QuestionHi Roland, I have a 1998 Sebring convertible with 143,000 miles on it. 2.5L V6. 4 months ago I replaced the crank position sensor, because I had a no-spark condition. (You helped me with that one - thank you.)
The car has been OK since then until yesterday, when it started acting up. After driving it for about 5 minutes, it started running very rough, like it was not firing on all cylinders. I thought it was going to stall, but it didn't. The accelaration was terrible though, and the check engine light came on. This lasted for about 10 minutes, and then it ran fine again, and I was able to get it home.
I checked the code, and it was P1391. That indicates an intermittent signal from either the crank position sensor or the cam position sensor (too bad it didn't specify which one!).
Maybe the new CPS is bad. Maybe I didn't install it correctly, although it has been OK for 4 months. Maybe it's unrelated to the work I did earlier.
I did some Internet searching, and others have had similar symptoms - it occurs after the engine warms up, and is OK when the engine cools down. But in my case, it got better all by itself as I was driving the car. I don't understand this.
Can you offer any suggestions as to how I might determine if either of the sensors are bad, or if it's a wiring issue? Thanks so much,
Bill
AnswerHi Bill,
Probably the way you will catch it in the act so be ready to measure the pulses from the cam and crank sensors when the problem begins. The sensor common ground wire (black/light blue) is on pin 43 of the pcm. You would put a voltmeter between that wire and either pin 33 (tan/yellow, cam sensor located in the distributor) or pin 32 (gray/black, crank sensor) to watch the signal pulses. If you carry a socket and handle to turn the crank by hand at the pulley bolt, and you put the ignition in the 'run' position, then having pins through the insulation to contact the wires, you can attach the voltmeter leads to the pins. As you turn the engine by hand, the reading should pulse between 5 and 0.3V (many times per revolution for the crank, just a few for the cam sensor). So ideally you catch one of those sensors not pulsing as described when the engine is not running well. You could also pre-check the wiring on those three lines, and there is a common 8v wire coming from pin 44 on an orange wire to the sensors (pin 2 of the 6 pin plug at the distributor, at the crank sensor plug) which you might also want to check when you are doing the sensor signal pulse check as it is possible that if that supply voltage were flaky then both sensors would have bad pulses (which is implied, sort of, by the 1391).
Please let me know what you learn.
Roland
