air leak

[daz the plumber]

just having a look at my engine again and ive found something , when it put my hand on to the plenum i can feel a air leak .can you get a gasket for this as its sealed with some type of silecone .

[MADMAX2]

silicone? sounds like a previous owner bodge job!!!!!!!!!!!!!1

[GreenV8S]

Where abouts is the leak? Is it at the join between the plenum top and the trumpet base?

[jaxdanjo]

You can get gasket sealant, usually blue or red. It helps the gasket get a good seal on the mating surfaces. It also holds the gasket in place while the two components are married up. I use it.

[That Daddy]

daz the plumber said:

just having a look at my engine again and ive found something , when it put my hand on to the plenum i can feel a air leak .can you get a gasket for this as its sealed with some type of silicone .

If its between the plenum and trumpet base then there is no gasket just a bead of sealer be it silicone RTV etc,Daz get a long piece of hose 8mm in diameter approx and while the car is running hold one end to your ear and have a good probe around the area you speak of with the other end the leak will be obvious when you are over it,failing that fog some WD40 with the straw attached around that area and listen to engine speed change,i use easystart(more noticable)but i am not going to recommend this as it is highly flammable and i know the risks

Edited by That Daddy on Monday 18th August 20:53

[blitzracing]

An small air leak completely mucks up the engines mixture control. Extra air at tickover gets picked up as a lean mixture, so the ECU compensates for it by putting in more fuel. As the throttle opens the air leak becomes less of an issue as the vacume in the plenum drops, but the ECU has already compensated for it, so it could start to run richer overall. Could have found your answer !

Mark

[Toma500]

daz the plumber said:

just having a look at my engine again and ive found something , when it put my hand on to the plenum i can feel a air leak .can you get a gasket for this as its sealed with some type of silecone .

You could try a mix of washing up liquid and water and brush it round the seals sparingly though, A bit like looking for a puncture.

[Pupp]

blitzracing said:

An small air leak completely mucks up the engines mixture control. Extra air at tickover gets picked up as a lean mixture, so the ECU compensates for it by putting in more fuel. As the throttle opens the air leak becomes less of an issue as the vacume in the plenum drops, but the ECU has already compensated for it, so it could start to run richer overall. Could have found your answer !

Mark

Sounds an attractive theory and certainly one well worth proving/eliminating. I suspect it's not the likely cause 'though, unless a relatively massive amount is getting in.... look at the breather arrangement for one thing, there's oodles (and varying) amounts of air coming in via that alone so 'another' little seepage through a joint gap isn't going to make 'that' much difference to my mind?

[daz the plumber]

im a gas fitter , ive used leak spray ,there is a leak .im surprised you can`t get a gasket .is it a big job to remove

[MADMAX2]

Gas fitter! can you fit Gaz shocks lol hehehe

[V8 Animal]

MADMAX2 said:

Gas fitter! can you fit Gaz shocks lol hehehe

Don't go there

[daz the plumber]

i mean gas engineer , don`t think i will bother with those shocks again ,my fiat scudo as better shocks !

[blitzracing]

Pupp said:

blitzracing said:

An small air leak completely mucks up the engines mixture control. Extra air at tickover gets picked up as a lean mixture, so the ECU compensates for it by putting in more fuel. As the throttle opens the air leak becomes less of an issue as the vacume in the plenum drops, but the ECU has already compensated for it, so it could start to run richer overall. Could have found your answer !

Mark

Sounds an attractive theory and certainly one well worth proving/eliminating. I suspect it's not the likely cause 'though, unless a relatively massive amount is getting in.... look at the breather arrangement for one thing, there's oodles (and varying) amounts of air coming in via that alone so 'another' little seepage through a joint gap isn't going to make 'that' much difference to my mind?

The ecu sets its overall mixture (long term fuel trim) at only tickover, when a leak makes the most difference. After that it makes only small adjustments to keep the engine near Lambda 1 (short term fuel trim). If the long term trim is out, it will cause the ECU problems keeping the short term trim within limits, but it takes a really rich or lean situation for the ECU to flag up an error. Below this the car simply drives badly as the ECU tries to compensate within the mixture limits it has.

Mark