Cam Position Sensor/Crank Position Sensor Testing

#1
I drove my 87 GN out of the barn and parked it. When I went to start it to move it back into the barn, it wouldn't start. I'm getting fuel to the fuel rail, but it looks like no spark. What's the best way to test the cam position sensor and/or the crank position sensor to see if one of them is causing the issue? Thanks!
 
#3
The first thing to check is the fuses. Check and recheck. The crank sensor, a simple check is just look under the car and see if its still all in on piece. If it is and to check cam sensor you'll have to go to the no start tree and follow it down untill you find out which is the prob. Could also be the module or coil pack. Just look up no start tree, it'll pop up.
 
#4
Thanks TurboBuRick and Gene! That "No-Start-Tree" is great, I'm going to print that and keep a copy in the glove box!! If I can't get the thing started after running through the diagnostics laid out in that tree, I shouldn't be allowed to own the car, lol. I'll keep you posted on my progress. Merry Christmas!!
 
#5
I started down the no-start tree and came to a step where it said, "If you're getting code such-and-such, go to this branch." So, I got out my scan tool, hooked it up to the plug between the console and the dash, and got "No response from vehicle". I checked the configuration of the scanner, the connections at both ends of the cable, and still nothing. Is that the only diagnostics port on the car? I know some have another port under the hood somewhere and didn't know if the GN was one of those. I don't have another scan tool to try, any other suggestions? Yes, I did have the key in the "On" position.
 

TurboBob

Resident mad scientist
Staff member
#6
when you key on, does the check engine light do its On-Off-On sequence? What scanner? Have you used it on this car before?
 
#7
Yes, the check engine light goes on-off-on. The scanner is an Auto Xray EZLink. I've used it on other vehicles successfully, but the GN has never bothered, so I haven't had a reason to use it on that until now.
 

TurboBob

Resident mad scientist
Staff member
#8
cam sensor failure is a common cause of no-starts. take the cap off and see if the screw in the middle of the trigger wheel is loose. try to turn it and see if maybe the roll pin at the bottom of the sensor snapped. Loose/weak pins in the ignition module plug is another common issue. Blown fuses (there are 2), failed ignition module, and crank sensor failure.

the no start tree is a good place to start of course. we can help you with the steps.

Bob
 
#9
The no-start tree refers to Code 41 which is Cam Sensor failure (no output pulses).

You don't need a scan tool to determine if an error code is stored in the computer. Just use a metal paperclip to short pins A & B in the ALDL connector. This is the port your scan tool plugs into and pins A & B are in the upper row, right most 2 pins.

With the ignition On and engine not running, pins A & B shorted puts the ecm in User Diagnostic mode. It turns on the fan and energizes all the solenoids. But more importantly it blinks the SES lamp to tell you if a code is stored. The SES light will blink a “12” (On – Off, pause, On – Off, On – Off) and does this three times. Then if any trouble codes are stored, it blinks the trouble code number(s). It repeats this sequence until the ignition is turned Off. If just the "12" is displayed then there are no codes.