Testing The Fuel Injector's Wiring
Having found that injector #6 was spraying fuel as soon as the Key was turned on, the next step was to check to see if the injector's return circuit (Ground circuit) was shorted somewhere between the PCM and the injector connector.
In case you're wondering: The CSFI ‘Spider’ on Charles' 5.7L Suburban has 8 individual fuel injectors and each one gets power and an individual pulse signal from the PCM.
I now needed to find out three things:
- First off, I needed to see if the activation circuit of injector #6 was really grounded 100% of the time and if it was...
- I then needed to see if this wire was shorted to chassis Ground and if it wasn't....
- The next step was to find out if this circuit was shorted to chassis Ground inside the PCM (which would confirm that the PCM was fried).
Now, since I've been working as a tech for many years, checking the three above ‘ifs’ isn't that hard for me and I'm gonna' tell you how I did it in some detail.
Verifying That A Short To Ground Does Exist
So, the first thing was to see if indeed the pulse circuit of injector #6 was really grounded and this is how I did it:
- I identified injector #6's power and pulse circuits
- This was pretty easily done since I had the plenum off of the ‘Spider’ injector assembly and the numbers of the cylinders are embossed on the body of the assembly (see photo 3 of 3 in the image viewer).
- Using a wiring diagram, I knew that I needed to locate pin #31 in the C2 (Red) connector of the PCM.
- This circuit is the one that provides injector #6 with the pulse signal from the PCM.
- You can find the Connector Pin Out Chart I used here: 96-97 PCM Connector Pin Out Charts.
- Disconnected the battery's negative terminal.
- Disconnected the PCM's C2 (Red) connector.
- The PCM has 4 connectors. If you disconnect them all, you'll notice that each has a colored plastic protector over the metal female terminals (that connect to the male terminals on the PCM).
- The specific colors are:
- Blue connector (C1).
- Red connector (C2).
- Clear -or Grey- connector (C3).
- Black connector (C4).
- Behind the C2 (Red) connector, I located the wire that corresponds to slot #31
- This wire is the y with black stripe wire.
- This is the wire that provides injector #6 with the pulse signal from the PCM.
- To this yellow with black stripe wire a connected my wire piercing probe (a good 4 to 5 inches away from the connector itself).
- Reconnected the C2 (Red) connector back to the PCM and disconnected the ‘Spider’ injector assembly's connector (the PCM must be connected to all of its connectors for this test to work).
- Reconnected the battery's negative terminal.
- To the wire piercing probe I connected my 12 Volt test light, connecting the test light's alligator clip to the battery positive (+) terminal.
- Turned the Key On.
- Checked to see if the test light came On.
Even before the Key was turned On, the test light lit up and stayed lit during and after the Key was turned On. Thus confirming that the circuit was indeed shorted to chassis Ground somewhere.
The next steps were to see if the short to Ground was just in the wiring between the PCM and injector #6 or inside the PCM.
Testing To See If The Short To Ground Is In The Wiring
To test to see if injector #6's Ground circuit (wire) is shorted to Ground inside the engine's Wiring Harness, the wiring between the PCM and the ‘Spider’ assembly needed to be isolated.
This I accomplished by disconnecting all of the PCM's connectors and the ‘Spider’ connector and then performing the needed tests to injector #6's Ground circuit (wire).
Here are the specific details of what I did:
- Disconnected the battery negative cable from the battery.
- Disconnected all four of the PCM connectors (C1, C2, C3, and C4).
- Reconnected the battery negative terminal to the battery.
- The ‘Spider’ injector assembly connector was still disconnected (and needed to remain disconnected for this test).
- Turned the Key to the On position.
- Probed the wire piercing probe still attached to the y with black stripe wire of the C2 PCM connector.
- The 12 Volt test light's alligator clipped connected to the battery's positive (+) terminal.
- Checked to see if the 12 Volt test light came On and the test light did NOT come On.
- Disconnected the battery's negative terminal.
- I then borrowed Charles' multimeter and tested to see if there was continuity between the wire and engine Ground, and there was none.
- For the continuity test, the vehicle's battery needs to be disconnected.
This result told me that injector #6's Ground circuit was not shorted to chassis Ground and also started to narrow my troubleshooting down to the possibility that the PCM was fried internally. So the next step was to test the PCM.