suspected air leak (not SOLVED!)

Thu Sep 17, 2009 7:59 pm

I have a suspicion of a air leak in 325i. Car is running lean (spark plugs are carboned up and there is a strong petrol smell from the back end of the car).

Anyone got any good advice on investigating this? The obvious one is the big boot, which I have already inspected and could not see any cracks. What are the other likely and UN-likely places?

Fri Sep 18, 2009 3:30 am

Thank you willnz. Atleast one person helped.

I will update with tomorrow by following what you advised. I got a feeling this leak will be a hard one to find.

Fri Sep 18, 2009 3:47 am

Spray around the inlet pipe,

inlet manifold where it joins the head,

throttle body,

and also around where the crank breather pipes comes up beneath the inlet (a black pipe that has a spring at the base and is in the middle of the inlet).

Also check that the rubber hasn't perished and cracked under your oil filler cap. Also while it's idling, take off the oil filler cap and see if it makes a difference to your idle. If it's significant you've got a small air leak somewhere, if not then it's a big leak you've already got.

I can't work out why you'd also have a strong petrol smell. Are these the only two symptoms you know of that are leading you to believe that you have an air leak? or are there any other symptoms?

Hope this helps.

Fri Sep 18, 2009 3:49 am

Also check the pipe from the fuel pressure regulator to the inlet, make sure there are no cracks and that it doesn't contain any traces/smell of petrol.

Fri Sep 18, 2009 5:59 am

Supafly thanks very much, that helps alot. I will be definitely be checking all those later. The only other symptoms which leads me to believe it is running lean are, hesitation when I sometimes press the throttle, and the engine faintly shakes at idle . I have already tried and tested the blue temp sensor and ICV. Tomorrow I shall be changing the spark plugs, testing HT Leads and the throttle position sensor. Hopefully the problem lies in one of them.

Also Supafly you mentioned in your second post of the vacuum hose from FPR to inlet containing any smell of petrol? Well when I smelled mine earlier, I could CLEARLY smell petrol within that vacuum hose. What does this mean?

Fri Sep 18, 2009 4:42 pm

I've not had this problem but I know that it does occur. It can mean that your fuel pressure regulator is knackered and allowing fuel to be pulled into the engine through that vacuum hose.

It will also cause similar problems to what you are already experiencing. I would look here first, get a clear pipe swapped in temporarily and look to see if there is any fuel being drawn through. If you have a fuel pressure gauge then you can check the pressure to make sure.

If you find that this is at fault, be careful that you get a FPR from a 325 as I beleive that the 320 fits but runs at a lower pressure.

Fingers crossed you'll get it sorted soon

Fri Sep 18, 2009 6:52 pm

I'm glad I am getting somewhere with this! It's been going on for quite a while now, and it has been letting my fun down as its obviously not running how it should. Especially, the fact that its a cabby and the sunny days are almost over. It's going to be garaged up when winter arrives.

I am going to try a working fuel pressure regulator, new sparkplugs and leads tomorrow and hope it runs fine after that. Also I forgot to mention one other thing, I can often hear my fuel pump buzzing as I am driving along most of the time. I have a feeling this could also be related to a foul FPR?

I will update tomorrow.

Thanks again!

Sun Sep 20, 2009 12:06 am

I changed the fuel pressure regulator and unfortunately it didn't make no difference. But when I changed the spark plugs and leads, the idling got MUCH better. Before the leads were loose and the spark plugs were a crap quality. Now that its changed to new ones, overall it's much better generally. BUT... even though the juddering and shaking at idle has gone down alot, it still does it, but now very faintly.

I am 95% sure there is a air leak, despite having looked at the obvious places, still not sure where it is. Willnz, I am not sure where the brake booster exactly is. I take out the glovebox and spray the carb cleaner where?

Also when I took out the old spark plugs today they all looked a mixture between black and brown. Some of them more blacker then others, some of them less.

Thanks!

