crank sensors

[knightrider31782]

How can u tell if your crank sensor is bad on a 1990 cavalier, 2.2L?, or how do u test to see if it is working properly?

[jdl]

I'm not sure what makes you think the crank sensor is bad? If it is a magnetic crank sensor, two wire. Take the connector loose from the crank sensor, the end that goes to the crank sensor, connect a dvom on the ac mv setting, crank engine, make sure the tranny is in park or neutral and the e-brake is set, block wheels, be careful. My info says you should see a minimum of 300 mv ac. You can also do an ohms test on the sensor terminals. Resistance should be 900 to 1200 ohms at 70 degrees. If the resistance is infinite or no resistance at all, either way it is bad. Might be wiring connector or wires, faulty. Cranking rpms can have an affect on the output of the sensor. Usually if the vehicle cranks good but won't start, I check for spark at the plugs and injector pulse, if I have neither then I check for an rpm signal. If you have spark or injector pulse while the problem is ongoing then it isn't the crank sensor, just my opinion. Any codes?

[knightrider31782]

Well thanks for the info but i already replaced the sensor and found that the old sensor was cracked, not sure why, but the reason i asked was because the engine would crank but not start, and i had plenty of spark and fuel + compression, and so after i replaced it the car started right up.

[jdl]

Glad you got it going. I've never seen a faulty crank sensor act that way. If the computor doesn't see any reference signal, it won't pulse the injector. It must have been seeing some kind of signal. On the ignition bypass mode, when cranking the icm controls the spark timing and the icm has to see some kind of crank signal or you won't have a spark. I guess it wasn't seeing the right timing signal? It would have been interesting to see the voltage output on the old sensor? I had a crank sensor problem on a different GM engine --- two wire magnetic sensor---no signal--- had no spark and no injector pulse. When I pulled the old sensor, I put a dvom on the two sensor terminals and waved a wrench in front of the magnetic end, I actually got a reading, don't remember how much, too long ago. Then I ohmed the same two sensor terminals and it showed open circuit, which I thought was weird. I wish I had checked the old sensor output with cranking rpms, before I pulled it, but I didn't. The new sensor fixed it. My vehicle never did set a code with this problem, did yours?

[Three_Fingers]

I've seen 'em crack almost in half and still work intermittently. I had a Chevy Celebrity that would just stall for the hell of it until I changed the CPS.
It too was broken all except for the center conductor which was the only thing holding it together.

[knightrider31782]

I don't know if there was a code i didn't check that, plus i don't have a scanner, the engine just wouldn't start but i was getting spark (maybe just at the wrong time?) and the injector was working.