[Gmecm] Surging Idle, was: Does $a1 have a "stall saver" algorithm?

Fri Sep 8 17:59:06 UTC 2006

It's not the OEM tables, it's been modified, and I think they're pretty darn smooth there already.  I flattened the spark table there as well.  Going strictly by what the narrow band says, during one surge/recover cycle, it goes from 1200rpm, 0.8 V/rich, 1.1mS PW, falls to 475rpm, still rich 0.8/no crosscount inc, 1.63mS PW.

By this time the IAC ratchets open 6 steps (as compared to the 1200 rpm value), and the RPM starts to increase (about 500), and it has a 1.9mS PW.

The normal steady state idle PW is about 1.3mS.  Should the low RPM/moderate load (40kpa) pulse width be lower?  I think I want more fuel when it's trying to stall, but I'm not 100% sure.

Ryan

davesnothereman at netscape.net wrote:  Check the VE (or load) and spark tables.  Check the MAP and RPM ranges that the engine is passing through as it surges.  Often the OE tables aren't really tuned for very low RPM and high load conditions, as the engine rarely operates under those conditions.  You might try smoothing the tables out to see if the condition improves.

Also, watch the surge to see if the engine speed increases as the mixture goes richer.  Often the condition you describe (runs fine open loop, surges under closed loop) exists when open loop fueling is a bit on the rich side.

Zaphod

-----Original Message-----
From: rgmecm at yahoo.com
To: gmecm at diy-efi.org
Sent: Fri, 8 Sep 2006 10:02 AM
Subject: Re: [Gmecm] Surging Idle, was: Does $a1 have a "stall saver" algorithm?

Well, it is.  I posted this on TGO, but here it is again:

If I burn a chip that runs in open loop, it will run all day with a rock solid 
idle. My P/N switch isn't hooked up (workign on it  ), but when I put it from P 
to D, the rpm dips a very tiny amount, but it catches it just fine.

 Now, enter the closed loop chip. BLM's are pretty darn good at 126, INT about 
the same. You let it sit for a while in park, and it will start surging. Desired 
idle is 700, and it starts bouncing up and down, usually getting more severe 
each time, till eventually it hits 300rpm and either stalls or revs to 1200+ and 
stalls the next time. 

 Additionally, when in closed loop, if I put it from P to D, it instantly 
stalls. So it's like it has no torque or momentum when in closed loop idle. Or 
it can't deal with any sudden changes in rpm fast enough??

 Oh - no surging in drive.  It handles itself just fine there...

 I don't understand what is causing this. How can taking out 1.6% fuel can make 
that much difference? There has to be some other idle constant that is being 
"enabled" during CL that causes these things to happen..... Any ideas?  TIA,

Ryan

davesnothereman at netscape.net wrote:  These are conditions to enable EST after 
startup.  Your engine RPM should not be dropping to 300.

Zaphod

-----Original Message-----
From: rgmecm at yahoo.com
To: gmecm at diy-efi.org
Sent: Thu, 7 Sep 2006 9:37 PM
Subject: Re: [Gmecm] Does $a1 have a "stall saver" algorithm?

Wait, what are these:

Low RPM thresh to disable EST [KESTRPMD] - 300 RPM
High MAP thresh to disable EST [KMAPSTAL] - 70 kpa

Both must be true at the same time, then the EST is cut?  Does that mean it 
defaults to the DIS module's advance of 10 degrees?  What's the point of that?  
If idle advance is 16-20, dropping it to 10 would surely kill the motor?

Second, there is:

RPM thresh to stop Spark Advance Filtering [KSFILRPM] - 800
I don't know what that does, but my RPM is about 200 lower than stock, should 
that be lowered too?  (my idle is about 700, stock 3.1 idle I believe is 900)

Thanks in advance,

Ryan

Ryan Hess  wrote: I can't seem to find any minimum RPM 
constants listed anywhere....  Any ideas?

Ryan

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