[Diy_efi] GMC 747 and Ford duraspark

Tue Jul 6 08:03:44 GMT 2004

Peter,

I started with a Howell kit and have been tweaking my bin for several
months. If you want a good starting point, I think it is pretty good. I
don't control the spark yet and may not ever. I purchased and am waiting
for a Davis Unified Ignition distributor/ignition. It is an HEI system
modified to house the ignition and coil on the cap and is curved for each
specific application. I'll let you know how it works when I get it.

In the mean time, here are some links I suggest you try:

http://www.customefis.com/index.html

He's a great help and sells a book targeted at tuning the 1227747. I
recommend it. He also sells kits and componentes. The biggest pain is the
wiring harness which is one of the main reasons I purchased the Howell kit
(I found Custom EFIS after I had the Howell kit or I would have purchased
the Custom EFIS one)

http://winaldl.joby.se/

Got to have WINALDL for tuning. Don't forget to donate a few bucks, too.

http://tunerpro.markmansur.com/

TunerPro and TunerPro RT. Must have for tuning. TunerCAT is also a good one
but personally, I like TunerPro. I have a very comprehensive ECU definition
file, too if you want it.

Now, I'll get at your specific questions.

Quoting Peter Jonasson <jonasso at mcmaster.ca>:

> Hello
>
> I am putting together my own TBI kit for my 87 Jeep yj, using an 88
> AstroVan
> as a donor vehicle. This will put a 4.3L 1227747 TBI system onto a Jeep
> 4.2L
> ex-carb breather.
>
> Initially I will only be using the MAP, TPS, CTS, O2 and speed sensors
> for
> feedback. Currently I am designing an adapter plate (TBI to intake),
> hopefully one piece.

These are the critical sensors. I found that even though the guys at Howell
said the speed sensor doesn't do much my system runs much better since I
put a speed sensor in and setup the appropriate parameters. There are only
a few parameters and tables which even look at speed, but they have an
effect on certain filters and determining what idle mode to select which
has a noticible effect in how well the system runs.

Re: the adaptor plate, Custom EFIS or Howell will probably sell you an
adaptor unless you love working on the milling machine :)

>
> Now to my questions...
> (all are assuming installation on a 87 Jeep 4.2L (258 cu. in))
>
> Does anyone have a bin, or recommend a bin from the diy-efi archives I
> can
> load as a starting point for tuning?

Yes, I have what I believe to be the last made "stock" bin as a starting
point or I will also give you my current working bin. It needs more VE
table tuning and I'm still fussing with the cold engine AFR settings, but
it is running pretty good right now. I've also had to tweak some of the
"accelerator pump" tables. Seems the Jeep engine wants a much bigger shot
than the Chevy 4.3 liter.

>
> I want to, at some point, control ignition timing with the 747. Can you
> hook-up the stock Duraspark ignition system to the GM 747?

Yes. The Custome EFIS book and web site covers this. The question I have
(with no real answer because I'haven't really asked) is can you use the
stock knock sensor for feedback or even some other knock sensor. The Howell
kit does not use it and I don't think the Custom EFIS uses it either.

>
> If the Duraspark is a no-go, can you recommend a GMC HEI system that both
> fits the 4.2L and works with a 747? I know the 77 to 84 GMC 250 HEI will
> work, stand alone (gear change required), but can it be modified to work
> with the 747?

As I said above, I'm buying the D.U.I. disributor/ignition which is setup
for the 4.2 liter. The Custom EFIS book and website cover how to modify a
HEI system to be controlled by the 7747 computer. I'm not sure how well
that will translate to the D.U.I. system since it is a self containted
unit. Honestly, I'm up in the air about controlling the timing. I
appreciate the ability to setup a timing map, but I think a well curved
distributor will do a good job, too.

>
> Does anyone have experience using the GM EGR electric solenoid in
> controlling the valve?

No. I kept the dual CTO and vacuum system. It works and I saw no reason to
change it.

>
> What is the Park/neutral switched used for in a 747? My Jeep is standard.

My guess would be for an automatic transmission. In the ECu definition, that
switch controls a target RPM if I'm reading it right for when the
transmission is shifted into park/neutral.

> What is an EAC solenoid?

Don't know, sorry.

>
> Lots of questions, but at some point I hope to make it all work.
>
> I am currently running a Weber carb with a Duraspark HEI system, both are
> upgrades from stock. I want to go TBI to improve emissions and
> driveability.

It really helped my Jeep as I was still running the Carter BBD.

Good luck and let me know how it is going. You are welcome to email me
privately if that's more efficient for you.

--
Thanks,

David M. Ingebresten, M.S., M.E.
Collision Forensics & Engineering, Inc.
2469 East Fort Union Boulevard, Suite #114
Salt Lake City, UT 84121

(801) 733-5458
dingebre at 3dphysics.net
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