I think I fixed it!

I removed all the intake tubing and cleaned up every tubing connections, I removed the MAF and cleaned it up with MAF Cleaner, cleaned up the electrical connections, cleaned up the IAT sensor and connections and tightened every tubing back really really tightly. I think however, that the connection on the top of the throttle plate is not super secure and may leak, so I will look into it soon.

I also cleaned up the throat on top of the throttle plate.

I also removed the battery to look at the 4wd engagement actuator for leaks and searched for leaks in general areas using carb cleaner spray (could not find any leaks).

I've put injector clearner in the gas tank as well, we'll see it that helps.

So I took a test ride, and now it runs very well, no stumble, no stumble at idle and it picks up speed. I do feel that it should be more powerful, but it's driveable.

Next is fuel filter and then I'm changing the differentials/transfer case oils.

I hope it was the MAF sensor, we'll see if it's going better this week!

 

Damn it's still acting up...


So I went ahead and cleaned up the MAP sensor, cleaned up and tested the EGR (seems fine). Checked for vacuum leaks once again, only found 1 suspicious hose but it doesn`t leak. I`ve plugged a vacuum gauge on a hose and the vacuum is steady at 20inHg and goes up to 25 when revving.

Unplugging the EGR makes idle extremely bad, so I guess it`s working right. Unplugging MAF or IAT creates bad idle as well.

I rechecked fuel pressure to be sure, it`s at 60 on prime 55 idling and when I shutdown the engine it stay`s at 55.

I checked and cleaned all connections I could.

So I`m left with CMP Retard and compression check.

What else could I check?

 

A compression test, when performed both dry and wet, is used for determining how well the piston rings are sealing. The sealing ability doesn't change with temperature. You're experiencing the problem moreso on a cold start, which eliminates rings as being the problem. A cylinder leakage test is used to see if the valves are sealing, which is not affected by temperature either. Your steady vacuum reading does not indicate a leaky valve either. I'd check camshaft retard and see where it's at.

The P0300 DTC is almost always caused by a fault in secondary ignition: plugs, wires, cap, rotor and ignition coil. Incorrect camshaft retard, a worn distributor gear, and worn distributor bushings can also cause it because they affect how the spark is distributed. Low fuel pressure can also set P0300: Your fuel pressure and leakdown readings are both at the bare minimum.

 

Hmm what should the pressure be again?

Btw, yesterday I had absolutely no problem with the truck, it worked almost perfectly! I guess that the injector cleaner I've put in the tank is helping with whatever fuel problem I have..

So I have to change the fuel filter, but I didn't see it, I thought it was under the driver side door, is it hidden under some part??

Thanks for your help, and btw, I have an appointment to the dealership to adjust the CMP Retard, it was the only place with a GMTech2 ...


** I also forgot to mention that I believe the fuel pump is louder.. I wonder if fuel pumps become louder when they are about to pop.. I guess it's simply that I am listening more to the truck since there's a problem. Most probably placebo.

 

Yep drivers side. Inside the frame, just follow it back.

 

Fuel pressure: Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi. Pressure must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, a problem exists and further testing will be required to determine what the problem is. Post your results.

 

Tomorrow is the big day, I'm going to the stealership to check the CMP Retard.

Btw, I can drive the truck, it got enough power, and starts fine and I have no more problems when it's in open loop (strange), but I DO have a problem when it's hot, on idle it's misfiring like crazy now, I didn't have that before. Wierd.

I feel that this is getting worse.