Got a vacuum leak from changing accessory belts - FIXED!

[bmw_325i]

Hi guys,

I'm hoping you can provide some advice on my predicament.

My 88 (late 87 ie facelift) 325i has been making some belt-ish noise on cold start and on inspection the belts are pa bit cracked and what-not so decided to change all three, p/s, a/c and alternator.

Apart from loosening those accessory bolts, and removing the intake up to the boot, all i did was clean a bit of oily gunk away from wher i was walking.

Immediately since then i have had extremely lean AFR's on the wideband o2 sensor - 3 to 5 points depending on throttle. To compensate ive upped the fuel pressure to richen up a bit but dont want to leave it like that for too long.


Is there anything i could have done that has opened up a hole?

I see that the a/c is bolted to the block, do the bolts for that go through to the internals.

I've pulled the intake 4 times and rtv'ed anything that looks a touch dodgy.

CHeers in advance
Brad

[SGP]

I'd try a shot of carb cleaner around the area while idling just to be sure it's a vacuum leak.

[bmw_325i]

Will do - i did that a couple of times already everywhere else up top while looking at the intake but only thought about the a/c mounting when looking again last night.

On the downside, changing the belts hasnt made a difference to the cold start noise.

I am leaning towards water pump now as:

a) removing a/c and p/s belts made no difference
b) squeeking is coming generally from the front engine area.


So, stupid question time. Is it possible that overtightening all of the belts on a worn water pump has created a vacuum leak at the front of the water pump?

[SGP]

No.

[Brianmoooore]

Nothing connected with water pumps, belts or aircon can affect mixture strength.
Any air leak weakening the mixture would have to be between the air meter and the cylinder head inlet ports, the brake servo (unlikely) or the crankcase.
To eliminate the crankcase as a cause, disconnect the breather hose on the rocker cover, block the pipe that disappears under the inlet manifold and leave the rocker cover stub open.
Have you plugged the air meter back in?
Run the car (for half a minute) with the fan/alternator belt off and see if the noise goes.
Don't forget that there's another very important belt under the cover at the front of the engine - the cam belt. It's not unknown for the tensioner bearing shaft to come loose, tilting the pulley inwards, and throwing the cam belt against the inside of the front cover. There's a rubber cover on the back of the belt casing on the LH side of the engine, near the top of the block, where you can get a glimpse of the belt. Rubber dust is not a good sign.

[bmw_325i]

Thanks for the detailed response Brian.

I disconnected the valve cover breather hose from the vc and blocked the pipe but left the stub - what would i expect to happen or observe by doing this?

I also removed the alternator belt and i believe that the noise was not evident, however it was 24C out so not really a good cold start test (most noticable at the 10-15c mark in the morning). In that respect i will assume that it is the water pump bearing, although i forgot to check for shaft play with the belt off.


I wasnt sure what doing what you recommended at the same time would mean?

[Brianmoooore]

Thanks for the detailed response Brian.

I disconnected the valve cover breather hose from the vc and blocked the pipe but left the stub - what would i expect to happen or observe by doing this?

If this makes no difference to the problem, then you can discount air leaks into the crankcase as the cause of the problem.

I also removed the alternator belt and i believe that the noise was not evident, however it was 24C out so not really a good cold start test (most noticable at the 10-15c mark in the morning). In that respect i will assume that it is the water pump bearing, although i forgot to check for shaft play with the belt off.


I wasnt sure what doing what you recommended at the same time would mean?

If the noise is gone with the belt off, then water pump or alternator are the likely suspects.
For the lean running, check and double check everything that you could have disturbed around the inlet area - the big air pipe, ICV connections, where the breather pipe from the rocker cover goes into the inlet manifold, the blanking plug for the emissions fuel tank vent pipe, the brake servo connections to the throttle body, etc.

[bmw_325i]

Re the lean running, i will look to replace the intake manifold gaskets and breather tube seals as their is a faint whistle / whine under the IM that i dont remember noticing before, but who knows...

I'm going to assume that the water pump is noisy, the alternator spins freely - i removed this to check play and replace the new voltage regulator *just in case* that fixed the lean running problem (hey i'll try anything right now).

Intake has been triple-checked. It's just so strange that the lean condition started immediately after the belt change.


Cheers mate.

[bmw_325i]

The lean condition has gone now that i have changed the injectors, suspect one wasnt sealing correctly although how it came about is pure coincidence.

Awesome