WOT AFR question
03-05-2006, 03:47 PM
#1
WOT AFR question Please look at the pic: the blue line is the commanded AFR, the red line is what I logged with my wideband.
The commanded AFR is a straight line, so I was expecting to see something similar. Maybe a parallel to the commanded line, but not a curve.
Do you know why?
COT is desabled, the engine temperature was around 200F, the MAF is stock, the MAF calibration is stock also. What else can influence the AFR at WOT?
PLS don't look at my sign: right now the SC is disconnected, I run a FIPK K&N filter, stock internals, stock VE, stock timing table.
The WB is installed few inches after the front passanger O2, before the cat.
The commanded AFR is a straight line, so I was expecting to see something similar. Maybe a parallel to the commanded line, but not a curve.
Do you know why?
COT is desabled, the engine temperature was around 200F, the MAF is stock, the MAF calibration is stock also. What else can influence the AFR at WOT?
PLS don't look at my sign: right now the SC is disconnected, I run a FIPK K&N filter, stock internals, stock VE, stock timing table.
The WB is installed few inches after the front passanger O2, before the cat.
03-06-2006, 02:13 PM
#6
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You need to get it tuned properly as the other guys say.
You start making sure your IFR is right for your injectors, then tune your ve by going open loop speed density, then you can get your maf right by comparing maf airflow with the now correct SD airflow reading and adjust the maf table. Go back to part throttle closed loop and reconnect the maf if you want to.
Finally at this point your WOT should be pretty much right on your commanded afr.
You start making sure your IFR is right for your injectors, then tune your ve by going open loop speed density, then you can get your maf right by comparing maf airflow with the now correct SD airflow reading and adjust the maf table. Go back to part throttle closed loop and reconnect the maf if you want to.
Finally at this point your WOT should be pretty much right on your commanded afr.
03-06-2006, 02:49 PM
#7
if you zero out all other factors but the VE table, then you can tweak the VE table until it matches that... then one at a time bring each variable back in, and correct it..
thats the basic idea behind the speed density tuning... and most aftermarket tuning.
right now, that curve could be anything... but my guess is the MAF... of all the sensors, the MAF sensor has the most effect over fueling.. with the O2s following a close second... if the maf or the front o2s are off, fueling is off... possibly a good bit.
thats the basic idea behind the speed density tuning... and most aftermarket tuning.
right now, that curve could be anything... but my guess is the MAF... of all the sensors, the MAF sensor has the most effect over fueling.. with the O2s following a close second... if the maf or the front o2s are off, fueling is off... possibly a good bit.
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03-06-2006, 03:48 PM
#8
At WOT the MAP value is pretty constant (about 90 kPa), the IFR will also deliver a constant value to the PCM for calculations. So I don't think it's the IFR.
VE: Are they really considered after 4000 rpm? I'm not even sure they are used below... this is a MAF based PCM!
Front O2's: surely not. This is open loop (PE)
MAF: it could be out. It's just strange that the error increases with the airflow.
The car is a 98 with the original MAF (65'000 miles): is it possible that the MAF is getting old and sees too much air?
Are ther other parameters I don't see in Edit that could influence the fuel quantity? In Edit I only see PE vs RPM and PE vs coolant temperature.
Timing is 28*, no KR
VE: Are they really considered after 4000 rpm? I'm not even sure they are used below... this is a MAF based PCM!
Front O2's: surely not. This is open loop (PE)
MAF: it could be out. It's just strange that the error increases with the airflow.
The car is a 98 with the original MAF (65'000 miles): is it possible that the MAF is getting old and sees too much air?
Are ther other parameters I don't see in Edit that could influence the fuel quantity? In Edit I only see PE vs RPM and PE vs coolant temperature.
Timing is 28*, no KR
03-06-2006, 05:45 PM
#9
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TiCi what other mods do you have on the car now? I know you said the FI is off. So all you have is the K&N FIPK? I mean as far as how the car breathes? What about exhaust? At any rate, have you tried putting the car in OLSD? The reason why I jumped on the VE table is for what little mods you listed, being a 98, with a stock MAF, I assumed the MAF was working correctly or good enough. OLSD would rule out a lot of sensors from which you could work back turning them on one by one as was mentioned before. I do believe that the stock MAF with stock tables won't degrade over time-either it works or it doesn't. I don't know everything but I feel your pain if that helps. Isolate.
Last edited by Doc; 03-06-2006 at 08:45 PM.
03-07-2006, 12:34 AM
#11
Originally Posted by Doc
TiCi what other mods do you have on the car now? I know you said the FI is off. So all you have is the K&N FIPK? I mean as far as how the car breathes? What about exhaust? At any rate, have you tried putting the car in OLSD? The reason why I jumped on the VE table is for what little mods you listed, being a 98, with a stock MAF, I assumed the MAF was working correctly or good enough. OLSD would rule out a lot of sensors from which you could work back turning them on one by one as was mentioned before. I do believe that the stock MAF with stock tables won't degrade over time-either it works or it doesn't. I don't know everything but I feel your pain if that helps. Isolate.
The injectors are #36 Bosch and I have an additional fuel pump (Raptor whatever). Those are for the supercharger which right now is disconnected.
Stock timing table.
What is OLSD? You mean speed density?
I ran SD for a while with the stock VE and saw that I had to run much higher IFR values than what I have now. LTFT's were all +/- 2% (stock VE table) but I haven't checked above 4000 (I used the front O2's and not the WB).
When I went back to the MAF I had to increase the MAF table by 5-6% to get the same LTFT's.
Strange because the injectors are scaled correctly: with the actual settings (IFR according to the injectors size and fuel pressure, stock MAF, stock VE) the LTFT's are also +/-2%.
As said: I was expecting a parallel to the commanded AFR but not a slope
SD is not an option because with the blower connected I need the MAF (1 bar PCM).
The 98 VE over 4000 rpm are almost the same as the 99 and 00 models so I don't think they are so much wrong (there should be at least 3 years with the same problem!)