I just got my 02 GC 4.7 liter back from the shop where the engine code told them I had a bad fuel injector #1, so they replaced that, and found the fuel rail was still flooding that side, so now it looks like i need a pcm, No big deal right, seem pretty easy to find online, but he does a compression test while he's at it, and says cylinder 1 is completely dead, and another is at 40 (not sure what, just 40, i'm assuming he means 40 percent of where it should be) and he says I've either got a blown valve, (seems likely) or there's a hole in the piston.

my question is, what's the best way to determine whether the head needs to be repaired/ replaced, or if i'm looking at an engine rebuild, or replacement?

Any advice is greatly appreciated

 

40 is the pressure in pounds. do a compression test yourself. it's easy on that motor as the plugs are right on the top. how to do it is on the net. if you reply I can get a little more involved but I have to open the chat room right now.

 

I did a compression check on 6 out of 8 cylinders, and cylinder 1 had 0 psi, and all the rest were within 150-170 psi, I was being melted by the sun, and ran out of time, and the last 2 on the passenger side are a tad ignorant to get at, but i am going to assume the info i got from my mechanic was accurate, and now am debating with myself what to do next, Should i pull the heads and check them out? do i remove the oil pan and check out the pistons and connecting rods with a scope? I am even entertaining the idea of a rebuilt engine.

 

getting nothing on a cylinder is really bad news. If I was in your situation I would be calling the scrap yards for a good motor, they made lots of them and they are usually a pretty good motor (other than the tendency to develop oil leaks from the front seal). The amount of work involved in pulling the thing apart which will probably involve removing it anyway is why I made my previous comment. I'm not trying to dissapoint you but the reality of zero pressure on a cylinder usually points to a major issue and with the cost of parts and time involved I would be seriously considering my options. Another thing you have to consider is how much you can do yourself and how much you have to have to have done for you. Something else you might consider is asking if the scrap yard will change the motor for you, some will if you buy the motor from them.
Regarding the injector issue, did you try pulling the electrical connector from the injector and then pressurize the system and see if it holds pressure, it would not be the first time I see a new injector that leaks.
please post what you decide, I apologise for a less than positive opinion.

oldfart.