Lagged FMIC pipes, now different AFR reading
31 August 2004, 08:36 PM
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Lagged FMIC pipes, now different AFR reading
Having lagged the Turbo->I/C pipe on my hybrid FMIC yesterday, I've observed some different behaviour in my AFR....
When the car is driven 'normally' (i.e. cruise and occassional push), the AFR is normal (i.e. Blue on WOT).
However, if the car is given a good thrap for a short while (say 3 or 4 40->80 full bores, through the gears, to overtake, in immediate succession), the AFR starts to show a slight lean (green light only) on WOT in 5th....
I lagged the I/C pipes, to try to get the underbonnet temps down, because AndyF and I were concerned about the intake temps (running a 57i induction kit). The next step is to get an induction scoop (on order).
But, I'm wondering if I've actually increased the charge temp due to the lack of heat escape into the engine bay from the I/C pipe. I'm thinking that the induction scoop (once fitted) will counter this, and some, therefore making the lagging a good idea, but I'm concerned in case I'm talking ..... cobblers (!)
TBH, I'm not sure how the increase in temp is reducing the richness of the mix, but I'm not sure if the PowerFC will be backing off ?
I'm not getting any activity on either knocklink (which IS working) or PowerFC Output (Dash Light), and all returns to normal after a few hundred yards of cruising...
Anyone any ideas ?
I'll update this post with data once the scoop is on - Also, if this makes no difference, I'll remove the lagging and see - (Its worth noting that this didn't happen when I lagged the I/C -> manifold pipe last week)
The only other idea I have is that the pipe is allowing air in, after the MAF, but I can't see how this can be temperature related....
Thanks for any ideas,
Mark
When the car is driven 'normally' (i.e. cruise and occassional push), the AFR is normal (i.e. Blue on WOT).
However, if the car is given a good thrap for a short while (say 3 or 4 40->80 full bores, through the gears, to overtake, in immediate succession), the AFR starts to show a slight lean (green light only) on WOT in 5th....
I lagged the I/C pipes, to try to get the underbonnet temps down, because AndyF and I were concerned about the intake temps (running a 57i induction kit). The next step is to get an induction scoop (on order).
But, I'm wondering if I've actually increased the charge temp due to the lack of heat escape into the engine bay from the I/C pipe. I'm thinking that the induction scoop (once fitted) will counter this, and some, therefore making the lagging a good idea, but I'm concerned in case I'm talking ..... cobblers (!)
TBH, I'm not sure how the increase in temp is reducing the richness of the mix, but I'm not sure if the PowerFC will be backing off ?
I'm not getting any activity on either knocklink (which IS working) or PowerFC Output (Dash Light), and all returns to normal after a few hundred yards of cruising...
Anyone any ideas ?
I'll update this post with data once the scoop is on - Also, if this makes no difference, I'll remove the lagging and see - (Its worth noting that this didn't happen when I lagged the I/C -> manifold pipe last week)
The only other idea I have is that the pipe is allowing air in, after the MAF, but I can't see how this can be temperature related....
Thanks for any ideas,
Mark
31 August 2004, 10:48 PM
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Mark
The std narrow band O2 sensor outputs a lower voltage as it heats up, it is normal for the lamda gauge to show leaner after a good thrashing. As long as it does the same each time then no cause for concern.
If however it starts to get leaner with time then I would start to suspect a maf related fault, or maybe just a failing O2 sensor.
The underbonnet temperature should have no effect on the AFR as the maf measures the mass of air and as such is temperature compensated.
It is possible that with cooler ambients and/or lower underbonnet temps that you are actually making more power, leading to slightly increased EGT, in turn resulting in a lower lamda voltage (but not leaner mixture)
Andy
The std narrow band O2 sensor outputs a lower voltage as it heats up, it is normal for the lamda gauge to show leaner after a good thrashing. As long as it does the same each time then no cause for concern.
If however it starts to get leaner with time then I would start to suspect a maf related fault, or maybe just a failing O2 sensor.
The underbonnet temperature should have no effect on the AFR as the maf measures the mass of air and as such is temperature compensated.
It is possible that with cooler ambients and/or lower underbonnet temps that you are actually making more power, leading to slightly increased EGT, in turn resulting in a lower lamda voltage (but not leaner mixture)
Andy
01 September 2004, 09:35 AM
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Andy, thanks for that. I did recall that the pickup seemed better (from our discussion on 'map day') when the exhaust was really hot (maybe better gas flow?) - so I'd started to wonder whether I'd effectively increased the power by reducing the intake temperatures (this was, after all, the idea !) - but didn't know why this would show 'lean'..
It's very reproducible and has changed behaviour since the lagging, rather than slowly developing, so again I'll take this as an indicator, rather than a developing fault.
The tickover / town drive / cruise is fine, so I don't think that the MAF is failing -
I'll keep an eye on it, to make sure it gets no worse - also, I'm only displaying the top 4 outputs from the 10 (Dawes AFR), so it has becomer leaner, rather than lean, if that makes sense.
I'm hoping that the induction scoop comes this week, so I'll see how it goes with that fitted.
Dean - how does that temperature compare with last week ? I must get a probe fitted, to see how well the system is now doing - the hardpipe on BOTH sides of the I/C were very hot to the touch prior to lagging, but I know that the return pipe is now cold, (there is a small exposed part - where I can test it...). It seems to lean out when hotter, rather than colder, which should make it un-related to the ambient temperature dropping ?
Micky - no, the covers are still in place, but should be removing the O/S one this week when I fit the reverse scoop.
Thanks for the input chaps,
Mark
It's very reproducible and has changed behaviour since the lagging, rather than slowly developing, so again I'll take this as an indicator, rather than a developing fault.
The tickover / town drive / cruise is fine, so I don't think that the MAF is failing -
I'll keep an eye on it, to make sure it gets no worse - also, I'm only displaying the top 4 outputs from the 10 (Dawes AFR), so it has becomer leaner, rather than lean, if that makes sense.
I'm hoping that the induction scoop comes this week, so I'll see how it goes with that fitted.
Dean - how does that temperature compare with last week ? I must get a probe fitted, to see how well the system is now doing - the hardpipe on BOTH sides of the I/C were very hot to the touch prior to lagging, but I know that the return pipe is now cold, (there is a small exposed part - where I can test it...). It seems to lean out when hotter, rather than colder, which should make it un-related to the ambient temperature dropping ?
Micky - no, the covers are still in place, but should be removing the O/S one this week when I fit the reverse scoop.
Thanks for the input chaps,
Mark
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