u/clutch2k32

Been chasing an intermittent Code 42 for a few months now and running out of ideas.

What's been replaced:

Spark plug wires ((ACDelco)

• Coil (GM Genuine)
• ICM (GM Genuine)
• Distributor assembly (GM Genuine)
• Both coil connectors (black and grey)
• 2-pin and 4-pin ICM connectors

Other relevant work:

• ECM/ICM signal wires (EST, Bypass, Reference, Ground) rerouted away from plug wires
• EGR and EVAP deleted
• Long tube headers, custom exhaust, 4.10 gears, 2" lift

The fault is completely random — no conditions I can identify to reproduce it. The Drivability shop manual for intermittent Code 42 basically just says route plug wires away from ICM wires and check for broken wires, which I've already done.

After reading this I'm thinking the tan/blk Bypass or the wht EST must be must be opening or shorting to ground while running. https://www.gmsquarebody.com/threads/87-91-chevy-tbi-issues-code-42.29926/post-584657

Any ideas appreciated.

Been chasing an intermittent Code 42 for a few months now and running out of ideas.

What's been replaced:

Spark plug wires ((ACDelco)

• Coil (GM Genuine)
• ICM (GM Genuine)
• Distributor assembly (GM Genuine)
• Both coil connectors (black and grey)
• 2-pin and 4-pin ICM connectors

Other relevant work:

• ECM/ICM signal wires (EST, Bypass, Reference, Ground) rerouted away from plug wires
• EGR and EVAP deleted
• Long tube headers, custom exhaust, 4.10 gears, 2" lift

The fault is completely random — no conditions I can identify to reproduce it. The Drivability shop manual for intermittent Code 42 basically just says route plug wires away from ICM wires and check for broken wires, which I've already done.

Any ideas appreciated.