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That's some vacuum leak...


geoffbeaumont
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Thought I'd got a bit of a vacuum leak on the Range Rover, so took it round to Sainsburys car park (well away from the houses) to have a tinker tonight - going up to the Lakes tomorrow and it isn't drivable at all on LPG. Bad on petrol, and it idles about 15k, but drivable. When you stop the engine you get that characteristic hiss from it. Hard to be certain what it sounds like when driving as the left exhaust header is leaking (or maybe it's not the exhaust header..?).

Tried sticking my hand over the end of the air intake - no effect whatsoever...expected it to at least stumble or slow down a bit... Took the entire intake off back as far as the LPG venturi and tried again. Just fingers so I didn't find myself attached to the engine (yes, I know it still wasn't very bright...) - very slight drop in revs - maybe 500-1k.

Put the intake back together and went round with an unlit blow torch - possibly a slight rise in revs around the front right of the plenum, but nothing conclusive. I've checked all the pipes and tried clamping the idle air bypass and vacuum line to the rocker breather. Slight drop on the bypass, but not much.

Guess I'm not taking it to the Lakes...

There's nothing that could cause this behaviour other than the mother off all vacuum leaks, is there?

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Thought I'd got a bit of a vacuum leak on the Range Rover, so took it round to Sainsburys car park (well away from the houses) to have a tinker tonight - going up to the Lakes tomorrow and it isn't drivable at all on LPG. Bad on petrol, and it idles about 15k, but drivable. When you stop the engine you get that characteristic hiss from it. Hard to be certain what it sounds like when driving as the left exhaust header is leaking (or maybe it's not the exhaust header..?).

Tried sticking my hand over the end of the air intake - no effect whatsoever...expected it to at least stumble or slow down a bit... Took the entire intake off back as far as the LPG venturi and tried again. Just fingers so I didn't find myself attached to the engine (yes, I know it still wasn't very bright...) - very slight drop in revs - maybe 500-1k.

Put the intake back together and went round with an unlit blow torch - possibly a slight rise in revs around the front right of the plenum, but nothing conclusive. I've checked all the pipes and tried clamping the idle air bypass and vacuum line to the rocker breather. Slight drop on the bypass, but not much.

Guess I'm not taking it to the Lakes...

There's nothing that could cause this behaviour other than the mother off all vacuum leaks, is there?

I had similar but not as severe symptoms with the o ring seal failure on two injectors.

Cracked hose anywhere?

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Won't get another chance to investigate 'til I get back from the lakes next week - I'll check out the MAP and try some WD-40 round the injectors then.

Can failed injector seals really flow enough air to supply a 3.5l engine at 15000rpm..? :blink:

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Won't get another chance to investigate 'til I get back from the lakes next week - I'll check out the MAP and try some WD-40 round the injectors then.

Can failed injector seals really flow enough air to supply a 3.5l engine at 15000rpm..? :blink:

I had similar but not as severe symptoms

I doubt it and even for a minor leak they were particularly loud, as IMHO any vacuum leak normally is.

Plenum not cracked etc, could it just be an accumilation of leaks, manifold gasket ok? - i.e. not leaking water.

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You've said it twice, once as "15k", then again as "15000". In both cases what you have written is 15 THOUSAND.

I think you meant 1.5k and 1500 respectively.

At no load I'd have said it doesn't take a lot of air to run at 15 HUNDRED rpm.

Do you have a vacuum brake servo? Have you isolated the rubber pipe to the servo? A cracked pipe or a faulty servo may cause enough of an air leak, and it might explain why you can hear a hiss when the engine is switched off, depending on where the servo's atmospheric pick up is located (frequently in the car).

The Lakes eh? At Easter? Brave man.

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You've said it twice, once as "15k", then again as "15000". In both cases what you have written is 15 THOUSAND.

I think you meant 1.5k and 1500 respectively.

At no load I'd have said it doesn't take a lot of air to run at 15 HUNDRED rpm.

Err... yeah. Wonder if anyone's ever got an RV8 to rev all the way to 15k?

Do you have a vacuum brake servo? Have you isolated the rubber pipe to the servo? A cracked pipe or a faulty servo may cause enough of an air leak, and it might explain why you can hear a hiss when the engine is switched off, depending on where the servo's atmospheric pick up is located (frequently in the car).

My car has ABS, so no vacuum feed from the engine. I've tried clamping off the vacuum line to the distributor and the megasquirt (currently using the pipe that should be going to the heater), the idle air bypass and the rocker cover breather. I've checked the vacuum line to the fuel pressure regulator and all round the plenum and not found anything, as described below, so the injectors sound like the only realistic place I haven't eliminated.

The Lakes eh? At Easter? Brave man.

Actually we had great weather. Big improvement on camping in the hail in the Yorkshire Dales last Easter...

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I doubt it and even for a minor leak they were particularly loud, as IMHO any vacuum leak normally is.

Plenum not cracked etc, could it just be an accumilation of leaks, manifold gasket ok? - i.e. not leaking water.

Which could explain the 'leaking exhaust header' I haven't been able to track down...

The valley gasket is only a few months old, done when I did the head gaskets. No coolant leaks, so probably okay but I'll check it.

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Won't get another chance to investigate 'til I get back from the lakes next week - I'll check out the MAP and try some WD-40 round the injectors then.

Or maybe I won't use WD-40, seeing it contains silicone and the truck has lambda sensors...

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