adrial

To bring everybody up to speed...I have an air leak, which I have recently determined to be a vacum leak. It appears to be coming from the AFM area...The car drives fine...boosts 100%...no drivability problems except that when I rev it and let off...it drops to like 800 and then picks back up to like 950 or so...the typical early 944 shudder. The only reason I care to fix it, is that the car is probably sucking in unfiltered air.


I just did some thinking...
At idle, a cold motor has more vacum than a warm motor (according to my factory boost gauge). The hissing is much louder when the motor is cold..than when it is warm....which indicates that the car is sucking air...not blowing air..

Now...I pressure tested the AFM...it didn't leak...
If it were leaking after the AFM, then the car wouldn't run right, correct?
However...I changed out the stock airbox with a K&N cone...the sound remains, and hasn't changed at all. So basically...nothing makes sense.

I would greatly appreciate it if anybody could help me in person.
If you're in the metro NYC area...I would love if you could check the car out...I'd of course drive to wherever you are, whenever you want after 2:30PM on a weekday. I live in westchester county..NY.

Perry 951

The airbox and AFM make some sucking noises. Hard to tell where it would come from.

I would check the small vac line under the throttle body. When that one leaks, it can cause a stumble. Hell.. any leak can do it.

An old trick that I have seen used is taking a propane torch, cracking the valve open just a touch, and gasing the areas where there are vac connections. A leak will suck in the propane and the idle will go up. Just have a bucket of water or an extinguisher handy just in case.

Renntag

Did you try any of the suggestions I made in the last thread of the same subject?

adrial

Perry, thats whats confusing me...that any leak will cause a stumble...but the car drives 100% OK!! Also, I don't think its a standard AFM sucking noise...cause my mech checked it out and thought maybe some hardware might be missing..I checked it out...it was all there. I've been by there 3 times in the past week for free...last time I was there they didn't seem to happy to see me...not the front desk guy anyway, the mech is awesome.

Colin, You know...Every time I think about/talk about my air leak I forget about the carb cleaner idea. Except when I bought the carb cleaner. I will definetely do that tomorow.

Although I pressure tested the AFM, I didn't vacum test it..I have a line on a used one for $65...I'm trying to see if I can borrow it just to test.

thanks,
Adrial

adrial

I went at it with the carb cleaner...couldn't get the idle to rise. I didn't really go crazy with it though.

I'm gonna have at it again tomorow...I hope I can find it. Other than the increased idle...I should also hear the sound of a liquid being sucked up by air...like finishing up a drink through a straw.

If I still can't find it...any other things to try other than replacing all the vac lines?

Oh...and my driver side sunroof gear is stripped. On sunday I noticed it was rattling when it was up...then I saw a gear tooth in the sunroof arm. Today, I tested it more cause the driver side was lower than the passanger side when raised. Then it stripped completely...in the unlatched position! I have the instructions from the 944 garage ( <a href="http://porsche-944-garage.tripod.com/shop-manual/body-04.htm" target="_blank">http://porsche-944-garage.tripod.com/shop-manual/body-04.htm</a> ) . Anything else I should know or do those directions just about sum it up? How many gears should I get? Replace all of them just for good luck?

thanks,
Adrial

Renntag

[quote]Originally posted by adrial:
<strong>I should also hear the sound of a liquid being sucked up by air...like finishing up a drink through a straw. thanks,
Adrial</strong><hr></blockquote>

Nah, I have never heard that.

Keep at it.

The tenacious usually see victory.

adrial

I'm looking at the starter kit from Hose Techniques...

<a href="http://cyber.virtualrep.com/hosetechniques/catalog_products.tpl?cart=1012271182284794&category=Universal%20SVH%20Ki ts" target="_blank">http://cyber.virtualrep.com/hosetechniques/catalog_products.tpl?cart=1012271182284794&category=Universal%20SVH%20Ki ts</a>

$60 for 10' 3.5mm, 15' 4.0mm, 6' 6.0mm, 4' 8.0mm...all diameters listed are inner diameters.

What do you guys think? How much of what size do I need (and any other things I may need that aren't in the kit...). No need for a quick response...I just wanted to get this up, I'm hoping I would have to do this...but if I can't find the leak I think this is my last resort.



thanks,
Adrial

sm

Adrial et. al. -

I've looked into that kit before and was wondering what do you do about the "triangle connectors" that the vacuum lines plug into. Do the silicone lines plug in as well?

