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Have a 07 yukon 5.3 p0300 random misfire with check engine…

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have a 07 yukon 5.3...
have a 07 yukon 5.3 p0300 random misfire with check engine light flashing, car has 170k on it. Hooked all wires up to a timing light and found #7 hitting intermittently. Replaced that coil, wires and plugs and cleaned injectors with no result
Submitted: 8 months ago.Category: GM
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12/17/2017
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago
david craig
david craig, ASE Certified Technician
Category: GM
Satisfied Customers: 5,988
Experience: owner/mechanic at 3D Automotive
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Hi my name is ***** ***** I'll be more than happy to assist you. Please allow me a few minutes to review your information. Thank you

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Customer reply replied 8 months ago
Ok
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

I would recommend a compression test of at least 4 cylinders for a comparison. thank you

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Customer reply replied 8 months ago
Compression tested good on all
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

ok, did you check for injector pulse on #7??

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Customer reply replied 8 months ago
No haven't done that
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

that should be next.

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Customer reply replied 8 months ago
Anything else
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

not until I see if there is pulse there. do you have a noid light?

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Customer reply replied 8 months ago
I wouldn't think it would be that I swapped injectors after I cleaned them stayed at #7
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

the injector has nothing to do with pulse command

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GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

its a command from the computer

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Customer reply replied 8 months ago
No I don't have a noid light
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

you can get one at the parts store

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GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

you can also use a long screwdriver with a plastic handle

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Customer reply replied 8 months ago
Ok I'll try that
Customer reply replied 8 months ago
Can you pout me anywhere else to check beside that
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

you use it like a stethoscope. put the metal end on the injector, and the plastic end to your ear and if the injector is pulsing you will hear a clicking.

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Customer reply replied 8 months ago
I hooked a battery to them to open them when I cleaned them I know they will click they all engaged
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

that doesnt matter. it can have power to it from the battery and not the computer. now please check it for pulse

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Customer reply replied 8 months ago
I'm not currently by the car until tomorrow can you offer anything else to check if this checks good
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

Ill be on tomorrow. have you checked for spark?

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GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

you have spark, you have compression, but you don't know if you have fuel. there's nothing else to check until we know if you have fuel............did you use genuine gm parts or aftermarket?

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Customer reply replied 8 months ago
Aftermarket, the intermittent spark is what confuses me
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

could be a wiring issue between the coil and the pcm

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GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

check engine light code is only showing p0300?

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Customer reply replied 8 months ago
that's it p0300 the wiring issue is what I had it narrowed down to where does the coil get signal from and where would I be checking
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

the computer looks for a rotation signal from the crankshaft position sensor. once the computer sees engine rotation it commands the injectors to pulse fuel. the computer also looks for cylinder identification order from the camshaft position sensor. once the computer is satisfied the firing order is correct, it tells the ignition coils to fire

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Customer reply replied 8 months ago
Ok would either of those sensors go bad cause the issue I'm having?
Customer reply replied 8 months ago
where would I look for faulty wiring for that system
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

you would have a p0340 if the cam sensor was bad and a p0335 if the crank sensor was bad. im betting on a wiring problem

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GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

you need to do a continuity test of the wires between #7 coil and the pcm.

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Customer reply replied 8 months ago
I have good continuity from the coil plug to the plug on the pcm
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

did you check each wire for a high resistance to ground?

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Customer reply replied 8 months ago
I just did a beep test all the way to pcm
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

both ends disconnected?

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Customer reply replied 8 months ago
the coil plug and the plug on pcm
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

ok, with both ends disconnected, check each wire for high resistance to ground. it doesn't matter which end you check from.

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Customer reply replied 8 months ago
Isn't that what I did with the beep test? Or your saying it could still be getting continuity but could be weak
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

no, you did not do that. you checked continuity from one point to the other. checking each wire to ground is totally different

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GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

hows it going?

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Customer reply replied 8 months ago
I found out it was a stuck afm lifter
GM Mechanic: david craig, ASE Certified Technician replied 8 months ago

nice work, very glad you found the issue.

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