7747-4cyl experiment

[rr]

Dan Griffin wrote:

> ----- 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..

The rock steady and climbing to 16 deg is good. I don't understand the 0
deg & 6 deg under the differing conditions. I'd expect them to be the
same. (If the car wasn't apart on the garage floor I'd try it myself).

> 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..

The 30-40 deg. could be correct. If the engine is cold and has a high idle
it could be that high. If the engine is idling and warm I would say that the
timing indicated is wrong. Too much. Check the map & rpm and then the
timing tables & see if they match. If so, then good, reduce it some. If not,
then have to look into it.


>
>
> 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...

This doesn't make sense to me either.

>
>
> 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?

Should be every other one. I'm also wondering if the netres you are using
is convoluting things. What happens with an 8cyl netres?

>
>
> <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..

>From what I've seen of the code it does support 4 cyl operation. The cylinder
select does make a difference as the number of cylinders is used to convert from

ref pulse interval based timing value to a time based SA value.

I really don't see a reason that this shouldn't work.

Interesting note: the injectors can be made to spray at a higher rate by
disabling the synchronous injection mode. Asynchronous mode may fire up
to 80 times a second. Which is higher than sync mode.

BobR.

>
>
> <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.
> >

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