Rich at idle after cam
05-12-2004, 08:11 AM
#21
There could be a couple things coming into play.
On a free flowing exhaust (read: large and unrestrictive) the overlap of the cam will jet fresh air into the exhaust if a large enough cam is idled low enough. The fresh air entering your exhaust raises the oxygen content of the exhaust gases. As a result your O2 wideband will indicate leaner than the actual a/f.
Additionally, the slow moving exhaust gas at idle and reversion (the exhaust gases actally move towards and away from the motor repeatedly as they make their way down the exhaust) can give your O2 sensor a bad sample of what is actually going on in the exhaust.
Where you have mounted your wideband will determine how sensitive and accurate it is at the lower exhaust flows.
Bomax: There are a couple things that you can do.
1) Put the car in full open loop and move your entire IFR table up about 15%. This will park your a/f right around 13.5 at idle. Compensate at WOT with the PE table for this shift.
2) You may be hung up on the Open Loop A/F Table. Move this down in the section that you are having problems with to lean the car out. The car references which a/f is lower between the lambda table (OL A/F Multiplier) and the PE table. See if that helps.
3) Injector Offset. Most likley you are using larger injectors. I haven't looked at your setup, but if you have larger enough (or shitty enough) injectors, then you won't be able to close them past their min pulswidth. As a result, you will be stuck with the a/f that you have in the lowe air flows. This problem is usually complimented by gurgling and popping whenever you get off the gas. This problem can be slightly compensated by playing with the injector offset table, but usually results are minimal.
Good Luck
On a free flowing exhaust (read: large and unrestrictive) the overlap of the cam will jet fresh air into the exhaust if a large enough cam is idled low enough. The fresh air entering your exhaust raises the oxygen content of the exhaust gases. As a result your O2 wideband will indicate leaner than the actual a/f.
Additionally, the slow moving exhaust gas at idle and reversion (the exhaust gases actally move towards and away from the motor repeatedly as they make their way down the exhaust) can give your O2 sensor a bad sample of what is actually going on in the exhaust.
Where you have mounted your wideband will determine how sensitive and accurate it is at the lower exhaust flows.
Bomax: There are a couple things that you can do.
1) Put the car in full open loop and move your entire IFR table up about 15%. This will park your a/f right around 13.5 at idle. Compensate at WOT with the PE table for this shift.
2) You may be hung up on the Open Loop A/F Table. Move this down in the section that you are having problems with to lean the car out. The car references which a/f is lower between the lambda table (OL A/F Multiplier) and the PE table. See if that helps.
3) Injector Offset. Most likley you are using larger injectors. I haven't looked at your setup, but if you have larger enough (or shitty enough) injectors, then you won't be able to close them past their min pulswidth. As a result, you will be stuck with the a/f that you have in the lowe air flows. This problem is usually complimented by gurgling and popping whenever you get off the gas. This problem can be slightly compensated by playing with the injector offset table, but usually results are minimal.
Good Luck
05-13-2004, 01:44 PM
#22
In response to #3: Using the Open Loop A/F table, I was able to get open loop idle to 13:1, which was my goal. However once the car is warmed up (closed loop) it goes back down to a 11.5:1 ratio at idle. So I know my injectors are able to deliver a small enough amount of fuel (SVO 42#) to be at the A/F I want at idle.
I will play around with the table some more.
I will play around with the table some more.
05-13-2004, 02:13 PM
#23
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Idle exhaust heat output does not keep the O2s
hot enough to be real, against higher header heat
shedding.
Output voltage droops (indicating lean falsely) and
reacts slowly if at all to mixture change by the PCM.
Running O2 heater power continuously might fix
this, but I believe you will see heater codes if the
PCM has to apply heater power longer than it likes,
or if applying heater power does not suffice to get
"live" sensor action. I'm still a bit unclear on this
aspect of things (whether PCM will reapply heater
power on its own after warmup, if O2 output turns
unresponsive, and what the heater code conditions
are).
hot enough to be real, against higher header heat
shedding.
Output voltage droops (indicating lean falsely) and
reacts slowly if at all to mixture change by the PCM.
Running O2 heater power continuously might fix
this, but I believe you will see heater codes if the
PCM has to apply heater power longer than it likes,
or if applying heater power does not suffice to get
"live" sensor action. I'm still a bit unclear on this
aspect of things (whether PCM will reapply heater
power on its own after warmup, if O2 output turns
unresponsive, and what the heater code conditions
are).
