Possible inlet Manifold leak?

[Chimmychanga]

Hi
Got a few more problems with my facelift 325i - seem like I spend alot of time posting in tech help. anyway:

The car has a very lumpy idle at the moment which I have been unable to trace so far, ICV seems good, cleaned it out, no obvious air leaks from any piping, all the plugs are sparking and in properly. After overtaking another car the engine developed a hissing sound. The hissing sound is pretty much a constant so doesn't change with the revs and sounds like its coming from somewhere around the bulk head cyl 5/6 ? I've had a listen using a pipe to my ear and poking around and haven't been able to pinpoint it.
The only other thing is that the hissing will stop under acceleration and then come back when the throttle is constant or idle.

Also the engine makes a mechanical trundling noise at idle which goes when I fully depress the clutch , is this a gearbox bearing?

Thanks for any help, really appreciate it

[Clarkey1988]

The noise could be your clutch release bearing. Also if you think there is an air leak. Get some DW40 or air intake cleaner and spray it around the areas you think its coming from. If the engine note starts to change as it sucks in the oil you'll know where its coming from.

[Brianmoooore]

Poor idle and a hissing noise that stops under full throttle points towards an air leak on the engine side of the throttle body.
Some change of noise is normal when you depress the clutch, since you are loading up the thrust bearings on the crank, but an abnormal noise is likely to be the release bearing, as suggested above.

[Chimmychanga]

ok, thanks for the replies,
I'll keep trying to track down the hissing, is there any chance that it could be a cracked head? Would a leak on the exhaust side cause this do you think?

[Brianmoooore]

No and no.

[Chimmychanga]

Ok thanks again

[Chimmychanga]

So I've had a poke around today and tried to trace the leak some more, took off the throttle body to get better access to the engine but still I have made no progress. I've tried to listen through a pipe again and it almost sounds like its coming from the plastic rail by the injectors on cyl 5?( 2nd away from the bulkhead). I'm thinking of taking off the inlet manifold next Saturday (it's my daily with no other car). I think I'll need an inlet gasket and some injector o rings, does anyone know of anything else?

[mcbonio]

Buy a can of carb cleaner and spray around the joints of the various intake components. A sudden rise in engine revs will indicate where the leak is.

[Chimmychanga]

I thought that but then on reading about carb cleaner and seems it could be bad for anything other than metal that it comes into contact with like hoses or gaskets

[teamalsoran]

use wd40 instead

[mcbonio]

Nah, used it many times as have lots of folks on here, it gives best results when looking for leaks. Don't believe everything you read.!

[Brianmoooore]

Carb. cleaner isn't going to hurt anything that isn't long past its best already.
A cheaper alternative, if you have one, is a (unlit) gas blowlamp.

[Chimmychanga]

So I've finally got around to some attacking with carb cleaner and it seems like the leak is from the injector nearest the firewall. Does that make sense with the symptoms?
Is it a case of removing the inlet manifold to get to them and are there any other things I should replace while I'm at it? So far I can oly think of all of the o rings and the inlet gaskets.

[mcbonio]

I believe you can remove the whole fuel rail with injectors attached without removing the intake manifold. I'd try that first rather than risking breaking any studs in the cylinder head...!

[Chimmychanga]

Yeah on looking into it that seems to be the way fwd. wasn't looking forward to snapping studs anyway
Cheers

[Kedge]

You sure it's not the inlet manifold gasket rather than the injector o-ring on that cyclinder?? I'd have thought that'd be the much more likely culprit.

Never heard of anyone snapping studs on the inlet side either, only tends to happen on the exhaust side due to the temperature changes.

[e30topless]

Mike, if your doing the inlet gaskets remove the injectors after it's removed.. they can be taken out in situ but it's a fiddle,
and there's always a chance of a brittle pintle cap dropping down one of the ports which gets very sad

[Chimmychanga]

all i've been able to work out is that if i spray some carb cleaner around the injector the idle rises and the engine runs smooth for a few seconds rather than lumpy. Maybe its worth doing the whole lot. Is it worth getting the injectors cleaned while i'm at it? problem is its my daily so can't have it off the road for too long - you can only drive your wifes car for so long.

[mcbonio]

Send them off to a seller here called injectortune, I think he charges 10 quid an injector with new o-rings fitted IIRC.

[Chimmychanga]

Anyone got a clue as to how I get the injector electrical rail separate from the inlet manifold? There is a wire that goes from a connector on the opposite side of the mani from the injectors through the manifold and it won't budge!

[mark_i]

there are 4 10mm bolts holding the rail the the inlet

[Chimmychanga]

It's the wire going through the manifold to the rail that is holding the manifold in that's the problem

[e30topless]

twist off the Injector loom plug Mike ! it's underneath the inlet,

[Chimmychanga]

I've un done the socket from underneath the mount but the plug won't shift. Maybe I'll use more brute force?

[mark_i]

yeah they can get corroded internally causing the pins to stick in the socket

[e30topless]

still got my number ? gimme a bell

[Chimmychanga]

Sorted! Cheers Steve. The hidden locking ring underneath has now come off and all is good!

For now

[Brianmoooore]

When you put it back together, give the pins and buckets of that connector a good coating of silicon grease, and check that the BMW issued mod. has been done - a small nick in the lower rubber boot, so that any water that gets in from the top can find its way out.
If its not already been done, check under the rubber boot to make sure that you aren't already too late, and the wires under it have started to rot through.