Frank@Work

While in Closed Loop mode the DME uses input from the stock O2 sensor to keep the AFR at 14.7:1. The initial amount of fuel injected comes from a fuel mapping. For optimum driveability it is best that the initial amount of fuel injected results in an AFR 14.7:1 or as close as possible.

Correct?

Is it wise to put the system in Open Loop mode while adjusting idle and cruising fuel maps?

This way I hope to accomplis that the initial amount of fuel injected while in closed loop mode results close to an AFR of 14.7:1.

It seems smart to me, but am I overlooking something?

Mike S

Nope, you're on the right track. I found boost comes on a bit earlier too with an A/F ratio of around 13:1 in the 2-3k rpm range. Most of my cruising is around 14.7:1.

Frank@Work

Thanks!

Laust Pedersen

If the “electronic acceleration pump” (fuel addition with rapidly increasing throttle position) is inadequate it may be an advantage to set the base-map slightly rich. Maybe that’s what Mike S is seeing.

Laust

Frank@Work

Yesterday I had some time to do the tuning on the fuel maps. I did all the tuning op "open loop" mode. I must say that the result is very good!

A great advantage of working in open loop mode is that an adjustment at a specific cell gives the wanted result. Before, tuning in closed loop mode, the AFR was all over the place and it was hard to determine what to change at a specific cell. In open loop I got an almost flat line for the AFR.

If I had known this half a year ago I think I wouldn't have burned as much fuel as I did (@ app. $ 1.60 per liter ).

Thanks again!

Lorenfb

"Is it wise to put the system in Open Loop mode while adjusting idle and cruising fuel maps?
This way I hope to accomplis that the initial amount of fuel injected while in closed loop mode results close to an AFR of 14.7:1."

This is correct. If you're not as close as possible to AFR=14.7, i.e. too low or to high,
then the Lambda system will never be able to function properly. It only has so much
range that it can correct the mixture in. This is in contrast to an OBDII system which
whiich can "adapt" and change the injector pulse width to lean or richen the mixture
if the AFR puts the O2 sensor out of range.

hally

so are people disconnecting the o2 sensor to trigger open loop. I remember some disagreement on this the last time that this came up.

Lorenfb

Disconnecting the O2 sensor is not that problematic, if running without a CAT and the
car doesn't have to pass an emissions test and the AFRs are set properly via the fuel
maps under most/all loads. Remember, at WOT the O2 sensor is ignored, anyway.

hosrom_951

I unplugged the stock O2 sensor because it failed and started giving me mis-firing on idle. Runs smoother now and yes, at WOT the O2 sensor is ignored.

hally

I just re-read Laust and Thomas posts on this thread:
https://rennlist.com/forums/showthre...+sensor+unplug
To quote thomas,
so to me it sounds like the DME is still theoretically operating in closed loop when the o2 sensor is diconnected, but because it is getting a stoich fake signal, there are no adjustments to do, so therefore it should allow you to tune PT and idle.

Lorenfb

"so to me it sounds like the DME is still theoretically operating in closed loop when the o2 sensor is diconnected, but because it is getting a stoich fake signal, there are no adjustments to do, so therefore it should allow you to tune PT and idle."

No, he's wrong. Without the O2 sensor connected, the DME has an internal voltage
bias of about .50 volts. This is the center point for a switching comparator in the
DME. Any voltage greater than .50 volts causing the DME to lean the mixture, &
any voltage less than .50 volts causes the DME to richen the mixture. The DME
takes progressive steps in either richening or leaning the mixture until the comparator
switches back or until the DME reaches its' max lean/rich correction state.

Bottomline: The DME is NOT in a closed-loop mode without the O2 sensor, i.e. there's
no feedback element to control the AFR. It's running in a open-loop servo mode. If the CO (AFR)
changes for some reason, e.g. small increase in fuel pressure, there's no correction
of the CO back to the ideal Lambda of 1.0 (AFR=14.7).

The DME doesn't know about any AFR or ANY AFR change without feedback, the O2 sensor.
Also, while in closed loop, any fuel map value which forces the AFR from 14.7 is "pulled back"
and has no effect. Obviously, if the fuel map value exceeds the O2 correction range,
then the AFR is no-longer maintained at 14.7.

Check out the O2 graphs on this web site for more info ( www.systemsc.com/graphs.htm ).

hally

My point was that the DME is getting feedback, a feedback of 0.5v regardless of AFR.
Closed loop algorithm executed on a 0.5v signal == open loop observable behaviour. Don't think anything that you said contradicts that by Thomas or Laust in the other thread.

Lorenfb

"My point was that the DME is getting feedback"

No, by the definition of feedback, i.e. there is none without a feedback element.
The bias voltage is NOT feedback. The 8051 is in the "don't care" state unless the
comparator switches one way or the other, i.e. the rich or lean state.

A better term to use would be to say that it's in the neutral (non-feedback) state.

"Closed loop algorithm executed on a 0.5v signal"

No, it's not in a closed loop algorithm. A closed loop algorithm has "if then branch" statements,
"increment"/decrement" statements, & etc. The disconnected O2 causes the u-processor
to bypass the closed-loop algorithm.

awilson40

I think you guys are arguing over a matter of definitions.
Hally... closed loop , in any electronic system, means feed back of somesort.
Without an O2 sensor, there is no feedback. Now...does removing the O2 sensor 'trigger'
a Non closed loop sitiation... no, not really, The bias voltage just holds the comparitor centered.
So no changes occur and the system runs off the 'unadjusted' maps.
You can place a 1.8K resistor in place of the altitude switch and trigger the ROW maps which operate in open loop as the ROW cars dont have Cats.But you would have to adjust a different set of maps than the USA maps.

toddk911

I remember reading in here a LONG time ago that it was suggested to just disconnect the O2, especially if you were running aftermarket chips etc.

Is there any benifit to running W/O the O2 even if not a tuning situation?