While my car has had plenty of strange problems, this is the most mysterious one I've run into.
First, my car is running MAFT-Pro Speed Density. It has been running well with the setup for perhaps 1,000 miles, including a 500 mile road trip that was nearly all cruise and did not show this problem. I noticed the problem spontaneously while driving a short time ago.
While cruising, especially at engine speeds around or above 2,000RPM, the AFR can show one of three behaviors. If I am very light on the throttle, such as 4th gear at 2,000RPM barely maintaining or even losing speed on level road, the car will run close to stoich (14.8-14.2). If I maintain speed or push enough for a very very tiny acceleration, my AFR instantly hits the 12s. Any reasonable acceleration (we're still talking very slow, less than 25% throttle) will immediately yield AFRs around 10.0. I do not notice any missing, which would produce falsely rich readings. Idle is usually close to stoich, but after driving around for 10 minutes or so, tends to move to the 12s and stay there. All of the readings I mention are with a warm engine.
Adjusting fuel pressure or MAFT-Pro settings has not helped. I initially suspected the oxygen sensor, even though no codes were evident, so I wired in a simulated signal from my wideband. The problem remained unchanged. I next suspected the TPS, but it passes the TSRM diagnostic, assuming I read the diagrams correctly and E2 is the bottom pin when looking at the unit from the front of the car.
And finally, the car's performance at WOT is simply golden. Great AFRs, blistering performance. No complaints whatsoever. That implies to me that the ignition system is strong, increasing mysteriousness
Any ideas would be wonderful. At this point, I'm quite frustrated, despite my extreme love for this machine. Thanks all!
First, my car is running MAFT-Pro Speed Density. It has been running well with the setup for perhaps 1,000 miles, including a 500 mile road trip that was nearly all cruise and did not show this problem. I noticed the problem spontaneously while driving a short time ago.
While cruising, especially at engine speeds around or above 2,000RPM, the AFR can show one of three behaviors. If I am very light on the throttle, such as 4th gear at 2,000RPM barely maintaining or even losing speed on level road, the car will run close to stoich (14.8-14.2). If I maintain speed or push enough for a very very tiny acceleration, my AFR instantly hits the 12s. Any reasonable acceleration (we're still talking very slow, less than 25% throttle) will immediately yield AFRs around 10.0. I do not notice any missing, which would produce falsely rich readings. Idle is usually close to stoich, but after driving around for 10 minutes or so, tends to move to the 12s and stay there. All of the readings I mention are with a warm engine.
Adjusting fuel pressure or MAFT-Pro settings has not helped. I initially suspected the oxygen sensor, even though no codes were evident, so I wired in a simulated signal from my wideband. The problem remained unchanged. I next suspected the TPS, but it passes the TSRM diagnostic, assuming I read the diagrams correctly and E2 is the bottom pin when looking at the unit from the front of the car.
And finally, the car's performance at WOT is simply golden. Great AFRs, blistering performance. No complaints whatsoever. That implies to me that the ignition system is strong, increasing mysteriousness
Any ideas would be wonderful. At this point, I'm quite frustrated, despite my extreme love for this machine. Thanks all!
