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"pinking" Noise On Mk3 Ls400


Ninety-Eight
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OK, I have a 187K mile LS400 Mk3 which I recently bought.

I am slowly putting together a "snagging" list and #1 problem is that it makes a noise like "pinking" when accelerating with more than a gentle pedal pressure and over say 2000 RPM.

I potter about at less than 2000 RPM or with a light right foot and its all pretty quiet.

If I put my foot down to overtake or pull onto a busy road etc. I get the hammering of a thousand tiny anvils.

I had originally thought it was an exhaust leak as they can sound "pingy" but I'm not so sure as its RPM and engine load specific.

Can any fine Lexus experts out there give me a bit of a check list of stuff I can look at (I'm a bit of a loss with all this electronic stuff, I'm used to cars with carburettors and distributors I can tweak up a bit to see if that helps)

Cheers.

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I always thought of pinking being down to a timing and fuel issue. Probably no noise when revving while stationary, only under load I'm guessing ?

Not sure what to suggest since I am not likely on the right track with what the problem is. Usually, for pinking or knock or detonation etc ( not to be confused with pre-ignition ) it can be traced to fuel and/or timing related ( including the Electronic control unit, or ECU though these don't seem to ever fail in any way ) I would be thinking of whether there are any leaks in the fuel system and causing air to be sucked in etc ( though lack of fuel would cause cutting out I should think as well maybe ? ), Throttle position sensor, air flow meter, cam angle adjuster if its a model with the variable valve timing. Then there is ( as said ) the usual checks on distributor coils, plugs, leads, etc.

Any additions to the car recently, new cam belt, plugs, fuel additives, anything like that ? And running on 95 ron fuel ?

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The car is a 1995 Mk3. Not a VVTI model. I am using normal unleaded. I will check tonight (with the motor properly warmed up) that it is as you suspect, that it does not do it with no load, just under load. I think this will be the case although I have not explicitly tested for it.

Only new addition to the car is me as its owner.

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Good, that eliminates a few things then. In a traditional sense ( as a mechanic/hobbyist only ) I'm inclined to think ignition issues, Plugs, leads, coils since the timing is ( I assume but not 100% sure ) controlled by the ECU or even if not, I have not known timing to go out. Not as it would way back when, on Cavaliers and escorts for example, where you could turn the dizzy cap to retard or advance the timing etc.

A coil, lead and plug inspection I would think is worth it, especially if you have not had the car to long maybe. Get to know it, seems many LS400's are still running 200,000 miles and more on the same coils and leads they rolled out the factory with. As the plugs foul up, sparks not strong enough under load, weak spark = weak ignition or even failure to ignite and therefore pinking. But I'm no expert, just some thoughts and free bump to the thread.

Hope the solution comes up soon and its nothing to drastic, all the best !

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Go for the simple approach 1st.

The LS400 is designed to run on super unleaded with an octane number of 95 or above so try a tankful of the good stuff "BP Ultimate Shell Optimax etc" and see if the problem goes away before going any further.

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OK, "RTFM", I assumed it would be OK on normal unleaded.

Next, it does make a non-factory noise when revved on no load (although I only revved it gently, I don't like to give any engine the gun with no load on it) but that sounded more like an exhaust leak than pinking.

Perhaps I have two separate problems with similar effects.

I will top up with "Super"

The car is a 1995 model Mk3 Which I think is a UCF20-1 if I got my model designations right.

Thanks for the suggestions thus far, I'll see where I get with them and report back.

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Hi

My Jan 1995 MK3 has 186000 miles without this problem (touch wood).

My own approach would be to change the plugs for the best I could afford. Alternatively, if your car has new plugs, I would buy another (make) and try it in each cylinder. Its a faff but I have had duff plugs before and even when supplied and fitted by a main dealer (Rover 827).

Steve

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My EGR pipe is split and sounds similar to pinking. Its not possible to hear it at low throttle but very distinct when loading the engine up more. I wouldn't rule out an exhaust leak.

How is the base timing set on these engines as maybe that would be something to check if your convinced its pinking.

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Its sounding more like an exhaust related one. I have got the car running on super unleaded (Esso I think, it was a motorway services and I forget which now) now I'm pretty sure the only noise it is making is exhaust related ticking on a leak somewhere.

Thanks for the input.

I think it was pinking a little on load due to the fuel.

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  • 3 years later...

Are we sure it's an engine " knock " at all ??

Looking at my Full Lexus SH and my EGR pipe has already been changed.

I have just developed an occasional ( so very very occasionally too ) and rare tinny noise at a low speed.

I'm thinking it might be one of the exhaust heat shields just slightly out of kilter.

Thoughts ?

Malc

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