Stock Intake Valve Seat Failure on TSP PRC Ported Heads with Big Cam
 

Last night I got a #7 cylinder misfire and a random misfire code after getting on it hard up to 3rd gear. I was hoping it was a loose plug wire but they were all good after checking. I then plugged a test light in series with the plug and it was good too. I started to get really worried and figured it was valve spring breaking time. I pulled the valve cover and everything looked fine.

I let it cool down overnight and pulled the #7 plug and it looked fine and has continuity and about 5 or 6k ohms. I put a borescope down in the #7 and it looks fine as well. I put a compression tester in #7 and cranked it over a few times and after fooling with my Chinese GDS scan tool to try to put it in "compression test" mode I gave up. You can see the compression tester gage bump up a little when its turning over but it will just go quickly right back to zero. Tried the compression tester on #5 and it did the same thing. I guess I just have to pull all the spark plugs for it to turn over fast enough to actually build pressure on the gage? I believe you should be able to hold the throttle to the floor while cranking and the throttle blade should hold itself open and fuel injectors disable, either way I guess I still have to pull all the other plugs and honestly pulling all the plugs is probably half as hard as just pulling the heads and pulling out the lifters.

Anyway I got the scan tool working enough, so I put the plugs back in and cranked it up and disabled the injectors on each cylinder one by one. When I disabled the #7 I could hear a difference in sound which told me my injector was still good which gives me the very bad feeling I have lost a lifter?

Anyone know what should I do? It looks like its time for me to pull the heads and cam and go for a more reliable lower lift cam.

I think I may try taking my valve cover up and cranking it over, has anyone tried running their engine without the valve cover on a LT1? Not sure if it likes to splash a lot of oil with the baffling not there?

Ok so maybe my lifter on #7 is good? I took off the valve cover again and turned it over and looks like the valves are actuating fine:
https://photos.app.goo.gl/M17sP8kFZvsDYUkC7

I also just changed my oil a few days ago and I filled it up with one of those bags and probably put way too much I wouldn't think that could cause the lifter to collapse.

I would get that compression tester working. It should have a check valve(Schrader valve) built into it that holds the pressure. See how the compression compares to some of the other cylinders. You don’t have to pull all the plugs or test them all. If 5 is 180 and 7 is 100 you have a problem.

If you lost a lifter, you would hear a distinctive tapping. You can also rotate the motor by hand to position the lifters on the heel of the cam and check the valve lash. With a collapsed lifter, the pushrod will not have any load on it at all.

Yeah its weird, I've used it before and the check valve does work and it will build up pressure until it releases, not sure why its not working now maybe because the throttle blade isn't open or what.

I also forgot to leave out some details. Before the misfire started I got on it a few times before that and everytime after I got on it, I would smell something burning, I know what burning oil on exhaust smells like but it didn't really smell like that but it did smell like something was burning. I stopped at the gas station and I could see a faint cloud of smoke in the headlights, I looked all around but I couldn't find anything, I kind of figured it was something in my exhaust hitting something and burning it since it seemed like it almost had a burning plastic smell to it. It had been happening a few days before then too but I don't remember if it was since I changed the oil.

I had to get one of those boxes of oil in 12 quarts instead of 10, so I just started filling it up after I drained the old oil out and just eyeballed 10 quarts from it. The dipstick shows all the way full, but no way to really tell if its overfilled.

I did notice when I pulled the 2 spark plugs there was oil, but only on the threads, I didn't think much of it then but now I'm wondering if maybe its way overfilled? The only thing I thought overfilling could do would cause excess windage and start arieate the oil which reduces its effectiveness, not sure how it could cause a misfire unless it was just pouring into the cylinder which would seem like it would have to be way overfilled.
Attachment 1059397

I am going to go drain some oil out of it and check the dipstick and at least try to get it to the proper level.

I also should have tried swapping spark plugs from the #7 cylinder, I did test the coil with a tester with the spark plug and wire attached and just assumed it was ok.

I guess it is possible if the crankcase had enough oil that it could be getting past the rings into the cylinders? It just seems that would take a huge amount of oil and from looking how much is still in the 12 quart "bag" of oil there is no way I have more than a quart overfilled. When I looked into the #7 cylinder it didn't look like there was oil anywhere but its hard to see with that thing. There was however oil around the sparkplug hole threads and that should have caught my attention but at that point I was so convinced I had broke a valve spring or a lifter with all the talk about high lift cams and valve springs only lasting 10k miles.

If you overfilled the oil the crankshaft can whip the oil so much it will froth it up and push it through the pcv valve.

Im not saying I know that happened but it is a possibility.

So I finally got my tester to working, I checked #1 and it was at 180, so I put it back on #7 and its only at 70.

So I can't believe this happened, the cylinder looks fine through the borescope, I just don't see how that much oil could have made it to the cylinder and hydro locked it.

I guess I should just start tearing it apart, since its easy for me to bend over and work on it on the ground I wonder if I should just pull the heads first?

I mean if there's 70 psi, that seems like to me a 100% tale tell sign it bent the rod?

Do a leakdown test. That will tell you if the top end is leaking.

Yes, true, but why would you think it would be leaking? I mean yeah I guess I could have messed up the rings or broke a ringland?

You may be right I just can't believe only overfilling it what seems like no more than a quart it whipped it up and sucked it into the PCV valve here is the bag that says it was 12 quarts and whats left in it seems like it is around 2 quarts but apparently not.Attachment 1059417

The thing is even if I put the whole 12 quart bag in there, I don't see how even 2 quarts overfilled could have messed it up.

When you overfill an engine by two quarts, (that’s a lot) your crank will turn the oil and it then aeriates it to a point where the oil pump can no longer pump the oil and your engine is starved of oil then oil pressure falls off. Game over for that engine if you drove it to long. IMO.

Hopefully in your case that’s not true.

a collapsed lifter won't open the valve. a leakdown test will tell you exactly what the problem is. id also say that pulling the cyl head on that side will tell you, as well. since the gen 3 motors, #7 was notorious for heat issues.

So I changed the oil last weekend I think and only drove the car a few times since then.

I was actually taking a HP Tuners log when it happened, but everything really looks normal, the only sign of the misfire is the rapid cycling, far higher than the normal switching frequency, that I drew an arrow too:
Attachment 1059457
So it started misfiring right after a WOT pull from dead stop to 3rd gear.

Tomorrow I am going to try to look for for some valves to make a valve cut off to do a leakdown. I might just buy a harbor freight one if they have it though. I did also check cylinder #5 and #3 and they were at 182 psi and 178 psi.