93 Hyundai Excel, unexpected loss of power/transmission oddity/unfamiliar sounds

Car has 133k miles…everything on it is pretty much new (mainly from previous owner). Everything in the fuel system and ignition is new. New sensors all over the place. New ECM. All fluids clean. Earlier today I charged my A/C, it went well (blows ice cold)…sat for a while idling, idled fine. Drove around with the a/c on and noticed the transmission was shifting odd. It would keep upshifting and downshifting I think between 3rd and 4th gear. Also starting doing this with the air off as well. After running a few more errands, the transmission seemed like it wouldn’t shift as early as it did previously. Upon coming home the last time, upon acceleration I began hearing a slapping/tapping sound and the car started losing power. If I took my foot off the gas the sound went away. Well it almost died on me making the last turn into my driveway and I parked it. Shut it off, checked everything over. Oil and trans fluid is good as well as everything else, it didn’t overheat or anything. It seems to idle a bit low now, and if I gave it any throttle while parked the unfamiliar sound returned. I asked the previous owner and he said he might have put the wrong transmission fluid in when he did the fluid/filter change months ago. He says he used DEX or the “multi vehicle import” fluid instead of the ATF +4 that it requires. Coincedently enough, I had just purchased several quarts today to start running the possibly wrong fluid out to get the right stuff in. I’m just wondering if anyone knows what else I should check, hoping the engine isn’t toast. Here’s a video of the sound, you can really hear it when I move my phone over the exhaust manifold heat shield.

It was idling, still kind of rough and the electric fan kicked on and it engine stalled/stopped running.

You could have a cracked exhaust manifold.

I’ll have to investigate when there is more light. There was no smoke or anything, though, but I suppose that would explain why the sound is loudest up front. I went around the valve cover and injectors with my ear to a screwdriver and didn’t really hear anything out of place. I’m just hoping it’s not something in the bottom end, although wouldn’t that be audible even at idle? And would a cracked exhaust manifold cause the car to run bad/die under load?

...you can really hear it when I move my phone over the exhaust manifold heat shield.
Sounded like some rod knocking to me, but that shouldn't cause the engine to stall.

This morning I tried starting it and it barely started. After a few tries it finally did, but idled sort of rough, sound still present when giving it throttle. Almost acts like it’s only running on 3 cylinders. After work I’m going to check to see if I have a bad spark plug or something, although I’m not sure if that would account for the odd tapping/knocking sound.

All fluids are in pristine condition. I’ve had the valve cover off and the valvetrain was spotless. The timing belt is nice and tight, no visible wear. I also had the oil pan off to replace the gasket, everything on the bottom looked nice and clean as well. I’m going on about 2k miles on this oil change using a Purolater PureONE filter and regular Wal-Mart dino oil and the oil is still a nice bronze color. Still hoping it’s nothing major.

Could it possibly be spark knock? I use regular unleaded fuel but only use top tier such as Shell. I did, however, add a bottle of Techron at my last fillup…but have put about 100 miles on it since.

That sound sure resembles a rod knock. Alternately, it could be a spun bearing. I was going to ask if the oil was up to safe level but you already answered that. The multiple instances of the engine dragging (loss of power, late shifting, slow erratic idle, stalling, hard cranking) also point toward a spun bearing that is still fused to the crankshaft journal. You might try turning the engine over by the harmonic balancer bolt to manually gauge the engine drag. Remove the spark plugs to help unload the rotation.

Good luck on this. Let us know what you find.

Hmm. Well, wouldn’t something like that be noticeable at idle as well?

More videos:

The “knocking” is only heard when my foot is pushing on the pedal. The second I let go, the sound stops (and rpm’s lower as expected).

It seemed to run a little better when warmed up, but would still try to stall under load. The idling in this video is usually how the motor sounds any other time until of course I give it throttle.

And one of my exhaust, which doesn’t normally sound like a helicopter. Everything in the exhaust is new except for the manifold.

I've had the valve cover off and the valvetrain was spotless.

If you mean literally “like new” this might be a sign that the engine had sludging problems and has been cleaned out. Meanwhile, some oil passages are still plugged. Time for a compression test.

(BTW, the “cat in the ultralight” video is a riot.)

I’m pretty sure he was just OCD about maintenance. An extremely thick stack of receipts and work orders came with the car when I bought it. Every oil change (3K on the dot every time), alignments every 6 months, every nut and bolt…there was a receipt. Hence why I’m really trying to figure this out…it’s extremely rare to find a car this old, especially an early 90’s Hyundai, that was pampered so much lol.