4.6 Engine Hesitation & Noise

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DoZZa

New Member
Posts
67
Location
North Devon
Hello all,

I have been doing a fair amount of driving in the RR over the last couple of days.

I have noticed that there is a fairly loud tappety type sound that comes from the engine bay when its just approaching 5000 rpm until the redline.

My car is fitted with a Romano LPG system and the noise will occur when on LPG or petrol.

The noise occurs when under load or with the box in neutral.

Any ideas on this one?

The next issue is a hesitation at 4500 rpm, if I kickdown, power delivery and revs will rise as normal to around the 4500 rpm mark and then there will be hesitation for a second until full power is resumed.

This does not happen all of the time, it is an intermittent fault.

I am not 100% sure if it is only when running on LPG, I have filled the tank up with petrol today so I will drive around on petrol for a couple of days and see what occurs while just on petrol.

I was wondering if the hesitation and the noise maybe related?

I will be putting new spark plugs, oil, oil filter and fuel filter in the car tomorrow to see if this helps.

I have noticed one thing in the engine bay that might be causing the hesitation, and that is the fact that the airbox is damaged, there is a piece missing from the front of the airbox which is exposing the air filter.

So maybe the MAF is dirty, but I would have thought the hesitation would happen all the time I hit 4500 rpm if this was the case..

Your expert advice is greatly appreciated.

Thanks :)
 
eightinavee said:
Either buy a sports car or keep the revs below 4000.:rolleyes:
Click to expand...

lol, I have a sports car, 2 actually :)

Still, the engine should probably not be making this noise, and if it was dangerous for the engine to be going over 4k then I would imagine that it would be restricted as such.
 
That stretched 1954 Buick v8 motor is not about revving its brains out,carry on - it will just go bang.Then the car is scrap cos they arent worth a new engine anymore.:doh:
 
eightinavee said:
That stretched 1954 Buick v8 motor is not about revving its brains out,carry on - it will just go bang.Then the car is scrap cos they arent worth a new engine anymore.:doh:
Click to expand...

I dont make a habit of taking the engine to those types of revs.

As the car is new to me I am just seeing what its all about.

But I still say that if an engine can operate within a certain rev range, then there should not be a problem.

This is why rev limiters are in place surely?

Does anyone actually have any ideas what this noise and hesitation could be be please?
 
if there is a hole in the air box then you should patch that up or get a one from a breakers it may not be causing the problem but it dirty air will be getting to the engine.
Also what made the hole has it at some point ran lean on LPG and back fired ?.
 
crossa said:
if there is a hole in the air box then you should patch that up or get a one from a breakers it may not be causing the problem but it dirty air will be getting to the engine.
Also what made the hole has it at some point ran lean on LPG and back fired ?.
Click to expand...

Hi, thanks for your reply.

I only picked the car up three days ago and I only noticed the hole in the airbox today, so I could not say when it occurred.

Since I have had the car I cannot say that I have experienced any backfires.
 
With the engine revving that hard a noise like that is most likely crankshaft related as valvetrain noise would be there all the way up from idle.So,possible big end,main bearing or piston to head face contact if the bigends are failing.
You need to at least partially strip the motor to find out what is going on,engine noise can be very difficult to diagnose from just listening.
 
eightinavee said:
With the engine revving that hard a noise like that is most likely crankshaft related as valvetrain noise would be there all the way up from idle.So,possible big end,main bearing or piston to head face contact if the bigends are failing.
You need to at least partially strip the motor to find out what is going on,engine noise can be very difficult to diagnose from just listening.
Click to expand...

The noise is coming from the top of the engine.

So it is unlikely to be crankshaft related.

Tappet noise is a lot different to bottom end noise.
 
Last edited:
DoZZa said:
The noise is coming from the top of the engine.

So it is unlikely to be crankshaft related.

Tappet noise is a lot different to bottom end noise.
Click to expand...
Yes it is - but its you asking the questions.What you need to remember is that big end knock only happens every power stroke,every other turn of the crank - same as valve gear running at 1/2 time compared to the crank.
Why not try listening to the motor with a tech's stethoscope,also remember a loose liner may only knock or tap during the power stroke.
ALso remember that a Rover V8 even as a 4.6 is quite tolerant of major faults if driven with a degree of mechanical sympathy - it all depends what you expect of it.
 
eightinavee said:
Yes it is - but its you asking the questions.What you need to remember is that big end knock only happens every power stroke,every other turn of the crank - same as valve gear running at 1/2 time compared to the crank.
Why not try listening to the motor with a tech's stethoscope,also remember a loose liner may only knock or tap during the power stroke.
ALso remember that a Rover V8 even as a 4.6 is quite tolerant of major faults if driven with a degree of mechanical sympathy - it all depends what you expect of it.
Click to expand...

Thanks for your reply.

I think I will have to have a proper listen to it. I have only had a quick listen as its so bloody cold outside at the moment!

If it is bottom end, can it be changed with the engine still in place or will it need to be removed.

I have no mechanical experience of Land Rovers, this is why I am asking so many questions which may seem obvious to others.

This is why I appreciate any help thats given to me.

Thanks
 
you said your gona service it, has this helped? TBH, it just sounds like an old v8 being over revved. It could be a worn cam and followers, or worn rockers. Even the timing chain.
As i and most on here would say, dont rev it so high and it will prob last you years, rev the balls of it and it will go bang.
 
v8hotrodboy said:
you said your gona service it, has this helped? TBH, it just sounds like an old v8 being over revved. It could be a worn cam and followers, or worn rockers. Even the timing chain.
As i and most on here would say, dont rev it so high and it will prob last you years, rev the balls of it and it will go bang.
Click to expand...

Hi mate, thanks for the reply.

I dont make a habit of revving the engine like that, I have only had the car three days and I am just making sure all is well before I go spending money on putting things right.

But as the noise is at such a high RPM I dont think it really matters as I would very rarely need to take the engine to those kind of revs.

If it gets to the point that the noise occurs at lower revs, I will then need to do something about it.

Thanks :)
 
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