Hello all, I'm new to the forum but it seems that the truck I just recently bought isn't since it came with a sticker from the forum. Well on to the reason I'm making this post.

Last Wednesday while driving, I noticed that I started to have a misfire. I pulled into my apartment complex and the truck stalled on me as I went up the hill. The truck wouldn't start back up that day what so ever.

Thursday, I went out to try to start it and it did, but it had a terrible misfire issue. Got the codes and I had 2 p0300 codes on the ecu, and that's it. I swapped all 8 plugs out and gapped them to the recommended 0.060 gap specified in the Chilton manual. Cranked the truck up, problem still existed. I bought a new coil to swap in at a later time due to family being around for the holiday. I was suggested that I buy a new fuel pump and I did, I got a Delphi replacement.

Today, after waiting for the rain to stop, I had some buddies from work come over to help remove the bed and install the new pump. Once again, I cranked up the truck and the problem was still there. Since the pump wasn't the problem I got the bed temp installed. After messing around with some vacuum lines I noticed that the line that goes to the pump attached to the brake Booster caused the truck to die after revved a little. Pulled the vacuum line off the pump and the truck would idle slowly down and stay at a idle after a Rev. I'm thinking the pump could possibly be causing the truck to starve itself of air. (I also have a "reduced brake power" notification at times) As I tossed more ideas around with a buddy we decided to unplug one spark at a time to pin point if a plug wasn't firing. We didn't really find anything different other than the second plug from the front on the passenger side didn't really change what the idle plugged or unplugged. We swapped in a new coil and still nothing changed with the misfire issue. I checked two spark plugs to see what they looked like and I got two black plugs, running rich.

I believe that's all I have so far. If anyone has any idea to help or if you ran into this problem, I'd appreciate any help I can get. Oh, and I have videos on my phone that'll I have to figure out how to post.

 

The line that goes to the pump attached to the brake booster....what line is this? Surely you dont mean the high pressure line from a hydrboost to the power steering pump?

Have you checked the wires for cracks/tears/burns?

 

I believe this line is apart of the pics system bit I could be wrong. It goes from the booster to the back of the intake manifold.

I have checked the wires they look fine to me but at the same time I'm thinking about buying a set just to rule the stock ones out.

 

You could use a spray bottle on mist to see if the wires arc too.

Also I don't want to say your chiltons manual is wrong, but I coulda swore that after 2001 or 2002 they dropped the gap to .040. If your truck still has the stock air box, the GM info sticker on there likely says the gap.

 

I do not have the stock air box. I can try new wires and new plugs and see where that goes.

But I'm still confused about the whole vacuum line causing the truck to die at random times.

 

So I swapped in new plugs with the right gap, new plug wires, as well as a map and maf sensor. I took it to a dealer for a diagnosis and a crankshaft variation relearn. They checked everything, and I have fuel, spark and air so they believe I have two broken valve springs between cylinders 1 & 3. Checked them and I'm able to spin the springs a little bit. From reading on ls1tech,if you can spin the valve spring they're bad apparently. How true is this?

 

A compression test and a leak down test might reveal more about your situation.

It is possible to have weak or damaged springs But the best way to test them is to take them off and verify them on a spring tester. Although I suppose if you can twist them by hand in a circular motion there probably isn't enough tension on them to seat the valves properly.

 

Well I got the #1 & #3 exhaust valves off this morning, as I did I could here the air in the motor. I don't know if this is normal or not but it was just a little concerning. It didn't slow me down as I removed the valve springs.

From a visual check all I can see are a few stress marks on the top and bottom flat surfaces of each spring. There are no cracks or unusual bends.

Tomorrow morning after I get off work I'm going to get the springs tested. If they're good, I'm going back to the dealer to give them a piece of my mind. After all they were the ones who told me to replace them after they did they're diagnosis.

On the positive side of things, I have ls6 valve springs on the way.... Woot Woot

 

Did the springs Change the way it runs?

Have you cleared the code and driven it to see if the code comes back?

 

The ls6 Springs aren't installed yet. They're on backorder until the 1st. So driving the truck isn't going to happen for a while unless I buy two springs from the dealer, but only if I find out the two springs are bad. (Apparently O'Reilly's can't get the springs.)