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SuperDave
SuperDave, ASE Certified Technician
Category: Toyota
Satisfied Customers: 1491
Experience:  over 16 years experience
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I have a 1998 GMC pick 305 engine. Receiving engine trouble

Customer Question

I have a 1998 GMC pick 305 engine. Receiving engine trouble code 301 - mis fire cyld 1. I have changed wires and plug. I think it is the fuel injector. How can I test for bad fuel injector? I was thinking about removing main coil wire and turning the engine over several times and then look for the presence of gas on the plug..no gas on plug bad injector. Will this work?
Submitted: 1 year ago.
Category: Toyota
Expert:  SuperDave replied 1 year ago.
Thank you for using Just Answer.I will do my best to answer your question.It sounds like a bad injector.The poppet valve on the injector is sticking.Click HERE for diagnosis.
Customer: replied 1 year ago.

Computer will not open link. Can you write what I need to do?

Expert:  SuperDave replied 1 year ago.
P0301 thru P0308 Misfire cylinder specific.


DTC will set if no DTC present for following sensors & circuits: TPS, MAP, ECT, CKP, MAF, CMP or VSS. Engine coolant temperature (ECT) between 19°f & 254°f, RPM between 300 & 6000, system voltage between 9 & 16 volts, throttle angle steady. PCM detects a crankshaft RPM variation indicating a misfire sufficient to cause converter damage or emissions level to exceed mandated standards.


PCM will disable TCC operation. If misfire level is non-catalyst damaging, PCM will illuminate MIL during second Key cycle in which DTC sets. If misfire level is severe enough to cause possible catalyst damage, PCM immediately flashes MIL while misfire remains at catalyst damaging levels.



Misfire code & rough running may be caused by CPI injector failure. Rough running may be intermittent & difficult to duplicate.


Monitor misfire Data to determine affected cylinder(s). Scope Engine & eliminate any secondary ignition fault before suspecting injector fault.



If intermittent spark, check coil wire for ground out condition. Coil wire grounds out to bracket & may not be able to see arcing through convoluted cover. (remove cover to inspect wire)



Perform injector balance test if supported by scan tool. There are are J tools for performing this task. Perform injector flow test if scan tool does not support. (If not supported by scan tool-Test may be performed using a injector pulse tool & pressure gauge) Techs report mixed results on cleaning injectors. Note: intake plenum must be removed to replace injectors as per service manual. Always use New gaskets when plenum is removed (upper o-ring swells, causing vacuum leak). Techs report using J tool with compressed nitrogen work well to clear plugged poppet valves on injector. See special policy bulletin #99066G (ca only) for special warranty coverage on injectors. See bulletin #00-06-04-003B for more info on cleaning and unsticking injectors & converting to updated style injector.

Vortec CSFI: centrally located injectors, 1 per cylinder, are supplied IGN(+). Injector ground side is switched by PCM. Central sequential fuel injectors are activated individually in firing order sequence as determined by PCM. Injectors discharge fuel into tubes for each cylinder. The tubes are closed at the manifold end with pressure relief (poppet) valves. When an injector is pulsed, pressurized fuel enters the tube and is discharged at the individual poppet valve into the intake port. See tech notes for vehicles that have updated/replacement fuel injection systems.