Ok, one more thing i just thought of, try shooting some carb cleaner or starting fluid or brake clean at the intake gasket above the problem cylinder and listen very closely for the engine to change pitch, im wondering if you have a vacuum leak to that cylinder causing it the run lean, also the PCV valve plugs into the intake just above that cylinder, you may want to pull that connector out of the intake and make sure the o-ring is there and check your pcv tube and elbow for cracks and replace the pvc valve while youre at it, extra air right on that cylinder can cause a lean misfire and would leave you with a clean spark plug, could also be the fuel injector poppet on that cylinder is stuck or plugged or of course the compression issue could be a problem too but compression tests arent foolproof, you really need to pull all plugs and crank engine until gage stops rising, not to a specified amount of time or number of strokes, the way i look at it is that the gage and hose are like an air compressor tank, they need to filled to the MAX amount that the cylinder can provide, depending on what position of the stroke that given cylinder is in and how good of condition your battery is in (if you dont have a charger connected while testing) the results will be all over the place, for example, if the 2nd cylinder tested was half way up its compression stroke when you first hit the key and it only gets 3 or 4 full strokes compared to another cylinder that may have have gotten 5 or 6 if it happened to be in the proper orientation to have an advantage, add in a slightly discharged battery and yeah...variables variables.... Another thing you can do if you have a volt/ohm meter is pull the big injector plug on top of the intake and test each pair of pins for Ohms they should all be relatively the same, also make sure the pins are all straight and be careful not bend any when plugging it back in.

Does your scantool provide freezframe data or live data stream? That would be extremely helpful.

 

Thanks DimeBLazr,

I've done most of what you mentioned before and tried about 1/2 of those again over the weekend.

I performed the leak down test as follows:

I first tried to find TDC #4 by hooking a multimeter to the Ignition wire and the #4 wire to get a continuity reading whilst rotating the engine with a 1/2 drive ratchet at the alternator nut. I got no reading after 2 rotations, so I thought that was the issue, so I hooked to the number 2 wire and got no reading as well. I guess that method will not work on finding TDC.

I removed the distributor cap and rotated the rotor to #4 firing position. I let my air compressor run to 120 psi and shut it off so I could hear air escaping. The compression gauge hose did not directly fit the air hose so I rigged something up. I supplied the 125 psi and the engine turned about 2/3 a revolution! Fan started spinning, scared the crap out of me! Of course now #4 is no longer TDC, so with the much lower psi supplying air, I move the engine to TDC #4 and constantly heard hissing (with stethoscope) from the open throttle body. I heard a small hiss from the dip stick opening and none from the exhaust. I am beginning to strongly suspect the intake valve as the culprit. It was getting dark and I had to put all back together. I do want to repeat the test to hopefully confirm. Use less psi this time, and test it 'warm' as the engine was cold yesterday.

If it is the intake valve, what can it possibly be to repair (besides a complete head job)?

Burnt? (I've heard of exhaust valves doing so, but intake?)
Dirty? (I've ran Seafoam intake cleaner, along with Techron, Lucas and other fuel system cleaners).
Bent?
Stuck?
Broke/weak spring?
Any/all the above?

I plan to remove the valve cover and take a look.
What all should I be looking for?

Thanks!

 

Another way to check it if you have the valve cover off is to loosen both rocker arms on the the #4 cylinder so the arent touching the valves, like this it wont matter where the cylinder is at in its cycle, both valves will closed and should be a sealed cylinder except the spark plug hole where you are putting air in. Make sure you do the test like this before condemning a valve and pulling the head, there is still a chance that you may have been off a cylinder off when trying to eyeball the cap/rotor orientation. When you loosen the rocker nuts put a paint mark on them and count the number of turns you back it off and write the number down, this way you can turn it back to exactly where it was and avoid doing the valve lash adjustement. When you have the valve cover off you can actually start the engine and watch the rockers move, you will get some oil on things but its not the end of the world, I lay a rolled up towel across the tops of the rockers, they usually dont squirt too bad anyway. If you see the intake rocker isnt moving as much as the other intake rockers then you could have a lifter sticking in its bore thats not allowing the valve to close fully or a lifter thats jammed or got a chunk of something stuck in it and its stuck in the fully pumped position maxing out its hydraulic lash adjustment. If it leaks with the rockers loose though and the spring is good then its a valve problem, only way to fix it is to pull the head.

 

Thanks!

You are a super help.

The only valve job I've ever done is on a Kawasaki two stroke dirt bike and a B&S go-cart engine. I have changed a couple of head gaskets on cars.

I will do as you described, afterwards (and depending on what I see), with the head still installed can I remove the rocker entirely and pull the rod out to inspect/clean? I think the lifter can not be pulled with the head installed? I also understand I can even replace a broke/weak spring with the head on, just have to find a way to keep the valve from falling into the chamber.