Sun Sep 20, 2009 12:45 am

thanks mate

will check it out tomorrow.

Just one thing, I DO remember hearing a hissing noise, but not sure if it was from the fan? Is that possible? A pulsating hiss.

Sun Sep 20, 2009 1:01 am

does the hiss stop when you touch the brakes? also if you run the engine press the brake and remember what it felt like, then turn it off, wait a couple of seconds, then press the brake again. does it still feel the same or has it gone hard? if its gone hard, keep your foot on the brake and start it up if the pedal pulls away from your foot then the servo is leaking.
if the servo is good with the engine off you should be able to pump the brake pedal at least 3-4 times before all vacuum has gone and the pedal goes hard.

Mon Sep 21, 2009 1:55 pm

Willnz - I can confirm there is no hissing noise from the glovebox. To make sure I sprayed WD40 on the bit you highlighted and made no change.

Do you think a dodgy airflow meter can cause this? Once again, just to be clear, my symptoms are juddering engine when idle (revs are solid) and petrol smell from exhaust fumes. CO2 check say it is running on the lean side. I am going to try another AFM tomorrow, if no change I will have to take it to a competent garage to find the leak.

Mon Sep 21, 2009 3:08 pm

have you considered the blue temp sensor? This is the device that tells the ECU the engine temp and thus the fueling is affected accordingly, they normally fail open circuit which produces a rich mixture (or a default cold engine setting) but your could be different.

it is located near the front of the fuel injection rail and you will see two sensors, a blue and ab rown one you want the blue sensor. take a multimeter and set it to measure resistance or Ohms ( Î© )

remove the plug is from the blue temp sensor and you will see two terminals on the sensor itself, one lead of the meter on each terminal. you should read about 3500ohms when cold and it should drop to about 250 when hot. the actual measurements may vary but should be close to this range. anything wrong here then change it.

mrlee

Mon Sep 21, 2009 3:12 pm

mrLEE30 wrote:have you considered the blue temp sensor? This is the device that tells the ECU the engine temp and thus the fueling is affected accordingly, they normally fail open circuit which produces a rich mixture (or a default cold engine setting) but your could be different.

it is located near the front of the fuel injection rail and you will see two sensors, a blue and ab rown one you want the blue sensor. take a multimeter and set it to measure resistance or Ohms ( Î© )

remove the plug is from the blue temp sensor and you will see two terminals on the sensor itself, one lead of the meter on each terminal. you should read about 3500ohms when cold and it should drop to about 250 when hot. the actual measurements may vary but should be close to this range. anything wrong here then change it.

mrlee

Cheers mrlee but I have changed the blue temp sensor for a brand new one still no good.

Here is a list of things I have tried/tested/changed:

ICV
Blue Temp Sensor
Spark Plugs (Bosch super 4)
HT leads
Fuel Pressure Regulator
TPS
Throttle Body Gaskets
Cleaned the long twisty pipe from inlet for rocker cover
Valve Clearence
Full Service

Next:
AFM (Could it be this??)

If still no good then I am lost.

Mon Sep 21, 2009 4:14 pm

yes or maybe try changing the ECU for a known good one

Mon Sep 21, 2009 4:47 pm

Yeah I will keep that in mind. I am hoping the idle mixture bypass screw on the AFM is out of adjustment, causing a wrong idle mixture. The car runs normal when under load. Trying another AFM tomorrow will tell.

Mon Sep 21, 2009 6:31 pm

SeymourCake wrote:hesitation when I sometimes press the throttle, and the engine faintly shakes at idle .

Hi mate. sorry to thread hijack but can you give me more info on the above as I'm having a similar problem. The car idles ok, but stamp on the gas with the engine running at less than around 1700rpm and the engine hiccups before pulling cleanly. Floor it at higher revs and it performs as it should though.

