I have narrowed the CTS problem down to two possibilities. The ECM or the SD integrator from Street and Performance. I base this on a few things:
1. I retested all the wires and got no resistance on either the yellow or the black wire.
2. I got no voltage out of the yellow wire.
3. There was good continuity in both the yellow and black wires.
4. There was continuity between the black wire on the CTS and the black wire on the TPS. There is also a good 5 VDC at the grey wire on the TPS, the grey wire on the MAP, and the wire (can't remember the color) on the MAT.
5. There is a large amount of resistance to ground on both the yellow and black wires.

Now, is there anyway that I can test the voltage at the ECM directly to ensure that it is not a wiring problem? Do you concur with my conclusions? I am assuming now that the wiring is no longer suspect. Thanks for all the help.
bsa

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"If they do not run, Then they will die." - Stonewall Jackson

'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Comp Cam, Comp 1.6 Rockers, Lucas 23# injectors, Edelbrock headers, Flowmaster 3'' exhaust, gutted cat, Mallory coil, Mallory HyFire IV ignition box, Mallory Sidewinder 8mm wires, Autolite platinum plugs, K&N filters, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter

[This message has been edited by irocbsa (edited February 08, 2001).]

 

ttt

 

IROC,

To eliminate all possibility of wiring problems, insert a 330 ohm 1/4w resistor in the 'C10' terminal and 'D2' terminals at the ECM. You can carefully push the leads into the connector from the back side (back-probe) and tape the resistor in place. This resistance will cause the ECM to assume a constant 179°F coolant temperature. Once the engine is relatively warm (by the dash gauge) you should get no more error codes. Unfortunately, the ECM will not like the false high temperature if the engine is cold, since the MAT will be so much colder. You may set a DTC from this alone.

The best way to diagnose the problem is to connect a serial data scanner to the ALDL and read the CTS temperature directly. If the CTS is reasonably close to what you would expect, the ECM and wiring are probably O.K.

As an alternate, you could test the DC voltage being returned to the ECM by metering the yellow wire ('C10') for voltage while the ignition is on. Reference the 'D2' terminal for ground. A warm CTS (180°F) should provide about 0.412 VDC. A cold CTS (about 100°F) should provide about 1.98 VDC at the terminal. This is by no means absolutely accurate, but should be close enough for testing. Anything above 4.95 V and below 0.010 V will immediately cause a code 14 or 15.

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Later,
Vader
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"I know how to solve your problem, but I can't tell
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