Crank Position Sensor

It was Friday afternoon and I had just settled in my Lazyboy to do some E-Mail reading when the phone rang. It was my buddy, Ralph, who had just been towed home on a flatbed. His 90 Chevy Celebrity 3.1L wagon had died suddenly on the way back from a windsurfing session on Lake Ontario. The car had died and refused to start although the starter motor cranked the engine over at a normal rate. Ralph has a bit of car savvy so he did some checks and found that he had no spark. He called AAA and they came in about half an hour to tell him that they would be right back - had a priority call or something. About twenty minutes later Ralph decided to give it a try and lo and behold it started and ran like there was nothing wrong. He drove back to his son's house and called home to tell his wife that he was OK and on his way home.

As he returned past the spot where he had stalled out earlier the engine sensed something and decided to die right there only on the opposite side of the highway - that confused the AAA driver who had just then returned to the scene to pick up Ralph. He flatbed towed Ralph to his driveway where Ralph decided to give it one more try and sure enough it started again!

Ralph decided that MisterFixit might give him a clue so he called me. After listening to his tale I was reminded of the Buick that acted up when the engine was hot. I suggested to Ralph that either the crank sensor might be heat sensitive and told him about the Buick. In his engine there is no distributor. It is called a DIS (Direct Ignition System). The ignition module receives a signal from the sensor which tells it when to fire number one cylinder. From then on the ignition module takes over and follows the firing order. With no signal from the crank position sensor the ignition module won't generate a spark. Ralph went to the auto supply store and bought one.

That when Ralph called me again and asked if Arleen and I wanted to go to his house for hamburgers on the grille. I told him that sounded like fun so I put on my work clothes and Arleen and I headed south.

After dinner Ralph showed me the picture of the engine in the shop manual which he had gotten from the library (I told you Ralph was a smart guy, didn't I?). It was a typical picture showing the location with the engine removed from the car and nothing else attached to it. Ralph thought he had found the correct sensor but it was up between the transmission and the block where one could hardly see it much less reach it.

I crawled under the wagon and looked up at the sensor - Ralph had succeeded in getting out the bolt that holds it in place but it wouldn't move out of its mounted position. It is just stuck into the side of the block and has an o-ring in a groove to prevent oil from getting past it. No big deal, just take a long screwdriver and a small hammer and urge it out of its hole. After a few light taps on each side of it I saw it pop out so I reached up and grabbed it. I could feel that something was wrong - it seemed to be coming out in two pieces. It seems that the plastic housing had cracked in half at the groove that holds the o-ring. The only thing that was holding the two pieces together was one of the wires that ran thru the unit. Luckily it held together long enough to pull out of the block.

I inserted the new one, put the retaining screw back and connected the connector. Ralph hit the key and it started and ran like a top. We let it run for an hour to make sure we had cured the problem. No problem!!

Here is a thumbnail of the crank position sensor taken from the business end. Note the shiny tip on the end. It is the pole piece of the magnet that is contained inside.

Looking at the connector end - this is the end you will see looking up between the back side of the engine and the transmission.

From the side view you can see where the o-ring fits into the groove - note that the unit is on two pieces now.

Message me at BobHewitt@Misterfixit.com

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