9C1 cam with stock TBI?

blackdeathmessenger said:

Well, turns out it was a couple of sensors going bad at the same time. The sad part is, they tested just fine. I finally said screw it and replaced them and it ran better after that. The sensors I replaced, aside from the obvious of the broken idle air control valve were the coolant temperature sensor, map sensor, tps, and o2 sensor.

Click to expand...

I had an O2 sensor that seemed to test OK, but produced false "lean" indications at higher speed. Beyond that, the other sensors should be test-able.

HOW did you test them?

blackdeathmessenger said:

I now have a new problem, which from what everyone has told me, sounds like collapsed lifters. What's wild is I was just sitting at a light and then there was a bang and now a mechanical tapping sound from inside the engine

Click to expand...

Possible--but unlikely--that a lifter would "collapse" with a "bang".

Pop the valve covers, look for bent pushrods, loose rocker arms, broken valve springs. If you don't find valvetrain problems, you're maybe looking at a failed connecting rod/rod bearing; or maybe a cracked/broken flexplate.

Well, I tested continuity and and resistance. I've done it before and was able to diagnose some stuff that way. I'm not the most savvy with electrical though, to be completely honest.

I was afraid you might say that. I have actually popped the valve covers already and things seem okay; though I wasn't able to go into depth with things since I keep getting called into work early and having to stay late. I didn't see any bent pushrods and no super loose rockers or anything. I also looked through the holes in the head that lead to the valvetrain and didn't see anything out of place. I plan on checking the valves in more depth tomorrow (later today, really) and doing so at a slower speed than before and doing a compression test if the valves/lifters seem fine after all.

My dad suggested taking the valve covers off and starting the engine to look at things, and that revealed nothing new (hence looking at it at slower speed/turning the engine over by hand and checking the rocker clearances)

Well, for anyone curious, everything points to something in the bottom end being broken. Did a compression test and showed cylinder 2 down 30 psi from the rest of the cylinders. With where I live, I can't just pull the engine and inspect it, so I'm going to have to swap in a junkyard engine and autopsy it later

30 psi from what? if you had 150 psi across the board and 1 cylinder is 120 psi, it's still within 20% not ideal, but not the end of the world either. doesn't necessarily point to something in the bottom end either. did you try putting a squirt of oil on and then rechecking compression?

tayto said:

30 psi from what? if you had 150 psi across the board and 1 cylinder is 120 psi, it's still within 20% not ideal, but not the end of the world either. doesn't necessarily point to something in the bottom end either. did you try putting a squirt of oil on and then rechecking compression?

Click to expand...

Actually, it was 150. Allowable tolerance is 10% according to every manual I've read. I'm guessing you didn't read the original post where I said there's a loud knocking sound coming from the engine that started with a bang (literally). The oil did nothing to the reading and there's nothing wrong with the valve train. The engine also barely wants to run now

Does the oil look sparkly?

if putting oil in the chamber did nothing then id say your problem isn't rings. this isn't a 100% foolproof method but from my experience it's probably valve related. maybe poor valve seal or excess buildup causing the valve to hang open. i have seen broken valve springs cause a dead cylinder or a cylinder to read lower than others, for example. i think you have other issues compounding to cause poor running but sounds like you've made your mind up on a solution.

FWIW, your orignal post mentioned nothing of the bottom end knocking.

Well, I have a little bit of an update for anyone that cares. Swapped in an 880 Vortec block and swapped on the tbi heads and intake with the 9C1 cam I happened to have laying around. It runs pretty good so far. Haven't had time to tear into the old block to figure out exactly what happened yet though. From what I saw when I did the swap, the top of the piston of cylinder 2 was discolored around the edges of the piston, and the rest of the cylinders looked even

tayto said:

if putting oil in the chamber did nothing then id say your problem isn't rings. this isn't a 100% foolproof method but from my experience it's probably valve related. maybe poor valve seal or excess buildup causing the valve to hang open. i have seen broken valve springs cause a dead cylinder or a cylinder to read lower than others, for example. i think you have other issues compounding to cause poor running but sounds like you've made your mind up on a solution.

FWIW, your orignal post mentioned nothing of the bottom end knocking.

Click to expand...

I kind of forgot what my original post was about, to be completely honest when the bottom end knocking started. I was mostly focused on figuring out how to fix it quickly (which took longer than it should have)

blackdeathmessenger said:

Swapped in an 880 Vortec block and swapped on the tbi heads

Click to expand...

An "880" block may or may not be drilled for the coolant bypass needed on the TBI cylinder heads.

This is a double-drilling, one hole down from the cylinder head gasket surface, at a goofy angle. The other drilling intersects the first one at the bottom, and leads to the water pump gasket surface.

I have the sense that most "880" blocks do not have this double-drilling. I've seen some that do.





The matching hole on the water pump gasket surface is the reason that SBC water pump gaskets have the extra, smaller hole under the water pump outlet hole.