Engine Sensors, Etc.
Maintenance FAQ for 7xx/9xx/90 Cars
Temperature Sensors. The B230F of the vintage discussed, 1989-1990
have in effect three temp sensors: the Engine Coolant Temperature (ECT)
and the temperature gauge sensor. Two of the sensing elements (NTC) are
combined in one ECT sensor housing with two connectors and ground through
the housing. One of the temp sensor "signals" goes to the LH unit, the
other to the EZK unit. The third temp sensor is the one used by the temp
gauge in the instrument cluster. It also has two connectors, one "signal",
Removing the Sensors. [Query]
How do I remove the gauge temperature sensor? [Response: Mark
Duval] I bought the "stubby" 19mm combination wrench and a 19mm crow
foot socket. First tried the open end side of the stubby and although I
could get it squarely on the hex head, I could not put enough force on
the wrench to turn the sensor. Then used the crow foot socket with
a long extension. This rotated off the hex and cracked the electrical connection
at the top of the sensor. The answer all along was to remove the electrical
connector (destroying the sensor) and gain access to the hex with an offset
19mm box wrench. Thereafter R & R in seconds. Replacement sensor
seems to be work and gauge
reads as expected so far. [Editor]
It helps to first remove the knock sensor nearby, which is merely
bolted into the block. Removing the ECT is a little tougher,
since it is buried under the intake manifold.
ECT Failures. [Response: Don Foster, adapted to 700/900 series
by Editor] Your engine has two temp sensors -- one for the gauge (it's
mounted in the head about under intake header #2, and one for the FI (it's
mounted in the head about under intake header #3). The latter is
the ECT sensor.
The sensor is an NTC thermistor -- negative
temperature coefficient. As the temp drops, the resistance rises, and as
the temperature rises, the temperature drops. Thus, if you have a broken
wire, defective sensor, or bad connection (I've seen it happen) the resistance
measured by the ecu will be very high or infinite. The ECU interprets this
as minus a zillion degrees and pours in the gas.
The car I saw filled the oil with gas
and certainly wouldn't run. And the problem was only a displaced spade
lug in the plastic connector housing.
According to Chilton's (you may choose
to disregard this):
"The coolant temperature signal to the
control unit has a great influence on the computed injection period...
For example, when the engine is being started and is cold, the amount of
injected fuel must be relatively large.
"If the control unit receives a signal
higher than 302F (150C) or lower than -40F (-40C), it will interpret the
signal as a fault...the control unit will assume a substitute value corresponding
to 32F (0C) on starting and 68F (20C) when the engine has started.
"With the control unit connected, connect
a voltmeter across LH ECU terminals 13 and 5 (ground), turn the ignition
At 68F (20C) the voltage should
be 2.0 +/-.5v volts.
The resistance values between pins 13 and
5 or between pins on the sensor are (by eye from the chart):
At 104F(40C) the voltage should
be 1.2 +/- .3volts
At 176F (80C) the voltage should be .5
32F (0C)-- about 6000 ohms within a range of +/- 10%
68F(20C) -- about 2300 ohms "
104F(40C) -- about 1300 ohms "
140F(60C) -- about 600 ohms "
176F(80C) -- about 300 ohms "
212F -- about 190 ohms "
[Response 2: Steve Ringlee] ECT resistance
"cold" should be around 6k ohms at 32 degrees F (0 deg C), 2300 at 68 degrees
F (20 C), and 200 at 212 F (100 C). However, try checking your ECT wiring:
Between pins 13 and 5 at the LH ECU (with sensor DISconnected) resistance
should be infinite. Voltage with the ignition ON and sensor connected,
measured between pins 13 and 5, should be:
0 C=around 3 volts +/-.5v
20C=around 2 volts +/- .5v
100C=around .3 volt +/- .1v
If these aren't correct, check the connections
in the ECT wiring harness. Check engine ground connections at the intake
manifold. If the voltage is zero, your ECU is at fault.
Sensor Life and Diagnostics. Oxygen sensors should last over 100k miles
under ideal conditions; various contaminants will shorten that considerably.
For testing procedures and other info see: http://www.f-body.org/oldfaq/html/tech/sect2.html#oxysensor
[Further Notes on Sensor Tests:].
