Speed Density Question

[nitroracer]

How does a speed density car run with the oxygen sensors unplugged? What factors change the fuel mixture then? Will it run richer?

[mrltd]

Default for any sensor being disconnected is rich. It'll run OK, but really rich. It uses the map and TPS to get the other info.

[Blaze86Vic]

It will run rich enough to possibly foul up your plugs at an increased rate.

[Grand Marquis GT]

I know on my old Omni GLHS, i pulled the wire for the O2, and it ran LEAN.

But it held me over till I got a new O2 sensor

[Southern_Pride]

I ran mine with em disconnected till I junked it. No more power just burned more gas.

[88grandmarq]

there is a book I highly recomend for anyone that wants to correctly understand how EEC-IV works, its called How to Understand, Service and Modify Ford Fuel Injection & Electronic Engine Control, by Charles O. Probst, SAE.

In chapter 5 they discuss basic ECM operation. Section 6.2 touches on the Failure Mode Effects Managment (FMEM). Basically the ECM has a module in it that has Fixed sensor signals stored to compensate when a sensor fails and stops giving a signal or an obviously wrong signal.

"FMEM shifts calibration in the event the Diagnostic program senses failure of one or more parts. For example, if the ECT suddenly signals an infinite resistance, as in an open, the control module ignores this input, which would otherwise drive the air-fuel ratio very rich. In effect, the ECM program says, "I know the limits of a signal from the ECT, so if it's outside those limits, something is wrong." In that case, the FMEM switches to a fixed resistance valure for the ECT, allowing the warm engine to operate as a warm engine.
At the same time, the ECM turns on the check engine light warning you to seek service. Each sensor has a seperate FMEM fixed value. In another logic, FMEM is programmed to remember the ECT signal just before the failure and continue at that input value."

Section 6.3 covers Loss of Signal (LOS)
Basically this is a "limp-home" strategy in the event of losing all or almost all input signals to the ECM. Under LOS the ECM sets the PIP signal to 10 degrees BTDC with out correction for temperature, load or any other condition.

[mrltd]

I've got that book, just haven't read it in awhile. Great info. I made an engine harness from scratch for my mustang with that book.

[Southern_Pride]

My check engine light was broke. I ran the car with damn near everything unplugged trying to make the random stalling quit. Ran the same, not like in a limp home mode but everything was ok mode.

[88grandmarq]

Just a side note... what I posted above, only applies to OBD-I.

I doubt CFI control modules, or EEC-III has any of those features.

[gadget73]

Mine had massive idle roll with the O2 sensors unplugged. Of course at the time the TPS wasn't set right and the engine had 10 miles on it too.