Originally Posted by ZR1CK
Hey guys.
I've also been having an issue with my '91 Z in getting a fault code 31 and I have the same or similar "Service Manual" but for the 1991. My engine does not run okay, it stumbles, bucks and sometimes stalls. The two pages you show here are the same as I have in my manual. I've gone through that diagnostic tree, cleared the code, checked the wiring & connections, measured the voltage, measured the grounds and keep getting a code 31, leading me to believe it must be the cam sensor. According to the info on the first page (6E3-A-50), last paragraph under Diagnostic Aids, "When probing CKT 633 at the ECM, DVM should read ignition voltage with the ignition "ON"...", (that is ignition ON, engine OFF) which makes sense according to the diagram at the top of that page. BUT, in the last paragraph under Test Description, it states "Normal voltage produced by the camshaft sensor is 0 to 5 volts", which does not make sense. The MAP sensor, Throttle Position sensor, IAT sensor and others have a 0 to 5 volts referencing. I believe that the "0 to 5 volts" for the cam sensor is stated in error as I have found several other errors throughout the manual. I purchased a NOS (I hope) cam sensor through e-bay and did a bench test. I applied 12 volts across terminals "A" and "C" and a DVM across terminals "B" and "C". The DVM read 12 volts until I placed a wrench near the face of the sensor, mimicking the movement of the reluctor wheel on the camshaft, at which time the voltage dropped out. Moving the wrench back and forth altered the output voltage up and down as in a square wave signal. According to the testing procedure in the manual, this sensor is working backwards, whereas I should be reading a high voltage when the wrench is near the face of the sensor and low when taken away. I'll be installing the sensor today and see what readings I get then. As far as the gap goes, I believe it needs to be between 1 and 5 mm, according to other references I've come across. I also butted the old sensor against the new one and they are exactly the same length, which tells me the gap will be exactly the same as the old one.
The reason I bought the sensor on e-bay instead of a Chevy dealership or any of the auto parts stores is...nobody, and I mean NOBODY, has one. And if you do find one for sale, you will pay dearly. Nothing against e-bay, I've purchased many items through them and have been completely satisfied. It just so happens I stumbled across it while searching just for the heck of it. And I did pay, I had to, the motor can't run right without it. Which leads me to my next issue.
The "General", back in the day, decided to build this "elite" engine to compete in the high performance world. And the results were awesome. BUT, how can you design and engineer such an "icon" and not factor in such a trivial replacement part that disables this icon useless without it? It is baffling to me to say the least. I have been able to find replacement sensors for the MAP, IAT, TPS, crank and pretty much every other sensor fairly easily and at a fair price for the engine except the cam sensor. From what I gather, the C4 LT5 cam sensor is only applicable to the C4 LT5, whereas the other sensors on that motor are compatible with other engines. Therefore, manufacturing aftermarket parts can be worth producing if there is a demand from a large category. BUT, with the C4 LT5 population being a very small one, it's not worth reproducing that cam sensor. Who's the brainiac that thought this up? If you cannot replace a failed part of this "icon", even as small as a simple cam sensor, then this "icon" is no more than a pile of scrap metal, or a boat anchor. Sorry.
If this sensor I just bought works, then I'll most likely be selling the "Z" in the spring. If it doesn't work, then I'll continue to search for one over the winter that does work OR replace the motor with an LS. I've pretty much bought the "Generals" vehicles throughout my life. Currently, along with the "Z", I own a 1992 full size Blazer, a 2009 Impala, a 1972 Corvette and a 1969 Chevelle. I'm not bragging, just giving a representation of the type of vehicles I lean towards. But after this fiasco, the issue that the C7 owners are having with the defective wheels and the issue of the ten year ignition problem in other Chevys in the past, tells me that the hierarchy at General Motors really places quantity well over quality, in my opinion. If it sounds like I'm venting, you'd be right. My next vehicle WILL NOT be a GM, most likely a Ford or Mopar.
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