smoove2022

When the engine is cold and being cranked, what should the voltage be at the cold start valve?

Vader

The injector should have 12V supplied to it while cranking, regardless of the engine temperature. The cold start control completes the ground path:



The control will open the N.C. load contacts if the coolant temperature is above 104ºF. This prevents cold start valve operation in a warm engine start.

The other thermal element of the control is heated by cold start valve current passing through it, and will open the contacts after some undetermined level of heat. If the control is allowed to cool with the coolant temperature remaining below 104º, the contacts will close again. The cooling interval is designed to be sufficient to prevent multiple "priming" operations by the cold start valve if the engine fails to start on the first attempt. If the engine is restarted cold after the cooling time has elapsed, the contacts will be closed and cold start valve will "prime" the engine again during cranking. In colder temperatures, the control will cool faster, allowing more frequent operations of the cold start valve.

smoove2022

Wow! THANK YOU VADER for that awesome response!

The voltage in the pink crank wire before the cold start switch/controller on my car is about 10 volts and the voltage after the switch about 5 volts at the cold start valve. So I'm losing 5 volts somehow thru the switch. I guess the next thing is to check the resistance thru the switch to see if it's bad.

Vader

The ignition switch provides power to a yellow wire when in the START position. This yellow wire is routed to a safety interlock switch, where it is switched to a purple wire (your suspect wire origin). If the car has an automatic trans, the connection is in the console near the PARK/NEUTRAL safety switch. If the car has a manual trans, the connection is at the clutch pedal arm safety switch. If the starter is engaging normally, however, chances are the safety switch itself is O.K., and you will read full battery voltage there. However, before tearing apart the console to check the switch, read on, and possibly save some unnecessary work.

That same circuit (after the starter safety switch) also routes through the "C100" connector, which is the main bulkhead connector near the fuse panel on the left side of the dash. From the bulkhead connector, the purple wire is split into two paths:

1. A larger purple wire on the engine compartment side of the connector is routed to the "S" terminal on the starter solenoid.
2. A smaller purple wire (your prime suspect) which taps off the purple wire on the interior of the vehicle, then routes to the back of the fuse panel to supply power to the CRANK fuse.

You can cut your diagnostic time in half by checking voltage at the CRANK fuse (both ends) while operating the starter. With your trusty meter in hand, dive under the dash and start probing at the fuse panel.

• If full battery voltage is available at BOTH ends of the CRANK fuse during cranking, everything upstream of the fuse is operating properly, and you'll need to proceed to the TPI harness.
• If the voltage reading is below battery voltage at the CRANK fuse during cranking, you'll need to investigate the fuse holder, fuse panel connection, "C100" connector and possibly the start safety switch.

Again, if the starter is operating normally, chances are that the ignition and safety switches are intact.

After the CRANK fuse, the circuit turns to a purple/white wire and routes to the right side of the dash, where it is connected to the TPI harness via the "C207" connector. The "C207" connector usually has a transparent plastic body and about 15 circuits routed through it. Check voltage while cranking on both sides of that connector to determine if the connection is resistive.

If full voltage is present going out of the 207" connector, the rest of the system is copper all the way to the electrical connectors for the cold start valve and control.

smoove2022

Thanks again vader, great info.

I definitely have some diagnosing to do. I've noticed my crank fuse has blown out twice since the tpi swap. I'm not sure it was because of the swap tho since most of the wiring isnt incorporated into the tpi harness. Most likely it is a problem with some of the original body wiring and the problem existed before the swap. I've tested the voltage at the C207 connector terminal R and got 10v. Would you consider this full battery voltage? Or should I really be getting a full 12v? I thought the 10v was good given i was using maybe a poor ground for the multimeter. I'll check what it is at both ends of the crank fuse in the mean time.