roaring in airbox

[jctilingservices]

hope John or someone can offer some assistance here guys, the problem:-

52 plate astra 1.6 club 8valve

failed m.o.t on blowing front pipe, changed pipe and it passed m.o.t.

next morning though, driving along I accelerated and heard what I thought was a car with a big bore fitted lol, it was coming from my car, immediate thought, blowing exhaust, at home checked exhaust and no blowing, sat in car and just pumped the pedal gently to lift the revs and theres the noise again, lifts the bonnet, gets our lass to rev it, and the noise is coming from the airbox, I put in a new air filter, made sure pipes were ok, no spits etc, airbox fitted correctly, and still same problem. went fishing Friday but on way back, approx. 70-80 mph the EML stated flashing, along with what I describe as a popping noise, foot off pedal light goes out, touch pedal again light starts flashing. got home, disconnected down pipe from cat but still same problem. the car starts and drives ok, but under acceleration in any gear, it sounds like I have a big bore. plugs were changed at the same time as downpipe as fault was reading misfire on cylinder 4, there are no fault codes showing up, but this noise is doing my head in. Any ideas really appreciated.

PS.
Guy at m.o.t station had quick look, said the noise is coming from airbox, but no faults there, he recons the fault is elsewhere but showing at the airbox

Jimmy

 

[Burnerman]

Usually a booming from the air box indicates that the pipe taking fresh air into it, has become disconnected....can you check this first?
Failing that, did you interfere with the lambda sensor in the front down pipe, and could it have blown out, or split from its boss that it screws in to?
John

 

[jctilingservices]

Usually a booming from the air box indicates that the pipe taking fresh air into it, has become disconnected....can you check this first?
Failing that, did you interfere with the lambda sensor in the front down pipe, and could it have blown out, or split from its boss that it screws in to?
John

hello John, I had the air box out, and the pipe from front grill and from top of the engine, put them all back in place with new jubilee clips. when you say lambda sensor, that's the one in the down pipe aint it, not the one in the cat,if so yes i disconnected it from the old one, actually had to heat the old pipe up and use stiltsons to remove it, then wound it into new pipe and nipped it up, the sensor is still in the pipe and the relevant plug is plugged in

 

[Burnerman]

If you put your palm of your hand over the tail pipe, can you hear any hissing?
If alls good there, I reckon there's a split in the air box or the pipes to and from it - somehow!
Is all well in and around the inlet manifold area (especially if its plastic )
John

 

[jctilingservices]

If you put your palm of your hand over the tail pipe, can you hear any hissing?
If alls good there, I reckon there's a split in the air box or the pipes to and from it - somehow!
Is all well in and around the inlet manifold area (especially if its plastic )
John

hi john,
No leaks on exhaust system, cant see anything wrong around inlet manifold, even looked to see if possibly a pipe was disconnected, but no such luck, reckon the air box and pipes are going to have to come off again tomorrow and double check, will let you know the result tomorrow, thanks again for taking the time to reply John, appreciated

 

[Belle427]

seems odd this fault has developed after the downpipe fitment

 

[jctilingservices]

seems odd this fault has developed after the downpipe fitment

you are correct, other people are saying it sounds like a misfire, but upon starting the engine, the car idles 100% spot on, remove any lead and immediately you notice a difference in the idle, which leads me to believe its not a misfire, unless a misfire can occur at higher revs only.
a neighbour said it could possibly be a burnt exhaust valve, but surely this would give an erratic idle,

the problem sounds a blow on the exhaust, but definately comes out the airbox, and when travelling at say 70-80mph, it sounds like its popping in the airbox, similar to the noise a big bore would emit

 

[jctilingservices]

Hi John, Defo cannot see anything wrong with the inlet manifold or around the inlet manifold, airbox and pipes been off today and there is definitely no splits or cracks anywhere.
Any other ideas, this noise only appears to be there as the revs go up higher, at speed it sounds like its popping in the airbox, similar to the noise of a boy racers big bore lol.
my neighbour said it could be a burnt exhaust valve and that the noise is actually a misfire and not a blowing noise, surely this would be hard to start and would give a fluctuating idle, the car starts without even touching the pedal, and idles 100% ok

 

[Burnerman]

Easily verified with a compression test, a burnt exhaust valve gives a definite misfire (particularly on tickover) and reduced engine performance......for the life of me, I can't see it being that if it starts as you say.
Try disconnecting the pipe from the air box to the throttle body, and gently see if there's anything loose in there.
John

 

[jctilingservices]

Easily verified with a compression test, a burnt exhaust valve gives a definite misfire (particularly on tickover) and reduced engine performance......for the life of me, I can't see it being that if it starts as you say.
Try disconnecting the pipe from the air box to the throttle body, and gently see if there's anything loose in there.
John

will have a try john, I didn't think it would be the valve because I do not have a lack of power at all, only the noise, I thought I would check for lack of power today, but still managed to get the car to 100 mph no problem

 

[Mursal]

Did you try another air filter, maybe even an old dirty one as a test? And the temperature sensor (the one for the ECU) is as it should be? Any fault codes logged?

 

[Belle427]

only thing i can think of is that they have left a bung or there is a partial blockage in the frontpipe fitted

 

[jctilingservices]

only thing i can think of is that they have left a bung or there is a partial blockage in the frontpipe fitted

cant be a blockage in the downpipe mate, I disconnected it from the cat, started the car, it started straight away but when I revved it, the proble was still there, and that's with the exhaust disconnected from the car, so I think it rules out a problem with the exhaust system, next thing I am thinking is could it possibly be the cat collapsed ?

 

[jctilingservices]

Did you try another air filter, maybe even an old dirty one as a test? And the temperature sensor (the one for the ECU) is as it should be? Any fault codes logged?

hi and thanks for the reply, no I have not tried tried another filter, reason being the problem was there before I changed the old air filter for a new one, so problem there with old and new air filter.
The temperature sensor for the ECU, sorry but I do not know what or where it is, or even how to test it.
No eml on, plugged my hand held memo scan and it showed as having no faults listed.

with the exhaust disconnected and the problem still being there, could the fault possibly be a collapsed or partially collapsed cat ?

 

[AlanE]

Showing complete ignorance here so one for John to comment on first really.

EGR valve operates, I thought from manifold, so was just thinking if this was faulty, such as faulty diaphragm, is it possible for say exhaust gasses to go where they shouldn't go, or inlet to be sucked from a place it shouldn't be sucked(!), either of which could cause, my theory goes roaring noises when passed through damaged diaphragm connected, eventually, to air inlet which might then form a trumpet effect accentuating the noise.

Don't even know if this vehicle is fitted with said valve, or a similar device.

As said this is total ignorance but as Sherlock Holmes (or Dr Watson) once said (or words to the effect) when all the possibilities have been eliminated its time for the impossibilities.