LPG ECU not connectoed to Lambda sensor

[DariusVargas]

Hi!

It's me again with my 2003 3.0 SType, with an aftermarket fuel return fitted. lpg kit: AC Stag 300 isa 2

very quick question. my LPG ECU is not connected to the pre cat lambda sensors.
Any disadvantages or advantages?
Should i go ahead and connect them now? and add them in the interface (i got the cable and software yay)

many thanks!
btw, one of my catalytic convertors is on its way out. (installed a spacer/extender on the aftercat sensor to fool the computer and graphs look ok)

[Brian_H]

There is generally little point in connecting them with most sequential systems, they are only showing information anyway in that sort of setup. You should calibrate using the displayed fuel trims on that kind of setup.

A single point closed loop system would need them (or at least a lambda feed from a sensor), but thats not what your using.

[DariusVargas]

thank you brian!
so i understand there is no real point in connecting them for this lpg kit.

now i want to bother you with another silly question if i may...
i will attatch a picture below with the cylinder numbering for these s types.
on the left side, we have the numbering and fire order for the old s types, and on the right side, for the newer s types (the one that i have)

my installer used the old (left side) diagram when he installed my kit, instead of using the right side diagram, which coresponds to my model.
I have also found the AC Stag leads diagram/description paper too (second attachment) where each petrol injector has its own colored wires and number.

so for example, green wires that correspond to petrol injector 2, were connected to 3 and so on ( i attached a picture to see better).

should i go ahead and redo the connections, or is it the same thing, being just a different numbering?
i guess the right question is: does the LPG ecu expect the colored cables to deliver signal from the exact petrol injectors as described in the stag lead? thank you

[Brian_H]

It doesn't matter which number cylinder is connected to which number injector on the loom. What does matter, is that the same injector is wired to the matching petrol cylinder injector wiring and manifold spud. This usually means matching the colour of the wire where it connects to the petrol loom to the corresponding lpg injector colour. Firing order makes no difference. Not sure on Stag, but some will allow you to also assign cylinders to a bank as well.

[DariusVargas]

Hi! Im Back with news

I have connected my sensors to my ecu.

Could you please help me with the necessary software adjustments? Is it only the selection of the lambda sensor type and then autocalibration?

My stag sfoftware displays 3.49 volts at the lambda readings.

I will attach pictures with the cables that i tapped into and the software.

Many thanks

[LPGC]

The Jag probably has wide band lambda sensors. Voltage readings from wide-band sensors are fairly meaningless, there's no point trying to connect an LPG ECU to them or take voltage readings from them, the best way to see mixture readings on a vehicle equipped with wide band probes is live data readings using an OBD scan tool.

Wide band probe readings are meaningful to the vehicle ECU because the vehicle ECU knows how much it is controlling the 'pump' on the wide band sensors but the LPG ECU cannot see the 'pump' data.

[DariusVargas]

Ok, thank you! I will select not connected then.
Should i bother disconnecting them?
My cheap elm327 doesnt see the upstream sensors, i believe i need something more sophisticated.

Regarding the mixture readings, do you mean the fuel trims?
Thanks!

[LPGC]

If an OBD reader can see rear sensors it can usually also see front sensors.

With wide band sensors the reading you want may not be under the usual (front/S1) heading, if you look at lambda sensor readings directly you may just see a milliAmp current reading... The reading you want may be under a heading such as 'Equivalence ratio'. Equivalence ratio of 1 would be stochiometric (correct 14.7:1) mixture, less than 1 rich, higher than 1 lean.

[DariusVargas]

Thanks a lot!
Yes i did some research and they are wide band.
Should i disconnect them?
Or are they uego?
If they are uego, i should connect the lpg ecu in series to them.

[LPGC]

I would disconnect them.

There is more going on with wide band / UEGO probes than my simple 'pump' explanation above. Still in simple terms but with a bit more detail... We could think of it as a normal probe except it has a tiny air pump attached, with a stochiometric mixture the normal probe part of the unit might give a 0.5V signal and the pump might be getting 0 Amps, as the mixture changes the electronics in the petrol ECU try to maintain the 0.5v reading by applying electrical current to the pump... so for example if the reading becomes 0.8v (rich mixture) the electronics might pump air into the unit (say 0.2mA of current to the pump) to try to bring the 0.8v reading back down to 0.5v, the amount of pump in effect adjusts the probe's air reference and the pump can work in reverse (be operated with a negative polarity current such as -0.2mA). The voltage reading doesn't say much about mixture without knowing the pump current but also the pump current doesn't tell the full story about mixture without knowing the voltage reading. The chip that controls the wide band probe in the engine ECU can fairly quickly 'home in' on an actual mixture reading (from being a bit lean to rather rich) and can even be fairly accurate in some situations when the voltage reading isn't 0.5v, where-as if you wire-in just something that monitors pump current and presumes voltage reading is 0.5v it won't give as accurate a reading (or be as accurate as often, particularly during changing conditions / throttle position changes etc) as the reading from the ECU.

Better to monitor the probe reading using a scan tool. Some engines even have 'command lambda' which is the mixture that the ECU is aiming to achieve for the current engine load conditions. Usually command lambda is very close to 1 but in some idle conditions it may be (say) 0.998 to achieve a bit smoother idle, or during low load cruise it may be 1.002 to maximise fuel economy, during high load enrichment conditions it may be (say) 0.87. With a separate scan tool you can monitor command lambda (if featured) at the same time as wide band readings, post cat lambda readings, perhaps even exhaust gas temp readings and cat temp readings on some vehicles.

Said before that most LPG autocal functionality won't work properly on an engine that normally runs a return-less petrol system and features a petrol pressure sensor (not that they give good results on any other engine lol). This is even more true regards setting proper calibration for high load enrichment conditions.

[DariusVargas]

amazing information simon, thank you!!! i saw the 0.998 and 1.002 readings and i was wondering what those mean as the numbers are so accurate. now i understand.

and so i disconnected those cables connected to the uegos. And for others reading this stag related stuff, i read the instructions and there apparently is no need to choose/connect uego in the stag software, because wiring would be done in series on only one senosr (AKA on only one bank) and this is a V engine.

i wont bother you on this tematic as i understood. im glad we discussed this topic.

i will update on my mixtrue readings on the other topic as i have news.