Lambda connected?

[colin33]

I have a King AEB system in my 2.5 V6 Vectra. A while back, it started losing power and stuttering when starting from hot, just for a few seconds, but it was annoying and slightly dangerous when pulling out of a garage for instance. I cut both lambda sensor wires, so the sensors were disconnected from the lpg system. This seemed to cure the problem, unless it was just coincidence and it cleared itself! Does my lpg system need these lambda sensors to be connected permanently in order to continually monitor/change the fuel trims, or does my system just follow it's original calibration?
Just wondering whether I should reconnect them....

[Brian_H]

If you've got access to the diagnostic software for the king ecu check what its showing voltage wise with them disconnected - My elderly Landi Renzo Omegas shows .35v on them when they aren't connected at all anymore, which seemed to be part of some issues i was having though only 1 of a few faults causing issues.

They aren't needed if its a multipoint, its only there to make the mapping "easier", the trim adjustments would be done by the petrol system anyway, all the gas ecu does is alter the petrol injector timings to suit the gas injection for the same amount provided the mapping is right.

If its working and they are off I'd leave them that way personally.

[Tubbs]

Did I not have a look at this in a car park in Cornwall years ago ? It had the k line connected anyway as I remember. Mind you I could be wrong

[colin33]

Hi Tubbs yes we connected the Lambdas then but i disconnected them a few days later.

[colin33]

They aren't needed if its a multipoint, its only there to make the mapping "easier", the trim adjustments would be done by the petrol system anyway, all the gas ecu does is alter the petrol injector timings to suit the gas injection for the same amount provided the mapping is right.
.

Do the lambdas effect the mapping of the petrol ecu then as it's being driven?

[Brian_H]

They aren't needed if its a multipoint, its only there to make the mapping "easier", the trim adjustments would be done by the petrol system anyway, all the gas ecu does is alter the petrol injector timings to suit the gas injection for the same amount provided the mapping is right.
.

Do the lambdas effect the mapping of the petrol ecu then as it's being driven?

Yes - The petrol ecu will use the pre-cat lambda sensor data to adjust the fuel trims (the first set in the exhaust after the engine end). Hence why if the sensor(s) fails or gets contaminated the car doesn't run properly though sometimes this is more noticeable than others.

Putting voltage that shouldn't be there will obviously do the same thing - the petrol ecu won't always pick up a failed sensor, and just keeps trying to adjust till it hits its limits.

If you want to find out then theres 3 ways to see if the failure mentioned before is the case
1) Put a multimeter between the cut end of the wire and a ground point - any significent voltage seen is not a good sign
2) Check the reading in the software itself (lpg software)
3) Reconnect it and check using the obd socket to view live data.

2 is probably easiest if you have the software. But surely if its working best to leave it as it is (the sensor wire does nothing beneficial to the lpg system, its only there for information anyway)

[colin33]

They aren't needed if its a multipoint, its only there to make the mapping "easier", the trim adjustments would be done by the petrol system anyway, all the gas ecu does is alter the petrol injector timings to suit the gas injection for the same amount provided the mapping is right.
.

Do the lambdas effect the mapping of the petrol ecu then as it's being driven?

Yes - The petrol ecu will use the pre-cat lambda sensor data to adjust the fuel trims (the first set in the exhaust after the engine end). Hence why if the sensor(s) fails or gets contaminated the car doesn't run properly though sometimes this is more noticeable than others.

Putting voltage that shouldn't be there will obviously do the same thing - the petrol ecu won't always pick up a failed sensor, and just keeps trying to adjust till it hits its limits.

If you want to find out then theres 3 ways to see if the failure mentioned before is the case
1) Put a multimeter between the cut end of the wire and a ground point - any significent voltage seen is not a good sign
2) Check the reading in the software itself (lpg software)
3) Reconnect it and check using the obd socket to view live data.

2 is probably easiest if you have the software. But surely if its working best to leave it as it is (the sensor wire does nothing beneficial to the lpg system, its only there for information anyway)

Ah, thanks for that. I have to tell you about the other factors involved here. Firstly, I don't have a cat anymore, just a straight through pipe. Also, a few weeks ago I replaced the inlet cams with a set from a 3.0 Omega engine. With these cams fitted in theory, my engine BHP should've been upped from 167 to 192 bhp. This new cam set up is identical to the GSI model Vectra.
The problem is, I don't notice any difference at all in power or torque since fitting the cams.
I presume this is because the mapping needs modifying to suit the new cams? Hence my question about the lambdas, and whether they automatically adapt to the the new engine set up?

[Tubbs]

It can adapt itself to a certain extent. But perhaps your new 'lary' cans could be affecting it. Personally I would take the gas system out the loop for a bit and see if the petrol ecu corrects itself. You had a Vauxhall code reader that did live data as I remember ? So you should see if the fuel trims (correction) is at a vaguely normal level after a bit of just petrol. After that switch to gas and see if the fuel trims are vastly different on gas. It's only got a certain amount of correction.

[LPGC]

The problem is, I don't notice any difference at all in power or torque since fitting the cams.

Would think peak bhp would be a bit higher at the expense of bottom end torque?

[colin33]

The problem is, I don't notice any difference at all in power or torque since fitting the cams.

Would think peak bhp would be a bit higher at the expense of bottom end torque?

Original spec is 167 bhp, 230NM torque.
With the cams it should be 192bhp, 262NM torque.

Perhaps I will only notice this difference if the ECU is remapped?
If so, if I get the petrol ECU remapped will the LPG ECU adjust itself accordingly or should this be redone as well do you think?

[colin33]

It can adapt itself to a certain extent. But perhaps your new 'lary' cans could be affecting it. Personally I would take the gas system out the loop for a bit and see if the petrol ecu corrects itself. You had a Vauxhall code reader that did live data as I remember ? So you should see if the fuel trims (correction) is at a vaguely normal level after a bit of just petrol. After that switch to gas and see if the fuel trims are vastly different on gas. It's only got a certain amount of correction.

Yes Tubbs, I've got the gear, I just don't know how to use it!
I did run it for a couple of days on petrol after I put the cams in but I'm not sure this changed anything. The only difference I've noticed since the cam change is that when running on LPG, I have to change down gear more often as it doesn't like pulling away in higher gears now. Still fine on petrol though...