FW: Help- Idle is driving me NUTS!

[rr]

Reid,

To troubleshoot without some data is tough. I'll list some
things that may help. All of the locations will be for the
'747 ecm. To disable the egr, set location 1B3h to 0. Do
not count of zero'ing out other tables.

The desired idle rpm table is at 60Eh through 616h inclusive.
This is by coolant temp, 611h & 612h is for 85C & 95C
coolant. Value is rpm / 12.5.

Due to the cam, it might help to bump up the idle 100 rpm
or so. Opening the throttle blades at idle can improve things
also. Just watch the IAC count isn't zero.

You might want to set your idle SA at 18 to 20 degrees
at the crank. I've found some engines like a lot of idle
timing.

To richen the closed loop idle, the idle O2 bias is at: 2F7. This
value will raise the O2 x-point window. Val * 4.34 == mvolts
of O2 threshold. (IE: 25 will raise the idle O2 thresholds by
109mvolt).

If you wish to stay open loop, the open loop idle on rpm is
at: 2A1h, off rpm at: 2A0h. These are by rpm / 25.

What is your open loop O2 idle voltage? Does it seem as
though the IAC can't keep up with the idle?  Is the '747 bin you
as using the original for that engine?

It is normal for the '747 to not go closed loop until the vehicle
is moving. I've seen this myself. Do all of your current tuning
with a warmed-up engine. Once that works, you can move
on to the cold tuning.

BobR.



Reid Bishop wrote:

> <I apologise if this is a repeat- I swear the two times I sent this message
> out before, it never made it to the list...>
>
> I'm about to tear my hair out.  I simply cannot get my 4.3 to idle properly
> (to my satisfaction) after several tuning attempts.  Tried on both a 7747
> and 8062 ECU.  Here's the skinny:
>
> BLM's are always running 101-109 at idle, no matter what I do with the VE
> tables.  Fuel pressure is fine- right in spec.  Every time I reduce fuel in
> the VE tables around my rpm/map idle combo, the engine idles WORSE, and the
> BLM's don't change.  This last change, my idle is precarious, and it
> generally nearly stalls before the ECU rescues it and brings it back for
> another attempt.  Within 5 seconds, it nearly stalls again... this goes on
> and on.
>
> Other possible hints:  Can't get into closed loop by just idling (even after
> 10 minutes with coolant at 180) in 40 degree weather, yet once it gets into
> closed loop it stays there, even after extended idleing.
>
> My O2 Cross-Counts move very slowly at idle when in closed loop- maybe 1-2
> per second at best- yet I see fairly full O2 swings, from 120mv to 850mv.
> When in open loop, the O2 cross-counts advance much quicker.
>
> I have EGR basically disabled at idle (Set EGR% to 0 at low map/rpm
> settings)
>
> Engine idles GREAT in open-loop.  Just gets crappy when the O2 comes alive.
>
> Can't get my IAC's down either (I have no throttle stop adjustment on my
> TBI).  IAC generally runs between 33 and 48, with a MAP of 30-40.
>
> What gives?  Is this a sign of a need for a heated O2?  Bad O2?  Is there a
> chance an exhaust leak is screwing up the picture?  Am I nuts?
>
> I do have a mild CAM in this engine, along with a Performer intake.  I'm
> sure it's affecting things to a degree.  All other VE's have been much
> simpler to nail down- and I have the engine running great everywhere but
> this darn idle.
>

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