Cold Air Feed Induction Kits K&N Type

[Laird Scooby]

Originally Posted by mhuk

I have however found the O2 sensor was screwed in about half way so not getting a good reading from the exhaust flow? I cleaned the boss up and waiting for the M18 1.5 die to come so i can clean the sensor up because it's been rammed in the hole.

That means it has no earth. There are 3 wires on the 940 Lambdas, two are the heater, the third is the sensor output. The heater has its own feed and earth, the sensor only has an output wire, the earth being the sensor body. Make sure the Lambda boss in the exhaust itself doesn't have a chewed thread or you'll be on a hiding to nothing.

The output is only 1V at the most and in practice, should rarely get near that. When the sensor is cold, the output is zero but as it heats up, the zirconia element heats up and reacts generating a voltage between 0.0 - 1.0V depending on the oxygen content in the exhaust. From this the mixture can be determined. At about 0.45V output, the mixture is stoichiometric - the theoretically perfect mixture of 14.7:1 air:fuel. As the mixture goes lean, the voltage drops so the ECU adds more fuel to bring it back up again. As it goes above 0.45V because the mixture is richer, the ECU reduces the amount of fuel to bring it back down again and so this cycle goes on.
If a Lambda sensor fails, it always fails with no output or if it's failing, the output is reduced. As such, the ECU is always trying to make the mixture richer until it finds it can't and then it throws a fault condition lighting the MIL and the fault can then be read.

Not having an earth on the Lambda sensor case because of a damaged thread could cause the mixture to be permanently too rich!

[940volvoman]

Which are the breather tubes that need clearing?Presumably that's part of the PCV system?I've had Fiats in the past that have needed cleaning,but I've often wondered about cleaning the 940 system. I can start a new thread if required...

[Laird Scooby]

Originally Posted by 940volvoman

Which are the breather tubes that need clearing?Presumably that's part of the PCV system?I've had Fiats in the past that have needed cleaning,but I've often wondered about cleaning the 940 system. I can start a new thread if required...

https://www.volvoforums.org.uk/showthread.php?t=257245

That's just one thread on it all - there are loads! As yours is a turbo, there won't be any form of mesh inside the flame trap and Volvo refer to it as a nipple instead but it performs the function of a flame trap so the jury has been out on that for a long time now.

[mhuk]

Originally Posted by Laird Scooby

That means it has no earth. There are 3 wires on the 940 Lambdas, two are the heater, the third is the sensor output. The heater has its own feed and earth, the sensor only has an output wire, the earth being the sensor body. Make sure the Lambda boss in the exhaust itself doesn't have a chewed thread or you'll be on a hiding to nothing.

The output is only 1V at the most and in practice, should rarely get near that. When the sensor is cold, the output is zero but as it heats up, the zirconia element heats up and reacts generating a voltage between 0.0 - 1.0V depending on the oxygen content in the exhaust. From this the mixture can be determined. At about 0.45V output, the mixture is stoichiometric - the theoretically perfect mixture of 14.7:1 air:fuel. As the mixture goes lean, the voltage drops so the ECU adds more fuel to bring it back up again. As it goes above 0.45V because the mixture is richer, the ECU reduces the amount of fuel to bring it back down again and so this cycle goes on.
If a Lambda sensor fails, it always fails with no output or if it's failing, the output is reduced. As such, the ECU is always trying to make the mixture richer until it finds it can't and then it throws a fault condition lighting the MIL and the fault can then be read.

Not having an earth on the Lambda sensor case because of a damaged thread could cause the mixture to be permanently too rich!

Very interesting read. I will have a look tomorrow. I already run a tap down the boss and it's all good now. It was awful and the PO had ram the sensor in. I only found it lose when losing the sensor cable and heard knocking.

Thank you :-)

[TonyS9]

Originally Posted by Laird Scooby

As long as the thermosttic air intake valve on the air cleaner is working correctly, the best economy will come from leaving it all as Volvo intended. It will only make a difference on tuned engines and even then the biggest restriction is the MAF so unless that has been changed, a CAI kit won't make much difference to either the performance or economy but might make it run rough due to colder air on idle and the pulses of air not being damped by the air cleaner housing.

There is no thermostatic air flap on a 940, such things are mainly for carb icing although some early injection systems like LE have them. LH doesn't use inlet heating, although there is a breather heater for the PCV pipe and the AFM uses a heater to determine air flow.

[TonyS9]

Originally Posted by Laird Scooby

That means it has no earth. There are 3 wires on the 940 Lambdas, two are the heater, the third is the sensor output. The heater has its own feed and earth, the sensor only has an output wire, the earth being the sensor body. Make sure the Lambda boss in the exhaust itself doesn't have a chewed thread or you'll be on a hiding to nothing.

