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Eliminating more vacuum leaks - last ones???

 
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924RACR  



Joined: 29 Jul 2001
Posts: 8387
Location: Royal Oak, MI, USA

PostPosted: Thu Oct 13, 2005 11:07 pm    Post subject: Eliminating more vacuum leaks - last ones??? Reply with quote

I'll just say, if the car continues to run like it did on the way in to work this AM - I'm a very happy camper! Ran lovely, nice torque down low (2000rpm, off boost), no misfiring any more. But I'll have to keep driving it (oh darn! ) to be sure, these things in my experience have had a bad habit of popping back up.

Anyway, what I did. I already replaced all the stuff up top, all the bad vacuum lines, using a spool of 3mm silicon hose (I think from Jeg's or Summit) and a stack of 3/4" elbows cut to fit (from a turbo place or the like - can't remember).

What I hadn't done was deal with the boost sensing line from the intake to the compressor bypass valve (actually called by a different name I always forget on these cars - help me out here) on the front of the turbo. I had suspicions about it because I could hear the piston in the valve slapping back and forth on occasion at idle - possibly due to idle vacuum fluctuations - and I had a noticeable delay when transitioning from coasting to on-throttle, even on boost, to build boost and begin pulling. Like turbo lag, but when the turbo's already spooled.

So I went in after it.

The worst part to get at is the elbow down by the turbo, that connects to the valve. It's VERY tight in there, and I practically had to cut the old one off. I found that in order to really get this one off, I had to take the other end off the pipe, disconnect it all, etc.

So I removed the alternator. Then you can see and work on the top end of the sensing pipe. It's a hard metal pipe with one mounting tab on the front of the water pump (I removed the belt and water pump pulley for access). Remove that one 10mm bolt on the bottom of the water pump (don't worry about leaks unless you forget to replace it) and you'll be able to move the pipe. The top end of the pipe connects to the bottom side of the #1 cylinder intake manifold runner with a straight section of hose. This I did have to cut off to remove.

Once the upper piece of hose was removed, and the mounting tab bolt removed, I was able to wiggle the pipe up enough to pry the old lower elbow out.

Reassembly with new parts was the reverse. I installed the lower elbow first (mind you, this is normally not possible without removing the turbo, so this was worth all the sweating). Using the silicone hoses and elbows helped, I think, in installation, since they're tougher and more flexible too than rubber. They were able to put up with a little more prying action, whereas I suspect a rubber hose might have been punctured by a screwdriver or prybar in there somewhere.

After the lower hose was in place with clamps, I installed the upper section of hose, locating the pipe in place. I then reinstalled the mounting tab bolt into the water pump, torquing it down. Only then did I tighten all hose clamps. Then reinstalled the water pump pulley, alternator, and belt.

Took maybe 2 hrs, not a trivial job, but passable. A fair bit of swearing and persuading hoses, but not intensive on tools or technique IMO.

Very glad I did it, as mentioned above. I think these may have been (cross fingers) the last vacuum leak sources in the car. I mention it here so you can be aware where that plumbing goes, to attack it in your spare time...
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Vaughan Scott
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Tigger937  



Joined: 11 Apr 2004
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PostPosted: Fri Oct 14, 2005 2:54 am    Post subject: Re: Eliminating more vacuum leaks - last ones??? Reply with quote

Thanks for that detailed procedure. Yeah, sounds like that's the Pop-Off Valve. Mine was rattling a lot this past summer and I fixed it by making some custom gaskets to prevent the piston from ramming against the metal end caps. However, as you so well described, I may have just covered up a symptom. I've been suspecting that hose for leaks for some time now. Just wasn't convinced enough to put forth the effort to replace it. I think you just convinced me, however, I'm not looking forward to the pain and suffering. Your procedure will definitely help!

Can you describe for me the misfire you were getting? I, too, have had a misfire (high RPM) that has been plaguing me since I bought the car. Thanks again.
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924RACR  



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PostPosted: Fri Oct 14, 2005 3:26 am    Post subject: Reply with quote

The misfire was low engine speed only, not top end. When off-boost, it was like running on 3 cylinders, or boost lag and 6.5:1 compression ratio! I was an obstacle in traffic. Just absolutely nasty hesitation.