Keep in mind I get a border line low compression reading (~130 psi). 1500 miles after the oil change I've only lost 1/4 quart (according to dipstick level). No apparent oil burn smoke, sparkplug is clean, not wet, not fouled, looks like #2 plug. However, if I short out #2 plug wire the engine runs noticeably rougher, if I short out #4 wire, no change at all, therefore the miss is real. Wouldn't 130 psi provide at least something if all else is well? Should I revisit spark? I use a $5 inline spark tester light that shows current flows, but is it enough? I also should pull the distributor and look at the gear. I did this in December with the LIM change and thought all looked good. I also changed the #4 injector and poppet assembly a month ago, so I assume it's getting fuel. Resistance levels are within range for all six injectors and all pins look straight.

Based on the paragraph above, what can I rule out? what should I look at in more detail?

Again, thank you all for bearing with me and your helpful suggestions!

I hope I can return the favor to y'all and future Blazer owners.

 

Lifters can be changed with intake off valve covers rocker arms and push rods removed. Heads can stay on. For finding tdc I leave plug in held by only a little threads. When piston is on compression stroke you will hear a hiss while rotating. When at tdc hiss stops. Hiss starts again when piston starts going back down but is sucking air in instead. I just had a valve job done. All 6 intake valves were leaking and trashed along with a crack. Valves wear, but in my car I bought it after it was overheated from running coolant low from bad intake gaskets. Cost me just under 500 for cracks to be fixed valves replaced and valve job with deck surface milled. I did the work except for machine shop work.

 

Did you ever check the injector wires like said in post#6? Also look at the numbers on the distributer and retrace them to the correct plug. Could just be a brain fart after one of the other fixes. Been there. Lol. What was compression on 6? A bad head gasket from overheating or whatever. Could have compression leak between 4 and 6.

 

A few days ago I did check the pins and female connectors, all looked good. I also checked the resitance and got all 6 in the neighbourhood of 13K Ohms (I think that's what it was, they were all close regardless the number). I have not yet checked the wiring from the ecm to injector number 4 but will. Do you happen to know which wire coming from the ecm goes to #4? Could I alternatively hook a voltmeter to the two connectors that supply #4 and see if I get voltage whilst turning the starter?


Coincidentally, yesterday I checked the compression on the entire bank. Engine was slightly warm (2 hours after driving). I removed one plug at a time for each test. I placed a large wrench in the throttle to achieve near WOT. I turned the starter 10 seconds and took two test each and both times got:

Cyl#2: 190 psi
Cyl#4: 165 psi
Cyl#6: 178 psi

In the process of removing the stuck on boot off plug 6 I pulled the wire out the boot. I rigged it up last night with Superglue the best I could and this morning on a 8 mile trip to the job site the Blazer ran very rough, flashing MIL on acceleration. First got a pending P0300 when I parked. I left about an hour ago, drove 4 miles to get another wire, had pending P0306. Drove 4 miles to home and have Confirmed P0306. No P0304 code at all. I am about to put the new wire on #6 over lunch and return to work. I will clear codes and predict the P0306 will be gone, but my constant nemesis P0304 shall return.

 

Yesterday after lunch and replacing the #6 wire, I drove it 8 miles to work
and it spittered and sputtered worse than ever. Still same flashing MIL upon acceleration, steady all other tiimes. Parked it and worried. Code P0306 still there. Ran a trial at work that took 2.5 hours. When I started it, the Blazer actually ran like 'normal'. Drove 4 miles, steady MIL. Code P0306 was gone and P0300 took it's place. I assume the plug on number 6 was wet and it finally dried out, giving me that cylinder back.

I reset the ECM and and drove 4 miles home. Pending P0304 is back. Cut my lawn as it was badly needed until dark. Did not check injector continuity yet. Confirmed P0304 this morning to work.

 

Saturday May 24th: I had intentions of removing the valve cover; however, back in December when I had the no run/LIM gasket change issue, I replaced the distributor cap and rotor. I noticed then that both screws for the cap were near stripped out (would not tighten fully), so I used oversized screws. I decided Saturday to check that out and noticed the cap was loose and the rear base attachment on the distributor was crack. To temporarily check this, I used a C clamp and clamped the cap to the base. When I started the Blazer, it idle better than I can recall in recent memory. I reset the ECM and drove it a little. Pending P0304 returned, oh well, no surprise.

Sunday - Drove Blazer just a few miles. Pending P0304 went away.

Monday - (Thank you Veterans!) - Drove 3 miles to store. Checked codes... pending P0410. I was somewhat happy as I understand you will not get P0410 is you have any P030X codes. Did not drive any more Monday.

Tuesday - Another cold start and to work. Drove 8 miles, stopped for fuel. No MIL. Checked codes: Pending P0410 and P0300. Drove to work another 10 miles. No hard codes. 3 hours later, started Blazer for business trip. MIL on. Codes: Pending P0410 and Hard P0304. Oh well. Cleared codes. Drove 200 miles, No codes at all. Stopped for gas, red lights, idling, etc. Back on road. Pending P0304. Drove another 100 miles. No hard code. Parked last night. About to leave shortly.

With all that said, I did get a day of no P0304 codes. I'm leaning towards replacing the entire distributor.

I just got the schematic for the injector wiring and will check that as well.

 

I've had this happen as well. The oversize screws that came with the cap cracked the screw holes. I had gear on along with cap and rotor. I super glued mine on with a couple of large zip ties, one on each side pulled tight when the glue was still wet. I also put the screws in. I left the zip ties on. Drove it for 2 years without problems.