Had the same problem with my 5.4l, guy said it ran great and just needed a tune up. Found out it had 1 cylinder that was around 60 pounds and should have been around 150. I ended up tearing the engine and transmission out and had them rebuilt. I was able to do most of the engine work myself which saved me a little bit. However, if you get into a project like that, it costs a lot of money because there may be hidden issues that you won't know about until you get it apart. I believe it cost me about $2500 to rebuild my 5.4. That being said, I also had to replace my heads (I did the PI swap) and I threw in a set of cams.

That was doing it by myself. I had quotes of $1700 just to remove and rebuild the transmission, and quotes of $3500 to rebuild the motor, that was if I pulled it.

I just ended up having the machine work done. I stripped the motor and put it all back together.

My guess would be that you have 1 of a few things going on:

1. Sticking/stuck valve(s)

2. Bad rings - This can be tested by a compression test, if a cylinder tests low, add a couple DROPS of oil, and then re-check the compression. If the compression goes up with the oil, you may have bad rings.

3. Bad head gasket - You can use a leak down tester to get a rough idea where it may be leaking. Sometimes, if one cylinder is leaking, the one right next to it may be leaking as well (Not sure if I worded that completely right)

Sounds pretty much like there isn't an easy fix for ya How many miles are on it? Mine had 172k when I bought it.

 

Ok what i have heard from another guy which i am not to sure about but hoping is that if the oil was washing the cylinder or wall or something for a while then it will loose compression in that cylinder , so what i need to do is buy some kinda cleaner from gm and spray it into the intake with truck running and then shut truck off and let it sit for a half hour or so and then take it out and give it a good run that shold clean alot of it out and compression should come back cleaning all the oil out of that cylinder now does this sound like it could work ??

 

Truck has 200,000 kms on it , mechanic says he is going to put air down cylinder and find out where it is leaking or what ever ,

 

think i could drop in a5.4 or simply a 5.0l for swap or what would be the easiest way i can do a swap

 

The easiest swap is another 4.6 out of a 97 or 98.