I'll say it as no one else it seems to want to go there...... Don, you are spinning your wheels on this one. He clearly does not understand the logic behind the tests as you outlined. He will do exactly what he thinks, be it right or wrong.

Lets see how it turns out for him.

 

OK, here is the thing... cylinders 1-3 are in fair condition, not good. Good would be somewhere in the 170-180 range. #4 is in bad condition. The fact that they all jumped dramatically indicates that all cylinders have worn rings. You could indeed do a leakdown test, as part of the poor compression could be due to coked valves. But it really does seem to be rings, and getting set up to blast is not cheap, unless you already have a good air compressor.

These injectors are not of the kind that you can just remove them and move them around. They take special tools to install correctly. And they cost over $100 each to purchase new.

 

I am well outfitted. I have access to an industrial compressor that is more than capable. So no issue there. And even a blaster and shop vac. So I really just need the media and the wand. I have MDF board to mockup a scenario like @cannuck did; I really like how he did it here. But even if I had to purchase all of it, I'm still ahead because an engine swap will be several grand and a big setback. I don't have the luxury of spare cash and time lying around to swap an engine. I'm open to donations though, if anybody is willing! Haha!

Yes, I know you can't just flippantly swap them around. Your posts as well as @cannuck's posts have helped me see that. Thank you both for your very thorough and informative posts. I have an injector seal kit ordered. I also have the special tool on its way to install the Teflon seals. So I'm good to go. All bases are covered.

Again, my driving motivation is that I need to sleep well at night, knowing I made the best decision, with the most information possible, if the engine lives or dies. I cannot shortcut such a big decision and I know it's frustrating to the rest of you that I'm unwilling to just shortcut the thorough diagnosis and scrap the engine. My apologies, but this is how I'm going to diagnose it. And I know you folks are well-meaning and looking out for me. But to be honest, I find it odd that I stand alone and no other mechanic in this thread has stepped up to say, "this is a big costly decision; you must check everything thoroughly, from all angles, to be certain it's the right decision on whether the engine is scrap."

 

 

"this is a big costly decision; you must check everything thoroughly, from all angles, to be certain it's the right decision on whether the engine is scrap."

I think that's what we have been saying. But once the problem is pinpointed, not much use in going further in the hopes of a miracle. Been there, done that.

What results from SeaFoam?

 

Just a quick update --- not that this is anything very meaningful given the information currently exchanged in this thread, and the impasse about the diagnosis --- But for a passerby who may stumble onto the thread and want more information about the progress, I had swapped ignition coils a couple weeks ago from #4 to #2. Code remained at #4. This past weekend, I put them back to their original cylinders and then I swapped the #4 and #2 spark plugs. For completeness, I wanted to check this to thoroughly assess the issue from all angles. Lo and behold, as I expected, the code remained at #4. So neither the ignition coil, nor the spark plug, is the culprit.

Onward ho, to intake removal this weekend to take a look at the intake runners and swap injectors, #4 and #2.

 

You seem to be fixated on chasing the "code". It's past that stage now that you know that cyl. #4 has low compression. Swapping all those parts around is just a waste of time and some money.
Go back to the basic mechanics of the internal combustion engine. It's pretty obvious now that the problem is compression, internal. (At least based on your posts and findings)
As Don ask. Have you even tried a Seafoam treatment ?
Or are we all just "spinning our wheels" trying to help you figure this thing out ?

 

No need to help me out much more since I know it's frustrating to you. I understand I stand alone in terms of getting to the bottom of this. Truth is, a little adversity usually motivates me to go further toward what I hope to find (life lesson there). Despite lower compression results, I believe #4 has life left in it; you folks do not and I understand we disagree, which is okay with me. No need for you folks to spin your wheels to help me; you can unfollow the thread is you wish. I was just providing this morning's update for the passerby who may come later and wonder how things progressed.

 

I've been reading this thread but have seen if you've done this. I understand that you would like to get to the root cause or your issue, I for one would interested in what you find. FWIW I've seen where the injector seals leaking would cause your issue. You will have to pull the intake to get to those so at that point blast the intake valves which is a know issue on any DI motor.

I'm going through the same process with my Impala SS. Motor was making some not so nice sounds while idling, I've got the intake pulled which is not an easy task with my setup and it looks my expensive lifters may have been part of the issue after seeing them I;ve decided to pull the motor and look at things in depth. Also, I have have pistons and rods from an zero mileage LNF that I have on a shelf if you are interested. The rings still have the paint marks on the face.

 

Good point about the injector seals DrLoch - but the earlier compression test with the addition of a bit of oil, wouldn't it rule that out - or would the oil hit the injectors as well as the rings?