I have done a search and haven't found anything that sounds like what's going on with my car.
A couple of weeks ago I decided to change my oil and while I was at it I changed out the spark plugs as well. When I cranked it up it was running rough like it was missing. I rechecked all the wires to make sure I didn't cross any of them up. I hadn't. I figured I might have a bad wire somewhere so I went ahead and changed them all out. Still no change, the motor idles rough and when I give it some gas it backfires out the throttle body. I've already checked timing and it was fine. The car was running just fine previous to me changing the plugs. I've also changed the cap and rotor and it made no difference. I'm very confused as to whats going on here and need some input before I start tearing the whole top end off looking for a problem that might very well exist right in front of my eyes.
Other bit of information:
* Car hadn't been ran for approximately a week and a half prior to my tune up.
* About 3 weeks prior I had an stuck thermostat and an overheating issue do to this. After a new thermostat there didn't appear to be any damage 'cause the car ran just fine.

Please help before I get in way deeper than I need to.

 

have you checked timing yet?

 

What about your coil?Have you notice any sensor or wire damage?ALso if you can check your fuel pressure.

 

I've checked timing and it was right where it should be. It acts like 2 spark wires are crossed up or something. I've been over the wires at least a dozen times and they are all fine.

I'm very stumped with this one!

 

Fuel pressure is fine. Don't know about the coil. How can I check the coil?

 

When you crank it,how long will it run?

 

Well I just replace it .Mine went dead on the highway and would not run ,just spin over.Fixed that then the fuel pump went out.When that happen it was a rough idle with alot of surging.The pump was barely keeping the engine alive.

 

It starts right up as usual and doesn't die out at any point. At an idle it runs rough, motor shakes pretty good, like one of the cylinders isn't firing. When I give it gas it backfires through the throttle body.

 

Some where the wires got to be crossed.

 

I've been over the wires more times then I care to count. I even walked away and came back to it a day later in the hopes that I had been staring at it to ong and maybe with a break the problem would jump right out at me. No such luck! I even broke out the book to check the wire routing, and it was fine.

 

What about any wires to any of your sensors?Like your oxygen sensor?ect.You could of knocked something off when changeing plug wires?

 

It's possible. I thought I checked all of them, but maybe it's worth another look.

 

Are you checking the timing correctly? Are you unplugging the EST when setting it? What is your base set at? With a 350 TBI you are going to need at least 8 to 12 degress of base (if you haven't gotten into chip work). Also, what is your feed line fuel pressure? It sound slike you need chip work, fuel and timing adjustments.

 

Timing was checked correctly.

I started to check cylinder compression. 145 - 150 at the first couple of cylinders tested and then I got to the #4 cylinder. It barely made 40psi

 

Sounds like you might have a burnt intake valve. Have you tried hooking a vacuum gauge up to see if you have an unsteady needle, which would indecate a possible burnt valve?

Steve

 

I've was finally able to perform exploritory surgery over the last couple of nights. And after getting the passenger side head off the problem was pretty obvious.

 

The big question is why did it blow out in the first place...

Id carefully inspect the block and heads with a precision straight edge to make sure its all perfectly level. Also look for signs of damage from the hot gasses that where cross-flowing between the cylinders. That can easily compromise the block/heads, or just plain torch them outright.

 

Also, that looks like one of the blue felpro stock replacement head gaskets. I dont know if GM ever used them but if you picked the motor up used that could be a sign that it was a reocuring problem.

 

The motor was used but had never had the heads removed for any reason. The different gasket is because before dropping the motor into my car I pulled th heads to inspect everything(cylinders, valves, etc...). That's also the time in which I put the better cam in as well as timing chain and what not. As for what caused the damage I'm guessing it' started from my overheating incident due to a stuck thermostat a while back. It seems everything went down hill from that point. I'm thinking of pulling the other head as well and taking them to the machine shop for a valve job and possibly a shaving because I'm concerned this might have warped the head.