7747-4cyl experiment

[Dan Griffin]

----- Original Message -----
From: rr <rrauscher at nni.com>
To: <gmecm at diy-efi.org>
Sent: Monday, August 20, 2001 2:15 PM
Subject: Re: Netres availability


>
> Dan,
>
> In the '747 harness near the distributor there is a single
> wire connector. The wire is tan w/black stripe. This
> connector needs to be open to set the base timing. It opens
> the bypass signal from the ECM and disables ECM control of
> the timing.
Ok, I disconnected it ( pin d5 )from the ecm end,( same as 165) since the
fender well has to be removed to acsess the distributor on a 4cyl... Timing
is now rock steady at "0"....it climbs to about 16 when I rev it up...makes
no diffrence whether aldl pin a-b is connected or not...other than ses
flashes...
with eprom removed,( limp mode? )( 747 plugged in entire time ) timing is
rock steady at "6" ..which is what I set base timing at with 165 plugged
in...when I rev it up it  climbs to around 16 and occasionally jumps outta
sight..
with d5 and chip plugged back in, timing is around 30 - 40? from what I can
tell, its way over there, the white paint dab sure helped... It still is
kinda jumpy, even with knock tables zeroed, but not as bad as
before...sometimes at idle I get double spark too...Idle never has been real
smooth, like it is in limp mode,or d5 unplugged..

I like the resistor trick, cant I just hook it directly to the esc pinout on
ecm and ground it to any ground? Or is it mandatory to go through an esc
module 1st.? Ill hafta find out what a esc module is...The 10mm nut on side
of ecm looks like a good ground spot...Ive got about 2' of 747 harness with
the ecm connector end..

There is now some question as to what 747 base timing is.. "0" with d5
unplugged,( more logical, imho)  or "6" with eprom out? I never moved
distributor timing throughout test...


snip<  What is probably happening is that only two of your cylinders are
getting a fuel shot and the other two are just tagging along.>

wouldnt I be able to see this? with timing light hooked to coil, pointed at
tbi, injector fires everytime light shines...shouldnt it be spurt spurt
then 2 dead spurts?

<This assumes
you are only using one injector driver. This also assumes that you have the
ECM bin set up for 4 cylinders, which may not even be an option in the 7747
bin.>

 Its only a winbin option.. I dont really undestand what its for, everytime
I burn a chip with it set to 4 truck runs worse...It runs good set 6 or 8...

<What is more likely happening is the ECM is trying to control the engine
as a 6 (or 8) cylinder, and therefore the alternate injector firings are
hitting each cylinder just in a very intermittent way. In other words, with
a
V8 bin, the ECM thinks the engine is turning only 500 RPM when it is really
turning 1000 RPM.>

wouldnt that screw up my idle speed? if idle is set to 800 then it should be
actual running at 400? I hope its not doing any of that...

 <This would also put you in a leaner part of the fuel table.>

the only code I get is 45 (rich).. although plugs look a little lean, light
greyish...

<The bottom line is that a 7747 on a 4 cylinder is a misapplication. What
you
are running into is that demand for reverse engineered (hacked) 4 cylinder
ECMs is very sparse.>

Yeah, I know, thats why im experimenting with this...

< You may have to do your own hacking of a known 4
cylinder ECM, such as the 165 you already have.>

Tried to, I dont know how to recognize what the tables, switches, constants
look like in the dissasembly...

< Maybe you ask the list for
other hacked 4 cylinder ECM applications. JW>

 tried that a long time ago, there arent any...
Dan
>
> You'll need to do this before any other timing issues. If
> the base isn't set right, then nothing else SA wise will
> be right.
>
> For the ESC module use any one you can find. Just plug
> one in. In place of the knock sensor try a 3.9K resistor.
> (This is if you are not using a knock sensor). The resistor
> goes from the ESC module to ground.
>
> Once you can get the base timing set things should get
> better.
>
> BobR.
>
>

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org