Do you think #4 is really missing or do you think the VCM is just misinterpreting a miss? If its a phantom miss you could try crankshaft position sensor relearn procedure at your local shop with a tech 2 gm scan tool. This has worked for me on a miss in #4. BUT my engine didn't have a real miss. If there is a real miss you should feel it. If 4 is already missing and you pull #2 plug wire then there will be a very big drop in performance. Is there any difference in the way it runs with #4 plug wire off than when its on at all?

 

There is a real miss that can be felt, especially after warm up and idle. There is no difference if 4 is connected or not. I would think that 130 lbs. of compression would have some effect.

 

I'm assuming you do have fuel and spark and low compression is the culprit. How many compression strokes with the throttle wide open did it take you to reach 130? Does the oil on your dipstick smell like gas? Is the compression leaking into the cooling system? Is the compression leaking out of the intake valve? Is it leaking out of the exhaust valve? A FORM of a leak down test could help you. Take the shradder valve out of your compression tester and with #4 at top dead center run compressed air through your compression tester as much regulated psi without the engine turning. I've wedged something in the belt before to help hold it still a bit, but if its exactly at top dead center it should stay OK. Listen for the air leaking out of the throttle body the exhaust the oil fill tube and look for bubbles in the coolant. This may help you determine how extensive of a repair this may be by what's causing the leak. The only miracle that I can see as having a slight chance would be the hotter plug. Even though not the best you might get it to fire on #4.

 

Thanks, I will try the compression leak test you described. I checked the compression with a warm engine, about an hour after driving. I disconnected the ignition and the fuel connector. I removed only plugs 2 and 4.
I first checked 2 and ran starter 5 seconds. got 170 lbs. I then moved to 4 and got 130 lbs. Added oil to 4 and got 140 lbs. I did not open the throttle at all. Should I? Are you referring to a running engine test? The oil does not appear to contain gasoline or coolant. (Checked before and after the change). The oil had about 5,000 miles on it and was dark brown, not coffee black like many I have seen. The numerous times I checked the number 4 plug, it looked just like the number 2 plug. Not wet, not black/fouled, slight greyish ash colour. There is no visible smoke or burnt oil smell from the exhaust. The Blazer also appears to pass the dollar bill test.

This is what I did yesterday:

Added Gunk Motor Medic cleaner to oil. Ran Blazer at idle for 5+ minutes. SES started to flash. Fisrt time it has done that for P0304 only, unless I had a spark plug wire disconnected, even then it would flash and first give the P0300, then the P0304. SES flashing and gave P0304 only.

Let Blazer cool a bit, changed oil. Added oil and a 16 oz. bottle of Rislone Compression Repair. I also changed plug 4 from the OEM AC R44LTS6 to R45LTS6.


Cleared codes. Started Blazer. let idle for 2-3 minutes, flashing SES returned. Check code. P0304 pending. Started Blazer, flashing SES, Drove it a couple of miles, flashing became steady. Hard P0304. Steady light.

Parked for the night.

 

Opening the throttle allows unrestricted air flow into the cylinder during the intake stroke and compresses cylinders full volume of air. But you did the test the same for other cylinders and got higher numbers so I do believe you have a problem. If you are in fact getting fuel and good spark its starting to look a little grim. I would try and determine where the leak is.

 

I have almost the same issue, mine is a random misfire, only time i have a noticeable miss is at idle, great gas mileage. Have done all these tests except the compression test, have been scared to find out what it is...but then again I am just south of macon with no smog test so I just leave it be.... But reading this post I guess I need to check my compression. Hope you can figure out something to get it to pass

 

It sounds like you are chasing a valve issue, do that compression leak test, you will need to make sure that the #4 cylinder is at top dead center on compression stroke, easy way to do it would be take the distributor cap off and rotate the engine by hand until the rotor points at the #4 terminal in the cap, follow the trail through the cap so you know where it should be, you really dont need anything fancy, just take the valve core out of your compression testers hose and hook shop air to it while screwed into tbe #4 hole, listen to the intake with the throttle open, listen to the tailpipe and also take off the oil cap and listen inside the crankcase, if you hear airflow (sounds like hissing or putting a large seashell up to your ear) in the intake or exhaust pipe you have a valve problem, if you hear it in the crankcase you have a ring problem.
Possible causes, mis-adjusted rocker arm or stuck lifter thats holding a valve open, broken or very weak valve spring thats not fully closing the valve or a burnt valve or just maybe just a stuck valve.
None of these are very common on this engine, but... idle misfires when you have known good spark and fuel present and a compression reading thats different by more than 10% are both major indicators pointing that direction.
Im curious about what you find, hope this helps!

 

Again, thanks for all your help. I have not yet done the leak down test, perhaps this weekend.

5/2 through 5/5 - I did not get a hard P0304, Sometimes it would show pending and sometimes not at all. I then got a P0410 and discovered the solenoid is stuck open. I understand you will not get a p0410 if you have a miss DTC, so this issue may have been around for a while.

Anyway, I was about to praise the Rislone Compression Repair stuff for doing the trick....

However, on 5/6 P0304 returned with a vengeance, Clear codes and first cycle you get the DTC pending, second cycle the hard code. I'd reset the ECM ever couple of days and same scenario. Sometimes I'd even get a flashing MIL. Yesterday (5/15) I removed the plug to see the ceramic cover spun around the stem, so I replaced the plug. This morning it did seem to run better on the way to work but I do have a pending P0304 and I expect to have the hard code on the way home this afternoon.

What would cause the insulator to 'break"? My installing and uninstalling it so many times? I also wonder why the code virtually went away for 2-3 days, 200 miles. Could the Rislone have actually worked for that time period and built compression up?

 

Probably just a fluke thing that it went away for a few days, humidity in the air can play a big role in ignition problems. Also you may want to check your other plugs just to rule them out, only reason they ever break is mishandling, either it came out of the box that way or it happened one of the times youve checked it, was it the outside ceramic thats broken and spins or the internal on the base of the electrode tip?

 

The outside ceramic spins.

I had to run a short errand a few minutes ago and the hard code P0304 returned, no surprise. Will perform cylinder leakdown test

Thanks!