The output is only 1V at the most and in practice, should rarely get near that. When the sensor is cold, the output is zero but as it heats up, the zirconia element heats up and reacts generating a voltage between 0.0 - 1.0V depending on the oxygen content in the exhaust. From this the mixture can be determined. At about 0.45V output, the mixture is stoichiometric - the theoretically perfect mixture of 14.7:1 air:fuel. As the mixture goes lean, the voltage drops so the ECU adds more fuel to bring it back up again. As it goes above 0.45V because the mixture is richer, the ECU reduces the amount of fuel to bring it back down again and so this cycle goes on.
If a Lambda sensor fails, it always fails with no output or if it's failing, the output is reduced. As such, the ECU is always trying to make the mixture richer until it finds it can't and then it throws a fault condition lighting the MIL and the fault can then be read.

Not having an earth on the Lambda sensor case because of a damaged thread could cause the mixture to be permanently too rich!

I'd expand on that to say its not a direct control loop as such. There is no stoich measure point on a narrow band. It is an O2 sensor nothing more, if its not sensing O2 it means the mixture is weak or stoich. A widband can measure 'mixture'.

What actually happens is the ECU cycles the mixture to find the cross over point (in both directions). If it can't find it in a certain range it lights up the lambda light. Hence on ECUs that you can monitor via ODB you get a nice sine wave for the mixture.

[Laird Scooby]

Originally Posted by TonyS9

LH doesn't use inlet heating, although there is a breather heater for the PCV pipe and the AFM uses a heater to determine air flow.

My LH equipped car does and has a MAF, not an AFM.

Originally Posted by TonyS9

I'd expand on that to say its not a direct control loop as such. There is no stoich measure point on a narrow band. It is an O2 sensor nothing more, if its not sensing O2 it means the mixture is weak or stoich. A widband can measure 'mixture'.

What actually happens is the ECU cycles the mixture to find the cross over point (in both directions). If it can't find it in a certain range it lights up the lambda light. Hence on ECUs that you can monitor via ODB you get a nice sine wave for the mixture.

Please expand the CORRECT way then Tony. You've got one bit right - it's an Oxygen sensor which means it can measure the percentage of oxygen in the burn and therefore work out the fuel/air ratio and hence give an indication of stoichiometric

Using your theory, the ECU would have to cycle the mixture with ever decresing offsets to obtain the perfect cross-over point for stoich, it doesn't. It's also not a sine-wave if you measure the Lambda output, more of a sawtooth and in some cases, a square wave.

https://www.picoauto.com/library/aut...ests/zirconia/

https://www.tiepie-automotive.com/en...ensor-zirconia

As you can see, neither of them are a sine wave, never mind a nice one!

Those were picked at random after checking they contained the information. Bosch use a closed loop mixture control system, if they didn't there would be a lot of poisoned and/or overheated cats around! Yes, it goes open loop under WOT conditions but as soon asWOT is released, it switches to closed loop control again, even if near full throttle.

[TonyS9]

Originally Posted by Laird Scooby

My LH equipped car does and has a MAF, not an AFM.





Please expand the CORRECT way then Tony. You've got one bit right - it's an Oxygen sensor which means it can measure the percentage of oxygen in the burn and therefore work out the fuel/air ratio and hence give an indication of stoichiometric

Using your theory, the ECU would have to cycle the mixture with ever decresing offsets to obtain the perfect cross-over point for stoich, it doesn't. It's also not a sine-wave if you measure the Lambda output, more of a sawtooth and in some cases, a square wave.

https://www.picoauto.com/library/aut...ests/zirconia/

https://www.tiepie-automotive.com/en...ensor-zirconia

As you can see, neither of them are a sine wave, never mind a nice one!

Those were picked at random after checking they contained the information. Bosch use a closed loop mixture control system, if they didn't there would be a lot of poisoned and/or overheated cats around! Yes, it goes open loop under WOT conditions but as soon asWOT is released, it switches to closed loop control again, even if near full throttle.

AFM/MAF ok but same difference really. I know BOSCH have special names for things, I don't subscribe.

The sine wave I was talking about usually comes from the mixture output on ODB (dwell), not O2 voltage. As you say its pretty binary, it doesn't give O2%. If it did you could achieve a steady state contol system that would stabilise with a little damping.

It maybe semantics to the point we are arguing. The computer won't change the injection dwell in immediate response to the O2 change, it will slow it down progressively in a very damped way (slow down the rate of change), with the end result of this sine wave cycle on dwell.

