That sounds good Les, I will do that sometime early this week hopefully. I did the measurements while running, and the intake and exhaust valves seem to open the same amount on cylinder 1. Videos below, let me know what you think!

 

I'm not seeing any big difference in the video. Probably your in-person eye is better, and you are comparing against a ruler. Problem not found - but if not valvetrain then what? Why I think we need to do a second verification of the snap test on #1.

 

Yup I am with you here Les, I'm confused after today. And honestly, I was looking at the readings while the engine was running but they are moving so fast it's hard to see, those videos uploaded are already slowed down some too, I find it easier anyways just to put it on 0.25x speed then you can see each valve open much clearer, they also seem to open for about the same time if you have both the videos playing above at the same time on 0.25x speed you can see pretty easily. Either I missed something while looking today, or the running compression test was flawed on that cylinder, we will see very soon. By pushing down on the pushrod, does this rule out problems with the lifter being collapsed? What was I checking when I did that?

 

Yes, you was checking for a lifter with clearances not taken up with oil (just internal spring).

 

I know you guys have your hands full with the #1 problem but I finally got the weather to co-operate with my fuel trim expedition:

I have only ever used fuel trims/O2 sensors under three conditions: idle, 2500 and full throttle. I have never thought much about the data that you guys presented where you watched fuel trims under varying driving conditions but it was interesting so I took a look. I took two vehicles out for measurements under varying load conditions, my Blazer (been sitting for months and running crappy today) and a 2003 Toyota truck (running good). That and some reading and here is what I found:

1) As you move the vehicle through different PCM/VCM/ECM fuel cells (a series of fuel delivery look up values for different load conditions) the LTFT value changes dramatically as you move through the load phases. LTFT is calculated and stored in each cell independently.

2) At full throttle the computer goes to a set forced rich condition. On the Blazer the LTFT's always go to +4.7 and the STFT's to zero. On the Toyota all trims go to zero

3) When you let off the gas and coast down/torque brake, the computer also goes to a preprogrammed lean fuel delivery which displays zeros on the Blazer and lean values on the Toyota.

4) Under some of the in between conditions the trims looked to be getting forced to the same exact conditions over again and I am not sure if that is a preprogrammed condition under more mild acceleration or learned LTFT cells that I just happened to be repeating exactly. I found very little written about this and nobody answered questions on this on a high end site that I use.

4) In a properly functioning engine (my Toyota) the LTFT+STFT stays below the magic 10 absolute value under all in between driving conditions.

There can be a place for tracking fuel trims under changing load conditions (full throttle for sure) but I continue to believe that for all of the standard issues diagnosis, idle/2500/FT is still most of what we need or can use without using differential equations.

Regarding your misfire and errant dynamic compression test (nice call by the way), I have an observation. I don't seem to remember a smoking gun from your piston love tap and bent valve. No wonky rocker arm, broken valve spring/keeper, bent push rod or hard collapsed lifter. That means that the smoking gun may still exist and since you think that you may have sent the #6 lifter to #1 that may be it. About the only explanation for what you found during your tear down is: intermittent collapsed lifter>hammering push rod and valve stem>bent valve>exhaust valve does not close>piston impact. If I am right then the perp may still be in the engine and sitting in number 1 now. Repeating the test is a good idea as is looking at the cam lobe but I am betting on the lifter. Either way if the root cause of #6 is still in your engine, it needs to be corrected. Some of this has already been stated so then I am basically agreeing.

George

 

Hi George, Zack did find a bent pushrod in #6. But I figured that was a result rather than a cause. He was supposed to have inspected the lifter thoroughly, but it still remains a possibility. Interesting stuff on the fuel trims! I'm waiting to see if the snap test repeats.

 

I did not remember the bent pushrod. I guess a valve can spontaneously freeze in the guide, maybe heat stress/worn guide/debri/lack of oil and go the other way and bend the rod when the lifter hammers on it so the root cause is the valve but then the lifter might still get stressed. I guess I really latched onto Zach saying that he thought the lifter followed to #1. Maybe that's a shiny object and not the issue given the reasonable running valve train observations this week.


George

 

yeah if #6 got switched into #1, its a possibility. But the action is seemingly correct at this time.

 

Thanks Les and George. It seems like I'm in the same position as you Geroge, I was planning to do the running compression test on cylinder 1 again today, but the weather had something else planned. Hopefully tomorrow, I'm so invested in finding what's wrong and fixing my engine for good after all the time I have put in that I don't think I will ever stop looking until I find it. Also, I really don't want to take it to the shop for multiple reasons but most prominently I want the satisfaction of finding what's wrong after all this time I have spent diagnosing, not somebody telling me what they found. I missed out last time when my valve bent and I was busy replacing spiders until I went bald from pulling my hair out wondering why it still didn't run well. When I had nothing left to do (and no compression tester at the time) I took it to the shop and a few days later they found the compression problem. This time I will find the problem myself, I have all the tools and you guys to help me do it.

Now, Les is correct here about the pushrod also so are you George that I never did find out why the valve bent. I looked at the lifter while it was out but I'm not sure what to look at other than the roller and for abnormal play, but it passed those tests. I would be beside myself if it turns out the lifter was bad after all this time LOL, but it would make some sense. I will see with the next running compression test on cylinder 1. Thanks for doing these fuel trim tests George, so I think we can say for sure that my PCM thinks the engine is running lean and adding gas (over +10 trim). What I'm thinking now is if my problem is cylinder 1 why are both bank's fuel trims going crazy? I would think it would just be bank 1? Hmm.

 

I don't know that your fuel trims are a problem. Grab all 4 numbers at idle and again at 2500 rpm and lets see what you have. The only time I saw your LTFT go way high was I believe when you floored it and that's when the computer goes to a pre programmed rich command. All that graphing under various load changes might send you off chasing ghosts.


George