Its called "exhaust reversion". Strange pulses of flow happen back and forth in exhaust systems. I'll see if I can find some text on it. More mechanical engineering!

Honestly I have never had to replace one of those Schrader valves!

 

Here's a bit on exhaust reversion from the boat people. They can even get engine full of water when they have a significant amount of reversion on a high performance engine. But they do explain how exhaust can back up in the exhaust and suck something in. In your case that could potentially be air drawn from outside affecting O2 sensor reading. Does it make any sense to you?

https://www.cpperformance.com/t-what...reversion.aspx

 

Thanks Les, it definitely makes sense. Do you know if there is enough overlap between the intake valve opening (compression stroke starting) and the exhaust valve closing on this engine that this would actually happen? So I have some things here, the first picture is the oil pressure cold, the first video is the oil pressure warmed up and what happens when I snap the throttle. The second video is my fuel trims idling at 2500 rpm, and the best last, third video is of valvetrain noise. Guys, getting in there today I think there is definitely excess valvetrain noise coming from the cylinder 1 area, see the video below. I didn't really notice it before, my belt likes to squeak a lot when it gets wet (it's an ongoing issue LOL), anyways I don't know how I didn't hear this with the valve cover off or anything, as the phone gets closer to cylinder 1 the sound seems to become louder, let me know what you guys think. To top this off, I am relatively sure my compression tester is good to go again, tested with an air compressor, and seems to give good readings and hold pressure again. So the tire valve cores have a much stronger spring in them, I mean much stronger, that I guess makes for inaccurate readings on the gauge, took the one out of the attachment that came with the kit and slapped it in the hose I use, good as new. Fingers crossed tomorrow I will be able to do another running compression test on cylinder 1, I will probably end up doing cylinder 5 again too just to make sure the gauge is in check.

 

On fuel trims we need normal idle speed and then 2500 rpm, both out of gear. Don't graph them just grab a screen shot of the tabular data pids in live data like in post 293.

George

 

In a 4-stroke engine, there is always overlap. Stock engines have maybe 50 degrees of overlap, while race engines with higher duration cams have more. For example, my S10 has a cam with 70 degrees of overlap. But they all have overlap and get backwards pulses in the exhaust - it's just how much of a pulse, and that depends on other things as well.

Oil pressure looks good.

Fuel Trims in the video look good to me.

Post #1 here has a video of a badly collapsed lifter in my Blazer - my very first post here (I was way off on my diagnosis at that point). https://blazerforum.com/forum/2nd-ge...g-valve-87514/ I think I am hearing the same kind of metallic tick in yours, but not nearly so loud (either that or your exhaust is masking it by affecting the video volume). You're going to have to be the judge on that. Maybe it would be a good time to fix the exhaust leak? Note that mine DID have low oil pressure at idle (yours doesn't) from a bad rod and main bearing. I link to it because lifter ticks have a pretty distinctive frequency / metallic sound and you can't miss the one in mine.

Really interested in the repeat snap test results. If our theory about the lifter is correct, it would most likely be worse with hot engine (driven miles). I don't think you had the valve cover off to listen when engine was hot. Just a FYI (not something you need to do at this point)....... if you ever have a valve cover off and can hear a lifter ticking, just put your palm on each rocker in turn and see which one changes the sound. Use a rag if it is hot or squirting oil.

 

Thanks Les, I didn't know any of this stuff before! That video there is also helpful, if you skip to the part where I'm on the bank 1 side and the part of your video where it's idling then play just a few seconds of each video at a time back to back, the tick sounds almost identical with the exception of yours sounding louder, but same sound, the same frequency. It's crazy, my BMW with the N52 can make the harshest lifter noise ever (can be heard over my straight piped exhaust at idle) and it doesn't mean anything but your not driving it enough, or the engine is cold, it's something with the lifters not pumping up fully, BMW engineers even put out something on it after the fact. But then if this engine makes even a peep of lifter noise it's bad news. Okay guys, I went in again for another running compression test, results were 150 static 70 idle and 120 snap for cylinder 1. On a halfway warmed-up engine. I went to test cylinder 5 and had it idling at 90 psi then snapped the throttle and the check valve blew up again LOL, I could just see the pressure go up and then all of a sudden drop to 0. So I think I'm pretty much done with this compression tester. I'm just going to get a new one off amazon and hope it works a little better. I'm still not satisfied with these tests here.

 

Yes I can hear the metallic tick on your driver's side.

Idle test is supposed to be at 1200 rpm. Snap test supposed to be from 1200 RPM to 2500 rpm. Didn't seem like full throttle, and that was from idle to maybe 1500 I think. Still the pressures in the video fit nicely with a normal cylinder so the cylinder was not a problem at the moment.

Whatever you do for the test, it needs to be consistent.

Maybe you should think about doing that #3 cylinder at some point! Noise in your video seemed to be on driver's side. The steering shaft comes loose with 1 clamp bolt and pries rearward (collapses some) to move out of the way Note that the steering shaft has splines with a blank one that needs to go back together on same spot. You can mark it on the top and assume the steering box shaft will not turn if you're not moving the vehicle.

 

Thanks Les, I've taken a few days off from looking at it here with my compression tester breaking again but I'm back with some stuff. First of all, an OTC compression tester is on its way to me right now and should be here in a few days so I can continue testing, kit is complete with extra Shrader valves. Okay so I've recently noticed some more things, the vibration seems to be a lot more sitting in the driver's seat. I was talking to my friend in the passenger seat about the vibration and they said they didn't really feel much, so I got in and felt for myself, sure enough, the driver's side vibrates quite a bit more. This leads me to believe even more that its that lifter in #1, once my new compression tester comes in I will do another running compression test on all of bank 1, and possibly some of bank 2 as well depending on the readings I get and if they match what I got before. I also plan to test cylinder 1 hot and cold. I just can't believe that it was a false reading before, 125psi must have been in that hose for the gauge to read 125psi right? Same with the snap, 160psi must have been hitting the gauge at that time for it to hit 160psi. And even more, that was the first cylinder I did, and it worked for all my other cylinders after. Now I am a little curious, I noticed today the tach RPM is not the same as the rpm on my scan tool, I am thinking the tach on the dash shows an adjusted rpm? Either way, I'm wondering what should this engine be idling at? With AC on? In drive? And are these measured on the scan tool or from the tach? At idle in drive, my tach will read 550 but on the scan tool will say 620rpm. George sorry I am a little late with this but here are my fuel trims, rpm is on each photo, let me know what you think.

 

Your fuel trims are not catastrophic but right at the limit for concern so there is something going on and it is not bank specific. The computer is correcting for a perceived rich condition at idle that mostly goes away at 2500 rpm. This can be an actual rich condition like from leaking fuel injectors or incomplete combustion or a perceived rich condition from say an improper sensor value like the MAF. Candidates are:

MAF sensor
Fuel injectors
exhaust leak
Ignition
compression
O2 sensors
Other sensors

The repair of that exhaust leak may do the trick. What’s the history on your MAF sensor?


George

 

I also have a hard time believing that your original reading on #1 was a fluke (but then again we have only seen it one time). I would think you are correct in your 125 psi and 160 psi comments. The tach on the scanner should be absolutely correct. The dash tach converts a digital signal coming from the PCM and uses a stepper motor to move the needle so there is room for error there. IIRC my Blazer has always idled 550 rpm in drive with or without A/C on. A little above 600 in park. Agree with George about fuel trims. PCM is controlling fuel mix, but something is going on that causes the LTFT on both banks to go towards negative at idle. However if you go back to post #56, you can see clearly in the plots that this was not the case at that time. So that seems a bit goofy to me.