Got some time again to work on the MK. The engine runs at the moment (3.0 volvo straight six on megasquirt) but the idle is odd. It'll go up to, say, 1200 then drop to 800 then rise again and repeat. I've noticed a hissing noise on the inlet plenum. Would a leak cause unsteady idle? Also when I floor the accelator the engine cuts out but if I slowly press it down it'll rev right up, could that air leak cause that? Also when I shut the engine down there's a hiss noise for about a second

How can I find out where the leak is? When the engine is running it's impossible to tell where the noise is coming from. Use something that smokes like incense and see where the smoke is drawn towards?

if you plant it and it cuts out but you can get the car to rev slowly then check your accel enrichments, r u running alpha-n or map? have you made sure that all your butterflies are balanced and opening evenly. check all the welds around your plenum and check all the joins etc

where abouts are you, the only waltham's multimap finds is lincolnshire and kent, not leicestershire

[Edited on 16/3/09 by omega0684]

if you get a squirty bottle and fill it with water and then spray a mist of water over the inlet area, when you spray over the air leak it will draw in the water and the exhaust fumes will become very steamy.

Be sure not to do it to a red hot engine though as you may risk damaging something.

Easier way is to spray wd40 around the inlet with it running. It will temporarily seal the leak and run well. Do different areas at a time and you should be able to locate the leak.

You could use a length of hose as a stethoscope. Point it at various bits of the intake plenum to try and locate the hissing.... Other trick would be to liberally smear something like exhaust gum over it. When the hissing stops you've found your leak (and also stopped it). Obviously not a good option if you want a nice looking intake manifold... You could do the same with something like grease (relatively easy to remove afterwards)... If you use WD40 it might work but its quite thin, if the leak is big enough to cause hissing it'll be sucking quite quickly...

Both the stethoscope and the WD 40 work although its sometimes difficult to direct the spray into the area thats suspect . I've never used water spray to find an air leak but I can see it may work.

Spraying WD40 or brake cleaner around will find it.

A less messy and more acurate way is to take a butane blow-torch. Unscrew the burner nozel and push a piece of pipe in its place. Now open the tap and pass the open end of the hose around the manifold. When you find the leak the engine will pick up as it draws the butane in. I got that from Dave Walker and if it's good enough for him...

adrian

Hunting idles are a sure a sign of an air leak on the manifold.

As others have suggested ways of finding the leak I shant bother. But the WD40 is a good one, if a little messy.

Thanks I'll try out the suggestions and see what I can find =^_^=

quote:

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Originally posted by omega0684
if you plant it and it cuts out but you can get the car to rev slowly then check your accel enrichments, r u running alpha-n or map? have you made sure that all your butterflies are balanced and opening evenly. check all the welds around your plenum and check all the joins etc

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quote:

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Originally posted by omega0684
where abouts are you, the only waltham's multimap finds is lincolnshire and kent, not leicestershire

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what MS are you running?

MS II V3

Megatune V2.25

can you upload your msq so i can have a looky?

Attached. It's been so long since I've been playing around with the car, I don't know if this is the most recent file, either way I don't think i changed the tables much/at all

r u sure thats the right file, i tried opening it in all modes, 400kpa,Alpha-N,car1 and MAF and it does open any file, there is no fuel table on there or values in the basic constants screen.

Opens fine for me, It's MSII

Ideal way to find intake leaks is with a smoke machine that puts pressurized smoke into the intake. Assuming you don't have one of those just spray brake clean or propane around until the rpm changes (not near the plug wires).

Cars with MAF sensors are very sensitive to air/vacuum leaks. Even air leaks between the MAF and throttle body will confuse it.
With a MAP sensor the car *shouldn't* care about a vacuum leak. For it to die on accel means you either have a very large vacuum leak, or another issue. I think you have the right idea looking for a vacuum leak first.
Good Luck.