My cel came on yesterday and a code check showed P0308...too many misfires within a predetermined time in cylinder 8. Car only has 7300 miles. Has anyone had much luck with fuel injector cleaner with this type of problem. I suspect possibly bad fuel purchased from a warehouse club station. The light came on after a little spirited driving. Thanks in advance.

 

Le t it cool down and the go in there and make sure the spark plug wire is firmly connected to the spark plug and the coil.


Elmer

 

Problem is more than likely electrical Vs fuel related.

Bill

 

thank you

 

There are other threads discussing misfires. Common causes-and the easiest to deal with- are loose plug wires, bad plug wires and bad plugs. After that varied causes have been identified- injectors, coils, chassis modules and more. Sometimes Service Rear Axle and/or Service Stability System error messages also appear in conjunction with a flashing CEL.

 

Had the same problem with my car a week or so ago, also had this problem with a Viper that I used to own. Although I had no codes show up on my car's screen, car had been sitting for about 3 weeks with about a little less than half a tank of gas in it. I like to keep gas tank full when my cars are sitting to keep down on developing moisture in the tank from sweating. When I cranked the Corvette, it had a dead skip in it, checked plug wires which were ok and drove it down the road about two miles, still skipping, then hit the 4 lane, opened the car up a few times and skip went away. Pulled in and filled the tank up with premium fuel and for good measure, opened it up again a few times, skip has not occurred again and hopefully won't.

 

My logical old mind says:

Fuel issue would not just be a cylinder #8 misfire code. Fuel would spread the love around and many cylinders would be singing the chorus. If, as stated, it's #8 that is mad, then it's something that is associated with #8.

The posts in here have covered the most common and easy to fix scenarios. If all our suggestions don't help, go to the dealer.


Elmer

 

Just something to consider: Replacing spark plugs on the right bank of the engine requires removal of the underhood electrical center, aka fuse box. While this is removed, you might want to replace other plugs and/or wires on the right bank. I learned this the hard way as I was chasing multiple misfires on different cylinders. Replacing all plugs and wires solved the issue. And my car had very low mileage at the time.

 

Thanks...I did add injector cleaner and did a little extra wiggle push on no. 8 plug wire even though it did not appear loose. For whatever reason, the cel went out. Never did experience rough idle, hesitation or any of the other common symptoms. Just glad it cleared. Drove about 30 mi. today with no issue

 

Good deal, easy fix. Like I said in earlier post, same thing happens with my Corvette and with the Viper I had if they sit a while without driving. A couple of days ago when it happened to my car, it was a dead skip like a plug or plug wire problem but I did not get a code showing up or if it did, I did not notice it. I think that moisture builds up in the fuel system and gets picked up in an injector, sometimes takes a little longer to clean out than it does at other times. May not make a difference but I try to keep the fuel tank close to full especially when the car sits, think it cuts down on condensation in the fuel tank.

 

I also had a misfire on #8 this past Saturday. I have a 2017 Z06 M7 with about 20k miles on it. Spark plugs were all changed in February 2020 with NGK LTR7IX-11 before the car was tuned. This past Saturday I was headed to the dealership for an alignment after getting new wheels and I was at WOT at one point and I got a CEL and "Rear Axle" came up on the screen. I experienced a loss of power and the rev match no longer worked. That is normal with a CEL present. I immediately slowed down and made it to the dealership. Once I made it there, we hooked up the computer and noticed a misfire on #8. We swapped spark plug wires, still had a misfire on #8. We then removed the spark plug and found that it was bad (see picture). We replaced the plug, no more misfire. I bought new spark plugs so I could change the rest of them once I got home. On the way home, I gave it about 1/2 throttle and noticed a popping sound from the exhaust that was not normal. Again, I slowed down and made it home. I removed all of the spark plugs and put a borescope in each cylinder to check for any damage. No damage was found. I did find that #7 spark plug was bad as well though (see picture). I have replaced all of the spark plugs and sent a log file to my tuner to help investigate the root cause. My best guess is a lean condition is what caused this. I have also noticed a new ticking noise coming from the engine bay. I'm hoping its injector related and not valve related. While waiting on his feedback, I have read a lot on the forum that points towards a possible injector issues. I will be looking at that next and post feedback once I know more.





**UPDATE** 10/29/20
Checked both valve covers all over with a stethoscope and didn't hear anything that stood out. The ticking noise was not very loud when parked in the garage at idle or increasing RPMs. When a load is applied at very low speed, the ticking noise is very noticeable. I did run across a bulletin from General Motors (PIP5395B) for a ticking/rattle/buzz noise that apparently comes from the HPFP. The bulletin says to put a stethoscope on in fuel line at the motor going to the HPFP. I'll try that tonight and see what I hear. The other thing I am going to try is to jack up the rear end and put the car in drive and see if that makes the ticking noise louder so I can pin point it. Other option is to find a dyno to help put load on the motor.

**UPDATE** 11/1/20
I had a friend drive the car slowly so the car would be under load while I sat in the engine bay and listened with a stethoscope all over. I could not hear any change in noise anywhere. He could still hear the noise inside the car. After looking into it further, it is more noticeable when listening under the car. Going to put it up on stands and dig in a little further today. I can say for sure the the noise does not change louder or softer with the clutch pedal in or out.

**UPDATE** 11/9/20
I've checked all over and under the car and cannot pin point the ticking noise. I'm hoping its an injector. I pulled the supercharger off this weekend and found a few things.
1.) There was coolant on the intake side of 1-3-5-7 but not the other side. I found that it is coming from the cooling brick. I am going to do a leak down on the system as it is now tonight but suspect a bad O-ring. I'm going to order all new O-rings for both cooling bricks. After I replace the O-rings, I'll do another leak down. I'll post the results.
2.) There was a lot of what looks to be oil on #1 injector as well as some blow back past the injector. I never had any issue with #1. I bought a leak down tester and I'm going to do a leak down on all cylinders Tuesday evening. I'll post the results.
3.) I did not see anything abnormal on 2-4-6-8 side.
4.) Once I complete the cylinder leak down I will be sending the injectors off to be tested and cleaned. I'll replace any that are bad. I am sending them to Fuel Injector Clinic.

**UPDATE** 11/18/20
Coolant leak was not an O-ring, it is a leaking intercooler brick which is bad news because they are not sold anywhere. I few places sell aftermarket ones for $1,800. Still looking for one. Leak down test show 3 bad cylinders (6, 7 & 8) leaking past the rings. Going to have to pull the motor and rebuild. Set up with shop to start the work in January. Worst news possible I guess. Injectors have been sent off to be inspected to see if that was the root cause. Other possibility is the leaking intercooler brick caused it. No fluid came out of the bricks when I removed them which is not right. I'll post another update when I have some new information.

 

Rocker arm or spring acting up on #8?

Elmer

 

I don't have the ticking noise narrowed down yet. Ill put a stethoscope on it this week and narrow it down. Rocker arm or spring is likely as well.

 

Had the same issues about a week ago and the probably ended up being MSD wires. I swapped over the FIRECORE wires after some research it was those or back to factory. All issues were resolved and the car drives a lot better.

 

Super common on LT4 cars, especially if they are modded. We usually recommend to change the plugs every year if you're modded and the wires every other year or every second time you take them off. We constantly get customers in the shop with misfires over plug wires that have been removed to many times. Once they are used a couple of times they never hold the plug as tight and can vibrate loose enough to misfire.