[Query:] Anybody know what the resistance of the O2 sensor heater should
be? mine says 2.2 ohms. With only the green wire connected to the ECU I
get a pretty stable .52 volts, which I have read in the archives to be
the ECU reference voltage. Hopefully all is well at that end. If I connect
the heater (there is ~13.5v on the harness side, btw) the sensor voltage
decays over about 30 seconds to .01 volts. At no time does voltage sweep
from .3 to .7 v. Also, can you replace the heated one with
non-heated? A Bosch Ford 5 litre sensor is $97.80 (cdn) at a local
import autoparts store, the Volvo sensor is $280 something. [Response
1: Abe Crombie] That is the right resistance on the heater. Before
you replace sensor warm up engine attach voltmeter to O2 sensor lead and
then momentarily pinch rubber return line behind fuel pressure regulator.
If the voltage of sensor goes to .7-.9 V then look for something else making
it lean. A faulty sensor can give you the low V reading but an air leak
or defective MAF sensor can do the same. With regard to heated (three
wire), versus non-heated (two wire), yes and no. The heated sensors
are used to keep the signal active while idling. Idling in cold weather
primarily, the sensor will fall below its 600F temp at which the reaction
that makes it output voltage begins to work. If it were to stay above this
temp the non-heated would be okay. There are different sensors out
there also. Most all the Bosch up to 92 have the same output voltage at
the same O2 gradient. After 92 there are differences in some of the applications
in this respect.
The Bendix/Siemens fuel sytem models use
a different type sensor and it is not interchangeable with the Bosch units.
This sensor does not work with a .5 V reference out of the ECM as does
the Bosch versions. This type uses the heater power supply to feed a sensor
circuit responds to O2 level variations. The Bosch type employs an electrochemical
reaction and the heater is for stability of the temp (and therefore the
signal) and not for the supply of current to be modified and used as output
Position Sensor Bad: No Re-Start after Hot Soak. Suppose the car already
has the upgraded silver-terminal fuel pump relay but won't restart promptly
after a hot soak. Take an educated guess on a weak crank position (RPM)
sensor. Replacing this permanent-magnet sensor, which is located in the
top of the bellhousing, fixes many hot restart complaints on 700s. See
[Note from Steve Seekins:] Note that if
your car is a turbo, you do not have the crank position sensor, but you
do have a Hall effect sensor in the distributor that can also be
the problem (cars with the crank position sensor do not have the
Hall sensor in the distributor). [Editor's Note: Not true in post '89 B230FT
cars: these have rpm sensors.) See also Intermittent
No Start Problems
Flywheel RPM Sensor. [Query:] I decided to find and remove my
flywheel sensor. Externally it's in perfect condition. The cable and ends
are pristine-looking. Is there a way to test it with a multimeter?
[Response: Ivan K] The problem with these rpm sensors is that they will
only fail intermittently. Usually, when they get hot. This makes it hard
to test. They are cheap enough. Just replace it. With high
mileage cars, it's only a matter of time before they fail.
a Knock Sensor. [Query:] How do I test the knock sensor? [Response:
Abe Crombie] If there is not a fault code for it then it is okay.
The ignition control unit tests it every time you exceed some thing around
3000 rpm with moderate to high throttle. If it is not torqued properly
it might not be as sensitive as it should or be overly sensitive. Torque
is 8-11 ft-lbs. It produces a high voltage pulse when it senses the
shock wave in the range of combustion knock. The voltage level is
proportional to the severity of the knock. It will read 1.5 or greater
megaohms but this is not really an effective test, only the control unit
detecting a sensor signal when the conditions would absolutely assure a
signal would be made is the real check. The knock sensor test by whacking
on block (better than on the intake) next to knock sensor (see Duane's
note below) is only effective on Chrysler systems with the throttle opened
as the closed throttle signal is supplied to Chrysler ignition ECU
and it cancels knock sensor retard activity. If you have Bosch
ignition systems you can't do the whack it and watch it test for knock
sensor operation. The Bosch systems are cylinder specific and you would
have to knock within a few crank degrees of a given cylinder firing and
be monitoring the timing light attached to that cylinder's plug wire. I
don't think any of us are that good. [Tip for Chrysler Ignition Systems
from Duane Hoberg] On the right side of the engine, in the area above and
to the rear of the oil filter, tap the block with a metal faced hammer
while observing the timing with a timing light. The timing should
retard 6 degrees then return. If not then the sensor or the circuit in
the control box is bad. When installing the new knock sensor, use
thread lock. Apply too much torque and the sensor becomes sensitive
as it is prestressed and reacts to normal engine vibration. When
this happens you will idle fine but above idle run at retarded timing all
the time. Acts like poor fuel delivery and doesn't like hills.
FAQ for 7xx/9xx/90 Cars
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