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Re: LT5 Info.., and 1228331 stuff in general.



On Tue, Jan 18, 2000 at 06:02:32PM -0500, Bruce Plecan wrote:
> 
> | They are operated through vacuum solenoid, but assuming the system is
> | operating properly, they open all the way up in one motion - there
> | aren't various stages of being open as far as the ECM cares, it
> | is either open or not.
>
> Have you used a PWM meter on it under load to actually observe it's
> operation?.  Just asking since I have seen things mistated before.  Or is
> this a quote from somewhere, and you have no direct info?.

I have not measured it with a PWM while it was on a dyno
(or driving down the road!).  It would be difficult, but
not impossible.

I base my statement on a multitude of different sources, all which 
agree (or point to) that the ECM considers the port throttle either 
open or closed.  I'll outline only a few below :-)


1. Tim Holland, a lead engineer for the LT5 project on the Lotus side,
said the following, "... the ECM will signal the ports to open, and
wait .5 seconds before turning on the secondary injectors.  As
the secondary injectors share the same drivers as that of the 
primaries, the pulse width signals are halved when the secondaries
operate."    So, there is no mention here of partial opening, and
in fact, the stated operation is that the ECM must wait for the
port throttles to open before it turns on the injectors,
.5 seconds later, at which point the pulse width is halved.
This also makes sense from a fuel and flow stand point - 
the port throttles are below the fuel injectors, so if they
were not opened all the way, the fuel would hit the port
throttles and drip onto the back of the valve.  That doesn't
sound like a good idea to me...

2. A Diacom capture of the LT5 running on a dyno or driving down the
road reflects that the port throttles are either open or closed.
There is no % open reading.

3. The wiring diagram of the LT5 confirms that the primary
and secondary injectors are controlled by the same driver in 
the ECM.  Considering the left and right side port throttles
do not necessarily open the exact same amount for a given vacuum
(I have observed this), and given there is no sensor to indicate 
to the ECM what % the port throttles are open, the ECM would
have to guess as to what pulse width to use if partially
open port throttles were to be supported, and it would almost
certainly not be correct for at least half the engine.

4. The wiring diagram of the LT5 confirms that the port throttle
solenoid is controlled by a single switch in the ECM to ground.
The other side of the solenoid is tied to the main fuse block.

5. The description of an error codes confirms it, by saying
"When the driver has the engine power switch in the FULL power
position, and pushes down the accelerator pedal far enough, and
if various input sensor parameters are within an acceptable range, 
the ECM turns `ON' the secondary port throttle valve solenoid
allowing vacuum to open the valves."  The diagram for this function
also shows the solenoid being controlled by a switch to ground.

6. And lastly, a logical reason: A variable pulse width, variable
opening solenoid would be too complex and wouldn't provide any
benefit.  The main reason for the port throttles is to increase 
low end torque.  As the rpm and air flow rises, the torque curve
of the engine with the port throttles open quickly approaches
the torque curve for when the port throttles are closed.  Why
involve a TON of complexity when you could just open the port
throttles all the way and be done with it?

In summary, I'm quite sure they don't partially open. :-)

Have fun,

   Marc

-- 
  Marc Randolph     -    mrand@pobox.com    -     PGP keyID: 0x4C95994D
     If you have any info on the mid-60's car called the Bill Thomas
       Cheetah, or know anyone that might, please contact me.