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Chevrolet Suburban 1500: I'm chasing a multiple misfire code…

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I'm chasing a multiple misfire...
I'm chasing a multiple misfire code 0300. So far I have change plugs, wires and ignition modules (all 8). So I am looking for vacuum leaks. Noting is standing out so I am getting lost.
Submitted: 3 years ago.Category: Chevy
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Answered in 17 minutes by:
6/3/2015
Chevy Mechanic: Gary, Chevy Technician replied 3 years ago
Gary
Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 18,026
Experience: 15 years GM master tech
Verified
Welcome! My name is ***** ***** I will do my best to assist you with this problem.Ask me about added features such as phone contact anytime if you wish !
I am sorry your having this problem
any access to a scan tool to see live data to see which cylinders are in fact misfiring ?
we need to know if its randomly all 8 or one or two specific cylinders
do you feel the misfires at all other than the code 300 being set ?
how does it run ?
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Customer reply replied 3 years ago
Here are the codes/messages received:
P0300 - CNF 1/6 Mod10 Random Multiple Misfires Detected
P0449 - CNF 2/6 Mod10 Evaporitive Emission Vent Valve Solenoid Malfunction
P0455 - CNF 3/6 Mod10 Evaporitive Emission System Leak Detected (Gross Leak / No Flow)
P0300 - Pnd 4/6 Mod10 Random Multiple Misfires Detected
P0449 - Pnd 5/6 Mod10 Evaporitive Emission Vent Valve Solenoid Malfunction
P0455 - Pnd 6/6 Mod10 Evaporitive Emission System Leak Detected (Gross Leak / No Flow)
The evoparative Emission just recently showed up. I have attempting to find this misfire for over a year.
Chevy Mechanic: Gary, Chevy Technician replied 3 years ago
any access to a scan tool to see live data to see which cylinders are in fact misfiring ?
we need to know if its randomly all 8 or one or two specific cylinders
do you feel the misfires at all other than the code 300 being set ?
how does it run ?
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Customer reply replied 3 years ago
idles ruff, slight hesitation when starting from idle, seems to run fine.
Sorry no access to scan tool. using actron CP9550 pocketscan plus tool.
Chevy Mechanic: Gary, Chevy Technician replied 3 years ago
with a code 300 the thing we have to know is if its all the cylinders misfiring or one or two specific cylinders to know which way to go with this issue
as so many things can cause a misfires
from vacuum leaks to crank sensors ect...
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Customer reply replied 3 years ago
I took the car in to dealership, and they wanted to replace the cam due to low compression. This was a ripoff since the only measured compression on one cylinder. Told me the cam lobes had flat spots. Since it runs good on the road, I don't feel like the cam is an issue. It took them 3 days to give me the diagnoses.
Chevy Mechanic: Gary, Chevy Technician replied 3 years ago
can you perform a compression test on all 8 cylinders ?
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Customer reply replied 3 years ago
I don't have a compression guage
Customer reply replied 3 years ago
135K miles on the car
Chevy Mechanic: Gary, Chevy Technician replied 3 years ago
ok the reason this issue has not been found yet is key important tests need to be like a compression test and then to see exactly which cylinders are showing a misfire to trigger the 300 code
if those 2 things are not done we will continue to guess at what the problem is
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Customer reply replied 3 years ago
ok. thanks. I'll have to follow up on this issue later.
Chevy Mechanic: Gary, ASE Certified Technician replied 3 years ago
Gary
Gary, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1,984
Experience: Senior Technician
Verified
Hi there,
I would replace the Evaporative Purge Solenoid, especially since you also have a DTC for it.
Very common problem for GM.
The P0300 misfire will be all cylinders at random.
The dealer is partly right, but they are most certainly wrong claiming low compression if they tested only one cylinder. Why would they do that? You MUST remove all plugs to do a compression test. At that point you would test all 8 cylinders.
They are correct about the cam, it could have a problem.
Gen III onwards are fraught with roller lifter/camshaft failure.
Just replace the solenoid first, clear your DTCs, and hopefully that fixes your issue.
Have seen it way too many times.
Gary
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