? Crankshaft Position Sensor? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 11-11-2014, 04:14 PM   #1
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Default ? Crankshaft Position Sensor?

I have 91 Buick, 3.3 engine,
a few weeks ago, it started to stall out on my wife, (noticed it would at times start hard) no codes, besides the one that say it is misfiring,

first thing I did was fuel filter, old one was not bad, and did a fuel pressure tests, all showed up as OK, from what I know, and according to the shop manual,

one morning when she went to start it it would not start, it would not start, so I check the fuel pressure, it was OK,

and used a test spark plug and had no or very weak spark,

later that day, it started up and ran, I ran it to the shop,

next I ordered a new coil packs, coil controller,

put on and it ran but when accelerating it would miss,

so I order a crank case position sensor, (actually two of them they were on close out)

put it on and no start,

figured I must have messed up some how,

so I take back apart, and I can not see that I had done any thing wrong,
(I have done this before a number of times),
I take the "new" sensor off and look at it,

so I get the idea to take an ohm meter and using the old one, (i took off or attempted to replace),
I put the leads on the first two pins to the right, with the security tab up,
the reading was some like 15.3 ohms,
the third pin, and the right pin was 1.2 ohms,
and the 4 pin was 1.3 ohms,

now I take the sensor I just took out and try the same and there is no Ohm, reading between any of the pins,

I take the other new unit and I get a small ohm reading on pins to the right, and none on the left,

I have another name brand unit coming.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

the question, is

is there a way to check the sensor out side of the car? I am not saying to know if it works necessarily but at least the circuity is intact,

is there some way to "test" it to see if it is dead?

I am not saying any of the readings are "right" but when I get three different readings, and the one that is know to function "some", has drastically different readings, and one known not to work, and the third is some where between but I do not trust it,

but since is a some what time consuming process I would like to be able to test be for installing, to see if it is a viable unit.

the simple question is, is there a way to TEST IT OFF CAR?
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Old 11-12-2014, 01:32 AM   #2
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There are some good threads to test the crank sensor and ICM under troubleshooting and diagnostics thread. Hopefully they can give you a little help.
https://www.gmforum.com/trouble-shoo...-start-296982/
https://www.gmforum.com/trouble-shoo...m-test-299761/
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Old 11-12-2014, 08:18 AM   #3
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Doesn't seem right. The sensor is only going to read the voltage when you are cranking, it puts out a square wave so you read the average with your meter. I can't think of a way to test it on the bench easily
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Old 11-12-2014, 06:19 PM   #4
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To my knowledge there is no way to test the crank sensor off the car. I don't think a bad crank sensor will cause an engine to not run. It may run badly, but it will run.
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Old 11-12-2014, 06:51 PM   #5
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Quote:
Originally Posted by 2kg4u View Post
To my knowledge there is no way to test the crank sensor off the car. I don't think a bad crank sensor will cause an engine to not run. It may run badly, but it will run.

I will tend to disagree with you as a bad crank sensor has left me in the middle of rush our traffic in the winter in the dark, in down town Denver, we were following a friend and called him on a cell phone and he circled around the block and pushed the car off in a parking lot for me, left it there over night and came back the next morning and it did start, and run (we dollyed it home the 3 hr drive as I did not want to be setting on the interstate and no way to get home, and destroy the transmission attempting to tow it,

I know a bad Crankshaft sensor will keep the engine from running, or put it this way it will keep my Buick from running,

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

thank you all for the replies, I know I could not find any info on checking it out off the car, found some info on with it on the car,

when it is interment problem (I think this one is heat related) as when it was cold it would not run/start, but when it was above 40 to 50 it would start, and I am guessing when it gets hotter, it my cut out again, as my wife was having problems in town in stop and go traffic,
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Old 11-12-2014, 09:34 PM   #6
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Hope this helps. Some auto parts stores can lookup resistance values for modules and sensors when testing parts.

•General System Description

COILS

Three twin tower ignition coils are combined into a single coil pack unit. This unit is mounted to the C3I module. Each coil provides the spark for two spark plugs at once simultaneously (waste spark distribution). However, all three coil packs must be replaced as a unit if one of the coils is defective. Between the coil pack and the module is a row of three terminals which run along each of the sides of the coil pack. One row of terminals is connected together by a common wire from the module, suppling all three coil packs with +12.0 volts. The other side row of three terminals are individually connected to the module. The module will only connect one coil at a time, in the correct order by suppling and removing the primary circuit ground to each coils at the proper time.

MODULE

The C3I ignition module monitors the camshaft sensor and the crankshaft sensor signals. This information is transmitted to the ECM so that the correct spark and ignition timing can be maintained during all driving conditions. During cranking, it monitors the cam signal or "Sync Pulse" to begin the ignition firing sequence. Below 400 rpm, the module controls spark advance by triggering each of the three coil packs at a pre-determined interval based on engine speed only. Above 400 rpm, the ECM controls the spark timing (EST) and compensates for all driving conditions. The C3I module must receive a cam signal then a crank signal in than order to enable the engine to start. The C3I module is not repairable. When a module is replaced, the coils must be transferred to the new module




The Computer Controlled Coil Ignition (C3I) system consists of a crankshaft position sensor, the Electronic Spark Timing (EST) portion of the ECM, an ignition module, three ignition coils, in a one piece unit called a coil pack, and the related connecting wires.

