I've got an inline six, stock cam, induction and exhaust, with a 1227747 ($42) GM 3.8L setup. I've had it running for almost two years, the fuel maps are pretty much spot on when the engine is fully warm. BLMs run 130 - 128 across the board with a few outliers. I have a non-ECM-controlled distributor.


My problem is the range between choke/startup and closed-loop. There, it runs very lean (with the usual bogs etc) until fully warmed up. I don't have wideband O2 but I'm an old carb guy and have been doing plug-cutting at various time intervals (from cold: 30 sec, one minute, 2 minutes, etc) and it's predictably and repeatably lean. I've been driving it just fine, but it's a bit unpleasant.

Running WinALDL, with BLM table ("wide average") showing, BLM data doesn't appear until coolant=120F, then I get VERY lean-indicating BLMs, most near 145 (max!). As temp rises from 120 - 180 (195 thermostat) BLMs drop, once at operating temp, BLMs run 128 - 129 in the most critical pressure/rpm bands.


I guess I have two related questions:

* what parameters control OPEN-loop fuel after cranking, when running?

and

* what parameters control CLOSED-LOOP fuel between start of open-loop until warmup?

From reading BMmonteSS's (FREAKIN' EXCELLENT!) "Free tune up!" thread (which I actually PRINTED OUT to SAVE!) there's a hint that maybe I need to look at what he called "PW Multiplier vs. Engine Temp" (which I think means, "Choke Air Fuel Ratio Multiplier vs. Coolant Temp" in TunerPro RT). Currently it's 92%@148C to 89%@-37C. Is this the correct table? If so, should I drop this vector by say 5% (eg. 92% --> 89%) and see how it goes?

Am I barking up the right tree?

Thirdgen kicks butt! This is a great site, so many good contributors, polite and civilized and full of incredibly useful information.

 

The table at $45A is the AFR vs Coolant used when in open loop. Once in closed loop the stoich AFR is used. Note that this table is further modified by the AFR vs vacuum table at $41D. They are added together to create the commanded AFR in open loop.

RBob.

 

Thanks for that -- I had to figure this out by experiment, but the table at 0x438 ($438), which TunerPro RT calls "Choke Air Fuel Ratio Multiplier Vs. Coolant Temp.", fixed my warmup problem.

It appears to be a temperature-selected multiplier of the target closed-loop AF ratio. I assume the built-in target is stoich 14.7, so if my table has a multiplier of 90% it makes the target be 13.23.

I dropped my table about 5% in a tapered manner, keeping the values at and above the thermostat temp the same (eg. lowered cold values). I now have 128 - 130 BLMs from coolant temps 120F up to thermostat.



Turns out, my immediate problem is that my O2 sensor is warming up slowly -- it's a 3-wire, so it should warm up fast, but maybe the heater died. It takes 4, 5 minutes to warm up I assume from exhaust heat. Oh well, it got me to figure out this last thing!

 

The table at $438 is the choke decay multiplier. It controls the rate at which the choke AFR (subtracted from the open loop AFR) is decayed out to 0. The smaller the value in the BIN the faster the choke AFR decays out.

The choke AFR modifier isn't used while in closed loop as it would throw the PW calculation off. The O2 sensor values and ECM control would need to skew the BLMs to bring the AFR back into line.

RBob.

 

Oops -- thanks for the correction. My choke was off, apparently, and the symptoms made worse by my delayed closed-loop problem.

Well then back to my original problem: lean bogs during warm up. When at operating temp it's perfect. In this post BMmonteSS says:

https://www.thirdgen.org/forums/post...74-post76.html

"I'm a 747 guy... [...] We have 3 tables to mess with here the first and the one we’ll leave alone for now is the “PW multiplier Vs. Engine Temp” if you notice you get a lean pop or rich bog when the motor is cold but not when it’s warm then you’ll need to mess with this. ..."

Then he never gets back to that table.

Then I'm still puzzled as to where the "PW Multiplier vs. Engine Temp" table BMmonteSS mentioned is in the $42 bin. Any idea? He didn't mention it's address, and likely my xdf has some other name for it.



Is there a general description of tables and their functions? I can puzzle out data relationships but all I've got to go on is the table names and past conversations. For my own use I'm trying to compile table functional descriptions. For example, fuel tables #1 and #2 are well defined. These lesser tables not so well.

 

“PW multiplier Vs. Engine Temp”, this sounds like an AE table. Used to compensate the volume of AE for various engine temperatures.

As for the tables and so on there is a hac of the '7747 code. Most likely can find it on Moates site.

Is the ECM in closed loop during this time? Is it only when the throttle is opened or during steady state?

Closed loop and steady state, up the closed loop enable temperature.

During opening throttle, then change the PW multiplier vs CTS table for AE (at $40C).

RBob.

 

How did I not know about those?! Yes, it filled in some blanks. Still making my own table descriptions, they're on my website, I'll post when "done" (sic).



GAK! CL enable temp was -4C! I checked, this is the value in the bin I started with. Shame on me for not checking that. Set to 60C for now, will fiddle. I'm at work now, but I may burn a chip for the drive home and see how that goes. SoCal here, so "cold" really isn't :-)


OK. GOT IT. Hmm... would the -4C CL enable mean that my closed-loop enrichment tables were interfering with cold-loop tuning? It would explain some of my difficulties.

Thanks AGAIN! and AGAIN! for persisting with helping me and people like me, working through this stuff! I'm taking notes and will share what I can.