Hey guys; I have some symptom data about a puzzling problem that has affected my car recently. If anyone knows anything about this, even a few words of guidance would be appreciated.
My car's air/fuel ratio, as measured by an LM-1 wideband and supported by listening to the sound of the engine and judging available torque, has been acting peculiarly at various highway speeds. Here are some "datapoints" of what it consistently does at speed in 5th gear:
60MPH : Totally stochiometric (~14.7 with normal fluctuation on both sides)
70MPH : Overly rich at perfectly steady-state cruise; about 13.8, without fluctuation. With slightly increased throttle opening, either to keep up with traffic or go up small inclines, this number has little hesitation to fall into the 12s around this speed.
80MPH : Slightly lean, but great for cruise. Steady at 15.4 or so, with little to no fluctuation as the computer would enforce around stoich. Closer to full stoich right below 80, but high enough above 70.
85MPH : Incredibly lean--missing occurs every few seconds. The severity of the leanness depends on outside temperatures, but usually hits at least 17.8, or as much as 19+.
90MPH : similar to 80, very comfortable yet decidedly stuck on the lean side, rather than stoich.
95+MPH : full stoich @ ~14.7.
My fuel pressure is close to where it has always needed to be for this car, and adjusting it does nothing aside from change the severity of the bad points (70 and 85). If I reduce the pressure a bit, 85 is undrivable; if the fuel pressure is boosted, 85 improves, at the expense of 70.
It nearly seems that for an entire range of RPMs from the high 2000s to about 3500, the ECU does not inject any more fuel regardless of the crank RPM. At least, that's a way to describe what's happening--it scales across engine speeds.
This has gotten worse recently--to my knowledge, I had never noticed the rich @ 70MPH issue, and I watch the wideband often.
What could this be? An ailing narrowband O2 sensor? It goes without saying that the ECU is not throwing a code at this point.
Thanks for any comments guys; this is a long post, but it's a pretty specific issue I've been messing with for a while now, so I wanted to include a good amount of detail in my first mention of it.
My car's air/fuel ratio, as measured by an LM-1 wideband and supported by listening to the sound of the engine and judging available torque, has been acting peculiarly at various highway speeds. Here are some "datapoints" of what it consistently does at speed in 5th gear:
60MPH : Totally stochiometric (~14.7 with normal fluctuation on both sides)
70MPH : Overly rich at perfectly steady-state cruise; about 13.8, without fluctuation. With slightly increased throttle opening, either to keep up with traffic or go up small inclines, this number has little hesitation to fall into the 12s around this speed.
80MPH : Slightly lean, but great for cruise. Steady at 15.4 or so, with little to no fluctuation as the computer would enforce around stoich. Closer to full stoich right below 80, but high enough above 70.
85MPH : Incredibly lean--missing occurs every few seconds. The severity of the leanness depends on outside temperatures, but usually hits at least 17.8, or as much as 19+.
90MPH : similar to 80, very comfortable yet decidedly stuck on the lean side, rather than stoich.
95+MPH : full stoich @ ~14.7.
My fuel pressure is close to where it has always needed to be for this car, and adjusting it does nothing aside from change the severity of the bad points (70 and 85). If I reduce the pressure a bit, 85 is undrivable; if the fuel pressure is boosted, 85 improves, at the expense of 70.
It nearly seems that for an entire range of RPMs from the high 2000s to about 3500, the ECU does not inject any more fuel regardless of the crank RPM. At least, that's a way to describe what's happening--it scales across engine speeds.
This has gotten worse recently--to my knowledge, I had never noticed the rich @ 70MPH issue, and I watch the wideband often.
What could this be? An ailing narrowband O2 sensor? It goes without saying that the ECU is not throwing a code at this point.
Thanks for any comments guys; this is a long post, but it's a pretty specific issue I've been messing with for a while now, so I wanted to include a good amount of detail in my first mention of it.