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I have an 03 Silverado with the 6.0. I have a random

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I have an 03...

I have an 03 Silverado with the 6.0. I have a random multiple cylinder misfire code I have installed a new battery, I also checked the voltage just to make sure and it is good, the alternator is putting out 14.25 volts, the ignition coils, plug wires and spark plugs are also all new

Mechanic's Assistant: Have you seen the misfire code before? Has the car been stalling?

I have seen the misfire code before. when i first saw it 2 years ago i got a slightly different code and it was for cylinders 1 and 7 only, now i just get the random multiple misfire code the vehicle has never stalled it always starts and starts easily as it should the misfire usually never occurs until underload or at a steady rpm while driving and sometimes will go away and come back I used a timing light to actually see what plug or plugs were firing and at times my 7 cylinder wont fire at all, but i just was looking at it again and it was firing fine, so i increased the engine rpm to 500 above idle, and lost spark, or at least what the timing light could pick up, so i checked another cylinder and it was the same result, and that occurred across all cylinders, which if i lost all spark the engine would stall, which it didn't, and it did not have a rough idle either while this was happening so i don't know if I'm getting just enough current drop to cause the code?

Mechanic's Assistant: Are you fixing your Silverado yourself? What have you tried so far?

Replaced the spark plugs, wires, ignition coils

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

No that is it

Submitted: 8 months ago.Category: Car
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Answered in 3 minutes by:
11/19/2017
Auto Mechanic: Pete, Technician replied 8 months ago
Pete
Pete, Technician
Category: Car
Satisfied Customers: 32,980
Experience: 17 years automotive training and experience.
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Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

when you saw the number 7 not firing at all with the timing light was the engine actually running rough then at that time like it had a misfire?

Let me know,thanks Pete

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Customer reply replied 8 months ago
No it was running smooth at that time
Auto Mechanic: Pete, Technician replied 8 months ago

O.k.,I am thinking your timing light was not picking up the signal properly.If there was actually no spark at cylinder 7 when the timing light signal cut out it would have ran rough.

Since the coils and spark plugs and wires were replaced and you do not have a code for coil circuit fault this most likely is not a spark issue.

What can cause this however that I have run into several times before and can be intermittent or at certain speeds or loads is one or more of the fuel injectors not atomizing fuel properly into a cylinder.They develop carbon build up or gunk in them that keeps the pintle in the injectors from operating properly which causes this misfire.In allot of cases either having a shop perform an injector clean with a cleaning machine will correct this or putting in fuel injector cleaner at 1/4 tank and running to near empty and repeating will resolve this issue.In some cases the faulty or affected injectors need replaced.I have had to clean the injectors on this model engine several times before for this fault here.I would have this checked into/ and or cleaned.

If the fault then continues then check the wiring running to the coils and injectors for any breaks or damage intermittently causing this fault.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

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