Code 31 - Camshaft Sensor

[Patton]

First and foremost Happy Labor Day weekend to all and even though most of us will be having fun, please keep your hearts and prayers with our fellow country men effected by Katrina.

Thanks to all who helped and are helping me with my secondary vacuum system problem I’m sure I will have my own project results to share with you all soon and just might help somebody in the same situation. I have one other problem I must address however, and I cannot find a copy of the shop manual for my '94 anywhere. I am still pulling a code seemingly unrelated to the others, 31 - Camshaft Sensor,... Where the hell is this thing and its related circuit? Maybe a part number or two? Any help would be great!! Thanks!!

[Patton]

Hmmm,... not a good sign.

[crjspo23]

Just had a similar problem. Backed my 90 ZR-1 out of the garage and it started idling rough, smoking, and Service Engine Soon light came on. Checked the code and found code 31, Camshaft sensor. Any words of wisdom to troubleshoot and correct?

[Mystic ZR-1]

Cut to the chase, Injectors...

[tomtom72]

Could be, or check the MAP hose at the rear of the plenum. As for the DTC 31 Cam position sensor, it's a hall effect sensor in the left cylinder head. I used to get that DTC quite a bit till I cleaned the harness connector.

In any event, if 31 does "set" the ECM puts the ignition and injectors into batch fire and locks out secondary port throttle activation. It assumes that with no cam position sensor, the car can't use our DIS box to control spark. It then chooses to use what I think is a limp home method of ignition control.

Are the injectors OEM? What color smoke? Kind of greyish to dirty white? You didn't happen to get a wiff of the smoke? Did it make your eyes water? That usually is a lean condition which supports bad injectors. It would be better to hook up a scanner to see what the ECM is seeing. Or pull a few plugs from both banks to see what combustion looks like.


Tom

[crjspo23]

Thanks Tom. When you got the 31 code did you just clean the harness connector up near the brake master cylinder with dielectric spray or something similar?

I don't think it's injectors as it ran fine until the SES light kicked on and it started running rough and got blueish smoke, like it was running rich and loading up.

I've seen a couple comments about the MAP hose. Where is it and what do you look for?

[tomtom72]

you're welcome! The MAP sensor is at the rear, center of our plenums. You can see the cover, and under that aluminum plate is the MAP sensor. The electrical connection and the vacuum hose are on the underside ( where you can't see them! LOL ) and that hose and it's ends are subject to the usual wear from heat cycles and the blow-by oil in our motors' internal oil mist.

Sometimes the MAP hose gets lost or gets soft. It is supposed to be a hard plastic hose so it can't get sucked shut by the vacuum that our motors produce. Sometimes oil blow-by builds up and blocks the vacuum from the MAP sensor, and sometimes people use a soft rubber hose as a replacement and it gets sucked shut. I now check my hose and MAP every month or two for oil build up. Just to keep a clean signal.

Oh, forgot this. If a back fire upon start up happens the MAP hose usually gets blown off and your symptoms are a result...the bad or rough running. The most common reason for the back fire is improper key work upon start up. Remedy is just to hold the key over to start until the motor actually runs.

The Cam sensor clean up I did is as follows. Spray contact cleaner in the female ends, and used a pencil eraser on the male ends, and then a dab of di-electric grease just to keep that rubber gasket and the terminals from having moisture get to them. I can't say as it's a permanent fix, but every so often I try to devote some time to going over all my connectors and ground points just to be sure.


Tom

[crjspo23]

So I assume you have to take the aluminum cover off to get to the MAP hose?

Thanks for the advice on the cam sensor connector. I'll try that.

[A26B]

Originally Posted by tomtom72

.....................I now check my hose and MAP every month or two for oil build up. Just to keep a clean signal.

.........................
The Cam sensor clean up I did is as follows. Spray contact cleaner in the female ends, and used a pencil eraser on the male ends, and then a dab of di-electric grease just to keep that rubber gasket and the terminals from having moisture get to them. I can't say as it's a permanent fix, but every so often I try to devote some time to going over all my connectors and ground points just to be sure.


Tom

Tom, I just gotta say, any ZR-1 would be lucky to have an owner like you! Mine are badly neglected compared to the treatment your ZR-1 receives. You are the top PM guy in my book!

[tomtom72]

Originally Posted by crjspo23

So I assume you have to take the aluminum cover off to get to the MAP hose?

Thanks for the advice on the cam sensor connector. I'll try that.

The only way I can actually see the MAP is to dismount it from the plenum. I'm a bit short ya see! However, as I've done it a few times I usually just reach my hand between the back of the MAP and the firewall now and I can feel the connector and the hose and work that way. Now all I do is climb up with my knees on the plenum or the tire and reach in and feel around! LOL


Tom