GM TBI info needed

[Shannen Durphey]

Stowe, Ted-SEA wrote:
> 
> Shannen, thanks a lot for the info, it has been very helpful.
> 
> interesting about the non-closed loop. Do you think that this is a good
> choice for something like a 77 mgb 1800 cc, manual trans? I am neutral about
> it, it is one thing less I have to do & worry about. then again it sounds
> like a nice idea.
> 
Closed loop operation can make up for moderate errors in calibration. 
Not needed, maybe not to worry about until other bugs are worked out. 
When the time comes, you might see if there's a closed loop calibration
available for your ecm.

> I wonder about the parameters stored in the ECU, for a 2.0 sunbird, I am not
> sure how well that relates to a 1800 BMC engine. or does that matter ? I
> would of thought that with a closed loop system, that would of worked itself
> out.
> 
Not sure myself.  Probably have to assemble everything and see how it
runs.  Many engineering and customer hours are put into driveability. 
There's little chance the system will be perfect from the get-go.  CL
can work fuel errors out up to a limit. 

> I think the ECU may of had some sort of power steering input too, I suppose
> that would of raised the idle when the ps pump was running or under load ?
> or something like that.
> 
Yes, in my experience.

> I think I have 2 main problems left. what to do about the VSS input, the
> books I have recently found show that the pulses came from a wheel in the
> speedo cluster, which were amplified & cleaned up by a little module on the
> speedo cable, this module did not, (at least in 85 ) generate the pulses
> itself, or so I am led to believe. someone here mentioned that 2000 pulses
> per mile/hr was the standard in that era ?
>
US vehicles' speedometer cables rotate at 1k rev/mi.  I wouldn't guess
about your mgb.  The ECM expects 2k/mi pulse input.  There were some
very recent posts discussing where to purchase speed sensors which would
install in US speedo cables and create the proper signal.  You will have
to decide whether or not they apply to your car.  Worst case, run with
no speed sensor.

> also the EFI stuff, I was wondering if I could actually use the gm EFI spark
> module with my current distributor, which now has an aftermarket hall effect
> sensor. the schematics lead me to believe that all of the action occurred in
> the module, and the rest of the distributor just fed it pulses, I need to
> check to see how many pulses, might be more than just 4 per revolution.

4 pulses per rev.  I have never tried to fire the module with a hall
effect switch, but as an electronically challenged mechanic, I would
probably give it a shot.
> 
> oh problem 3 is the TSS ? switch which I think was from the transmission
> solenoid via the brake pedal (+12). some books tell me that a solenoid got
> engaged in 3rd gear, which I guess was the top gear of the auto trans. so
> did the ECU actually engage 3rd gear with this ? it brought the line low, I
> know that, so I am wondering what exactly the solenoid was for ? kicking it
> into 3rd ? at the appropriate speed & conditions ? I suppose I could ignore
> that line. or just simulate the load in case it checks for current draw.
> 
If you mean the TCC switch, Steve Ravet was accurate in his description
of the circuit. It's for the torque converter clutch, which your mgb
probably isn't equipped with. It "locks" the torque converter at road
speeds.  On manual trans GM cars, this connection is used for an
"upshift" light.  Ignore it.  If your car is a manual shift you might
want to get a calibration from the same.  It will make a difference.

> thanks for your help. this has been interesting to research.
> 
No problem.  Share the story when/if you do this.
Shannen
> Ted.
> 
> -----Original Message-----
> From: Shannen Durphey [mailto:shannen at mcn.net]
> Sent: Saturday, September 19, 1998 7:36 AM
> To: diy_efi at efi332.eng.ohio-state.edu
> Subject: Re: GM TBI info needed
> 
> Stowe, Ted-SEA wrote:
> >
> > Hi.
> >
> > I have an ecm/throttle body from a 1985 Canadian sunbird.
> > I am trying to figure out a little more detail on the cpu
> > and what the ecm requires
> >
> > the Serv. No. is 1226867        DJU
> > 861611 M51197560
> >
> > the eprom has on it "DJU 4085"
> >
> That's the Broadcast code, the calibration if you will.  This is from a
> 1985 J body (cavalier, sunbird) 2.0l tbi, non closed loop (no O2),
> without air conditioning, 3spd thm125 automatic, 3.18:1 final drive
> ratio.
> 
> > the throttle body has the following numbers
> > 17085082
> > 0385HSK2S
> >
> > I do not know the VIN code of the engine, nor anything else about the car.
> >
> > I am trying to figure out if it had an O2 Sensor and what/where the speed
> > sensor was.
> >
> > also as I ponder over the chilton's book , looking at generic examples
> from
> > '85
> >
> > I see that there was an input from the brake pedal through the torque
> > converter solenoid, C2 pin 19 ,I presume that was just an input 0 volts =
> > brake pedal pressed ?
> >
> > I suppose I can ignore the air conditioning inputs/outputs ? (C1 7,9,21)
> 
>  I'd say yes.  The prom will.
> 
> > what would the gear selector switch do ? (C2 pin 6) looks like it was
> > grounded in some selector position, or positions ?
> Signals the ecm to bump idle speed slightly when engaging a drive gear,
> preventing stalling.
> >
> > & finally, the 4 lines to the hei distributor, C1 10,2,3,19 ? were these
> > inputs or outputs ??
> >
>  Yes to both.  One is reference to ECM, one is 5v bypass output, one is
> timing signal from ecm, one is a ground shared with ecm. Don't remember
> wire colors offhand.
> Shannen
> > thanks, this looks like it's going to be fun.
> >
> > I am going to attempt to put this on a 77 mgb.
> >
> > Ted Stowe
> >