311badger

My 08 LS3 MZ6 suddenly started to run rough and a home scan shows this code.

P0300 Random/Multiple Cylinder Misfire Detected

I've checked the conections on both sides of the coils and didn't find anything loose.

My LS3 has been forged and stroked and has the last gen A&A S-Trim by a local shop that has closed it's doors.

I know it has to go to a shop and there are several in my area with great reps. I'm looking for some input for the possible culprit.

Bad Fuel-It's only seen the great CA Chevron 91 octane
Loose connection
Did I break something?

patton

ignition tester

'VETTE PHASE

That is where I am right now. Mine was running rough with a P0300 code. I pulled in the garage and did the same thing as you, pulling wires off and listening for a change in the idle and not really noticing any. I had logged with HPTuners, so I went in the house to go over that.

A couple of days later, I was going to change the oil in another vehicle. It was cold and rainy so I decided to back the vette out of the garage and pull the other vehicle in to change the oil in it. Well, it wouldn't start, no starter, nothing, just the lights came on. Really strange since I had started and stopped it several times when I parked it. I checked the codes and had a crank sensor code. I bought a crank sensor today, but didn't get a chance to put it in. I'll post back and let you know the results.

jonjon

Possible that you broke a valve spring. It's also possible that you have a vacuum leak somewhere as well.

timd38

Just a shot in the dark. Is the battery charged? If not it will make the computer do funny things.

'VETTE PHASE

Mine was the crank sensor.

miroch

P0300 can be a lot of things...ive had this on my Grand Prix...turned out to be a clogged cat. Things to check..

Plugs and wires
Coils
Check vacuum line connections
Checks for leaks around your injectors

Keep scanning after each drive to see if you get more codes (ie. cps)

Victor'sVette

If all else fails, you can go back to the old school and hook up a vacuum gauge. Look at it during idle:
1) reads very low, you have a leak
2) reads low and steady, late ignition (which you should see with HPTuner)
3) reads high and steady, early ignition (same as above)
4) neddle fluctuates as engine speed increases, ignition miss or valve spring
5) gradual drop in reading at idle, excessive back pressure
6) intermittent fluctuation at idle with good vacuum, ignition miss
7) stead from 17-22 in Hg, your are right on!

Just some ideas to look at, there might be more ways to interpret a vacuum gauge, but that is all I can think of...

311badger

Thanks for all the feedback. I took it down to Andy Green @ A&A Corvette and the cats were toast.