Sensor school

[James Scott]

Please someone (anyone) learn me about some of these sensors I keep hearing about. Please tell me the FUNCTION, and SYMPTOMS of MALFUNCTION, so I can understand how my engine works [and also how these might be involved in my present problems - intermittent rough idling and car shuddering (shaking) that are undiagnosable to date]:

1. Crank sensor
2. Cam sensor
3. Knock sensors
4. Throttle position sensor

THANKS Jim

[svx_commuter]

The crank sensor is a magnetic pick-up, there are two mounted to the oil pump frame right at the top of the engine. There are two revolving plates with points attached to the crank, the points pass by the crank sensors. When the point passes by the sensor it generates a voltage pulse that tells the ECU where the crank position is located. This is used to adjust the timing of the engine so that the ECU know where top dead ceneter is for each pistion. If these fail the engine will not know when to fire.

The CAM sensor is also a magnetic pick-up the reads the position of the driver side cam shaft. I am not sure why it's there. I'll check the SM.

Knock sensor are accelerometers used to measure the engine vibration and to find firing detonation and adjust the timing thru the ECU. If these fail the engine should still run but may detonate.

TPS tells the ECU where the throttle position is. This is a variable resistor that changes value in proportion to the gas position. The ECU and the TCU use this device. If it's got dead spots the ECU would know what's happening. Search on TPS test.

Maybe someone could you loan you working sensors to see if the problems go away.

[Noir]

so how do you tell if your knock sensors are out?

[Beav]

Originally posted by svx_commuter


The CAM sensor is also a magnetic pick-up the reads the position of the driver side cam shaft. I am not sure why it's there. I'll check the SM.

The engine rotates twice for any one given cylinder to fire (four cycle.) The crank sensor only tells the ECU when #1 is at TDC (top dead center.) In order to determine if the cylinder is at the top of the firing cycle or the exhaust/intake cycle it needs to read from the camshaft, as it only rotates once per two crankshaft rotations.

[James Scott]

OK! I appreciate the info on the sensors, but what about the Knock and Throttle Position Sensors:

Would either (on intermittent failure) produce a rough idle or poor performance as I've described earlier (under transmission post by James Scott).

THANKS, Jim

[Beav]

The knock sensor will not affect the idle and it would be very odd that the TPS would either. The TPS can cause many assorted maladies as the computer tries to figure out how an engine would produce a rpm figure with the throttle only open a certain amount (if the TPS was reporting incorrectly.) The TPS can also affect shift quality and shift timing, as the transmission relies upon it also. I'm not saying that this is or isn't your problem, but it is worth checking into. It's not, in my opinion, worth buying one just to find out though. There are ways to check the TPS with meters, etc. The knock sensor(s) will cause the computer to light the check engine light if bad.

[James Scott]

Thanks Beav! That helps my understanding alot!

I forgot to mention one more sensor in my post > > > > >

What about the Mass Airflow Sensor? Please give me some schooling and your opinion on its possible involvement.

THANKS AGAIN for all your time and expert advice, Jim

[svxistentialist]

Jim,

You might be interested in the following;
The Workshop Manual has a troubleshooting chart for the fuel system. It lists probable causes in order of priority, #1 being first call.

This priority system indicates which part to check first,but I am not sure this means it indicates this part is most likely culprit, or is the easiest and most sensible to eliminate from the list first.

Here's the list for "Rough Idling" :

#1 ECU power supply*
#2 By-pass air control solenoid valve
#3 Air flow sensor
#4 Ignitor
#5 Ignition coil
#6 Spark plug
#7 Fuel pump
#8 Pressure regulator
#9 Fuel Injector
#10 Throttle Sensor
#11 Water temperature sensor
#12 Crank angle sensor 1
#13 Crank angle sensor 2
#14 Cam angle sensor
#15 02 sensor 1 & 2

* Instructions to "Include ECU grounding circuit"

Joe

[James Scott]

Yes Joe, Thanks for the nice diagnostic priority list. [I just typed a long response to bring this up to date and deleted it by mistake. YIKES!] I'll have to update my story later >>>

THANKS AGAIN, Jim