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.

:cheers:
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]

:handshak: 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. :o

:cheers:
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]

:handshak: .....................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. :o

:cheers:
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! :fahne:

[tomtom72]

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

:cheers:
Tom

[A26B]

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.

Here is a picture of the MAP hose Tom is referring to.
http://i190.photobucket.com/albums/z224/A26B/MAPSensorHose.jpg

[tomtom72]

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! :fahne:

You make me blush Jerry! I would like Her Majesty, Mistress, to read your post if that were possible. She is giving me the evil eye lately since my PM operations have moved outside to my parking space. She rather takes exception that She's not being worked on "indoors" so to speak!:sign10::sign10:

:o
Tom

[crjspo23]

Well Tom, looks like I'm not that lucky. I serviced the sensor connector as you said, checked and cleaned the MAP sensor hoses, reset the ECM, and got the SES light back when I restarted it. Got the same code 31. Looks like I need a new sensor. Anybody know if the camshaft sensor is still available thru GM or elsewhere?

[Mystic ZR-1]

31 was one of the many spurious codes my car had before injector
replacement. "Ohm out" your injectors before you get too carried away
replacing stuff. You can find out how to do it in the FSM
or somewhere on this site. Anyone know where it is in the site?
It seems after hanging around our site for a few years now, that
injector replacement cures most of the crappy running ills that 90 and 91s suffer...

[Hammer]

31 was one of the many spurious codes my car had before injector
replacement. "Ohm out" your injectors before you get too carried away
replacing stuff. You can find out how to do it in the FSM
or somewhere on this site. Anyone know where it is in the site?
It seems after hanging around our site for a few years now, that
injector replacement cures most of the crappy running ills that 90 and 91s suffer...

This thread might help. GL
http://www.zr1.net/forum/showthread.php?p=17299

[tomtom72]

Hi Charlie! Nice to make your acquaintance! I just checked over at RockAuto and they list one. You could contact Jerry at jerry's gaskets or Kurt White at White Racing to check to see if they have any NOS on the sensor.

Humor me for a moment, even tho I'm a bit eccentric. This sensor is an electro magnet and a reluctor wheel. I would pull the sensor from the head and check the face for sludge or dirt or anything that could weaken the magnetic field. Okay that's just me because I don't understand how an electro magnet breaks, sorry.:o Now mind the spacer that I think should be present to keep the correct gap between the magnet and the wheel.

Also, if you decide to ohm out the injectors using the ECM main harness plugs be aware that you can/should not use the probes from your VOM directly into the harness plug cavities. Those probes are just a bit too big to fit into the female terminals with out distorting them. You don't want that to happen. I'd use some phone wire to probe the cavities and then touch the VOM probes to the wire. If you spread those terminals even a bit you get an intermittent contact at the harness plug and it drove a member crazy with weird symptoms. Search threads under "TCrabs" to find his story. I just related the short version.

On another note. Is there another brother near you that would be willing to let you use their ECM. I had one of my ECM's go bad and give me a DTC61 and after pulling the plenum to check all the electricl aspects of the flow chart I found it to be the ECM and not any parts on the motor. Just bear that in mind. I don't have my FSM handy to look over the DTC diagnostic chart for #31 so I don't know if the ECM is listed as a suspect.

:cheers:
Tom

[crjspo23]

Seems to get more complicated by the minute. Anyone know a knowledgeable Z mechanic in the Piedmont area of central NC I could take it to?

[tomtom72]

I don't know of anyone that I could send you to. Are you anywhere near Hendricks, he owns the snake skinner car so I would think he might have some one familiar with an LT5 on his staff. That's just a shot in the dark on my part.

However if you are inclined to want to do this yourself we are standing at the ready to render any assistance we are able to thru this forum. If you were a bit closer I'd just drive over with my stuff and we could see what's up. Are there any other Z Brothers near you?

:o Also forgot this. I never actually found the reason for my car giving me the DTC 31. I noticed one thing that was consistent about the episode though. It seemed that if I altered the way I start my car I could avoid getting that DTC. Yes, weird right? I learned to not be in a hurry when starting her. Now I turn the key to "on" and light up the DIC, wait till most of the lights go off, and then go to "start". When I wasn't doing that I would get the 31. Yea I know I should pull the cam sensor and look at the face or just buy a new one. I'll get around to it eventually I guess. :o

:cheers:
Tom

[crjspo23]

Guys, need some more help. I took my car to a mechanic that knows Corvettes well but is not expert level in ZR-1's. He has confirmed the cam sensor is not causing the problem (tried a new one with no change) and also confirmed 2 injectors are bad after ohm testing (#1 and #2 primary), but he says he can't check the secondaries without removing the plenum and he is not convinced the injectors are the only problem.

Any other ideas or advice to isolate the issue?

[A1990]

The overriding consensus is that if you have a bad injector, that you replace all of them.

Order a new set and pull the plenum and check other parts "while in there"

[crjspo23]

Are the Accel 150821 injectors still the choice for replacements? From the research I've done, they appear to be direct replacements.

[tomtom72]

Check out this link. It is Marc Haibeck's take on doing some of the diagnostic operations that may be of use to you.

http://www.zr1specialist.com/HAT%20Web/articles%20index.htm

:cheers:
Tom

[A1990]

Are the Accel 150821 injectors still the choice for replacements? From the research I've done, they appear to be direct replacements.

I have RC injectors in my car, but a lot of the members here use the FIC injectors (new ones)

Call Jon, they are a member of the Registry and a supporter here.

fuelinjectorconnection.com/shop (http://www.fuelinjectorconnection.com/shop)

[crjspo23]

Actually got a referral to the Fuel Injector Connection today and ordered a set of the Delphi replacement injectors. They are supposedly prepped for direct installation, flow tested and matched. They also sell the plenum gasket set with it.

Anybody had experience with these? Also, any nice step by step instructions for injector replacement and plenum R&R out there?

[tomtom72]

Charlie, a large number of the Z brothers have used Jon's new s/s replacement injectors with great results. Good parts at a fair price, and the gaskets are a very high grade of reproduction gasket from Jerry's gaskets.com.... it's one stop injector r&r shopping at it's best. Great choice!

:cheers:
Tom

Over at Marc's site I believe there is a step by step on the injectors. I know over at PNWZR1.com there is a "how to" write up, over at corvetteactioncenter.com I also believe there is a thread. Also, I think in Cliff's "Solutions" section here there maybe a step by step. If after checking all of these you still have Q's post up. :handshak:

[crjspo23]

Ok guys, the saga of the poor running Z continues. Got a new set of Delphi SS injectors installed, started it, and it still acts like it's running on 5 or 6 cylinders. Ohmed out the new injectors and they all check fine. Checked fuel pressure - good. ECM seems to be communicating with the scanner fine. Only theory at this point is the plugs may be fouled from the injector failures. Any other thoughts or suggestions?

[tomtom72]

Charlie, hummmm now this is going to be something stupid, ya just know it! Trouble is we have to noodle the answer. I think you should start a thread of your own on this subject so your issue don't get lost in Patton's stuff. Just give a synopsis of what was done and the symptoms.

I'll go get my FSM and start reading and check back at coffee break or lunch and see if I can contribute something useful. Fear not! No Z left behind!
I'd check the plugs for sure though.

:cheers:
Tom