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Gary
Gary, ASE Certified Technician
Category: Chevy
Satisfied Customers: 744
Experience:  Senior Technician
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Chevrolet Suburban 1500: I'm chasing a multiple misfire code

Customer Question

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: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.
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 ?
Customer: replied 1 year 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.
Expert:  Gary replied 1 year 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 ?
Customer: replied 1 year 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.
Expert:  Gary replied 1 year 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...
Customer: replied 1 year 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.
Expert:  Gary replied 1 year ago.
can you perform a compression test on all 8 cylinders ?
Customer: replied 1 year ago.
I don't have a compression guage
Customer: replied 1 year ago.
135K miles on the car
Expert:  Gary replied 1 year 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
Customer: replied 1 year ago.
ok. thanks. I'll have to follow up on this issue later.
Expert:  Gary replied 1 year ago.
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