Sick motor in '96 LX450

[TexasDoug]

So my brother-in-law and I rolled the dice on an LX450 with F/R lockers and 199K despite the motor making some not-so-good sounds and limited service history. It drives great and pulls strong (I have a '97 LC for comparison) and was cheap enough that I can tolerate a motor replacement if it comes down to it. It's only throwing one code on the OBD scanner: P0401

That said, I'm no mechanic. I realize engine diagnosis over YouTube is next to impossible, but maybe your ears are better tuned than mine. One shop told us the wrist pin was gone and it needs a replacement or rebuild, but that seems like a weird conclusion given the tapping occurs at idle?

I'd appreciate any input from you guys. I'm gonna have a few shops around town weigh in. Note that head is a different shade than the rest of the block, which suggests a previous top end rebuild at some point?

 

[TexasDoug]

Am I crazy or does it just sounds like valve clatter? It sounds like my old BMW E30 when the valves would be ready for adjustment (every 20K miles or so). Exact same tempo, although the sound is slightly different. Perhaps wishful thinking is clouding my judgement.

 

[inkpot]

The block is cast iron and the head is aluminum so they should not look the same!

 

[math]

Could be an exhaust leak, and P0401 is EGR related. Taking off the clamshell and cleaning it very thoroughly, as well as wrapping the engine harness near the EGR tube fixed ours.

 

[TexasDoug]

The block is cast iron and the head is aluminum so they should not look the same!

Good point. Makes sense but they look identical shades on my '97, which is my only real frame of reference. Mine also runs a lot quieter despite having 325K miles.

Could be an exhaust leak, and P0401 is EGR related. Taking off the clamshell and cleaning it very thoroughly, as well as wrapping the engine harness near the EGR tube fixed ours.

That's what I was thinking when we first looked at the truck. But after the diagnosis from the first shop I'm second guessing everything and don't trust my own ears. I'll cross my fingers its something this easy.

 

[baldilocks]

Correct me if my thinking is off but it seems that as the valves and seats wear, the valve to lifter clearance on the 1FZ will get smaller and smaller essentially making the valve train quieter if anything.
I have two engines, a 1994 and 1993. The 94 was rebuilt by a very experienced shop about 20k miles ago and it makes very even and rhythmic valve train noise that sounds similar to a loud sewing machine. The 1993 is original wih 269k and when you open the hood all you can here is the fan and fuel injectors. Otherwise the engine is dead silent. They both run well in all conditions and pull the same. Neither smokes at all. I have wondered why the distinct difference? Which is correct or if it even matters?
I had the 1994 first so I never thought anything of the noise until I bought the 93 last winter.

 

[sbman]

Rod knock can be diagnosed by pulling one spark plug at a time and listening if the noise goes away on a particular pull. the rod won't knock nearly as loud with no combustion event. It does sound like a bottom end issue to me, but impossible to say for sure without proper diagnostics. There are YouTube videos on diagnosing rod knock.

 

[TexasDoug]

Rod knock can be diagnosed by pulling one spark plug at a time and listening if the noise goes away on a particular pull. the rod won't knock nearly as loud with no combustion event. It does sound like a bottom end issue to me, but impossible to say for sure without proper diagnostics. There are YouTube videos on diagnosing rod knock.

Thanks sbman. We'll pull the plugs and see what we observe. I

 

[math]

Rod knock can be diagnosed by pulling one spark plug at a time and listening if the noise goes away on a particular pull. the rod won't knock nearly as loud with no combustion event. It does sound like a bottom end issue to me, but impossible to say for sure without proper diagnostics. There are YouTube videos on diagnosing rod knock.

Mud has great tips for novice mechanics like us. This is a very useful trick, thanks!

 

[Kernal]

Is the engine quiet(er) on a cold start up, then does the noise increase significantly after the engine warms up? Does the noise change between idle and a constant higher rpm, say like between 650 rpms and 1500 rpms? Less knocking/ticking or more/louder at higher rpms with a warm engine?

 

[sbman]

Mud has great tips for novice mechanics like us. This is a very useful trick, thanks!

I should clarify that you can pull just the spark plug wire. People that are OK handling high voltage and don't mind being knocked on their butts do it by pulling them one at a time with the engine running.

 

[TexasDoug]

@sbman yes of course, but thanks for clarifying just in case.

I spent some time with it with fresh ears, and I do hear the tick more clearly now and also just slightly from inside the truck as it approaches 3000 RPM. It's definitely a different sound than rod knock but there's a definite non-valve ticking alright. It's hard to discern over the other bits of engine noise (exhaust leak, loud belts) but I was able to zero in on it. It's soft and dull, but it's there. Bummer.

That said whether or not wrist pin is the source of the issue or not is hard to confirm without tearing it apart. I've got it at another shop right now for a second opinion just to make sure it's not related to something simpler. I'm leaning on advising my BIL to just drive it until it becomes a problem and we'll replace the motor when that day comes.

Meanwhile we might as well start sorting out the EGR bits.

 

[slow95z]

i cant listen to the video because the work computer has no sound but could it be the power steering pump? i have seen those put together wrong and make all kinda noises.

 

[SWCruiser]

I have a very similar noise and have been driving it for a few thousand miles. Truck runs smooth, plenty of power,no vibration and no excessive heat. Just an annoying noise for someone that's ocd! I replaced the pump. Ran it without belts and could t figure it out. Keep going so I get an answer

 

[SWCruiser]

I have a very similar noise and have been driving it for a few thousand miles. Truck runs smooth, plenty of power,no vibration and no excessive heat. Just an annoying noise for someone that's ocd! I replaced the pump. Ran it without belts and could t figure it out. Keep going so I get an answer

Someone also mentioned a bad gear box, pump gear alignment and tensioner as possible culprits

 

[excessive]

Pull your oil filter and cut it open to see if you have metal shards inside .

 

[SWCruiser]

I had an oil analysis done on mine and no metal detected. It's hard to believe it's something major with the way it runs. I hope u find an answer

 

[bloc]

Oil change and properly catch a sample to send off for Used Oil Analysis.

 

[bdruff]

i cant listen to the video because the work computer has no sound but could it be the power steering pump? i have seen those put together wrong and make all kinda noises.

I scared my gear rebuilding the power steering pump by using large channel lock pliers to take the gear off. There was an obvious tick. I changed the gear and it was gone. Worth looking at. After reading through threads...it's wasn't the first time someone did it. Also worth noting, I read that if not fixed...it could scar the flywheel.

 

[Pin_Head]

The noise frequency is an important clue. It sounds like about 5 ticks per second or 300 RPM, when it is idling at 600 RPM. The cam runs at half the speed of the crank, so it seems more likely cam / valve related than crank / piston.