4.2 running on four cylinders

[zkepler00]

Trailblazer troubleshooting:
This all started with a po203 code for injector 3
The issue: It fires right up and the cylinders that work run smooth, cylinders 3 and 4 do not run I believe it to be electrical related but am unsure
Whats known: it gets spark and fuel, and all coil packs are receiving the appropriate 12 volt power
What I've checked/replaced: its not coil packs, spark plugs, injectors, cam angle sensor, computer
Next things to check: injector harness, wiring harness, crank position sensor, vvti sensor, maybe knock sensors, compression test

 

[mrrsm]

(1) Look for any Hidden Damage from Mice Gnawing somewhere along the length of the EFI Harness and right at the Harness to PCM Main Connector. Also check the Wire Bundle-Harness leading to and from the C2 Connector on the PCM:

EFI #3: PCM Connector C2, Color PINK/BLACK, PIN # 16 (Control Wire) Circuit # 1746

EFI #4: PCM Connector C2, Color Light Blue/BLACK, PIN # 8 (Control Wire) Circuit # 844





(2) After a "Scope-On-A-Rope" Lighted Probe check for confirming 'Powers and Grounds' on the #3 & #4 Cylinder Fuel Injector Circuits and making a second DMM Check to measure that the necessary DC Voltage is Nominal at both... If either EFI #3 or EFI #4 were stuck OPEN... with the Engine running, you might see Plumes of White Smoke coming out of the Exhaust while the Motor struggles along on 4 Cylinders at Higher RPM.

This might suggest a Blown Head Gasket.... BUT THIS WILL NOT BE THE CASE. If the White Smoke is present, it is just an artifact of having a constant stream of Unregulated Fuel being dumped into either the #3 or #4 Cylinders and adds to the Diagnostic Information to determine if either the #3 or #4 EFI would need replacement.

(3) How to Test for an OPEN CIRCUIT on the EFI System with Basic Tools and confirm that the PCM is NOT the Problem:

 

[zkepler00]

Thank you! After I posted I figured I'd go out and check the injector harness and sure enough those two cylinders had torn up wires. You were right on the money