The crankshaft sensor sends a signal through the ignition module to the ECM. The ECM uses this reference signal to calculate engine speed and crankshaft position.

In much the same manner as the distributor type ignition system, this system uses the EST signal from the ECM. Above 450 rpm, the ECM applies 5.0 volts to the ignition module (bypass circuit) signaling the module to allow the ECM to control the dwell and spark timing. This is called EST mode. During EST mode, the ECM compensates for all driving conditions.

Three separate coils are mounted to the module assembly. Each coil provides the spark for two plugs simultaneously. Each coil can also be replaced separately. A "Waste Spark" method of distribution is used on this system. Each cylinder is paired with its opposing cylinder in firing order so that one cylinder on the compression stroke fires simultaneously with its opposing cylinder on the exhaust stroke. Requiring less voltage to fire the plug on the exhaust stroke, most of the available voltage is sent to the compression stroke cylinder. This process is reversed as the cylinders' roles are reversed.

The ignition module controls spark timing under 400 RPM and must receive a "sync-pulse" followed by a Crank Signal in that order to enable engine start up. The ignition module monitors the crankshaft sensor signals and based on these signals, sends a reference signal to the ECM to allow the correct spark and fuel injector control to be maintained during all driving conditions.
•Electronic Spark Timing

In the EST mode, the ignition spark timing and ignition dwell time is fully controlled by the ECM. Above 450 rpm, the ECM applies 5.0 volts to the ignition module (bypass circuit) signaling the module to allow the ECM to control the dwell and spark timing. This is called EST mode. During EST mode, the ECM compensates for all driving conditions. The ECM relies on the following inputs to calculate the EST signal:


•Crankshaft sensor
•Coolant Temperature Sensor (CTS)
•Mass Air Flow sensor (MAF)
•Knock Sensor
•Park/Neutral switch
•Throttle Position Sensor (TPS)
•Vehicle Speed Sensor (VSS)

To diagnose any of the above components refer to COMPUTERIZED ENGINE CONTROLS .

The EST system utilizes several input circuits. These input circuits include the Crank Reference, Bypass signal, the EST output, ESC (knock sensor), all of which are described below.

Crank Reference - This circuit provides the ECM with rpm and crankshaft position information from the ignition module. The ignition module receives the signal from the crank sensors hall effect switch. This signal will either be high or low, depending on the position of the interrupter ring. This high-low signal is used to trigger the ignition module for ignition operation and by the ECM to calculate fuel injection timing. Both the sync-pulse and crank sensor signals must be received by the ignition module in order for a reference signal to be produced on CKT 430. A loss of the reference signal would prevent the engine from running.

Bypass Circuit - The ECM either allows the ignition module to keep the spark advance at module mode 10°BTDC, or the ECM signals the ignition module that the ECM is going to control the spark advance EST mode. The ignition module determines the correct operating mode based on the level of voltage that the ECM sends to the ignition module on the bypass control circuit. The ECM provides 5.0 volts to the ignition module if the ECM is going to control spark timing EST mode. If the ECM does not turn ON the 5.0 volts, or if the ignition module doesn't receive it, the module will keep control of spark timing module mode. An open or grounded bypass control CKT 424 will set a code 42 and the ignition system will stay at module mode advance.

EST Circuit - The EST output circuitry of the ECM sends out timing pulses to the ignition module on this circuit. When in the module mode, the ignition module grounds these pulses. When in the EST mode, these pulses are the ignition timing pulses used by the ignition module to energize the ignition coils. Proper sequencing of the 3 ignition coils is always the job of the ignition module. If CKT 423 is open or grounded when the engine is started, a code 42 will set and the ignition system will stay in the module mode. If CKT 423 becomes open or grounded during EST mode operation, The engine will quit running but will restart. Upon restart, following an ignition cycle, a code 42 will be set, and the ignition will operate in module mode.

ESC Signal - The ESC system is comprised of a knock sensor and the ECM. The ECM monitors the ESC signal CKT 457 to determine when engine detonation occurs. When the knock sensor detects detonation, the ECM retards the timing EST to reduce detonation. Retarded timing can also be a result of excessive valve lifter, pushrod or other mechanical engine or transmission noise.

MODULE MODE

While the engine is being cranked the ignition module controls spark timing. This is known as bypass timing mode because the ignition module bypasses the ECM. The ignition system operates independently of the ECM, with module mode spark advance always at 10°BTDC. The ECM has no control of the ignition system when in this mode. In fact, the ECM could be disconnected from the car and the ignition system would still fire the spark plugs, as long as the other ignition system components were functioning. If an ECM/EST fault is detected while the engine is running, the ignition system will switch to the module mode. The engine may quit running, but will restart and stay in the module mode with a noticeable driveability complaint.
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Old 11-12-2014, 09:34 PM   #7
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The only "quick test" on a crank sensor, that I know, is get the vehicle to normal operating temp....then take a long extension, and lightly tap the PEDESTAL of the sensor, not the sensor itself......

This has to be done while the engine is running......however you have a running serp belt in that area....

So first, you should practice doing this with the engine not running.....it'* fairly easy.....once confident, then do it with the engine running, and be very mindful of that serp belt....YOU DO NOT WANT THAT EXTENSION TO GET CAUGHT IN THE BELT....

If the sensor is bad, the slight jarring caused by tapping the PEDESTAL, will cause the engine to stall or stumble....found many bad crank sensors this way...hit the PEDESTAL, not the sensor/harness....
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