[Diy_efi] Importance of TPS with lightweight cars

[Shannen Durphey]

Ne14RoxCJ at aol.com wrote:
> 
> In a message dated 1/14/03 1:07:15 AM Central Standard Time,
> shannen at grolen.com writes:
> 
> But you're talking closed loop operation, anyway.  Why do you need to
> run closed loop?
> 
> I suppose this is where my confusion lies. I thought that whenever the O2
> sensor heats up and the ECM goes closed loop, it stays there. I know that the
> ECM does not correct fuel when in park/neut and when engine speed is above a
> set RPM.
??  I've never seen this happen.  Is this something you've heard, or
seen?

> Other than those 2 exclusions, I thought the ECM adjusted the fuel
> for stoich (14.7:1). Are there other times also? Is this something I should
> change? 
This is something you can change.  Whether or not you should depends on
your needs.  I like to go open loop at idle if the cam has a little
overlap to prevent lean O2 readings from skewing BL #'s.  Open loop idle
is also handy if the O2 sensor tends to cool down at idle.

> Also, Is it safe to assume that the ECM is correcting the fuel flow
> any-time the CL flag is set (light on scantool)??
IIRC, in the 7747 the CL flag will stay set in Power Enrichment.  PE
mode is open loop, so the cl flag is incorrect at those times.

> Should I not be running in
> closed loop? 
Do you have a catalytic convertor?  Is your vehicle subject to emissions
testing?  These questions would be at the top of the list when
considering full time open loop operation.  I generally leave the ecm
running in closed loop unless there's a specific situation that seems to
demand open loop.


> Sorry for all the questions, but this is really throwing off my
> understanding of closed loop operation. Im going to go read these papers a
> few more times. Thanks for your help.
I'm not sure you're understanding of closed loop is wrong.  Typical
closed loop mode is a way to keep the catalytic convertor happy.  It's
not for power or economy.  In fact, "closed loop" indicates that there's
some type of feedback for making corrections to the system.

It is possible to prevent any closed loop operation.  The easiest method
might be to set the enable temp to 250 degrees F.  

Shannen

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