looks like you have an issue with the evap purge solenoid.

 

I think your not understanding the GM random missfire. The computer has NO idea what did not work it only know that the RPMs varied in a unexpected way that indicates that one or more cylinders did not add power to the stoke.

Random missfires only show up when the computer has no indication of why this happened. The computer can not monitor the secondary ignition system, the mechaincal part of the injector or the mechainical part of the motor.

Yes one craked wire can cause a random miss fire as can a coil failing in the winding or an injector randomly not opening or a sticking valve. Although a sticking valve would have other syptoms.

Drivning a car with a miss (depending on how random it is) can be hard on the O2 sensor. If your car is due for O2 sensor then it is a good idea to replace them. But if you get the miss sorted out drive the car a week and see if it get better. Replace plug wires as a set, like I said before how they look mean nothing. Old plug wires will kill your coils. I have seen people find a bad coil, replace it only to have it fail again in a month. Why cause the wire had the coil firing at max voltage all the time it overheated.

 

Thanks for the reply Gorn, now I understand how the random misfire works a little better now which will help a lot in figuring this out.

After work I plan on trying the water mist test on the plugs to look for arching.

I will replace the wires and upstream 02 and see how it goes from there. Does it make a difference if I use stock wires as to NGK wires as to thicker wires?

As for the OBD test, I don't think the EVAP system is failing, I think the codes shown are what was tested, the X infront of the tests are shown as critical failure. I could be wrong on this but that is what I assume.

 

Replaced the wires, no difference. Will return the wires for a compression tester tomorrow and go from there.

 

You really should get the car hooked up to a engine analyzer and looked at by someone that knows what they are looking at,

One of the more common causes for a random missfire. Sparkplug wires are left on too long, it causes a coil pack to overheat and short internally. At first it only does it under hvy loads/ but this leaves behing carbon tracks. As this get worse the coil will fire along a carbon tracking. A scope will pick this up.

There is a way to test for spark. It will not tell you is you have a cracked plug but it will tell if the sparke is making it from the coil to the wire. I keep 8 of these in my box so I can hook up the whole ignition at once.

90º Inline Ignition Spark Checker

 

Yes, I should have it looked at. But I am cheap and don't have the money right now. I will phone around for some quotes.

I was thinking about a spark plug tester, but since I've replaced the plugs and wires, sprayed water on each header output for mist, unplugged each coil pack and heard a difference, I am beginning to think it may not be spark related.

I seafoamed the car the other day and I have not seen the p0300 code since, but it does shake the wheel pretty good at 2,000rpm and has **** for what it coud for power.

I think ill still do a compression test, although I am scared that it could be an internal problem. Either way I am very machanically inclined and have a secondary car Im willing to do any work myself.

I just want it running smoooooth and fast!

 

have you looked into what the knock sensor is doing?

 

Your issue can be found by checking for spark at the end of each wire going to each plug. It sounds a lot like an engine running with ****ty plugs, or ****ed up opti maybe.. But first check for spark at each wire, because if each cylinder is sparking, u can bet plugs are shot.

 

Scratch that, LS1, but same thing. Check if spark is running through the coil, to plugs

 

Back to the spark eh? After all my tests on the spark I'd assume it's working fine. BUT I have not physically checked for spark yet... So as a free surefire way to make sure the spark is good, I will remove each plug, keep attached from the coil to the plug and setup a ground wire to the spark plug. I will physically check that each spark is sufficient before I completely rule out the spark.

I can't wait for that dam #8 plug again, it's always fun to deal with. Although I managed to change it out from the top last time with patience.

And no I have not checked the knock sensor. How would I go about that? I'd assume it would set a code if there was an issue?
I am not throwing any codes at all and it runs pretty decent despite the shaking and loss of power. Like I said it was pending a P0300 code, but since I seafoamed it and removed the battery to clear the codes I have not seen it since.