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2008 Base model having misfire but not storing codes
Hey everyone. Having a technical and want to pick some brains or maybe some of you have had the same thing happen and can maybe point me in the right direction.
I have a C6 base model coupe 6 speed. Bought this corvette back in January and it’s been great with no issues at all. Surprisingly flawless. Well all of the sudden a couple of days ago my check engine light starts flashing indicating a misfire. It is an intermittent but consistent misfire. The weird thing is that it isn’t throwing any codes at all. The flash will go away and come back if I throttle or climb a hill and sometimes even if I don’t throttle. Without codes I don’t know what cylinder is misfiring or what direction to go. I went ahead and replaced all my spark plugs and plug wires. Cleaned the MAF, and looked for grinds, breaks, and contact on the wiring harness to fuel rail and coils. Reset the battery just to rule out.
The mods are long tube headers, high flow cats, SLP mufflers, cam, and tuning. All work was done by the very reputable LSXPERTS in ballground GA.
If the car does throw a DTC it will only show you a p0300 (random misfire)...you will need a scan tool to tell you which cylinder is misfiring...is the car actually misfiring under the conditions you stated or does it run smoothly ??...the crank sensor is actually what senses the misfire to set the DTC...any type of vibration in your car can set a misfire DTC...a harmonic balancer going bad, an accessory such an AC compressor...anything that will cause the crankshaft to slow down....find someone who has a scan tool and see what you have !!
If the car does throw a DTC it will only show you a p0300 (random misfire)...you will need a scan tool to tell you which cylinder is misfiring...is the car actually misfiring under the conditions you stated or does it run smoothly ??...the crank sensor is actually what senses the misfire to set the DTC...any type of vibration in your car can set a misfire DTC...a harmonic balancer going bad, an accessory such an AC compressor...anything that will cause the crankshaft to slow down....find someone who has a scan tool and see what you have !!
thats good advice. Are you suggesting the sensor itself is potentially bad or something else triggering the sensor? It doesn’t store any codes for me to read unless there is a way I can see it in real time. I put a scanner on it after it happens and it shows that there are none. When it’s happening it doesn’t feel like it’s misfiring by running sluggish or anything like that but my instant MPG drops to about 4 and goes back up when it stops flashing.
Yes, you can have a bad sensor. Does your scanner have a misfire “history” ??...it will be stored there !!...sometimes after a crankshaft sensor, a harmonic balancer, a PCM, or an engine change will require a “crankshaft variation relearn”...usually performed with a bi directional scan tool or Tech 2. Unfotunately you can’t read the DTC’s through the DIC like on a C5 !!
If it does I have no idea how to pull up a history. I just plug in OBD2 and run diagnostics and it comes back with no faults or codes. Is there a specific scanner I should look into buying? I’m with you in thinking it’s electronic because a physical misfire would have to run sluggish wouldn’t it? This is why I haven’t spent the money on new coils yet.
Some scanners have a “special function” and “active tests” menu for the various modules...PCM, BCM, ABS, etc......yes, if it were a real misfire the car would be running poorly...no, don’t buy coils !!...as far as which scan tool to buy you’d have to look at what features they offer and how much you want to spend...I use a higher end Autel but I need it because I do diagnostic work on the side...I need it !!
Hey everyone. Having a technical and want to pick some brains or maybe some of you have had the same thing happen and can maybe point me in the right direction.
I have a C6 base model coupe 6 speed. Bought this corvette back in January and it’s been great with no issues at all. Surprisingly flawless. Well all of the sudden a couple of days ago my check engine light starts flashing indicating a misfire. It is an intermittent but consistent misfire. The weird thing is that it isn’t throwing any codes at all. The flash will go away and come back if I throttle or climb a hill and sometimes even if I don’t throttle. Without codes I don’t know what cylinder is misfiring or what direction to go. I went ahead and replaced all my spark plugs and plug wires. Cleaned the MAF, and looked for grinds, breaks, and contact on the wiring harness to fuel rail and coils. Reset the battery just to rule out.
The mods are long tube headers, high flow cats, SLP mufflers, cam, and tuning. All work was done by the very reputable LSXPERTS in ballground GA.
Make sure that the spark plug wires are seated on both the spark plugs, and the coils sockets above.
Also, may be a good time to let the motor cool down to room temp, and pull the spark plugs to check them (don't pull the plugs with the head still hot). Hence may have lost the electrode off one or more of the spark plugs. As for spark plug gap, .040".
When you put the spark plugs back in the cold heads so you don't strip the threads out of the heads, the spark plugs only get torqued to 11ft lbs.
Are you actually feeling a misfire or is the light just flashing?
Like rwobs777 said, if you are seeing just the p0300 code then it could be numerous things (possibly the sensor).
If you see a p030X (the "X" being 1-8) code. The number where the "X" is will indicate the cylinder that is misfiring. Check the plug and wire on that cylinder (as Dano suggested). If they appear fine then it's time to check the coil. Move the bad coil to a new cylinder. If the p0300 code moves to the new cylinder then it's time to replace that coil.
If the coil is fine then it could be an injector, not sure of a way to test the injector so I'll stop there.
Yes, jaredtxrx we have to know if it's real or just a "perceived" misfire. If it's a real misfire you'll know it !!...if it is a real misfire narrowing down which cylinder helps...when I diagnose a misfire I look at 1) mechanical (low compression) - valve, broken valve spring, worn/loose timing chain ..2) ignition- coil, plug, wire. 3) fuel- weak fuel pump, injector clogged or stuck closed. As far as checking the injector a plain old screwdriver will do the trick if it's stuck closed. Checking power to the injector and signal that it's receiving it from the PCM is also necessary. As far as a clogged injector you would have to do a injector balance test...just have to have specialized equipment for that one....can be done with a Tech 2 I believe... I've included a picture of an injector current ramp on my own car...the "pintle hump" is where the injector pintle opens noted by the little "notch" in the signal. !!...keep us advised !!
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2008 Base model having misfire but not storing codes
