Thread: Replaced Crankshaft position sensor, now won't start

This is my first post, so it will double as my introduction. I just bought a 2003 grand prix for 500 dollars because the p.o. thought the transmission was going out. It shifts pretty hard between gears. However, I noticed the tach was not working and after some google searching I thought maybe the problem was the crankshaft position sensor. I drove the car to autozone and their scanner confirmed. So I drove it home fine, pulled it into the garage, and got to work on replacing the sensor. I got the pulley removed, replaced the sensor, reinstalled the pulley and belt, and disconnected the battery to reset the check engine codes.

I came back out about 30 minutes later and reconnected the battery and it wouldn't start. It cranks and turns over but it won't start. At first I thought maybe it was due to the crank being turned and putting it in a different position, but since the pulley is slotted that didn't make sense. Then I thought maybe the new sensor was faulty, but I believe it should still run, just poorly. Maybe disconnecting the battery did something to the anti-theft?? I'm not sure how the anti-theft works on this car.

My other thought is maybe both c.p. sensors are bad and I need to replace the other one on the back of the block, but why would it run before hand?

Any advice or suggestions? I'm out of ideas, and I hated having to push the car outside after I drove it in..... :/

Thanks in advance,
Jason

UPDATE: Took the new sensor back off, exchanged it, and reinstalled another cps. Put it back together and this time it started. It was a bad sensor out of the box. However the check engine light was still on so I replaced the 7x cps on the backside of the motor and light is now off. However the car still shifts in an almost pulsating way. It stumbles and buckles when changing gears, and the tach is still intermittent.

Any ideas? I was thinking maybe a bad ground for the ecm? But I'm not sure where the ecm is located.

is it a 3.8 NA or S/C?

It's a 3.1

The trans pan was dropped and the filter was replaced not too long ago by the p.o. in hopes it would fix the problem. The level is still good and it looks pretty clean. I'll check the maf but that wouldn't explain the tach. I'm thinking maybe a bad ground somewhere the the pcm

Another update. I took the intake apart to get to the computer. The connections looked good, but I unbolted it anyways and left it all unplugged for a while. I also cleaned out the intake with throttle body cleaner and cleaned as far into the throttle body/intake manifold as I could. Let it all dry and put everything back together. It fired up the first try but the tach still doesnt work and the shifting still "chuggles" as I've seen it called.

I saw another thread talking about installing shift kit shims and springs to help the shifting, as it is caused by torque converter lockup due to slow shifts. I ordered a shift kit, and it should be in within a few days.

Can anyone tell me what gives the tachometer a signal? I thought it was the crankshaft sensor but those are now both new and it still isn't working.

It should be the crank sensor that signals the tach. turn on the engine and tap the gauge or top of dash and see if it works. could be a dirty connection behind the cluster. you could also connect a scanner and pick datastream to see if computer is receiving an rpm reading when the gauge isn't.

The crank sensor didn't seem to make any difference. I've tapped all around the cluster, that didn't do anything. And every once in a while the tach will either work properly, or jump around like its having a seizure, but the engine will stay consistent.

I cut the tcc solenoid wire to the transmission to disable lockup and this did stop the "chuggle" during shifting, but the next day it started doing it again and the tach went nuts.

Another thing is sometimes the car won't start and I have to disconnect the battery for 10 minutes to get it to start.

I'm thinking with both of those problems and the fact that the cps goes into the icm, could the icm be bad?

Got the jerking shift to go away by clearing the codes and driving it long enough to relearn the sensors. However the no-start problem is still there. Seems like it starts fine the first or second time but after about an hour of not driving it, it won't start. Tach signal is still in and out as well, but seems like it starts working after the learn procedure is complete (driving for about 15 minutes). I have new crank sensors in, so I'm thinking the icm is bad.

Would that make sense? My thinking is the crank sensor goes through the ignition module, and once the sensor finishes the learn procedure, the tach works but the icm has a problem and can't read it correctly after it's learned the next time I try to start it, so it won't start. Anybody agree with that or have a different idea?

Bump.

Anybody have any ideas? I need to get this car back up and running. It still won't start without disconnecting the battery for 10-15 minutes. WHY?!?!

Originally Posted by 03grandprix

Can anyone tell me what gives the tachometer a signal? I thought it was the
Crankshaft Position Sensor but those are now both new and it still isn't working.

I do agree that the crankshaft position sensor sends the tachometer a signal. It measures magnetic fluctuations and sends it to the car's computer as well as the tachometer.

Replaced both sensors, rewired the sensor, and still no help. I sold the car to someone else, they can waste their time on it now.