Chevy Misfire cylinder 3

Asked by Jun 03, 2016 at 08:58 PM about the 1999 Chevrolet C/K 1500 LS 2WD

Question type: Maintenance & Repair

Okay I'm done throwing money away I can't solve
this one what I have already replaced: fuel pump
and filter, spark plugs and wires, Cap and rotor,
fuel injector lines checked for vacuum leaks w carb
cleaner, air filter i have 155000 mi on her only thing
i can think of left that i can do is replace the coil
and or timing chain she runs quiet w no sign of a
mis but wont pass smog and starts w little
hesitation and the catalytic converters are good
and i replaced a few sensors but w used ones any
help would be tremendously appreciated

7 Answers

12,615

First why do you think its misfiring? was it scanned and had a DTC code for cylinder misfire / P0303? it appears as if you've changed most of the parts, 5.0 or the 5.7 engine you need a real scanner that can check misfires per 200 revolutions in real time data stream...also a misfire can be caused by a NONE injected cylinder meaning its lean not RICH people forget this!. give me more info .. so I can reply

2 of 2 people found this helpful.
Best Answer
72,145

P0303 CHEVROLET - Cylinder 3 Misfire Detected... Possible causes - Faulty spark plug 3 - Clogged or faulty fuel injector 3 - Faulty ignition coil 3 - Fuel injector 3 harness is open or shorted - Fuel injector 3 circuit poor electrical connection - Ignition coil 3 harness is open or shorted - Ignition coil 3 circuit poor electrical connection - Insufficient cylinder 3 compression - Incorrect fuel pressure - Intake air leak... The P0303 code means that the cylinder 3 is misfiring or is randomly misfiring. Start by checking for intake leaks an if no leaks are found the next step is to replace the spark plugs on cylinder 3. If the problem persist more tests needs to be done to diagnose problem, like a compression test on the cylinders... Engine Cylinder 3 is Misfiring.. Possible symptoms - Engine Light ON (or Service Engine Soon Warning Light) - Lack/loss of power - Hard start - Engine hesitation

2 of 2 people found this helpful.

Yeah the code is 303 installed new plugs And wires and spider injectors fuel pressure is good I don't honk its possible but could the timing cause the two hard codes p0300 and p0303 she runs great very quiet no sign of miss a tiny I mean tiny hesitation at start I need to get a more detailed scan now that the light has come back on

72,145

No, timing does not cause a miss-fire. You actually have a random miss-fire by the looks of it. po300 is random, po303 is a miss in cylinder #3 now. Here are some things to check....P0300 CHEVROLET - Cylinder Misfire Detected Random Cylinders... Possible causes - Faulty spark plug (s) - Faulty ignition coil (s) - Clogged or faulty fuel injector (s) - Intake air leak - Fuel injectors harness is open or shorted - Fuel Injectors circuit poor electrical connection - Ignition coils harness is open or shorted - Ignition coils circuit poor electrical connection - Insufficient cylinders compression - Incorrect fuel pressure...........P0303 CHEVROLET - Cylinder 3 Misfire Detected.... Possible causes - Faulty spark plug 3 - Clogged or faulty fuel injector 3 - Faulty ignition coil 3 - Fuel injector 3 harness is open or shorted - Fuel injector 3 circuit poor electrical connection - Ignition coil 3 harness is open or shorted - Ignition coil 3 circuit poor electrical connection - Insufficient cylinder 3 compression - Incorrect fuel pressure - Intake air leak.............../ pretty much the same code.

3 of 3 people found this helpful.

Could engine wiring harness cause a misfire if it is cracked? i have a misfire on cylinder 4 and ive changed spark plugs, crankshaft sensor, camshaft sensor, coil pack, i think the problem is on the harness for the coil pack? what do yall think?

72,145

Eros...if you have wiring that has rubbed threw the insulation, that runs to the coil then yes, it could cause a miss fire. Peal the wiring harness insulation away at the bad spot around the wires and inspect the wiring. Look for bear wires and repair.

2 of 2 people found this helpful.

okay thank you, ill check the wiring after work, i read online that the coil pack wiring tends to break or after a while tear due to the heat from the engine but idk how true that is ill keep you updated if it fixes the problem!

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