4.6 Engine rattle on load and high RPM

**clubagreenie** · 20th March 2011, 11:27 AM

Originally Posted by Old Rangie

My suspicion is that oil relief valve is sticking and lifters are pumping up and the rattle is the lifters bouncing on cam or some where in the valve train. The engine does not miss so valves seem to close.

I am fairly confident the noise is not detonation but a wise technical person once told me that it was difficult for human ear to hear detonation in the alloy V8 over 3000 rpm due to all the other noise.

So you're thinking that the relief valve is sticking closed & excess pressure is holding the lifters solid. The valve train then bouncing on what is effectively solid lifters.

Is it a new 4.6 with old heads? If so which heads? Had issues with early heads on a 4.0, also pinging. But thinking is there an oil gallery that doesn't kline up somewhere slowing/stopping flow and pushing more pressure somewhere else.

FWIW: On my D2 4.6 high comp, anything other than BP premium will ping it's head off, especially under load. I carry a couple of bottles of ELF octatne additive for when I can't get anything else.

**Old Rangie** · 20th March 2011, 11:35 AM

Dyno will probably eventuate but not readily available to me now as I am in the sticks so to speak. I have yet to locate a fourwheel dyno and a competent dyn operator. I have found a competent Rover (sympathetic) mechanic but no dyn.

Only done a couple of these trips so I have tried to resolve with my own knowledge, limited as it is.

On the rpm thing, I don't normally ring its neck but it has heads done, CDI and extractors with 300 Impco mixer on top of Holley 390. It goes okay with 31 tyres but the gearing is a liitle tall for my liking but I am not up for 4.11 gears. So third and fourth gear get used a lot. hence the high RPM Oh and stock cam what ever is in 4.6.
Seems to peak power at a tap over 5000 on gas. (surprisingly better power on gas than on petrol but I have spent a little time on the ignition curve. I have backe off advance till I am happy I am not doing damage....

**Old Rangie** · 20th March 2011, 11:48 AM

Rocket Industries have a Knock sensor kit for $500 which I am not prepared to spend.
Heads have been polished But I would assume these would be early 4.6 heads say '95. Bought the engine in a modified 84 Rangie and stripped the good bits out so know little history.
I suppose one of the cam bearings may have slipped or something stopped flow but then it reverts back to normal after the event.

I am still convinced it is not pinging but a good look at plugs should help confirm if it has been seriously pinging.

Gas is in excess of 102 RON (or should be), engine is low compression. 8.3 or thereabouts. Pinging would be a result of high AFR ie lean of stoich, or some local hotspots. Plugs should tell the story. It does not sound like pinging either, I know from when I have cocked up the timing what pinging sounds like on petrol especially on sand.

**Old Rangie** · 20th March 2011, 11:53 AM

Thanks to all replies, (I am sure there is an easier way to do this blanket thanks to threads)

Any new ideas welcome. Quite a few things to go and check and look for.

When more information transpires I shall come back otherwise we could go on for a bit.

Really impressed with this forum, some of the of the other tech forums I have experienced are a bit of a time waste but gentlemen (sexist assumption) you have been a great help.

Old rangie.

d@rk51d3 · 20th March 2011, 03:07 PM

Originally Posted by bee utey

It sounds a bit like your head gaskets are leaking out the sides. My P76 engine used to do this. Use an inspection mirror and a light to check along the block/head interface for black spray marks. Possibly also loose exhaust manifolds.

Had something similar in an XC Fairmont. Rattling under load, like a hammer bouncing around inside a cylinder. When I would back off, it was all smooth again. Turned out to be a burnt head gasket between 3 pots, and the beginning of a piston failure.

**Old Rangie** · 23rd March 2011, 12:28 PM

That does not sound good, I also have VX Commodore 3.8 and it makes the same noise up long hill. I used a thicker oil but still the noise. Hope both engines don't decide to spit it together...that will be a pain.

Old Rangie

**Old Rangie** · 1st August 2013, 05:36 PM

Never did resolve what was happening and subsequently swapped out the engine into another car. Interestingly it necessitated the heads be changed to fit the later serpentine belt ancillaries and guess what there was evidence of head gasket failure between two cyl for compression (can't remember which ones.) then after numerous oil and filter changes a sudden new problem... slow to build up oil pressure after starting. Changed oil and used Ryco cartridge problem eliminated!

In the meantime the 4.6 worked hard in its new role towing 2.5t up the Dorrigo Hill and out of Tamworth (two exceptional long hills) without repeat of the noise. The oil pressure gauge not fitted to this car and no LPG either.

Moral to story.... oils ain't oils and filters ain't filters. The bypass in the filter must have been different to normal. Don't remember the brand as somone else got their hands dirty and I was remote from the vehicle (Simpson desert somewhere) when I received feed back. Anyway we shall see.

Old Rangie.

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