[Diy_efi] GM TBI electrical details

[Steve Ravet]

=20

> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org=20
> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Charles McDowell
> Sent: Wednesday, December 15, 2004 7:54 AM
> To: 'A list for Do-It-Yourself EFI'
> Subject: [Diy_efi] GM TBI electrical details
>=20
> I'm working on getting started on my DIY-EFI project and I'd=20
> like to learn more electrical interface detail.  Can someone=20
> explain, or point me to a source of info about the injectors=20
> and the IAC on a GM TBI?  For the injectors, I believe that I=20
> feed 5V to one connection and then ground the other to fire=20
> the injector?  If this is correct, can someone tell me for=20
> sure how much current I will need to sink when I make that ground?

There are 2 kinds of injectors, high impedance and low impedance.  High
impedance injectors are around 14 ohms resistance, they then draw about
1 amp.  Low impedance injectors are a few ohms, they need a driver that
supplies a peak of current initially but then ramps it down to keep the
injector from burning up.  These are like 4 amps peak/2 amps hold or 2
amps peak/1 amp hold.  They all run off battery voltage.

TBI injectors are usually or always peak/hold.  They are wired to B+ and
the computer switches the ground side.

>=20
> For the IAC, I need to start from the very basics.  Maybe=20
> there's some reference material available on-line someplace? =20
> A useful start would be if someone could give me a real basic=20
> functional description of the 4 connections to the IAC.  Can=20
> I control it directly from my processor, or do people usually=20
> use some sort of stepper interface chip?  I'd like to avoid=20
> extra hardware like that if possible.

You can control the stepper directly from the processor if you feel like
writing the code.  Your microprocessor won't supply enough current to
run the motor so at a minimum you'd have to use some transistor drivers.
Or you can unload the details about driving windings onto a driver chip.
There's no point in explaining steppers in an email, there's plenty of
info available on the web.  do a google search for "stepper motor
basics" or something like that.

>=20
> I plan to use TPS, CTS, O2 and MAP for my sensors (maybe I'll=20
> add VSS later).  I think these all work by applying 5V and=20
> seeing how much voltage you read back.  TPS would be 0-5V =3D=20
> 0-100% I assume.  MAP would be the same except 0-1 bar (or=20
> 1-0 bar?).  How about CTS, what's the range in F or C vs.
> voltage?  Also, do these sensors pull any significant current?

I think this was answered on the gmecm list...  All of this information
is answered in the GM service manual.  Get a copy if you're serious
about GM based DIY EFI

>=20
> Oh yeah, ignition module: What do the pulses look like=20
> electrically from the module?  Is the pulse width relevant,=20
> or just the edge?  How is external (to the module) spark=20
> control enabled/disabled (there's the connector that you open=20
> to disable, is that grounding the module connection or=20
> applying + voltage?).  What electrical characteristics is the=20
> module expecting for the spark control pulses sent to it? =20
> Again, is the pulse width important, or just the edge timing? =20

Look in the ftp "uploads" directory for all files that have "DIS" in the
filename.  It shows the EST signals.

--steve
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