CODE 31 Cam Sensor circuit fault.. Help

[GOLDCYLON]

Who has seen it on their car? What were the symptoms? Mine is intermittent. THe cam sensor is fairly new. I used to get an occasionaly SES light and 31 was the culprit so I replaced the Cam Sensor and the problem went away.

About 9 months later now I see brief stumbling and then the car self corrects whith a hit of the accelorator. Almost like is missing on two cylinders, I see this particularly at idle. It only happens occasionally but this morning the SES set and 31 was was hard set I could not clear the code. First time that has ever happened. Usally the code clear I just used my auto X-ray on it I havent put the tech-1 to it yet.

Hoping somebody has seen something simular. Did the replacement Cam Sensor just go bad?

[sammy]

ck the connection ,when i first got my 90 i had this code set and found 2 things that caused it the connection wasnt solid at the sensor and i had a wire that had gotten hot over a long period of time and was very sneeky how it melted couldnt see it from just looking at it but when we ohmed it out poof it showed its open little head

[Aurora40]

From the Fuel and Emissions training guide:

Possible causes for Code 31:

1. An open in Circuit 633 or high resistance in any connections
2. An open in Circuit 450 (ground)
3. ECM failing to send out a signal voltage or recognize a signal on Circuit 633
4. Sensor pin 3 connector or sensor failing to operate
5. Too many CAM pulses -- EMI

Test Conditions:

1. Engine running above 400 RPM
2. No CAM pulse for three minutes since engine has started
3. Extra CAM pulses are detected for one second

Default Action Taken:

1. If Code 31 is due to extra pulses -- CAM pulse is ignored
2. Sequential fueling will continue, but not properly synched with the intake valve openings

[VetteVet]

Darryl,

You may want to check your crankshaft position sensor and it's circuits.

The ECM looks at cam sensor(CMP) pulses and compares them to crankshaft sensor(CKP) pulses. A problem with a crankshaft sensor or crankshaft sensor circuit can set a code 31. I've seen this problem with a GM 8.1L engine. Installed a Mercruiser reman long block. Engine would idle normally with only a very slight burble but would set a cam sensor code shortly after startup. Turned out that it was a damaged reluctor wheel on the crankshaft. I'm not saying that you have a bad crankshaft, just pointing out that when the CKP to CMP relationship check is done by the ECM, a problem on either the CKP or CMP side will set a CMP code.

I hope all of that makes sense.

Jep

[GOLDCYLON]

Well Ive checked the wiring it looks ok. I dont see and melting or breaks and the wires are well shielded. I ordered another cam Sensor just in case. When I return home next weekend I will try to get into the harnessing some more. Last time I have heard an engine stumble like this was when I blew an exhaust donut on a camaro. Of course the camaro didnt self correct. Its entirely possible the snesor has just gone bad but it is not very old so.....
Thanks for the ideas. I have a crank sensonr somewhere in the parts bin as well as for now the only hard code set is the 31.

[Aurora40]

Since they are a Hall-effect sensor, the distance the sensor is from the reluctor can matter. I don't think the cam sensor used any kind of a spacer, but maybe make sure it seats properly?

The crank reluctor wheel has unevenly spaced gaps, to help the ECM determine if it missed one. Though that said, the ECM is pretty simplistic on these older cars. I do believe there is a difference in crank sensors, the earlier cars had some kind of shim or something, and the later ones didn't? Has the crank sensor been replaced at any point to your knowledge?

[tomtom72]

This is a shot in the dark.

I used to have 31's set all the time. I finally used contact cleaner to clean the plug and some dielectric. I had done the dielectric without contact cleaner first and no joy. It seemed to want both. I'm not saying it's your solution, but if you never used contact cleaner it could be worth a shot.


Tom

[ittlfly]

Darryl,
I can't add a lot here but if you have to change out the cam sensor you are going to learn some new words. As you may recall, I just did it on my 94 a few weeks ago. The screams coming out of me weren't from being on "Mr. Toads Wild Ride".

[GOLDCYLON]

Originally Posted by Aurora40

Since they are a Hall-effect sensor, the distance the sensor is from the reluctor can matter. I don't think the cam sensor used any kind of a spacer, but maybe make sure it seats properly?

The crank reluctor wheel has unevenly spaced gaps, to help the ECM determine if it missed one. Though that said, the ECM is pretty simplistic on these older cars. I do believe there is a difference in crank sensors, the earlier cars had some kind of shim or something, and the later ones didn't? Has the crank sensor been replaced at any point to your knowledge?

Bob if I was to venture to gues I dont believe the crank sensor has ever been replace. just the cam sensor. I dont understand how the cam sensor can move out of place unless the bolt was not in tight enough. All there is is a single bolt and an o ring. But I will look into that as well thanks

[GOLDCYLON]

Originally Posted by ittlfly

Darryl,
I can't add a lot here but if you have to change out the cam sensor you are going to learn some new words. As you may recall, I just did it on my 94 a few weeks ago. The screams coming out of me weren't from being on "Mr. Toads Wild Ride".

Yep I remember but you replaced yours due to a leak only correct?