mark944turbo

Is there a way to tell at what times the DME is in closed loop and what times it is in open? Such as hooking a multimeter up to a certain wire on the DME? I suppose I could just compare a run with the o2 sensor to a run without one, but that would be more difficult.

My reason for asking is im trying to figure out which partial throttle situations I need to tune and which are controlled by closed loop anyway.

Thanks!

Also, I know this must be possible somehow because vitesse's mo-monitor has this output.

fast951

The MoMonitor reads its data from the custom chip, where the DME code was rewritten.

mark944turbo

In other words its impossible with instruments avaiable to me for cheap, damn.

Laust Pedersen

You can install a switch on the O2 wire on its way to pin 24 (please check for correct pin number) and measure between the sensor and switch. When the switch is off, you are always in open loop mode. When it is on, the DME decides.

Laust

UK952

Narrow band hooked into the factory O2 sensor - How you planning on tuning your part throttle?
Tony

mark944turbo

Could you expand on that reply a little? I cant make out the meaning.

UK952

Well if you put a narrow band air fuel guage (such as an autometer) hooked up to the standard O2 sensor it will scan back and forth in closed loop mode when you hit open loop - hopefully - it will show rich.

The 2nd part was a question on how you were planning on tuning your part throttle mixture as I couldn't see an obvious way in your list of mods. However looking again is guru stage 1 a Map kit with link?
Tony

mark944turbo

I see what you mean now, I was just thinking more along the lines of a light that lights when in closed loop and doesnt in open, but oh well, I will just tune everywhere close with the o2 sensor unplugged, then plug it back in, that solves all problems.

Thanks for the idea,yes I am using the link hand held programmer to tune.

hally

Hi Mark i am thinking that that approach might be flawed, as if o2 sensor is unplugged i believe the DME gets a "i'm running lean" voltage and therefore increases fuel delivery when in closed loop. (someone please correct if wrong). Your tuning efforts would then be corrupted.

edit - Mark what u read is probably right, i could be getting confused with the typical o2 sensor failure behaviour.

mark944turbo

Hally, Im not saying you are wrong but that theory goes against what I have read. Anyone else have a definate answer? I dont really feel like tapping into the o2 wire to check.

Laust Pedersen

Hally & Mark,

In the process of debugging what turned out to be a broken wire to the O2 sensor (not the heating wires) I discovered that the voltage at the DME was about 0.5V (or stoichiometric). With a switch now installed (just before the DME) and in off position I have also observed that the O2 meter shows max rich (=1V) at start-up and stoichiometric when the switch is on also at start-up.

From this I believe that the DME generates a high impedance 0.5V signal, which is used in case of disconnect (i.e. no fuel correction) and which also is easily overwritten with the lower impedance O2 sensor signal when it is connected.
In other words the closed loop feature can be disabled, with no other side effects, by unplugging the O2 sensor.

mark944turbo

Glad to hear it, thanks laust. BTW, what is happening with your car? Are you going to rebuild the engine and keep trying to run high boost? Im copying most of your ideas but im stil waiting on Dannos high boost chips to arrive.

UK952

This has just triggered my memory, the UK cars with no cat (and no O2 sensor) have a link in the plug (at the back of the cylinder head where the O2 sensor normally goes) not sure which pins are linked though.
Tony

Tomas L

As Laust says, when you unplug the O2 sensor the DME has a "fake" signal that corresponds to stoichiometric A/F. In countries where it wasn't required, a 951 could then be delivered without O2 sensor. You should not bridge the O2 sensor input when you disconnect it, then you will short out the default signal causing the DME to interpret it is as a lean condition.

awilson40

Actually , In countries that dont require a converter, a 'Coding' plug is used which selects the ROW fuel map which doesnt use the O2 sensor. The O2 sensor signal is then shunted to ground via a plug that fits the sensor connector.
If you unplug the O2 sensor without using the coding plug on the DME, then you will be running off USA maps and running open loop. This way you should not shunt the O2 sensor.