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Old 11-14-2009, 04:36 PM   #1 (permalink)
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'95 3.0 GL

What kind of damage or issues can be caused by driving it with the sensor unplugged and the CEL on?
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Old 11-15-2009, 02:26 AM   #2 (permalink)
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You might kill your catalytic converter by having the engine running rich. A catalytic converter is like $300. Not to mention your gas mileage will tank so you'll be paying more just to drive around.
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Old 11-15-2009, 09:52 AM   #3 (permalink)
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QUOTE (Ryan T @ Nov 14 2009, 06:36 PM)
Quote:
'95 3.0 GL

What kind of damage or issues can be caused by driving it with the sensor unplugged and the CEL on?[/b]
Why would you want to do that?
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Old 11-17-2009, 07:41 PM   #4 (permalink)
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do drive to long with it like that. If you unplug it your car computer will notice quickly. It'll the throw a CEL and your car will go into "limp home mode'. Basically Your computer will know it's missing and it will actually try to guess mass airflow based on the other sensors that register. for more info see: http://www.fordfuelinjection.com/?p=64 , I have cut and pasted a couple excerpts:

Failure mode is a stand in strategy in the EEC designed to maintain vehicle operation should one or more sensor inputs fail. When a sensor input is perceived to be out-of-limits by the EEC, memorized data from the computers KAM memory will be initiated. EEC continually checks the sensors against its records of normal readings during operating conditions similar to its current state. Hold on that sounds hard! Not really, randomly EEC looks at the past to see if the engine is somewhat where it usually is. If for some unknown reason a sensor is off the charts, it can’t be trusted. So instead of tuning the engine to a possible faulty sensor reading and harming the engine and drive-ability; EEC replaces the sensor reading with a best guess from a past memory. This is why unplugging the battery to fix something works against you. Unplug the battery causes EEC to memorize all the sensor data as base line and normal. If it memorizes a bad sensor it will take it longer to call it a liar. Ford did however give EEC a very broad idea of what the sensor should be reading in its permanent ROM memory, so it will catch on to failed equipment sooner.
I am going to divide up the sensors into two groups. Ones that will cause failure mode but allow drive-ability and the sensors that will cause a no-start or barely drive. Actuators can cause failure mode to take over, but only if the failed actuator is giving a sensor reading way off the chart.

Adaptive Strategy
Now this one is a little complex. EEC likes to toy with the fuel ratio at random. It does this to run complex math equations. She is calculating how much fuel is required to reach certain lean or rich states. Why you ask? Because playing this cat and mouse game with the fuel ratio allows us to fine tune the engine parameters in other strategies. Confused yet? EEC cuts back on the injectors for a spit second and counts how long it takes for the HEGO to report back a lean environment. EEC leans and enriches at different amounts and get back different numbers. These numbers tell EEC if the engine needs a tune up, or if you’ve added a performance parts and allows us to actually alter the fuel amount delivered. What do we do with those numbers EEC collected? Well there is a Table called “Adaptive Fuel Table” (makes sense huh?) This table is used as a multiplier, it is held over the master load table. It then multiplies each number in the master table to get a better control of fuel delivery over time. In a computer that has been just connected to the battery it is full of “1’s”, if you multiply the master table by “1″ you get the same number. I’m not good at math
and I understand it, 14.7:1 X 1 = 14.7:1, simple!. After many days of driving on the highway it begins to fill with multipliers like “1.2’s” and “0.9’s”, which will alter the master table. Don’t believe me? 14.7:1 X 1.2 = 17.6:1, and 14.7:1 X 0.9 = 13.3:1, and we just fine tuned our fuel curve without doing anything special. Isn’t that cool? Well not always, this entire technology depends on the Oxygen Sensors being fresh, clean, new, and in good condition. And it can’t be responsible for displacement changes, cam changes, or other big performance add-on’s. This technology is only meant to keep EEC on the same level as an ageing engine with diminished performance. It is not meant to be relied upon for performance engine tuning!
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Old 11-18-2009, 10:34 AM   #5 (permalink)
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If u unplug the maf sensor, the computer goes into open loop. You still have a MAP sensor that can tell the computer the load in dynamic conditions. So basically instead of correcting fuel based on MAF and MAP combined, they will simply read the MAP, RPM, temperature and look up in a table how much fuel to inject. That fuel would be slightly richer than what you would be injecting in closed loop. But it is calibrated carefully so that the it is not excessive. (in fact under hard acceleration, you use this table only cuz the sensor are not fast enough to provide useful feedback).
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Old 11-18-2009, 01:18 PM   #6 (permalink)
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QUOTE (yiranhu @ Nov 18 2009, 11:34 AM)
Quote:
If u unplug the maf sensor, the computer goes into open loop. You still have a MAP sensor that can tell the computer the load in dynamic conditions. So basically instead of correcting fuel based on MAF and MAP combined, they will simply read the MAP, RPM, temperature and look up in a table how much fuel to inject. That fuel would be slightly richer than what you would be injecting in closed loop. But it is calibrated carefully so that the it is not excessive. (in fact under hard acceleration, you use this table only cuz the sensor are not fast enough to provide useful feedback).[/b]
The Taurus in question uses a MAF only, no MAP. When the MAF is unplugged, the PCM guestimates how much fuel to put into the engine based off it's fuel tables, TPS, ECT, IAT and current RPM
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