Einzelherz

Last night I was going to make a late night Target run and I turned on the LS400 (98 115k miles). It made a loud-ish metallic clank that I isolated to the passenger side bank. It was dark and I couldn't really figure out what the issue was.

The car was cold idling at 1500 and it felt smooth for the 30 seconds or so I let it run.

A couple weeks ago I did an 8 hour trip in it, and it had only been run briefly to move it into and out of the garage since then. This lead me to think that turning it off cold might have left too much gas in the cylinders that stripped any cylinder wall oil off and maybe I was hearing piston slap?

Does anyone have any ideas where to start looking? I'm worried that it might be the dreaded broken cat chunk up into the engine, but I don't know how it would be. Another thought is a dead coil, but it didn't sound like misfiring to me, unless a bad coil can cause knock like sounds?

Thanks in advance.

CLLEXUSS

You are describing some extreme circumstances for an engine with lower miles. And I don't see a piece of catalectic converter getting up into the engine, not on this car anyways. Cylinder wall problems and piston slap problems are not common on these engines especially at the miles stated. What comes to mind is this is an interference engine, anyone ever replace the timing belt? I mean I hope its not that, that could cause severe damage. As long as the car is not being raced like a race car red-lining all the time etc, and as long as its not being severely neglected I wouldn't think it's a mechanical failure inside the engine but it's possible though.

Yamae

Without listening to the exact sound, I can't say any definitive answer but your description, "a loud-ish metallic clank that I isolated to the passenger side bank" reminds me of the noise from the VVTi area. So I'd rather think that it's a VVTi related noise caused by an insufficient oil flow at the VVTi system.

BNastee

My high mileage 99 LS400 had a sound like that when the timing belt skipped a tooth at startup.

Einzelherz

I started it up again after work Friday because I needed to move it. It's now sounding and feeling more like a cylinder isn't firing. I went ahead and ordered a set of coils since I was concerned about their being 23 years old last summer when I did the timing belt. I also figured swapping out a full set of coils is a fairly safe way to troubleshoot the issue.

I'll let you guys know what I find.

timmy0tool

iTrader: (7)

any codes? changing the coils is shot-gunning the issue. it may or may not help. a misfire usually immediately throws a CEL.

BNastee

I'd pull the two metal cam covers and check the cam timing. Bad cam timing can sound like a misfire.

Einzelherz

Yeah that's why I'm a bit stumped. I figured a bad coil or a clear misfire would give me a CEL but so far it's not.

Today I went and swapped out the passenger side coils one by one with a fresh NGK unit. Because of the big intake resonator I couldn't figure out a good way to just disable any given cylinder to see if that could tell me which one was bad so this was my best solution. The result - every swapped coil had the idle the same.

For reference, today it was a little rough, definitely noisy, and the exhaust smelled almost like burning oil, but not exactly. It just smelled very rich to me. I think I would recategorize the metallic sound I originally mentioned as just a louder moment. As if in the normal cycle of 8 firing, one or two were louder than the rest.

I continued on and pulled all the passenger side coils and plugs. All the plugs were a little wet, and dark-ish. Looking into the cylinders though the pistons didn't look wet. The plug tubes are all clean and dry. I still need to pull the drivers side plugs to see if they're also damp.

This then lead me to investigate the intake manifold, which while being damp looking, didn't seem that much worse than most engines? I'm thinking PCV valve dumping extra oil into manifold which fouled the plugs cause of the last couple times running the engine never got up to temperature? The PCV valve is Toyota, and although the car was serviced pretty well at the lexus dealer based on the lexus site service history, there's no PCV replacement mentioned, so maybe it's original? Of course the hose cracked as I was taking it off, too.

Edit:

I went back out and cleaned off all the plugs. They were carboned up and smelled of gas, which makes sense from my short starts checking the coils. I took the PCV apart and it still functions properly. Just a little oily and gunky inside, but I swabbed it out.

I got the passenger side cam pulley cover off (well, in its hanging on but moved state - I don't think you can remove it w/o further disassembly). The crank isn't at TDC and I'm not sure I can rotate it without pulling the fan, which iirc means pulling the upper coolant hose? Which I also seem to need to pull to get at the driver's side cam pulley cover?

Einzelherz

Good news - it was just fouling. I buttoned everything up this morning, started it and recorded the sound to post here, but after it warmed up it smoothed out and test drove fine.

Fun times. Thanks for the help troubleshooting though, guys.

timmy0tool

iTrader: (7)

what was fouling? the plugs?

Einzelherz

Yeah. Just from very quick start/stop action it seems, along with letting them sit there a while. Never got warm enough to burn off the excess gas it seems and it covered them in carbon.