BTW Adrial, I'm trying to figure out the same vacuum leak problem as you. Mine may be worse as I can't reach full boost. This has happened since taking off and replacing the intake manifold. I bought a can of carb cleaner today, so I'm ready to attack it and be "tenacious".

Bryan

Some info on vacuum leaks:

Most of the time, small vacuum leaks won't cause a major problems on cars with oxygen sensors and closed-loop air/fuel feedback control - basically all 944s in the USA. When the car starts using the O2 sensor signal, a minute or so after cold start, it compensates for the air leak. So you can have air leaks and a car that runs mostly fine.

If your car makes full boost, and I'm winging it here because my 944 isn't a turbo, then the air leak is not in the pressurized section of the intake track and/or it's not a big leak.

For practical purposes, common 944 air leaks occur in the hard plastic vacuum line that's routed around under the intake manifold. It might look OK at first glance, but the underside against the engine will be abraded/melted through. I just got a bunch from a junkyard and replaced the melted/abraded stuff on my car. The next place to look is at any "terminated" vacuum connections. Porsche standardized a lot of the intake parts over the whole 944 line, so depending on the version, you will have a couple vacuum connections that don't do anything, so they're capped off with a rubber cap and one of the lovely "Oetiker" single-use clamps. These caps crack apart with age and heat. Again, it might look OK, but if you squeeze it a bit you'll see that it's cracked through and crumbling apart.

Between the black plastic line and the rubber caps, I fixed all my 944's vacuum leaks.

Bryan

adrial

OK....thats it...all the vac line have got to go..

I sprayed the carb cleaner everywhere, even where the sound wasn't coming from (the AFM, maybe right under it?? but there are no vac lines under it!!). Sprayed it on the vac lines, the intake boot either side of the AFM (being careful to avoid the electrical/sensor part of it), everywhere I could think of that could be leaking...nothing. Is it possible that the AFM is leaking when a vacum is pulled on it, but not pressure applied?? I'm really at a loss...

So, on to the vac lines. I would expect that the silicon line would go inside the connections, same as the hard lined stuff...

So, how much and of what size do I need?? Any other special tools? (a crimper???).

thanks,
Adrial

pikey7

Adrial,

Sounds like I have the same problem as you! It even gets as bad as the car stalling as I let off the gas!

Does anyone know where I can order the hose tehniques stuff for delivery into sweden.... or order from europe somewhere???

RPG951S

Just another data point for you.
I had a very similar problem on a previous car. (not a 944).

Turned out to be a bad/slow O2 sensor.
Easy way to test it is to unplug the O2 sensor (don't worry, the DME will recognize that it is dead and simply ignore it), and see if the problem persists.

Another, easy way to check for leaks is to take half of an old fuel filter with the inlet/outlet nipple(just happens to be the right size), stick it into the intake boot and use a some compressed air to pressurize the intake system. You'd be amazed how many leaks I found this way

adrial

Raagi, while the bad/slow O2 sensor may be the reason that it drops to 800rpm and then recovers...that's definetely not why I can hear a huge hissing sound coming from under the hood.

I was thinking about the pressure testing thing...but I can hear it very distinctly when the engine is cold. It's loud enough that I can hear it with the hood closed and the roof off..from inside the car. With it as loud as that...I still can't find where its coming from!
I'll check if my mech has any old fuel filters lying around (I heard 944 and 84-89 911 will work).

thanks,
Adrial

RPG951S

&gt;&gt;Raagi, while the bad/slow O2 sensor may be the reason that it drops to 800rpm and then recovers...that's definetely not why I can hear a huge hissing sound coming from under the hood.

Doh! You mean your O2 sensor doesn't hiss loudly? Maybe that's the problem!

The good part about the pressurizing thing is that you can literally stick your head right in the engine area with no fear of losing some important body parts

Good Luck!

txhedg

I just replaced all my vac lines with hose from hose techniques. The sizing I used was the 3.5 ID thick walled hose. it fit perfectly over pop-off, fpr nipple, intake maif banjo bolt ,etc. I then used brass t-fittings from the hardware store to make the connections. it doesn't look like the 3.5 ID hose will fit over the brass fittings, but they will. I think I bought 15 ft, but used less than 10 ft (and 2 brass fittings)

hope that helps