Cyl 6 misfire only at idle (1 Viewer)

[Hugh Heifer]

So I may have isolated my idle/low rpm mis. Probably won't help your situation, but I just learned today that I am a moron!
I went off 25 years of working on german marques with every one of them having the same cylinder configuration.
I was very unaware that Toyota happen to have an even and odd cylinder/bank configuration. My diag was going nowhere
and out of the chance I could be wrong in assuming what I was accustomed to all the years I decided to search Mud and sure enough
I discovered to never assume.

I'll follow along with your diag and maybe I can offer some direction.

Don't feel bad. I did that while traveling in La Union, Philippines a number of years ago. Misfire. Changed coil. Fixed....for a minute. Misfire. Changed same coil. Fixed...for a minute. Checked the diagram. I was changing it on the wrong side.

 

[OklahomaOvrland]

Yep. What was compared to, good cylinder PSI?

2 was 155 psi, 4 was 125 psi, 6 was 55 psi, 8 was 125 psi. 285,000 mile 2000 LX470. I’m going to do leak down tomorrow to see if we can identify the location of the leak. Wish me luck that it is a head gasket. That seems like it would be the easiest least expensive problem to fix. If it’s anything else I think I’ll be looking for a salvage engine to swap in.

 

[2001LC]

2 was 155 psi, 4 was 125 psi, 6 was 55 psi, 8 was 125 psi. 285,000 mile 2000 LX470. I’m going to do leak down tomorrow to see if we can identify the location of the leak. Wish me luck that it is a head gasket. That seems like it would be the easiest least expensive problem to fix. If it’s anything else I think I’ll be looking for a salvage engine to swap in.

In searching for engine, if it comes to that. Do your homework. So many will claim, low miles and or JDM engine (no verified 4.7L JDM, ever in USA). Get pictures of VIN # plate on BK2 head. Run carfax and vehicle history. Look for regular oil, filters and coolant services. Some of the "red flags" are: Any coolant issues and starter R&R history. Starter R&R, all to often, top of engine was not cleaned before intake manifold pulled off. Sand drops into intake ports. This is a compression killer.

#4 & 8 being adjacent to #6 cylinders, lower at 125 PSI, is interesting. Does suggest head gasket. Which is usually, from warp head. Which is usually due to overheating. But numbers suggest, not extremely warped if that the cause of #5 55PSI.

During compression test:
Was fuel cut off, throttle body wide open and cranking speed 250 RPM or better?
Was engine cold, warm or at operating temp?

One trick is listen at oil fill spout, while engine idling. Same as we do when using a leak down tester.

I suggest:

1. Do a wet compression test.
2. Borescope inspection of cylinder walls and valves. Directional borescope very hand here.
3. Coolant combustion gas test?
4. Inspect head gasket around outside?

Some additional consideration:

• Have you been loosing coolant and or coolant in radiator low (not to very top)?
• Any white smoke?
• Oil look like milkshake?
• Did #6 have any thread repair in heads, spark plugs capture threads?
• Was starter replaced?

Coolant in oil, looks like light browne milkshake. Bearings, cam journals & oil pump take a beating.

Head gasket leaks

Debris in cylinder, spark plug thread repair.

Minor scoring on cylinder wall. Lower but passable compression.

Major scoring cylinder wall, resulting in loss of compression.

Decarbonize piston top, indicating coolant enter cylinder.

 

[OklahomaOvrland]

In searching for engine, if it comes to that. Do your homework. So many will claim, low miles and or JDM engine (no verified 4.7L JDM, ever in USA). Get pictures of VIN # plate on BK2 head. Run carfax and vehicle history. Look for regular oil, filters and coolant services. Some of the "red flags" are: Any coolant issues and starter R&R history. Starter R&R, all to often, top of engine was not cleaned before intake manifold pulled off. Sand drops into intake ports. This is a compression killer.

#4 & 8 being adjacent to #6 cylinders, lower at 125 PSI, is interesting. Does suggest head gasket. Which is usually, from warp head. Which is usually due to overheating. But numbers suggest, not extremely warped if that the cause of #5 55PSI.

During compression test:
Was fuel cut off, throttle body wide open and cranking speed 250 RPM or better?
Was engine cold, warm or at operating temp?

One trick is listen at oil fill spout, while engine idling. Same as we do when using a leak down tester.

I suggest:

1. Do a wet compression test.
2. Borescope inspection of cylinder walls and valves. Directional borescope very hand here.
3. Coolant combustion gas test?
4. Inspect head gasket around outside?

Some additional consideration:

• Have you been loosing coolant and or coolant in radiator low (not to very top)?
• Any white smoke?
• Oil look like milkshake?
• Did #6 have any thread repair in heads, spark plugs capture threads?
• Was starter replaced?

Coolant in oil, looks like light browne milkshake. Bearings, cam journals & oil pump take a beating.
View attachment 3800561

Head gasket leaks
View attachment 3800583
View attachment 3800580View attachment 3800579

View attachment 3800581

Debris in cylinder, spark plug thread repair.View attachment 3800584

Minor scoring on cylinder wall. Lower but passable compression.
View attachment 3800586
Major scoring cylinder wall, resulting in loss of compression.
View attachment 3800589

Decarbonize piston top, indicating coolant enter cylinder.View attachment 3800590

Leak down test today revealed air escaping from 4 and 8 when 6 was pressurized. No coolant observed in oil or oil in coolant. No exhaust in coolant per the combustion leak test we did today. We are going to proceed with doing a head gasket job on bank 2. Will check for warping and have the head machined if needed.

 

[OklahomaOvrland]

Update.
The right cylinder head was removed, revealing cracked valves on cylinders 6 and 8. Cyl 4 has also been misfiring.

 

[Kernal]

Ideas on how those intake valves got damaged (valves burned from carbon build-up on seats, valves out of adjustment from age/wear??)?

Is this common to that particular engine (IDK)?

 

[OklahomaOvrland]

The burnt valves were exhaust valves. I really do not know why they burned. I hear this is extremely rare on this engine, but that might be a bias due to the 2UZ's bulletproof reputation.

Ideas on how those intake valves got damaged (valves burned from carbon build-up on seats, valves out of adjustment from age/wear??)?

Is this common to that particular engine (IDK)?

 

[2001LC]

IMHO: This is rare and only know to happen AFAIK, due to external (up-stream) condition. Burnt exhaust valves are due to them not transferring heat properly. When engine serviced properly and run as designed, it doesn't happen.

The 2UZ-fe is consider one of, if not the best, engine ever built. It is "near" bulletproof. I say "near" as I've seen my share that were shot, by improper service and or mod. Even running fuels, not rated for, can result in issues.

 

[OklahomaOvrland]

I’m happy to report that she is back together and running very well.