Cam Sensor or Crank sensor???

[lazaris]

I was having a missing problem at around 3500 rpm light throttle. I did the usual tests along with changing the coil pack and the cam sensor. The reason the I changed the cam sensor was that I tried disconnecting it with the car running to see if the miss went away. What I discovered was that while coming up at arounnd the same rpm that it was missing at with it disconnected the car just shut of. So I changed the cam sensor figuring it was that. Well the miss is still there and if I disconnect the cam sensor while running it shuts off still. Is the cam sensor influenced by the Crank Sensor? Any ideas would be appreciated.

 

[y-hate]

Check your plugs, plug wires or coilpack

 

[lazaris]

The coil pack is new and why should it shut off at that specific point with the cam sensor unplugged. I think its beyond the wires/plugs.

 

[HighPSI]

If you unplug the cam sensor and the car shuts off instead of misses, it's not the cam sensor. In fact, the cam sensor is doing it's job and "resincing" the engine when it misses. I would check the crank sensor first.

 

[lazaris]

Thanks Cal. After disconnecting it, it only shuts off when getting to that specific rpm of around 3500, where it would start breaking up when it was connected. It must be re-sync ing itself when its connected. What should I look for or test on the crank sensor other than the correct gapping ?

 

[Garycar]

I tried measuring the resistance of a bad crank sensor as well as a new crank sensor. The resistance values were identical. I believe there is a way to test the crank sensor with the motor running but it involves a scope and the diagnostic knowledge to go along with it. In lieu of that I simply replaced the crank sensor and my skipping/popping went away. I have had 2 crank sensors go bad. In both cases the motor would start and would run ok under light throttle. This has only happened with my state 1 motor. I have never had a bad crank sensor with my stock block original motor. The gap was correct on both sides and the bracket holding the sensor was tight and not broken. I keep a new crank sensor on hand just in case.

 

[lazaris]

I'll be going out today and testing the grounding and may add another ground to the module. If that doesnt work I'll buy a crank sensor and module to test. Either way I'll have a spare of one that way. Any other ideas are appreciated. I'll post the results.

 

[ijames]

Put a timing light on it. You should be able to see missing flashes or big jumps in timing as you slowly rev the engine. Also, have you reset the cam sensor lately? Maybe try rotating it a little each way to see if that affects the miss - you might be right on the edge of the window.

 

[GNVenom]

The cam signal must be present to initiate sequential spark. From that point, the crank sensor takes over to sync the spark. The cam sensor sync's the injector sequence via ECM. So, if the crank signal is missing or inadequate, you won't see spark, and if the cam signal is not present, you'll get neither spark or fuel delivery. That's usually how you can determine which of the two sensors are bad; CRANK: Fuel thru injectors but no spark. CAM: No spark and no fuel thru the injectors.

I have seen crank sensor problems occur when the thrust bearing at the crankshaft wears out. The crank slides forward too far, causing the interruptor ring to move out of the range of the crank sensor slot, causing a loss of spark. Deceleration causes the crank to slide back, bringing the interruptor back into the slot, engine runs fine. This one will drive you crazy.

Are you using an aftermarket module? The reason I'm asking is that our CCCI tester won't work properly with some aftermarket modules...the cam sync signal generated in the tester is only a single pulse at power-up. The GM modules work perfectly, but the sync signal sometimes doesn't make it to the aftermarket style modules. Check to see if you have an OEM style module. If not, GET ONE!

-John Spina

 

[lazaris]

Well first off a big thank you to all that replied!
It was the crank sensor. I dont know if it was in fact an internal/electronic issue as much as I found the sensor to have some play in it where it attached to the bracket. It appears as though the plastic was worn or shrunk a little (original) . I think what might have been happening was that the play created was causing it to move and changing the gap between the interupter ring. The new one sat in there nice and snug with no play. Thank you again. Maybe this will help out some others in the future.