table questions

[b1500]

I have some questions regarding tables in general, but specifically I'm working with a 7427 ECM, $OD mask, and the BJLF bin.

In open loop cold idle at start up does my fueling come from VE vs MAP vs RPM?

If so, and I adjust the table values down would this result in a leaner idle?

Must the values be change individually or is there something I could use to make more sweeping changes?

My cold idle is very rich with the o2 reading around .924V and BLM at 126 for most cells, I would like to lean it out before continuing.*

[steveo]

few points..

cold start is supposed to be pretty damn rich. it should also have a bit of extra timing advance to assist in burning that extra fuel. the cylinders aren't hot enough yet, they need that extra fuel because most of it wont vaporize, and just pools and dumps out the exhaust. thats the nature of a gasoline engine. i assume you know that, but just thought i'd mention before continuing.

your measurements are useless because:

- cold idle, or actually anything in open loop should read 924mv+ on the o2 sensors, which just means 'richer than stoich' or 'o2 not warm enough yet'. this isnt a wideband and cant be trusted to measure outside of average 500mv=about stoich, and is extra untrustworthy until your exhaust temps are really high.

- you CANT use the o2s to tune 'startup' or 'cold' conditions. hell even a wideband doesn't heat up quickly enough for cold readings to be reliable.

- you have to do plug chops, or just lean it out until it cold start starts to get a bit rough, then go a bit richer and leave it. that's the only real way to tune cold start.

- blm being at 126 while the o2 is reading that high isnt happening. that just means you arent in closed loop yet, it isnt taking o2 input.

anyway,

there is an open loop target AFR vs. temperature vs MAP table in $0D that should be adjusted for temperature-dependant fueling. you CANT trust the afr values in there until you've got your VE tables right on the mark, so if you do lean it out a bit at cold temperatures, make sure you revisit the table after your VE tables become more accurate.

[RobertISaar]

- cold idle, or actually anything in open loop should read 924mv+ on the o2 sensors, which just means 'richer than stoich' or 'o2 not warm enough yet'. this isnt a wideband and cant be trusted to measure outside of average 500mv=about stoich, and is extra untrustworthy until your exhaust temps are really high.

semi-tangent: with a cold engine running noticably richer than stoich(as one would expect), the O2 sensor voltage reading is a decent indicator of how warm the O2 sensors are.... as they creep away from the ~450mV reference point, they're warming up, i still don't want to use any data from them until the coolant temp has been at the thermostat temp for at least a few minutes. once you can get the sensors to creep up to ~900mV, they're pretty warm to register that much voltage, enough for the ECM to do some slower than normal closed-loop correction IMO. too quick of fueling changes probably wouldn't end well though since the sensor likely won't be reacting fast enough for that, and the engine will be a lot less tolerant of the lean cycles.


play with something that you can cold-idle at/above stoich, things get fun there too. sensor voltage will start at the same ~450mV, but head in the opposite direction(as one would expect). i've actually set off an O2 lean DTC reliably with a radically different open-loop AFR table, for some reason the code wasn't aware that closed-loop operation hadn't yet been enabled, but it saw the long period of time at ~300mV or less and fired off the code, disabling the O2 sensor. after patching in the requirement for closed-loop to be active before testing for that DTC, it never happened again.


i also recommend the "lean it until it becomes wonky, then back it off" method. i'm not a fan of dumping excessive amounts of fuel out of the exhaust, it does a good job of heating everything from the exhaust valve/after(including the cat, especially when you have a functioning AIR system help combust fuel directly in the exhaust manifolds).

[b1500]

I did know it should run rich at cold start, though I've never seen an o2 sensor reading out in real time. Guess I should have stopped looking at the screen and started listening to the motor.

I'll warm it up and check Blm in closed loop, then look at making adjustments to the VE and spark tables.

[steveo]

i do want to clarify, i'm not saying dont pull any warmup fuel. one advantage of a less rich but still stable warmup mixture, is the engine will warm up more quickly. which is good. a bit more timing helps there too (but dear god not during cranking....); and its much more difficult to get spark knock on a cold engine like that, so you can run it up pretty high. a good goal of cold start behavior is to stop it from being cold as soon as possible.

[b1500]

Well I pulled a little fuel from afr vs temp vs map only in my idle map range to 104 deg. It leans out a little, good deal.

At 104ish deg it starts to pull spark at cts vs vac vs temp like it should. Since this temp is at the end of the table AFR vs TEMP vs MAP, it looks like fueling starts to come from my idle VE table at the same time. At this transition RPM jumps by 800.
I'm not sure why it does this.

As soon as I go closed loop the O2 looks like its hunting, she falls back steady to 840ish then drops to very lean, a second later picks up again. would adjustment to one of my fuel trim tables smooth this out?

[steveo]

during steady cruise, once your blms have settled on a number, your o2s should be switching in fairly quick patterns.

lean lean rich lean rich lean rich rich rich lean rich lean. that's good.

but until the BLMS have settled, it's a crap shoot. keep in mind how it's calculating:

lets say its 10% rich.

it's going to go hmmm rich, pull maybe 1-2% of fuel. no reaction? pulls more. still nothing? pulls more. this entire time, the o2 is going to be high voltage. this happens fairly slowly too, because there's a delay in between the time that a correction is made, and the exhaust reaches the o2 sensor.

once it's finally pulled enough fuel, the o2 will go LEAN! you'll see it go to very low voltage.

... and then it adds a bit of fuel. then it goes rich again. and it pulls a bit of fuel. and so on.

at this point, the integrator will be set to how much fuel to pull to keep it near stoich in that particular cell, and it will continue to add and remove small amounts of fuel to keep it near stoich. this is proportioning.

if it's hanging after maintaining a cruising speed for over 4 or 5 seconds, like lean rich lean rich rich..................lean rich lean rich............ and this is happening while you're in closed loop and your BLMs are fairly stable, that's bad.

that means either your closed loop configuration is broken and it can't correct quickly enough to get it switching around stoich (o2 delay too high, proportioning too low, whatever), or your o2 sensor is lazy and needs to be replaced.

[b1500]

I should mention this is at idle in park. at the same moment I see the o2 drop off to 90mv motor goes pop sputter, then she picks it back up to 800mv or so, repeat. looks like the sensor is responding pretty fast.

map is around 25-30kpa at 800rpm idle

[b1500]

I've posted up the log from my first short trip in closed loop after the exhaust was put on. I'm a little unsure whether I've got the good o2 switching or the bad, but I can really feel it driving and I definitely don't want to tear up the motor.