Vettedan

The PCM/ Electronics

I was able to get the entire engine harness from the '95 Z28 including same dash components . I wanted to keep the harness installation as stock as possible. The VAT module (Vehicle anti-theft) was the first part of the harness I wanted to get working. Most people remove this system from their PCM. They shouldn't its a great anti-theft system. The VAT module sends a signal to the PCM when the correct resistance is measured across the key. Late model Corvette & Camaros keys have a resistor embedded within the key. If the VAT module doesn't get the correct voltage drop, then it doesn't send a acknowledge signal to the PCM. The PCM will than disable the starter, fuel injectors and fuel pump. I received the original key from the donor car and found the correct resistance. I simulated this key resistance with a carbon resistor and put it in series with a toggle switch and hide the switch. It works great. When the switch is open the starter, fuel pump, and injectors won't operate.

I removed the smog pumps and EGR valve from the engine, but left the relays intact. The PCM is unable to detect that there gone. I haven't detected any failures except for rare EGR fail code, I can live that because the "service engine light" doesn't come on. It beats spending $500.00 on programming the PCM. Since I decided not to modify the tail shaft to relocate the VSS sensor I installed a digital speedometer from Autometer. I hooked up the VSS signal directly to the speedometer.

Adapting the '95 Z28 alternator was pretty easy. The old 10 S1 series alternator has a 4 wire hook up (red wire-Batt, Brn wire (no. 1 terminal), small red wire (no-2 terminal) & the Blk wire-ground) The CS-130 alternator has 3 wire hook up. The red wire goes to the (Batt terminal), small red wire off of the weather pack connector goes to the (B terminal), and the Blk wire goes to ground. When installing the CS-130 alternator, splice the 2 red wires ( Batt & no.2) together and connect to the (Batt) terminal of the CS-130. Connect the Brn wire with a 470 ohm , 1/2 watt resistor in series to the ( B terminal). The charging system works great.

I used the stock dual cooling fans off of the '95 Z28 for cooling the radiator. I removed the old fan shroud and modified the fan shroud from the Z28 . I also install a Hyper Tech 160 degree thermostat. My C3 runs cool. I knew I would have a problem matching the LT1 coolant temperature transducer (sending unit) to the stock coolant temperature gauge. First I replaced the PCM coolant sending unit ( located on the water pump) with a 3 wire dual purpose sending unit which includes both the PCM and gauge senders in one unit. The reason I did this is because the sending unit for the gauge doesn't ( located in the left cylinder head, between cylinders #1 and #3 spark plugs) give accurate reading due to the reverse flow coolant. When I compared the reading from my X-Ray PCM reader, the PCM coolant temperature always read higher than the Temperature gauge. This means the cold engine coolant entering the engine from the radiator is directed to the cylinder heads first. In addition to this I had to calibrated the coolant sensing unit to my gauge. The stock sending unit for the '76 gauge measures around 800 ohms cold, where as the '95 sending unit reads 2400 ohms. I installed a 150 ohm resistor in parallel to the sending unit wire and read the exact temperature as the PCM. One down fall to this is the temperature gauge will not start reading the engine temperature until around 130 degrees. The needle will only drop down to around 130 degree. From there on the Gauge is very accurate. The part numbers for the 3 wire dual sending unit and connector pigtail are available at any Chevrolet dealer are:

PN-10096181 - PCM/Gauge sending unit. Used on the'94 thru '95 LT5 ZR1 Corvette

PN-12102748 - Connector Pigtail

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