I was under the impression that open loop is when the car is cold. Once warmed up it would go into closed loop and stay. Does a car go in and out of closed loop throughout a run?

I put a heated O2 in a month ago and I'm looking for a reason why I'm always running rich.
Anything other than the O2 or CTS that can cause it to run rich?

 

Typically once the ECM goes into closed loop it stays in closed loop. Although PE mode is not true closed loop. But the ECM will immediately return to closed loop upon existing.

Can also have open loop during lean cruise and during deceleration.

What is it that makes you think that it is running rich in closed loop?

During closed loop the exhaust AFR is controlled via feedback from the O2 sensor. So even if another sensor reading is off, it is all on the O2 value.

RBob.

 

thanks for the reply bob.
At cruise I've noticed a couple of things
1) When I'm accelerating (not hard, just normal at cruise) my WB jumps up to 17/18. When I decelerate is jumps back down to about 13???

2)At cruise again the car is going in and out of CL. When it is in closed loop my BLM's are 108-110. So its definetly running rich

The O2 doesn't appear to be going over the crossover of .500volts. I'm assuming its either because of the rich condition or that o2 is fouled.
Its a heated o2 and was new within the last couple of months.

My WB is the LM-1 and I'm still using the orginal Bosch sensor that came with it. About 1 1/2 old.

I was going try going back to the orginal o2 to see what that does and also ohm out the CTS. (btw- what should that ohm out to?)

does it sound like I'm going in the right direction? any others reasons for going rich?

Fuel pressure is 43 and using 28lb injectors

 

The fluctuating AFR is normal. During light throttle acceleration there probably isn't any AE, which is why the AFR jumps up. As long as it isn't causing hesitation or backfiring out the intake. It is nothing to worry about.

During decel, the AFR drops as additional fuel is being taken from the head runners. Again, completely normal. IAC throttle follower and DE can be used to control how rich it spikes if HC emissions are too high during this time.

> At cruise again the car is going in and out of CL.

Is the ECM going into lean cruise mode? Is the throttle position so low that open loop decel mode is being used?

> The O2 doesn't appear to be going over the crossover of .500volts.

It should if it is in closed loop. During closed loop cruising the O2 value should oscillate. Let me see if I have a screen shot here. Yep, here is a good one. Note the crossing rate is faster at the higher engine speed.

Then does a rich swing on the throttle lift. Then as cruise resumes at a lower engine speed the crossing rate decreases.

The 108-110 BLM means that the VE tables are still high. Some additional VE Learns should take care of that. Also note that the fuel composition changes throughout the year. So that too will affect the BLM values.

RBob.


{edit: picture won't attach as it is already in another thread. See this link:

https://www.thirdgen.org/forums/diy-...-progress.html

}

 

I'm gonna start with this one.
How do I know if I'm in lean cruise mode?
The TPS is set at .54 and what is OL decel mode?
thanks


FYI- I did find LeanCr on my WUD screen and noticed that it is going in and out of that mode. Is LN in the analysis screen the same thing? Is there a way to lock that out?

 

> How do I know if I'm in lean cruise mode?

The LeanCr indicator on the main display. Other ways to tell is that the commanded AFR goes lean, INT locked at 128, and learn is off. And the O2 NB value drops below 100 mV. Set the MPG threshold high to disable.

>The TPS is set at .54 and what is OL decel mode?

OL decel is when the vehicle is moving and the throttle is closed. The ECM can revert to open loop to prevent surging from proportional gains and/or fuel trim making the AFR too lean. It is selectable via an option flag. Usually set in the EBL calibrations.

LN is learn mode for the long term fuel trim (BLMs). The EBL_WhatsUp.html doc covers the data in the analysis display and the log dump file.

RBob.

 

HI guys, one other thought. What about "Highway Mode" I recall seeing my BLM's lock at 128 during periods of highway cruising, and thought this was likely to be attributed to Highway Mode being active, where after a ceratin conditions are met, then the AFR ratio is looked at and brought up to a predetermine level, higher than 14.7 as a fuel savings control.

Yes, I know GM was forced to abandon the practice, (cheating the CAFE numbers?) but the code is still there on an $8D mask.

I turned mine off temporarily by raising the minimum speed to a ridiculous number. (200mph) That way I could get more data points collected for my VE tables without it kicking in and hampering that process.