Started getting an engine misfire, noticing it mostly at a steady speed on the highway then going to accelerate car stumbles, and misfires..
Took it to the dealer they’re telling me to put new gas in the car and drive it around see how it is.
that technician took it out with scanner attached, and was showing all cylinder misfiring..
Engine is also misfiring at high rpm, cracking and popping CEL light flashed and I pulled the codes “ ignition module/engine misfire”
they told me to put new gas in the car?? WTF

I put in Sunoco ultra 94 octane booster and Techron .
no resolve..

taking it back to dealer Wednesday I’m going to accelerate the case with GM .

 

Why did the tech suspect your fuel? Were you using something different before, or maybe filled up on trip and an unknown gas station? I have friend that was on trip out West, and filled up with bad gas - had to stop on the way and have the tank drained. It is possible to get bad fuel, though rare these days.

And what does "octane booster" mean? Did you add an octane booster, or did you just mean you used Sunoco 94 octane fuel? You should not need to add anything to the fuel, and if I were having engine issues the last thing I would consider is adding anything to the fuel. GM generally discourages use of fuel additives - and especially discourages the use of an octane booster. Techron should be safe, but not necessary in this case. Its really the same additive as already in Top Tier fuel (of any octane rating, doesn't matter). And GM recommends a Delco fuel additive when Top Tier fuel is not available (and I believe it is either Techron or a similar additive). But even in that scenario, the manual recommends it use every 9000 miles - so not really needed that often.

Not sure if you will need to elevate the case. Did they check anything else before making the recommendation? Alcohol/Contaminants-in-Fuel Diagnosis is one of the procedures called out when multiple cylinders are misfiring. They told you to try different fuel. Since that did not help, they will (hopefully) look further into a mechanical issue when you go back on Wednesday.

 

Car was towed to the dealer in February for non-starting just crank over and spit and sputter.
again, they told me bad, fuel, and spark plugs were fouled out they change spark plugs ($650) and put in fresh air for tank of fuel.
General manager of the dealership drove the car 30 miles said it ran good. I picked it up, put it in my garage since it was the middle of February and barely drove it..
then last Sunday started noticing that hesitation, steady speed on the highway, then accelerating slightly .

so the dealership has a history of telling me it’s bad fuel..
Picked up the car yesterday they said it was still doing the same thing to put fresh gas in it and Techron.
just a bunch of BS they don’t wanna be bothered with diagnosing the car.
i’ve had three other Corvettes never had any issues with fuel, and many of them sat in the garage in the winter starting occasionally.

 

Sorry for typos .. Siri ..🙈

 

Fixed it myself ..
Found 3 spark plug wires not securely on plugs .. As a former Ford tech the first thing you check when car has misfire is check spark plugs and wires.
Also dealer had changed the spark plugs back in feb ..
beyond ....

 

Well, its good that it was s a simple problem, but I wonder why the scan tool showed "all cylinder misfiring"? Were they all loose?

 

I don't remember a code for all cylinders misfiring but P0300 is the code for Random Multiple Cylinder Misfire on older vehicles. I don't know if new vehicles are the same.

 

Its a family of codes P0300 through P0308. From what I can tell in the manual, P0300 means the "control module K20detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value or a misfire rate high enough to cause catalyst damage." It not cylinder specific.

Codes P0301-P0308 means "the control module K20detects a crankshaft rotation speed variation indicating a single cylinder misfire rate sufficient to cause emissions levels to exceed mandated standards." It appears that these are or cylinder specific.

It has this general description about this family of codes:
"A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. The engine control module (ECM) is able to detect these
variations by closely monitoring the crankshaft position sensor signal. The signals of the camshaft position sensors are used to determine which
cylinder is misfiring. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300ts. Under
certain driving conditions, a misfire rate can be high enough to cause the catalytic converter to overheat, possibly damaging the converter. The
malfunction indicator lamp (MIL) flashes when catalyst damaging misfire conditions are present and DTC P0300 set."

 

Yes, P0301 is cylinder number one misfire, etc. I think they go up to P0312 for 12 cylinder vehicles.

 

Sounds like a lazy *** dealer. When you mentioned misfire, loose plug caps was the first thing that came to mind, since I had read some other posts where that was the problem. Is your C8 an HTC where the dealer was too lazy to unbolt the engine cover to check the plugs. If it's not an HTC then it's even more incredible they didn't check.

 

Service adviser told me (all cylinder misfire ) guy has no clue ... Service advisors should be vetted before being hired and have some working knowledge about cars ...lol.
I always like to talk to tech who worked on car but they seemed very not into that .. need to find another dealer God forbid ever need a real work done scary **** .
I pulled the code after I did few FT pulls and code was ( Ignition Module / Engine misfire )

 

Unbolting the engine cover? On a C8 Corvette with stock exhaust, coupe or HTC, nothing relating to spark plugs or wires is serviced from above. It is either done from below the car, or removing the rear wheels and wheel liners. The stock wires and heat shields are fiddly and not easy to feel if they are clicked fully onto the plug terminal.

 

Good Lord, find a new dealer ASAP. Glad you got it figured out.