run 8D natively. and due to it's 7727 roots, if the 7427 style MEMCAL worked in a 7727, i'd bet it works in a 8708.

you COULD add in the second driver to a 7727 to fire it alternately, but you would still have to deal with modifying the code to utilize it. that may or may not be simple. this would actually need to be done with the 8708 as well, assuming still using 8D as a base.

i could change the bit pattern to either TBI mode on my nAst1 bench BIN(and set it up for V8 operation) and watch the results from that on LEDs. i just need to know what pattern you want to see.

**dave w** · 08-12-2012

I think the '7727 could be used for TBI, even with one injector driver:
If the '427 memcal can trigger TBI injectors on every other DRP?
When the cylinder select error is disabled (when using the '427 memcal), will "limp home" become active?
Install resistors in series with the TBI injectors to "electrically look like" 4 port injectors.

I'm thinking with the cylinder select error disabled, the '427 memcal will still trigger the injectors every other DRP without causing "limp home".

I'm thinking the $8D injector flow setting will be very odd when firing the TBI injectors every other DRP, compared to a normal $8D injector flow setting firing the injectors every 4th DRP?

I'm thinking it would be better if the TBI injectors would alternate, but my O'scope video leads me to think both TBI injectors will trigger at the same time on every other DRP, but not alternate?

dave w

**RobertISaar** · 08-12-2012

disabling the cylinder select DTC will only prevent it from causing the SES to come on. when in non limp-mode, the injectors SHOULD fire based off of the BIN setting, when in limp mode, it SHOULD fire based off of the MEMCAL setting.

flowrate in the BIN WILL be odd... but that shouldn't be too difficult to figure out. yes, with a normal 8D BIN, you would see 1 injector pulse for every 4 reference pulses.

i don't think it would be too difficult to use some of my dupont cables and use some resistors in place of the MEMCAL to test what happens in and out of limp-mode in terms of what the MEMCAL based cylinder select does.

**yelruhde** · 09-18-2012

Originally Posted by dave w

I think the '7727 could be used for TBI, even with one injector driver:
If the '427 memcal can trigger TBI injectors on every other DRP?
When the cylinder select error is disabled (when using the '427 memcal), will "limp home" become active?
Install resistors in series with the TBI injectors to "electrically look like" 4 port injectors.

I'm thinking with the cylinder select error disabled, the '427 memcal will still trigger the injectors every other DRP without causing "limp home".

I'm thinking the $8D injector flow setting will be very odd when firing the TBI injectors every other DRP, compared to a normal $8D injector flow setting firing the injectors every 4th DRP?

I'm thinking it would be better if the TBI injectors would alternate, but my O'scope video leads me to think both TBI injectors will trigger at the same time on every other DRP, but not alternate?

dave w

Dave -

Try this bin on your bench. It's 8D with 0293 set to 10 for 4 cyl pfi. If a 4cyl pfi and dual injector tbi memcal are throwing the same voltage off of the memcal then the computer should be looking for the same bit.

It is not throwing a code with a TBI memcal on the 7727 in my truck. But that doesn't mean its is firing the injectors the way it should.