Just an interested observer on this thread, but dang George, you are amazing. I love your approach to diagnosing and I learn something from so many of your posts! Thanks!!

 

Thank you Christine, I am glad to be part of the team


George

 

Alright, once more as requested.
1. Cam retard is dead on 0 after doing a little adjusting and re-checking once bolted down.
2. Pulled the crank sensor and cleaned it up, absolutely no damage on it or the wheel teeth, I thought about touching the timing chain with something while the hole was open but I completely forgot to do so before re-installing
3. I performed drop cylinder both at the distributor and plug wires, results below4. I haven't pulled them since the distributor install on Wednesday but I can do so soon and send over some pictures
5. Fuel trims provided before are ranges, minimum~maximum, should have clarified before
7. Got some measurements at ambient8. I know you didn't request it, but I know that a vacuum test can tell a lot about valve health, so I attached a gauge to the booster line from the manifold, video attached, tested at idle and 2400 - 2600 RPM.

 

1) Did your misfire stay as cylinder 3 after cam retard set to 0?
3) This does suggest that cylinder 3 is contributing less power although the results are not dramatic
5) Your fuel trims are interesting. Always add st and LT trims on a given bank. Using averages for your ranges, none of the readings are way out of bounds and bank 2 is totally normal. Bank 1 however goes from +5 at idles to -5 at 2500 rpm. That suggests unmetered air on that bank (cylinder 3). Have you done the LIM gaskets yet? Have you checked for exhaust leaks, especially on bank 1?
7) How do those sensor readings compare to ambient at your location that day? Precat O2 sensors should vary between approx 0.15v and 0.85v, switching about one per second at idle. The post cat sensor should be steady between 04v and 0.7v. Your previous graph suggests this but your current description does not. Can you clarify? What is the history on the 2 precat sensors?
8) What conclusion do you draw from your vacuum gauge test?


George

 

1. Misfire has stayed at cylinder 3 with retard at 0 yes.
2. I have not done the LIM gaskets yet and have no idea if they have been, the only exhaust leak I KNOW of is at the cat but I can hook up a smoke tester to really check it out
3. I'll attach the video at ambient engine off to show you what I mean about the 02 voltage, temps checkout good though, I've got no history on this truck at all.
4. I think the vacuum test suggests solid valve health but I've never done a vacuum test to see what a good one would look like before, I'm a Toyota tech and most if not all of our engines are Atkinson cycle so manifold vacuum means very little.
Guessing next steps are LIM and maybe pulling the valve cover?
Decided to just attach the cylinder drop video as well with graphs

 

I would mist the engine first to make sure you dont have any crossfire problems. Also make sure that #3 plug is ok. Swap the plug and wire to make sure the problem does not follow. We call #3 the PITA plug because of the steering tube in front. Thats the easiest plug to crack or for the cable not to seat correctly. We all have to do the LIM gaskets anyway to avoid a major issue and your testing suggests that could be it if there is no exhaust leak. Your vacuum gauge test looks pretty godd. Normal idle vacuum, no evidence of an exhaust restriction, good snap throttle. The only possible issue is the vibrating as engine rpm goes up. I cant tell if the gauge is resting on the engine (vibration). If not there may be some minor valve issue like guides or springs.

George

 

Already misted the engine a couple times in the dark, no arcing even when fiddling with the wires and distributor. Plug and wire swapping was actually one of the first thing's I tried and nothing changes miss location.
Currently on my second set of plugs and wires this month just to make sure secondary ignition wasn't the issue.
The gauge was resting on the cowl just in front of the hood but it might be worth having someone hold it just to make sure. Sounds likely I'll be digging deeper into this thing to see what's going on mechanically. unfortunate to see but oh well, anything worth knowing about these valves that a quick google search won't tell?

 

The engine sounds pretty good in that vacuum gauge video but of course I’m not standing there listening to it in high Fidelity. I didn’t hear any lifter tick but that’s another possibility for cylinder number three. An interesting side comment. Years ago, my Blazer develop lifter noise at start up And shortly there after coolant showed up in the oil because the LIM gaskets had blown. We all use the upgraded Fel-Pro gasket set for the intake manifold.

Regarding the valve train one of our better contributors here Les Meyer has more internal engine experience than I do so I’m going to ask him to answer that question for you.


George

 

Hi Jacoby, you have eliminated a lot of possible problems already, but there are a few more tests I would definitely do before pulling anything apart.

• Clear codes and perform crank sensor relearn on same key cycle. PO300 code will not set on first key cycle, and PCM prevents crank sensor relearn once a P0300-P030X sets. Have you done these before? If not please know there are specific conditions that have to be met such as brake depressed and park brake on (at least enough to light up the brake light). Knowing this can keep you from repeatedly over-revving your vehicle trying to get to the fuel cutoff. Procedure is attached.
• MAF reading at absolute full throttle 1-2 shift. Yes it is almost 5000 rpm. This will finish checking MAF sensor (needs to be in certain range). Will also let us know if there is any restriction in the exhaust (like plugged converter).
• MAP sensor with KOEO. This checks it's accuracy against normal barometric pressure.
• IAC counts at idle in drive and in park - also KOEO. Want to verify normal operation.
• Dynamic Compression Test. The advantage of a running compression test is that it gives you an idea of the volumetric efficiency of each cylinder. In other words, how efficiently each cylinder is pulling air in, retaining it for the correct amount of time, then releasing it into the exhaust. If a cylinder cannot perform these functions properly, the result can be a loss of volumetric efficiency or a density misfire. This will check out your mechanical stuff, including your valvetrain. Not the easiest to do on a Blazer, but worth it if all else fails. Make sure engine is warm and static compression readings are taken with throttle wide open. You can kill the ignition during static compression by unplugging connector on the coil. I personally wouldn't worry about shutting off injectors. Then hook up the coil and start the engine. Take the idle reading and then open the throttle to full as fast as you can (with your hand operating the throttle body lever). Let the engine RPMs come up to 2500 or so at full throttle before letting off, and record the highest pressure reached. https://www.alldata.com/us/en/suppor...pression-tests

Good luck and let me know if you have any questions.