Which table controls (cold) Idle A/F ratio?

[Thedude]

Trying to get my Idle leaned out for cam.
Got EFILive, confused on just what controls idle fuel ratio.
Is it "commanded fuel in open loop" - (b3605 ) or the VE pri or sec tables (b0101/b0103) that controls idle when engine cold (open loop) ??

Also, is this correct, in the VE table, adjusting the numbers smaller leans the AFR, and in the "commanded fuel in open loop" table, adjusting the numbers higher gives higher A/F ratio (leaner) ... this correct ??

[caver]

Trying to get my Idle leaned out for cam.
Got EFILive, confused on just what controls idle fuel ratio.
Is it "commanded fuel in open loop" - (b3605 ) or the VE pri or sec tables (b0101/b0103) that controls idle when engine cold (open loop) ??

Also, is this correct, in the VE table, adjusting the numbers smaller leans the AFR, and in the "commanded fuel in open loop" table, adjusting the numbers higher gives higher A/F ratio (leaner) ... this correct ??

Its b3605 but the VE tables have to be right for it to work properly if you are running is SDmode. If running with a maf then the VE tables and the maf table have to be right.
My experience is that cammed engines like to run richer at idle not leaner. Has to do with the increased overlap allowing fuel to blow past the exhaust valve.

[dfe1]

Also keep in mind that the O2 sensors are going to see somewhat of a skewed readings if an engine is running a camshaft with measureably more overlap than a stock cam. During overlap at low engine speeds, some of the incoming charge flows right through the chamber and out the exhaust valve. The O2 sensor will therefore indicate a richer mixture than the engine is actually processing, hence the need to lean things out. The best thing you can do is give the engine what it wants, not what it "should" want.

[VetPet]

:exactly: At low speeds, larger camshafts make the engine less efficient (poorer VE) as part of the intake charge is sucked back out through the exhaust valve because of the amount of overlap. The sensor will see less oxygen (because more fuel molecules are in the exhaust) and therefore try to reduce fuel. Remember, the O2 sensor is exactly as its name implies, it senses the amount of oxygen left in the exhaust gas after combustion has taken place. It sees less oxygen, therefore it assumes you need less fuel. Cams with significantly larger duration than stock require a richer mixture at idle because part of the fuel charge is being sucked out the exhaust.

:cheers:

[curtbriggs]

Also, is this correct, in the VE table, adjusting the numbers smaller leans the AFR, and in the "commanded fuel in open loop" table, adjusting the numbers higher gives higher A/F ratio (leaner) ... this correct ??


It's my understanding that:
Adjusting VEs up, adds fuel. High VE tells the PCM, the cylinder has more O2.
Adjusting VEs down, subtracts fuel. Low VE, tells PCM there's less O2.

Curt

[caver]

At low speeds, larger camshafts make the engine less efficient (poorer VE) as part of the intake charge is sucked back out through the exhaust valve because of the amount of overlap. The sensor will see less oxygen (because more fuel molecules are in the exhaust) and therefore try to reduce fuel.

The problem is when the engine is cold therefore in open loop so the oxygen sensors are being ignored.

[SSbaby]

An extract from LS1Holden forum...


I made some changes to the [Commanded Fuel when in Open Loop PID {B3065}. These are a part of my current settings for that PID, the rows correspond to temperature rows of 0*, 10*, 20*, 30*, 40* and 50*...



0* 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.88658 0.865596 0.845582 0.845582 0.845582 0.845582
10* 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.909414 0.88658 0.865596 0.845582 0.845582 0.845582 0.845582
20* 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.92922 0.906997 0.885813 0.885813 0.885813 0.885813
30* 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.92922 0.906997 0.885813 0.885813 0.885813 0.885813
40* 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.92922 0.906997 0.885813 0.885813 0.885813 0.885813
50* 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.952558 0.92922 0.906997 0.885813 0.885813 0.885813 0.885813

I'm suspecting I'm running a bit too lean on the after-start enrichment. As soon as I fire up the engine I don't normally let it idle, I drive off slowly while not exceeding 2000rpm for the first 5-10mins until warm. During this warmup period, I experience a doughy response from the engine... a bit like its on the power and off. It never happens once the engine warm.

What I have done to compensate is increased enrichment for Initial Coolant Temp Enrichment {B3632} and the problem appears to have been addressed without introducing a dip in revs... and without compromising the idle quality. Although, it's slightly warmer today than yesterday evening.

Have others experienced the same symptoms on cold startup? :?

[dfe1]

It's my understanding that:
Adjusting VEs up, adds fuel. High VE tells the PCM, the cylinder has more O2.
Adjusting VEs down, subtracts fuel. Low VE, tells PCM there's less O2.

Curt VE changes do not have a DIRECT effect on O2 readings. When you alter an entry in the VE table, you're essentially telling the PCM that the engine is using more or less air, (depending on whether you increase or decrease VE) and to adjust fuel flow accordingly. A higher VE doesn't "tell" the PCM that a cylinder has "more O2", it simply tells the PCM to increase fuel flow. The O2 sensors monitor exhaust gas oxygen content and tell the PCM about the level of O2 in the exhaust stream. Whether VE changes increase or decrease O2 voltages depends on the relationship of the original value to actual air/fuel ratio. In the majority of cases, increasing a VE value, results in a richer mixture, and consequently increased O2 voltage. But not always. As an example, if an enigne is running exceptionally lean and misfiring intermittently, increasing VE can actually result in lower O2 voltage. (More efficient combustion results in lower levels of unburned or partially burned fuel, an higher oxygen levels in the exhaust.) Also note that in closed loop, changes in VE will have a minimal effect on O2 readings because most of the alteration in fuel flow will be trimmed out as the PCM tries to maintain stoichiometry.

[SSbaby]

Btw, these are my VE settings and other calibrations for a cammed application... I have a great idle that doesn't hunt the moment I drive off: :)


Cam:
224/224 110 lsa .537"

Induction:
MAFless/GTS MAF pipe

Idle Speed:
900rpm

IAC counts:
20

Idle Airflow (ECT):
ECT (C) -40 -28 -16 -4 8 20 32 44 56 68 80 92 104 116 128 140
Airflow (g/s)20 18.5 17 15.5 12.099609 10.200195 10.099609 9.900391 8.599609 6.799805 6.299805 5.700195 5.700195 5.700195 5.700195 5.700195

Idle Airflow Parked (IAT):
IAT (C) -40 -20 0 20 40 60 80 100 120 140
Airflow (g/s)33 28 23 21 19 14 10 8 8 8

VE (0-1200rpm):
MAP (kPa) 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105
400 (RPM) 37.000430 38.270523 39.540615 40.810708 42.080800 43.350893 44.620985 45.891078 47.161170 48.431263 49.701355 50.971448 52.241540 53.511633 54.781725 56.051818 57.321910 58.592003 59.862095
800 (RPM) 40.634972 41.785244 42.935517 44.085789 45.244050 46.394322 47.544595 48.694867 49.845139 50.995412 52.145684 53.295957 54.454217 55.604490 56.754762 57.905035 59.055307 60.205579 61.355852
1200 (RPM) 43.598521 44.716841 45.835162 46.961470 48.079791 49.198111 50.316432 51.434752 52.561060 53.679381 54.797701 55.916022 57.034342 58.152663 59.278971 60.397292 61.515612 62.633932 63.752253