Leeet

iTrader: (-1)

My 98 z28 is running rough and throwing a P0300 random/multiple misfire code. I found 1 broken valve spring and replaced it. It still runs rough and throwing the same code (after clearing the previous code).

My question: is there a way to find exactly which cylinders are misfiring? Because I believe the way it works is if one cylinder is misfiring, a code will be thrown for that specific cylinder. If two or more cylinders are misfiring, the random/multiple misfire code is thrown.
It would make diagnosing this problem much easier if I knew exactly which cylinder(s) to look at.
Thanks in advance for any help.

redbird555

iTrader: (14)

you would have to find someone with an advanced scanning tool or use hptuners which has the ability to monitor all cylinders individually

havoc04

iTrader: (1)

Just do a compression check. You'll find it. Most likely broke piston like they always do. Mine did the same thing

7008ccGTO

^^^ Agreed. Run a compression check. My 02 Z28 was running a little rough and throwing code. Held 190 psi on all cylinders except 1. Good 'ol #7 only had 90 psi. Pulled the piston to find a broken ring land.

hardrock21

iTrader: (6)

In my experience p0300 is usually caused by unmetered air entering the engine. I.e. bad throttle body gasket, leaky intake gasket or cracked intake. Secondly I check for weak fuel pressure. Next I ohm out cam/crank Position sensors. 4th step is leakdown/compression test. Almost always specific cylinder misfires will throw a relative code to that cylinder. My .02

Leeet

iTrader: (-1)

Well I did a compression check. Cylinder #2 was low. Air was coming out of the exhaust. That's what I figured it would be since the valve spring broke on the #2 exhaust valve. Looks like the heads are coming off... again. Second time this month. Hopefully the valve didn't cause any damage (I was lucky last time).
I'm not sure why it wouldn't be just throwing a #2 misfire code though. I'll probably end up finding something wrong with another cylinder.