Put another 40 miles on it this AM (driving to the track), after driving 12 in to work. Still running beautifully, though I think I need to check the idle mixture and speed - probably off to compensate for the leaks. It also now has a much smoother idle (used to be cammy/lumpy) and doesn't drop badly anymore with the AC on.
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Vaughan Scott
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Tigger937  



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PostPosted: Fri Oct 14, 2005 4:00 am    Post subject: Reply with quote

Sounds like you nailed it! Kinda makes it all worth while after you fix it.

After your description of the symptoms, now I'm beginning to wonder if that's my problem. Mine runs nice up until 5700 RPM, then misfires. Doesn't matter if I'm on boost or not. Still, I may replace it anyway since that old rubber hose definitely looks deteriorated.
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924RACR  



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PostPosted: Fri Oct 14, 2005 4:41 am    Post subject: Reply with quote

Sure does!

For your situation, I'd wonder what shape the ignition system is in - tends to be harder to fire at higher revs/boost...
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Vaughan Scott
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Tigger937  



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PostPosted: Fri Oct 14, 2005 12:05 pm    Post subject: Reply with quote

Could be..................I'll have to check it out after I finish replacing the fuse/relay panels and get the car running again.
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Tigger937  



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PostPosted: Fri Oct 14, 2005 3:39 pm    Post subject: Reply with quote

I forgot to mention, my A/F gauge pegs out at 6 or 7 LED's max. So that has been leading me to think it is a fuel delivery related issue. It's only a NB O2 sensor hookup, but I would still think it should peg out at close to 10 LED's (corresponding to A/F=11 or 12:1)? This is what led me to the fuse/relay panel and associated wiring. I've found several wires associated with the fuel pump circuit that show evidence of overheating/corrosion possibly leading to low system fuel pressure.
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924RACR  



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PostPosted: Fri Oct 14, 2005 11:08 pm    Post subject: Reply with quote

That certainly won't help. Also make sure your connection for the flywheel sensor is good and clean, no corrosion. Mine used to have some, I cleaned it off, now it's touchy again (engine stumbles when I reach down and wiggle the connector) and I suspect I may have some more corrosion to be cleaned off and sealed against further such with some dielectric grease.

To follow up on the above, my source for the silicon hose elbows was Racer Parts Wholesale (www.racerpartswholesale.com). Their 19mm/.075" 90 degree hose elbows are $15 each. They also come with extra lengths on the straights, which you need to trim to fit. I then used those extra bits to replace straight sections of vacuum hose that needed replacing, like at the Aux Air Regulator.

Now, the bad news. Car ran great all yesterday, even in the evening after a bath - took it up the street to hang with the 928 club guys... nice guys, always friendly, and they checked the car our... anyway, so my wife even drove it home and - hell, she could tell on the way there that it was so much better. She thought I was driving smoothly! She drove it home and said finally, this I could drive! Much more civilized.

Drove it again to work this AM. As I get close to my exit... I notice the off-boost missing is back.

Apparently it needs more attention. I don't know if a hose clamp worked its way loose, or what. But something I messed with was better, then crapped out again. Argh! Still have to put another 90 miles on it today (usually manage around 100/day), we'll see what it does, but I guess I'll pencil in a little time this weekend, after F1, to try and get it back where it should be.

Hey, on the bright side, at least it did run right for 24 hrs (for the first time since I bought it years ago)! Surely if I can make it run right for a little while, I can get it back there permanently...
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924RACR  



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PostPosted: Fri Oct 14, 2005 11:11 pm    Post subject: Reply with quote

Link to the hoses:
Hose elbows:
http://www.racerpartswholesale.com/silhose3.htm

coil of 3mm hose (in pretty colors!):
http://www.jegs.com/webapp/wcs/stores/servlet/CategoryDisplay?lang=-1&catalogId=10002&storeId=10001&categoryId=18839
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Tigger937  



Joined: 11 Apr 2004
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PostPosted: Sat Oct 15, 2005 12:56 am    Post subject: Reply with quote

924RACR wrote:
That certainly won't help. Also make sure your connection for the flywheel sensor is good and clean, no corrosion. Mine used to have some, I cleaned it off, now it's touchy again (engine stumbles when I reach down and wiggle the connector) and I suspect I may have some more corrosion to be cleaned off and sealed against further such with some dielectric grease.


Yeah, I'll certainly check that connection out. Thanks for the headsup.

