OK.
About a year ago, driving to work one day, cruising at like 70 mph, and the CEL starts flashing out of nowhere.
TechII showed misfires in 3,5, and 7.
After alot of troubleshooting, it was suggested to me that it may be valvesprings getting soft. No prob, replaced the springs on the drivers side with LS6 units (running LS6 cam) in place of the weak SD Pro springs that were on there.
Problem solved.
At the time I did notice that the intake springs were real soft (could push them down by hand), but the exhaust springs seemed OK...

Now, this past Monday, same ****.
Car has been running fine since the springs were swapped.
Cruising up 95, CEL flashes out of nowhere. So I think, it must be the passenger side springs going soft, since they were not replaced.
(Mind you, in the past year going back before the first spring swap, the car has been soley used for day to day transportation. No track, no WOT even on the street...cant believe I just said that).
So, hook up the ol' techII and guess what...cyl. 5 misfiring like a bitch.
It does not misfire at idle, but it idles rough.
Rev it at all, and the misfire graphic fills up in about 2 seconds.
So, I pull the valve cover, and check the #5 intake spring, sure enough it is softer than the exhaust, so I make a quick fix attempt by replacing the intake spring. Changed nothing.
Keep looking, swap the 3 and 5 coil, no change, swap the 3 and 5 injector, same, swap plug wires, still cyl. 5 misfiring like crazy. Changed the plug, no change.
Ran the car in the shop with the lights out, nothing arcing anywhere.

So, considering the fact that this happened without any abuse taking place, I have (perhaps incorrectly) ruled out mechanical issues. There is no noticeable tick or noise from the head. The pushrods on cyl 5 are fine. The intake valve moved freely in the guide.

I am at a total loss. I NEED this thing fixed so I can get to and from work.
The car has had a shitty exhaust leak for a few months, as I have not had a chance to fix it (crappy Mac ORY pipe). It leaks right at the flange where it bolts to the stock header on the drivers side...I remember back in the day hearing about possibly burning an exhaust valve from running open headers, any relevance here?
I also have not fully ruled out a small vacuum leak. Can anyone give me some info to look for to determine if there is a leak? Can I look at MAP pressure at idle or under cruise to figure it out?

ANY AND ALL INPUTS APPRECIATED HERE, that is if it pertains to finding a solution.
I know there is an answer here on Tech...help me out guys.

 

To see if you have a bad valve you can easily just check that with a leak down test. The problem though is, That unless you did a crank relearn after your cam swap, the missfire tests are not accurate. I would say, clear all the codes then perform the crank relearn on it, then check to see what the bad cyl is.. I would say it is the other side,. It is really easy for the misfire test to be inaccurate if you have changed the rotating mass.

 

Interesting....but I did the cam swap like 3 years ago, before the first issue, would that still be the case?
I have a techII here, and will do a relearn if necessary. I am also thinking about swapping out the PCM to see if that helps.

Thanks

 

It isnt a pcm issue.

 

Good to know....

 

Is it okay to do a CASE relearn on a car that's acting like this? My SES is flashing and I'm showing bad misfires on 5 and 6. A shop tuned my car and I have no idea if they did a relearn or not. But what your saying is if the CASE relearn wasn't done, it might not be 5 and 6 that are misfiring?