Mon Sep 21, 2009 10:23 pm

SeymourCake wrote:Yeah I will keep that in mind. I am hoping the idle mixture bypass screw on the AFM is out of adjustment, causing a wrong idle mixture. The car runs normal when under load. Trying another AFM tomorrow will tell.

if you plan to play with this then make sure you have emissions diagnostic equipment as just playing with it tends to do more harm than good. but as you say a new AFM will tell you its wrong.

Tue Sep 22, 2009 5:18 pm

Update.

Tried the AFM and still no change.

However I did find that the big round rubber intake right at the front of the airbox, near the headlamps, which allows the air to go into the airbox, is cracked up underneath. Does it matter that it is cracked? I was thinking the air will flow through it regardless, remeber I am only having this problem at idle.

Also is it normal to smell a bit of fuel in the exhaust fumes?

Appreciate all the help zoners.

Tue Sep 22, 2009 7:14 pm

SeymourCake wrote:Update.

Tried the AFM and still no change.

However I did find that the big round rubber intake right at the front of the airbox, near the headlamps, which allows the air to go into the airbox, is cracked up underneath. Does it matter that it is cracked? I was thinking the air will flow through it regardless, remeber I am only having this problem at idle.

Also is it normal to smell a bit of fuel in the exhaust fumes?

Appreciate all the help zoners.

Mine also smells of petrol AND changing the AFM did nothing either. I think the way forward for me is to strip the inlet side of things and replace all gaskets/pipes as I go. Time to play the elimination game.

Tue Sep 22, 2009 7:15 pm

SeymourCake wrote:Also is it normal to smell a bit of fuel in the exhaust fumes?

BTW mate, can you tell me what the results of your MOT emmision check was, just to see if we're singing from the same songsheet here.

Tue Sep 22, 2009 7:56 pm

Alright mate I'll try the figures, if I can find them.

Also regarding your earlier post,

N00b wrote:
SeymourCake wrote:hesitation when I sometimes press the throttle, and the engine faintly shakes at idle .
Hi mate. sorry to thread hijack but can you give me more info on the above as I'm having a similar problem. The car idles ok, but stamp on the gas with the engine running at less than around 1700rpm and the engine hiccups before pulling cleanly. Floor it at higher revs and it performs as it should though.

I'm not sure what the cause could be but have you tested out your tps? Can you hear the click? Or it might not be registering properly until wide open throttle.

Tue Sep 22, 2009 8:05 pm

SeymourCake wrote:I'm not sure what the cause could be but have you tested out your tps? Can you hear the click? Or it might not be registering properly until wide open throttle.

No mate, what should I do and more importantly where is it? lol
Sometimes, when starting from cold the hesitation isn't present, although once the car has warmed up it's back.

Tue Sep 22, 2009 8:21 pm

Oh right! Since you said that it definitely sounds like the blue tempreture sensor. Look on the thermostat housing, theres a brown plug and a blue one. The blue one tells the ecu what tempreture the car is running. It is probably fudged and thinks its on cold start all the time. Have a search for blue temp sensor and you'll find what you need. Wouldn't harm to have a check and clean through the idle control valve, tps and air flow meter.

By the way tps (throttle position sensor) is under your throttle body housing. Its a little black sensor with a plug attached to it.

Tue Sep 22, 2009 8:30 pm

SeymourCake wrote:Oh right! Since you said that it definitely sounds like the blue tempreture sensor. Look on the thermostat housing, theres a brown plug and a blue one. The blue one tells the ecu what tempreture the car is running. It is probably fudged and thinks its on cold start all the time. Have a search for blue temp sensor and you'll find what you need. Wouldn't harm to have a check and clean through the idle control valve, tps and air flow meter.

By the way tps (throttle position sensor) is under your throttle body housing. Its a little black sensor with a plug attached to it.

Think that would explain the well within tolerance CO figure but an extremely high HC count?

Tue Sep 22, 2009 9:45 pm

Not sure mate, could be.

I have added a pic highlighting where the cracked rubber is:

(this isn't my car, mine is a m20b25)

So could this cause air leak problem?

