LS 430 Bank 1 misfire

[rz1c13]

Hi,

For past few months I was puzzled by the car giving me a few light shakes on idle every now an then.  These jerks last a sec. or two, and are are a bit stronger when starting from cold engine, and they are more pronouced when the engine temp gauge passes about the first mark on the dash. On normal operating temp. the effect is very light, however still noticeable, as these V8s should be super-smooth if running properly.

Today I've connected the Techstream, and read the monitors.

I have misfires detected on Bank 1, - cyls 1, 3, 5, 7. As you can see on the pic, cyl. 1 seems to be the most affected (26 counts), cyl. 3 (24), cyl. 5 (8), and cyl 7 (2).

There are no other fault codes, check engine lights, etc.

I have taken the VVTi valve of bank 1 out - it is clean, moving freely, the coil seems to have the right resistance (about 7.5 ohm).

Also when idling, the voltage on the valve is about 1.5 V.

 

Any ideas?

Would this be a symptom of the VVTi valve starting to fail?

[rz1c13]

any takes?

[cruisermark]

HI

I cannot help with your query but I think I may have the same problem as you - I feeling a vibration through the driver seat on hot engine idle - I've had the bonnet up on when running and the engine is definitely not smooth as it used to be - I hoping to have it hooked upto a code reader when I get a chance.

Please do post up a solution if you get to the bottom of it.

[rz1c13]

On 10/5/2019 at 1:13 PM, cruisermark said:

HI

I cannot help with your query but I think I may have the same problem as you - I feeling a vibration through the driver seat on hot engine idle - I've had the bonnet up on when running and the engine is definitely not smooth as it used to be - I hoping to have it hooked upto a code reader when I get a chance.

Please do post up a solution if you get to the bottom of it.

Fixed quite some time ago, and reviewing my posts just now. So it turned out to be valve clearance issue - getting to near-zero... ! I did total timing job (all by myself) plus full readjustment of the clearance by buying the right sizes of valve shims - only where it was a must, and reshuffled the remaining shims wherever was possible. Heck a lot of work - all cams out, then redo the timing with attention to marks, details etc. but worth it. It runs smooth like butter now.

[ColinBarber]

5 hours ago, rz1c13 said:

So it turned out to be valve clearance issue - getting to near-zero... !

Are you saying the valve clearances closed up? I don't see how that is possible, wear can only cause the gap to increase between the cam lobe and follower/shim - unless something happened to the VVTi/timing.

[BodgerBen]

Very common for valve clearances to close up, as the head of the valve hammers into the valve seat so the stem gets closer to the cam lobe. Old British OHC engines like Triumph Stag/Dolomite/TR7 etc. would close up much earlier than a 1UZFE, as the valve seat material is much better on the 1UZ, and TBH most unleaded engines have much better quality valve seats and valves. The valve itself rotates as it opens/closes and will loose a minuscule amount of material every nK open/close cycle, hence closing the gap to the cam.

 

Also remember that the cam/follower is lubricated, the valve and seat are working in a much harsher environment than the cam and follower. 

Edited March 4 by BodgerBen
Add lube comment

[ColinBarber]

That's true but it isn't common these days on something like the 1UZ-FE. It also isn't expected to be an issue on a cold engine as the valves will expand with heat and then close up the gap.

[BigBoomer]

On modern engines the valve seats and corresponding part of the valve do wear slightly, but so does the cam and follower so the net effect is minimal change.
The metallurgy of modern valves and seats is such that wear is good for the life of the vehicle and beyond. They just need regular clearance checks.
On the LS430 the clearance should be checked every 60k miles but once it gets beyond that first check I'd be amazed if it needed any adjustments over the next 600k miles.

One of my motorcycles has shim-under-bucket valves (like the LS430) and at 25k miles four of the 16 were close to the wear limit (all 4 exhaust), so were re-shimmed to the middle of the acceptable range. I ignored the 50k check so they were checked again at 75k miles and all valves were fractionally closer to the wear limit but still closer to the middle of the range.
This is on an engine that does 10,500rpm and puts out 180Bhp from 1400cc so it is pretty highly tuned.

Now on my 1986 motorcycle I had an issue where 2 of the exhaust valves "tuliped" at around 120k miles, but that was due to poor metal hardening from the factory and was a known issue. I didn't touch the valve seats as they were fine, I replaced the valves, lapped the valves into the seats and that engine is now at 200k miles and still goes like stink. That engine uses tappets (screw and locknut) adjustment for the valve clearances and needs to be checked every 10k miles mostly due to follower wear.

[rz1c13]

On 2/29/2024 at 9:36 PM, ColinBarber said:

Are you saying the valve clearances closed up? I don't see how that is possible, wear can only cause the gap to increase between the cam lobe and follower/shim - unless something happened to the VVTi/timing.

That's absolutely possible - think again - you are assuming cam lobes or shims wear up, but in my case cams and shims were untouched, smooth and not a notch of wear. But if you think the valve itself or the valve sits wear, then you have the opposite case - clearance cancels out, and that's my case at least.

[rz1c13]

On 3/4/2024 at 4:21 PM, BigBoomer said:

On modern engines the valve seats and corresponding part of the valve do wear slightly, but so does the cam and follower so the net effect is minimal change.
The metallurgy of modern valves and seats is such that wear is good for the life of the vehicle and beyond. They just need regular clearance checks.
On the LS430 the clearance should be checked every 60k miles but once it gets beyond that first check I'd be amazed if it needed any adjustments over the next 600k miles.

 

Absolutely agree. In my case the lobes were clean, with no wear sings. When I bought my LS430, the car had about 150k miles, started having issues at around 200 - 210k miles. After doing the full timing and clearance job it runs like a charm, but honestly I think the valve clearance was never done before. As a side note, I run the car on LPG, so I would imagine the seats and valves may experience a sight more wear since LPG burns at higher temperatures, and does not provide as much cooling and valve lubrication as petrol.