I put a scan tool on my '06, and code PO 300 showed up indicating "random/multiple cylinder misfire". If any of you have an ideas, input, or suggestions as to what's going on, I would appreciate it! Thanks in advance.

 

Check to make sure all of your plug wires are on tight at both ends. Kind of a common C6 problem and it will only take 5 minutes to check them.

 

I just had a similar issue last weekend. Check engine and traction control light was on. Ran like crap and shuddered. Pulled the engine cover off and one plug wire was off the coil pack. Put it on and back to normal. Ended up taking the other cover off just to make sure they weren’t loose or about to come loose.

 

Doesn't your code reader tell you what cylinder is misfiring? My cheap $30 one tells me everything about the car including misfire like P0301, P0308 etc...that would really help you narrow it down.

 

As already stated, check to make sure the plug wires are tight on both the coil end and the plug end. If that's not it, how many miles on the plugs? Wouldn't hurt to pull them and take a look, and it's not that expensive to change them. Next I would take a look to see if all of the coils are good. Last would be to check the injectors

 

Don’t know if your scan tool is a just a basic “code reader” but it really helps to identify which cylinder is misfiring…beyond just replacing plugs and wires the diagnosis can be a little more difficult without specialized equipment like a scope…do you actually feel the misfire or you only have a P0300 showing or a flashing MIL ???…I’m moving this thread to Tech !!

 

Here's a recap: About a week ago, ScanTool indicated misfire cylinder #7. I replaced the coil and cleared the code. In a few miles, CEL came on again - steady. Thinking the coil had not been the problem, I replaced the wire. I figured all wires, being the same age (15 years and 15500 miles) might also be bad so I replaced all wires. A friend, who is Corvette savvy, and I pushed all boots firmly on the plugs, and ascertained the attachments to the coil packs were tight and secure. I cleared the code. After starting engine, CEL again came on and ScanTool said PO 300: "random/multiple cylinder misfire". I don't suspect bad/fouled plugs due to low mileage and use of only Conoco non-ethanol 91 gas.

It seems the only solution is find a shop w/ a more sophisticated equipment and have them diagnose the problem.

 

Yes you can do that. They can read the live data on each cylinder as it is firing and see the misfires, gets a lot easier at that point, when you know how to read the data. Good luck!

 

Could be injector related too or valve train...or the plugs...what do your fuel trims look like when it is misfiring ??...a fuel related misfire will have long term fuel trims of 12-16% or so...with a cylinder with no combustion (excess O2) your fuel trims will be very positive on that bank...your bank 1 !!

 

My 05 has 70k miles, it runs perfect, then stumbles and misses, check engine flashes, then clears up and runs good. It does it every couple minutes, I don't drive it far, just trouble shooting. I had 02 and knock sensor codes, replaced them, codes cleared, but still getting 300, never get a cylinder misfire code, 302 or something. Thinking its 16 years old and ignition related, replaced plugs, coils and wires. It's better, doesn't stumble as long, but still breaks up. When it runs right, it runs strong, headers, x pipe, corsa exhaust, vararam intake and tune. buddy thinks it's fuel pump related. I blamed it on bad gas, ran it to 1/8th of a tank, couldn't get the rest out. Filled it with 93 non ethanol. Live in the south so no rust issue, but could be a ground issue. Help! Searched the forum and never found anything like this.

 

It can be spark, fuel, or mechanical related but the hardest part is narrowing it down. Without a decent scan tool and a scope you will only be guessing and that can get EXPENSIVE !!…you don’t want to guess on a bad pump !!…can be a bad injector or injectors or it’s wiring, a “lying” O2 sensor stuck rich that may be “pulling” fuel, broken valve spring etc…my advise…if you don’t have this tooling take it to a diagnostic shop and not Joe’s auto repair and if they’re good they can nail it down pretty quickly…can’t believe you’ve never found anything like this on the Forum…P0300’s are very common along with a stumble…if you lived a little further south in Florida I’d be happy to look at it for you !!…I would also start a new thread instead of piggybacking off this one !!…makes it less confusing !!…thanks !!..oh BTW, what you can do is do a “clear flood crank”…hold the gas pedal to the floor and hold it there…try starting the car (it will only crank)…listen if if cranks over evenly and with a steady cadence !!..if not steady you should concentrate on a mechanical issue !!

 

It's not mechanical, runs strong, no bad engine noise, and is as fast as ever. i will start a new thread later, have to go to work. i read alll po 300 threads and didn't really answer my questions. my buddy is a guru and said if not wirres and coils, then maybe crank and cam sensor. other friend said fuel pump. right, troubleshooting is getting expensive, lol. but doing it all myself and had the car for 8 years, so worth doing either way.

 

run 93 with e10... its a myth that it will do something bad.

 

Is this misfire a misfire you can feel or are you just getting the flashing MIL ??…if it’s just a flashing MIL you can try a crank variation relearn with the scan tool…can be a crank sensor but if your Buddy doesn’t have a scope to check the sensor that will only be a guess too…does he have a scan tool ??…coil packs are pretty much bulletproof on these engines…you will not have a bad engine noise with a broken valve spring so you can’t say it’s not mechanical..good luck and keep us advised on your progress !!..below is the current ramp on my fuel pump so you don’t have to guess…average about 5 amps at 5346 RPM…fuel pressure should not drop during a snap acceleration !!

 

Had a similar issue and car would go into limp mode. Check your injector fuses are seated correctly. I bumped my accidentally and chase down this demo for months.

 

It misfires really bad, like it's running on 4 cylinders, it is limping to run and won't accelerate, then clears up, runs perfect and the CEL starts flashing.

 

Well if you think it’s 4 cylinders dropping out maybe you can quickly pull a plug wire off the coil pack on each side keeping the plug wire about s 1/2 inch from the coil pack and see if the spark jumps…if you can probe into an injector feed wire on each side (pink wire) see if you see 12 volts when it starts missing…look in this section of the rear of the left fuel rail and look for chaffing in the harness wiring…injector and coil
wiring are in this harness area…there is normally just tape here but I added some plastic loom. !!

 

 

Final update: the misfire was caused by cracked porcelain insulator on the plug; two longitudinal cracks. A new plug immediately solved the problem.

 

Thank you for updating your post with the solution you found. Kudos!