How many sensors does the '90 Festie have?

[clev]

I'm aware of the one in the thermostat housing for the temp gauge; the one that activates the fan relay; the O2; and the coolant sensor. What others are on this engine and where are they located?

[stefan]

theres one for the oil pressure on the back of the block

and i think there is an incoming air temp sensor in the VAF

and you could call the TPS a sensor

[FB71]

cooling fan temp sensor, engine coolant temp sensor, EGO (O2) sensor, these three you already know. They provide the PCM with information. I'll list wether the sensor provides info to the PCM or gauge.

Throttle Posistion Sensor, on throttle body, PCM
Vane Air Flow Sensor, on top of air filter, PCM
Power Steering Pressure switch (if equipped), on PS line, PCM
Crankshaft Position Sensor, inside distributor, PCM
Clutch Engage Switch (mtx), on clutch pedal, PCM
Neutral Gear Switch (mtx), on transaxle, PCM
Neutral Safety Switch, (atx), PCM
Ignition Module, inside distributor, PCM
stop lamp switch, rear def switch, headlamp switch, blower motor switch, both AC relays, and atx kickdown switch also provide a load input to the PCM.
Fuel tank sending unit, in tank, gauge
oil pressure switch, back of block, gauge/lamp
brake fluid level sensor, master cyl res, gauge/lamp
brake warning lamp switch, brake combination valve, gauge/lamp
park brake switch, park break lever, gauge/lamp

[stefan]

cooling fan temp sensor, engine coolant temp sensor, EGO (O2) sensor, these three you already know. They provide the PCM with information. I'll list wether the sensor provides info to the PCM or gauge.

Throttle Posistion Sensor, on throttle body, PCM
Vane Air Flow Sensor, on top of air filter, PCM
Power Steering Pressure switch (if equipped), on PS line, PCM
Crankshaft Position Sensor, inside distributor, PCM
Clutch Engage Switch (mtx), on clutch pedal, PCM
Neutral Gear Switch (mtx), on transaxle, PCM
Neutral Safety Switch, (atx), PCM
Ignition Module, inside distributor, PCM
stop lamp switch, rear def switch, headlamp switch, blower motor switch, both AC relays, and atx kickdown switch also provide a load input to the PCM.
Fuel tank sending unit, in tank, gauge
oil pressure switch, back of block, gauge/lamp
brake fluid level sensor, master cyl res, gauge/lamp
brake warning lamp switch, brake combination valve, gauge/lamp
park brake switch, park break lever, gauge/lamp

wow! all hail FB71! :cheers:

[jglutz]

Isn't there also a barometric pressure sensor inside the PCM?
The air inlet temp sensor (thermistor) and the vane, both in the VAF, come in as one combined signal and the barometric pressure sensor valvue is added (actually multiplied) to provide the CPU with a true mass air flow.
The combined temp and baro values equal the air density...the vane position represents inlet air speed. The result represents the amount of oxygen going into the combustion chamber....thus the CPU knows how much fuel to add.
Also, the barometric pressure sensor is also necessary for automatic altitude comppensation.

[stefan]

^^ oh yea i remember seeing that in the factory manual

[FB71]

jg, yes, I forgot about the baro sensor in the pcm. The Festies don't have a separate or integrated IAT. The PCM uses the ECT to guess at inlet air temp. IAT sensors showed up Aspires.

[neanderpaul]

Holy crap! Something got by Jim!!

[clev]

Thanks, I appreciate the list.

[jglutz]

From memory...last time i had the VAF off...when i looked in the outlet...I saw the thermistor penatrating below the circuit board.

Also just guesing....i think the cooling fan relay input to the PCM to prevent the idle from droping out.

[FB71]

correct on both counts, Joe.

cooling fan input is for "electrical load", to stabilize idle speed.

The thermistor you see in the VAF is not a separate IAT, and it's not considered to be an IAT at all. The MECS guys used to call it a 'temperature compensator". It modifies the VAF signal directly. Aspire got a separate IAT with direct input to the PCM

[GenevaDirt]

^^no one would believe how many smart people we have here on the site... I really appreciate them sharing the knowledge.

[clev]

^^no one would believe how many smart people we have here on the site... I really appreciate them sharing the knowledge.

So do I!!! If you don't do it yourself, you can't be sure it's done correctly.

I don't trust ANYONE to work on my vehicles and any advice that I can receive is well appreciated.

I was out of town when the engine went out my festiva (hole in the piston, year 2000) and I instructed my wife to contact a local garage/engine repair/replace shop. I was in touch by phone but the engine has never been right since that time. That's the same problem that I'm working with now. Final words from a 60 year old retired Army Green Beret (VietNam), retired Texas advanced math teacher, and general all around 'old school' tinker'er; if you can do it yourself, DON'T TRUST ANYONE!!! Follow advice on this board and do it yourself.

[WmWatt]

There is an engine electronics diagram in the back of the Haynes manual which shows the wiring for the sensors connected to the car computer, also the wiring for the "actuators" which do stuff. "Sensors" and "actuators" are generic names which were used in a real time computer course I took in the early 90's. There is one sensor on the carburetted engine which is only required in California. I suppose they add it at the Cailfornia dealerships as part of the dealer prep.

[phantorn]

California(and Green state )cars are set up from the factory with all the extra sensors and special PCM calibrations.They also have a different warranty period for certain emission components