Maybe that bad connection is contributing to your problem. Makes me wonder what condition the rest of the cable is like. It gets bloody hot down there by the sensor. Check out www.EagleDay.com for replacement connectors. I think they have the connector and pins for the flywheel sensor cable.

Thanks for that link on the hoses too.

You had it cured for 24 hours, so one would think it's related to something you fiddled with.

Then again, vaccuum leaks can affect other things too, most notibly the fuel system since with CIS, air and fuel metering are so intertwined with each other. By plugging up an air leak in a supposedly "closed" system, you just changed the operating point, so that could put additional strain on a borderline fuel system component. Or, maybe the A/F mixture just needs to be readjusted now to compensate for the leak that you just fixed, especially if you adjusted it prior to fixing the leak. But, I wouldn't go off on this tangent until you've verified that everythng you've just repaired is working properly. Just brainstorming here.

Another source for vaccuum leaks that I've found in the past is the vaccuum hose to brake booster connection. Not a real good connection. I wish they had a male fitting welded to the brake booster to plug the hose on to instead of that plastic adaptor that pushes into a rubber grommet. Mine was leaking at this junction and it caused poor idling, especially when the engine was cold.
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924RACR  



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PostPosted: Sat Oct 15, 2005 2:58 am    Post subject: Reply with quote

Just put another 40 miles on the car; wasn't happy when we started out, but cleared up and was happy again (I won't call it "normal" - yet!)...

You're right, though, gotta rework with the operating points...
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Tigger937  



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PostPosted: Tue Oct 18, 2005 3:13 am    Post subject: Reply with quote

924RACR wrote:
Sure does!

For your situation, I'd wonder what shape the ignition system is in - tends to be harder to fire at higher revs/boost...


Your comment inspired me to do a quick check again on my plug wires and to my surprise, I found evidence of arcing between the #4 plug wire and spark plug tip, ie., inside the metal shroud that fits over the plug. Lots of residue. Looks like the spring inside completely disintigrated. I'm using NGK resistor plugs and it appears the threaded tops are not the correct diameter, ie., too small. Maybe this is contributing to my high RPM misfire. Also, I'm not too sure whether the NGK brand is proper for a 931. I recall some time ago, someone told me to use ND's.
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scotchw  



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PostPosted: Tue Oct 18, 2005 10:21 am    Post subject: Re: Eliminating more vacuum leaks - last ones??? Reply with quote

924RACR wrote:
What I hadn't done was deal with the boost sensing line from the intake to the compressor bypass valve on the front of the turbo. I had suspicions about it because I could hear the piston in the valve slapping back and forth on occasion at idle - possibly due to idle vacuum fluctuations...

So Vaughan - did all that work on the recirc valve vac control line cure the valve rattling-at-idle?? And was the rubber elbow down at the turbo badly split?

I ask because my car also has "the rattles" at [hot] idle & I don't want to take-on the elbow replacement unless it cures the symptom!

Incidentally, my car idled badly due to a vac leak on the small vac line that leaves the throttle body & goes down & under the TB to connect to the decel valve etc. - it had split just as it left the TB 'connector'. Now it idles fine when warm, although its still a little rough when cold (AAF to be investigated!).
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924RACR  



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PostPosted: Wed Oct 19, 2005 12:44 am    Post subject: Reply with quote

Yes, I haven't heard any rattling since. Yes, the one elbow was badly split - I knew this from when I installed the turbo - should've done it then. But I'd replace it anyway, even if it didn't look bad, but was just old.
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Wagdog  



Joined: 26 Jul 2020
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Location: Victoria,Australia

PostPosted: Tue Dec 01, 2020 9:28 pm    Post subject: Reply with quote

Thanks for the writeup. It helped me a lot. I have just replaced these connectors with silicone, having done the timing belt so access was not too bad. I also disconnected the lower radiator hose and the waterpump forward transfer hose. I fitted the turbo end first, starting with the pop off valve nipple. I was not able to fit the elbow with the hose clips loose on the hose so I opened up the clips and threaded them around after installation. I lubricated the hoses with WD40 and used wooden paint stirrers as well as screw drivers to push and prod the hoses into position. I also positioned wooden packers at the manifold end to steady the hard pipe during the process. I found the procedure difficult and it all took me several afternoons ( my hands arent as strong as they used to be). The rubber bits I removed both looked OK - replacement was a precautionary measure.
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