Tue Sep 22, 2009 9:50 pm

That pipe is before the air flow meter so would not cause a problem, mine dosent even have one.

Tue Sep 22, 2009 9:54 pm

thought so.

anyway good thing is that is it running better then it ever has since I bought it, due to me testing and changing alot of things along the way. It's just this judder at idle and smelly exhaust fumes thats letting it down...

will update again when I solve it...

Wed Sep 23, 2009 2:42 pm

I think if you did a quick logical write up of the steps you've been through so far and their results, it might help highlight something we've missed.

Eg
1) sprayed carb cleaner at points x,y,z - no difference
2)tested TPS - idle, wot etc tested - fine
3) CTS etc etc

Hopefully it might show something up and if not, it will be of use to someone else when they have a similar problem.

Fri Oct 09, 2009 11:55 pm

Hi guys, still got this problem. I will follow Supafly's advice and do a quick list of what I have exactly done.

1) ICV - tried a definate working one.= no difference.
2) Blue Temp Sensor - brand new one from dealers.= no difference.
3) Spark Plugs (Bosch super 4) - = overall car ran better but no difference to the original problem.
4) HT leads - replaced with a brand new set. Distrbutor cap and rotor wasn't changed as they looked fine from what I could see. = ran little better.
5) Fuel Pressure Regulator - brand new bosch.= no difference.
6) Gaskets - I have replaced: Rocker cover gasket, throttle body gaskets, inlet manifold gaskets.= no difference
7) Checked for air leaks - all around the air pipes, pretty much covered everything from afm to inlet. Sprayed wd40 all over the place. The C191 plug under the inlet manifold looks fine, the long bendy pipe from inlet manifold to rockcover is fine too. Big rubber boot - check! Elbow rubber connecting to the ICV - check. As I have said, I have covered all general areas and I can't think of anywhere else.

Valve Clearence - set correctly.= ran little better.
9) AFM - tried another unmolested working one. I thought the settings had been fiddled with on mine, but guess not as it didn't make no difference when I tried the other one.= no difference.
10) Fuel pump relay = no difference
11) New rubber vacuum pipe from fpr to inlet = no difference
12) Full oil service (incl. all filters etc)

I have accidently missed the TPS, which I don't think is the problem anyway as it clicks when throttle is opened, and I don't think it would cause lean idle? I will test it out tomorrow with a resistor. Anyway, I must say the car itself pulls really well when on the move.

Someone mentioned to me that it could be injectors? They do seem to be ticking (quite loud, but not extraordinarily loud)

I am getting frustrated because the signs point to an obvious air leak, but the problem is I can't find any, and trying all those things I have listed above ^ still no sign of the cause. Loosing patience!

Sat Oct 10, 2009 12:52 pm

I understand the feeling, keep at it, all will be well in the end

7) the c191 plug, did you peel back the rubber on the lower half and check the pins as they enter the back of the connector?

WD40 - I've not used it to find air leaks so unsure about how quick the engine would respond to it. I normally very carefully use carb/brake cleaner as it evaporates very quickly and if there is a hole the engine responds very quickly to it. Be careful though as it's highly flammable.

Have you checked the metal pipe that comes up into the inlet manifold beneath the TPS?

TPS - don't leave it to chance, it's a quick 10 min check with a multi meter.

Injectors are known for giving problems but thats mainly due to them having worked for twenty odd years with no maintenance, I've read lots of good reviews for ultra sonic cleaning. On my list of things to save up for

Good luck

Sat Oct 10, 2009 3:42 pm

Anyone actually read the OP for this thread! (which I've only just spotted)

SeymourCake wrote: (........spark plugs are carboned up and there is a strong petrol smell from the back end of the car)..........

Hardly the signs of car with an air leak and running lean!!
I've only skimmed through the thread, but I'd be giving the wiring UNDER the boot of the C192 connector some close attention