So today I fitted an Innovate Motorsport LC-1 wideband controller and a G3 gauge into my 1984 Lux. I have just been for a drive and have some interesting results. Firstly I would like to say I am aware that these results might be specific to my engine/sensor as for all I know either/both may be in some way malfunctioning. I guess at this point I would be interested to know if anyone could confirm/reject and help explain my findings.
As a bit of background and for clarification I'll list some of the values that are important in terms of air to fuel ratio (AFR) taken from http://en.wikipedia.org/wiki/Air-fuel_ratio#AFR
Stoichiometric at 14.7:1 AFR. Maximum power at about 12.5-13.3 AFR.
After doing an in air calibration of the sensor I started my engine from cold and went for a 10 minute drive. This is what I found:
Firstly when the engine was cold it was running a rich idle at around ~10:1 AFR. I'm aware an engine runs rich when cold, could anyone confirm this is the correct AFR for a cold engine?
Once the engine had warmed up it idled at ~12:1 AFR. This is also rich, richer even than you would want for maximum performance and was not what I was expecting. I though it would be closer to stoichiometric.
Constant speed at partial throttle the mixture was ~12:1 AFR. Again far richer than I was expecting.
Accelerating at partial throttle the mixture went slightly leaner to ~14 AFR.
Under full throttle the mixture was generally ~13, the results here were harder to follow due to the fast change in RPM so are perhaps the least accurate of the lot, but it did seem to show a trend towards 13.
I will now offer my own attempt at an explanation of these findings. Ill talk from a perspective of how the DME is calculating what to inject.
AFM signal: For low-med air flow rates at partial throttle the 944's DME injects based on the signal from the AFM. At constant speed/idle the DME is injecting very rich at 12:1 AFR, assuming a correct sensor reading and fully functioning engine I would say that's how its mapped. Under acceleration at partial throttle the AFR goes to around 14:1. I'm not sure but I would say this might be down to the failures of the AFM and is not down to the DME deliberately leaning the mixture. This seems totally backwards to what I would expect. I would want it stoichiometric at constant speed and richer under acceleration, in fact the exact opposite is happening. One explanation might be that its is a workaround for the AFM and that it runs so rich just so that when accelerating under partial throttle it doesn't go really lean and loose all its power. Another is that my AFM is faulty, however I tested it a while ago according to FRWilk and it was shown to be OK. In fact I have another one I could test should I need it.
RPM Based: This is pretty much what I expected, the engine runs at around 13:1 AFR which is good for performance. This leads me to think the injection system is OK, however does not rule out a faulty AFM.
It would be interesting to know what anyone else with a Lux has found any what anyone else's thoughts on this might be. This is putting in a stronger case for doing a MAF conversion if what I am seeing at partial throttles is correct.
As a bit of background and for clarification I'll list some of the values that are important in terms of air to fuel ratio (AFR) taken from http://en.wikipedia.org/wiki/Air-fuel_ratio#AFR
Stoichiometric at 14.7:1 AFR. Maximum power at about 12.5-13.3 AFR.
After doing an in air calibration of the sensor I started my engine from cold and went for a 10 minute drive. This is what I found:
Firstly when the engine was cold it was running a rich idle at around ~10:1 AFR. I'm aware an engine runs rich when cold, could anyone confirm this is the correct AFR for a cold engine?
Once the engine had warmed up it idled at ~12:1 AFR. This is also rich, richer even than you would want for maximum performance and was not what I was expecting. I though it would be closer to stoichiometric.
Constant speed at partial throttle the mixture was ~12:1 AFR. Again far richer than I was expecting.
Accelerating at partial throttle the mixture went slightly leaner to ~14 AFR.
Under full throttle the mixture was generally ~13, the results here were harder to follow due to the fast change in RPM so are perhaps the least accurate of the lot, but it did seem to show a trend towards 13.
I will now offer my own attempt at an explanation of these findings. Ill talk from a perspective of how the DME is calculating what to inject.
AFM signal: For low-med air flow rates at partial throttle the 944's DME injects based on the signal from the AFM. At constant speed/idle the DME is injecting very rich at 12:1 AFR, assuming a correct sensor reading and fully functioning engine I would say that's how its mapped. Under acceleration at partial throttle the AFR goes to around 14:1. I'm not sure but I would say this might be down to the failures of the AFM and is not down to the DME deliberately leaning the mixture. This seems totally backwards to what I would expect. I would want it stoichiometric at constant speed and richer under acceleration, in fact the exact opposite is happening. One explanation might be that its is a workaround for the AFM and that it runs so rich just so that when accelerating under partial throttle it doesn't go really lean and loose all its power. Another is that my AFM is faulty, however I tested it a while ago according to FRWilk and it was shown to be OK. In fact I have another one I could test should I need it.
RPM Based: This is pretty much what I expected, the engine runs at around 13:1 AFR which is good for performance. This leads me to think the injection system is OK, however does not rule out a faulty AFM.
It would be interesting to know what anyone else with a Lux has found any what anyone else's thoughts on this might be. This is putting in a stronger case for doing a MAF conversion if what I am seeing at partial throttles is correct.
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