It doesn't need to cross over at the exact middle of its cycle, but it may well adjust the cycle. It is a way to measure the cross over point to find the trim value for the rest of the map. Its the injector dwell figure at cross over (or an average of certain points of the wave form) that is the output.

The point is that its very slow and can't respond immediately. If the mixture is way out of expectation, the cycling is too slow to compensate and the engine will stall or not start.

[Laird Scooby]

Originally Posted by TonyS9

AFM/MAF ok but same difference really. I know BOSCH have special names for things, I don't subscribe.

The sine wave I was talking about usually comes from the mixture output on ODB (dwell), not O2 voltage. As you say its pretty binary, it doesn't give O2%. If it did you could achieve a steady state contol system that would stabilise with a little damping.

It maybe semantics to the point we are arguing. The computer won't change the injection dwell in immediate response to the O2 change, it will slow it down progressively in a very damped way (slow down the rate of change), with the end result of this sine wave cycle on dwell.

It doesn't need to cross over at the exact middle of its cycle, but it may well adjust the cycle. It is a way to measure the cross over point to find the trim value for the rest of the map. Its the injector dwell figure at cross over (or an average of certain points of the wave form) that is the output.

The point is that its very slow and can't respond immediately. If the mixture is way out of expectation, the cycling is too slow to compensate and the engine will stall or not start.

Bosch have special names because the AFM and MAF are two very different animals! The AFM is the flap type sensor mounted in the airbox on L/LE-Jetronic systems, the LH uses the AMM - Air Mass Meter that is commonly known as the Mass Air Flow sensor - the hot-wire variety that is essentially a resistance bridge. Two fixed value resitors form part of the bridge, the two heated wires form the sensing and compensation parts of the bridge, the sense wire is the one exposed to the varying air flow into the engine and the compensation wire is shielded from that, held in an ambient enclosure. I've never destructively pulled one apart so can't be more specific on the exact construction, the Gunsons Gastester works on a similar principle but uses NTC thermistors in place of the hot wires, the CO cools the sensing thermistor proportionally to the volume of CO so the CO content can be derived.

If you're talking about the sine-wave coming from the OBD port, it's fair to say that signal has been processed by the ECU before it gets near the OBD port.
I didn't say the Lambda sensor output is binary, far from it! It's an analogue sensor and the voltage decreases proportionally with oxygen content or if you prefer, increases with reduced oxygen content. The output is ~0.45V @ stoichiometric mixture so it can be used to identify when the mixture is lean or rich in comparison to that.
It cycles because the engine speed is never perfectly steady so the ECU makes adjustments to the injection time around what it sees from the Lambda sensor. This is what causes the cycling effect.
As you're well aware, eveything is a compromise of cost, practicality and so on. Digitising an engines control is in some ways a good idea but the engine is by its very nature, an analogue device. If you're an audiophile, you'll know all the arguments against CDs, MP3 files etc Vs vinyl. Music is also primarily analogue so you can see tha analogy i'm drawing here.

Semantics had crossed my mind as well, the thing is we're dealing with what is essentially a precision digital control of an analogue device with some very specific components.

I get what you're saying about the control cycle being slow but it's fast enough within preset values that are the "ideal" range, it takes a bit of time to adjust outside of that range to within certain wider limits whereby the engine will still run but not optimally.

As for non-starting, the Lambda sensor is not used on start-up, particularly on a cold start and the engine runs open-loop until it's warmed to a certain temperature.

By that time, the Lambda heater has (or should have) done its stuff and the Lambda sensor itself is hot enough to provide feedback to the ECU so closed-loop control can start.

If the mixture can not be brought back within the pre-set limits and remains that way for an extended period, the ECU lights the MIL - Malfunction Indicator Lamp - which on the Volvos is signified by a Lambda letter. On other cars it can be an engine outline with a transistor symbol inside, others show the schematic symbol for an IC, others have the words "CHECK ENGINE" and so on. None relate to a specific component including the Lambda letter used by Volvo.
On more sophisticated systems, failure of a component or of the ECU to bring the mixture within pre-set values deploys the "Limp Mode" which defaults to preset values for certain components. This almost always results in a steady voltage out of the Lambda sensor as the mixture cannot be adjusted by the ECU and usually this voltage will be higher - in other words it runs rich to preserve the pistons and/or exhaust valves.

[Dirty Rooster]

Thanks for your explanation of the O2 sensor, stuff I didn't know.

Now ;

Originally Posted by Laird Scooby

... Yes, it goes open loop under WOT conditions but as soon asWOT is released, it switches to closed loop control again, even if near full throttle.

I've had two turbo engines (in the same car) both bog-standard, and found them to accelerate slightly better under part-throttle than wide-open (2nd to 4th gear, not from standing), am I imagining this or could it be mixture?