LT5 Info.., and 1228331 stuff in general.

[Ken Kelly]

Marc,
	Let me barge into this thread and see if I understand what
is going on! I don't know if we all understand how the LT5
works. Here is my AssUMption. It is from logic only, I have
not worked on an LT5. I assume there is only one throttle
body, The secondary throttle that are all open or all closed
are after the one throttle body. This would make sense in
your argument. If this is not true, then I have a problem
with this discussion. If both injectors have the same pulse
width, then both runners must have a similar airflow. If one
set of runners have an On off throttle plate to the
atmosphere, this would not be true. If the On-off throttle
is internal, and therefore sees the same manifold vacuum as
the other runners, all should work well.

		Ken

Marc Randolph wrote:
> 
> 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 at 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.