Bad Sensor or Outsmarted by Engine Computer
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3rd Gear
Joined: May 2014
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From: Stillwater MN
Bad Sensor or Outsmarted by Engine Computer
Hi, I have a2003 2.5 gas Freelander that I picked up cheap and up until this point has beatall the odds. That is up until a monthor so ago when it started exhibiting intermittent severe losses of power. I have an inexpensive Blue Tooth code readerthat I use with the Torque app on my smart phone. Various fault codes come up equating to oneor both banks too lean then various misfires. When started from cold it starts up as normal for the first 5 to 10seconds (must be starting on some sort of predefined rich starting mixture andcontrol) then when it would normally back down to idle rpm it begins to runvery rough and often dies. Pressing theaccelerator during this drop off has little or no effect. You can hear the extra air flow but the rpmsdon’t pick up and instead it either coughs and jumps or just dies. At this point if you try starting it multipletimes and keep the rpms up during and after the 5 – 10 second startup cycle itwill eventually “clear itself” and run pretty normal - for a while.
Then usingmy code reader and having my son ride along and monitor some of the engineparameters I’ve been able to test drive it and make a few observations: When it’s running well the short term fueltrim on both banks is up around 27%. Then for some reason these trims start stepping down (he can watch themon a graph and they tend to move together in what looks like a stair steppattern) and eventually go to zero. While this is happening the engine loses power and all but dies. Keeping the rpms up can prevent or reversethe step down in trim and roughness. Soit seems that higher rpms help the situation but I’m not sure. Also, once the engine is warmed up, shuttingit off and restarting always brings it back to normal for at least the first 5– 10 seconds and often it will continue to run fine for up to 10 minutes ormore (as long as it’s not just at idle).
I don’t knowwhich is the cause and which is the effect. The engine control unit seems to be stepping the fuel mixture down tothe point that it’s too lean to even run but I don’t know what the root causeis. And keeping the rpms up eithermitigates the underlying root cause or puts the engine control in some othercontrol condition that automatically tells it to call for a richer mixture.
I’ve testedthe fuel pressure, looked at the spark plugs, monitored the O2 sensors, cleanedand monitored the mass airflow sensor, looked for vacuum leaks etc. but I’m notsure what to try next. Oh and by theway, I have had some trouble with the butterfly valves and motors in theplastic part of the intake manifold so they could be acting up again but I’massuming they couldn’t cause these more serious symptoms?
Anyone haveany ideas?
Then usingmy code reader and having my son ride along and monitor some of the engineparameters I’ve been able to test drive it and make a few observations: When it’s running well the short term fueltrim on both banks is up around 27%. Then for some reason these trims start stepping down (he can watch themon a graph and they tend to move together in what looks like a stair steppattern) and eventually go to zero. While this is happening the engine loses power and all but dies. Keeping the rpms up can prevent or reversethe step down in trim and roughness. Soit seems that higher rpms help the situation but I’m not sure. Also, once the engine is warmed up, shuttingit off and restarting always brings it back to normal for at least the first 5– 10 seconds and often it will continue to run fine for up to 10 minutes ormore (as long as it’s not just at idle).
I don’t knowwhich is the cause and which is the effect. The engine control unit seems to be stepping the fuel mixture down tothe point that it’s too lean to even run but I don’t know what the root causeis. And keeping the rpms up eithermitigates the underlying root cause or puts the engine control in some othercontrol condition that automatically tells it to call for a richer mixture.
I’ve testedthe fuel pressure, looked at the spark plugs, monitored the O2 sensors, cleanedand monitored the mass airflow sensor, looked for vacuum leaks etc. but I’m notsure what to try next. Oh and by theway, I have had some trouble with the butterfly valves and motors in theplastic part of the intake manifold so they could be acting up again but I’massuming they couldn’t cause these more serious symptoms?
Anyone haveany ideas?
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cheqbay1997
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Jun 11, 2014 10:24 AM
