[Gmecm] Surging Idle, was: Does $a1 have a "stall saver" algorithm?
davesnothereman at netscape.net
davesnothereman
Sun Sep 10 11:32:05 UTC 2006
At idle, engine speed will respond to spark changes first, fuel next, and IAC last. It might help to eliminate IAC as a variable by unplugging the connector. It might also help to mark the balancer / lower pulley and view spark activity with a timing light. You might increase the RPM at which EST becomes active to some value well above idle in order to check the effect of fuel alone.
Richer mixtures generally fire easier. If watching the engine run well in open loop, watch O2 and PW values for an idea of what does work. Your tables should generally be leaner at lower MAP or lower load. During transitions, conditions where the car almost stalls and idle is really hunting, you need to ensure that AE isn't activated. At low rpm the O2 signal can tend to lag behind the fuel changes causing one to misinterpret the datalog results.
The tables may be smooth, but remember that it's the engine, not you, which decides how to set the calibration up. You just need to be understand what it's trying to tell you. My approach if using an emulator would be to set closed loop enable values to force open loop then let the engine idle in open loop for a significant amount of time. 1 min? 2 mins? Maybe more. If the idle seems stable I'd note as many values as I could from the ALDL monitor. Then I'd adjust the closed loop enable parameters so the ecm enters closed loop. At this point I'd try to distinguish which factors start the cycle. Without an emulator I'd be forced to burn a chip which would cycle into closed loop after a fair amount of time. Maybe set enable temp to something between fan on temp and the thermostat open temp, or set an enable timer to a fairly high value. But the point would be to watch things go from good to bad, not necessarily try to fix them after they're bad (that's a game for another day).
Think of it like a car wreck. Trying to evaluate the last 10 seconds of the driver's performance with the intent of pinpointing why he crashed might be tough. It would probably be easier to determine the reason the car went out of control in the first place.
HTH.
Zaphod
-----Original Message-----
From: rgmecm at yahoo.com
To: gmecm at diy-efi.org
Sent: Fri, 8 Sep 2006 1:59 PM
Subject: Re: [Gmecm] Surging Idle, was: Does $a1 have a "stall saver" algorithm?
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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