Random misfire
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8th Gear
Joined: Feb 2021
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Random misfire
I have 2007 Corvette 6.0L with auto and 43,500 miles on it. We recently purchased it from used dealer couple months ago. I have what seems like an intermittent random misfire that comes and goes frequently and a stumble/near stall when coming to stop intermittently.
It came with Hurricane air intake and Kooks long tube headers and catalytic converters and Corsa exhaust. I have no idea if it has custom tuned ECM but it idles around 550 rpm.
I have already changed all the fluids except for coolant. Replaced the harmonic balancer and put in OEM spark plugs and wires and OEM MAF sensor and OEM alternator and OEM battery. I also checked the starter to make sure it is good condition and wiring to starter is good too.
I borrowed my friends scanner to monitor the fuel trims and misfire counters and cam and crank waveforms and other sensor inputs. They all looked good as far I can tell but shows intermittent random misfire but does not set the code.
I also noticed that post catalytic converters o2 sensors are almost same waveform as the pre catalytic converters o2 sensors indicating possible inefficient catalytic converter
It came with Hurricane air intake and Kooks long tube headers and catalytic converters and Corsa exhaust. I have no idea if it has custom tuned ECM but it idles around 550 rpm.
I have already changed all the fluids except for coolant. Replaced the harmonic balancer and put in OEM spark plugs and wires and OEM MAF sensor and OEM alternator and OEM battery. I also checked the starter to make sure it is good condition and wiring to starter is good too.
I borrowed my friends scanner to monitor the fuel trims and misfire counters and cam and crank waveforms and other sensor inputs. They all looked good as far I can tell but shows intermittent random misfire but does not set the code.
I also noticed that post catalytic converters o2 sensors are almost same waveform as the pre catalytic converters o2 sensors indicating possible inefficient catalytic converter
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Joined: Sep 2013
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From: Cape Coral, Florida
Was the misfire noted before the HB change ??...well at least your using a scan tool to gather data...excellent !!...after the HB change did you do a “crankshaft variation relearn” ???...it can set a P0300 random misfire. I’d get your friends scan tool and do the relearn...only takes a few minutes...as far as the O2 you have to look at the waveforms after you get the O2’s HOT...I’d hold the RPM at 3000 and recheck...is this one bank or both ??...no P0420 or 0430 set ??...for this I would first look for any exhaust leaks upstream of the downstream O2...a shop vac and soapy water on a cold engine works well !!...if your friend knows how to do an “oxygen storage tests” with the scan tool using propane you can see if the downstream cat has the ability of storing oxygen...what do the fuel trim numbers look like ???
Last edited by C5 Diag; Apr 15, 2021 at 07:52 AM.
