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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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 Posted: Wed Sep 07, 2005 5:58 pm Post subject: Vacuum Test Gauge |
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I now have a Vacuum Test Gauge & want to start using it to check for leaks etc. Where would be a good spot to connect the test gauge based on this diagram of my vacuum setup
Also, I recall seeing something about being able to set the timing using a vacuum gauge. Can anyone explain how I can use the test gauge to do that?
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TJ
Silver '82 924 NA 5-Speed Manual |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Thu Sep 08, 2005 6:53 am Post subject: |
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Thanks for the links leadfoot.
| Quote: | | Connection of the gauge is to a simple "manifold" vacuum source |
If I understand that correctly, using my vacuum diagram, I shouldn't use the small line that runs off the throttle body, but rather one of the 2 lines thats run off the back of the Intake Manifold (one runs to the vacuum limiter off the "Y" piece & the other runs to the brake booster & intake boot). Is that right?
If so, it seems to me that the line to the vacuum limiter would be the easier one to put a temporary t-piece on for testing. Would that work? I'd rather not mess with that brake booster line unless I have to!
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TJ
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augidog
Joined: 03 Mar 2003
Posts: 1360
Location: New Jersey
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| Posted: Thu Sep 08, 2005 11:00 am Post subject: |
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To set your timing.
Turn the distrib to reach the highest vacuum then turn it back 1 lb to get within 1 degree of your correct timing.Vacuum lines disconnected.
This way of timing the engine is set to the actual engine wear and tear and performance and may not reflect the oem spec's.
I found it to be usually more advanced than oem spec.
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1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work. |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Thu Sep 08, 2005 5:56 pm Post subject: |
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Any line that's post throttle plate will work fine, the one coming off the throttle body should be post throttle plate too but a source that is direct from manifold such as you suggested (between Y join and limiter) would be better as less likely to have vaccum variances.
If you have a stock cam and no leaks you should see a base value of around 18-20Hg ,could be more or less due to engine wear/timing/leaks.
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Sun Sep 11, 2005 5:53 pm Post subject: |
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Got the vacuum gauge hooked up today after removing & plugging all the lines from the decel valve as I suspect it isn't working properly.
At idle I can get a maximum reading of around 17.5 inHg when I adjust the distributor & I have taken it back to around 16.5 for normal running. I have found the needle drifts slowly between the 16.5 & 15.5 & never actually sits steady. The drop cooincides with a slight pop from the exhaust.
If I increase the revs the vacuum drops, then rises again & if I give it alot of throttle it will drop to 0 then up to around 25 then settle back to the 16.5 mark.
Would that be normal behaviour as it is only a small drop (1 inHg), or is it likely to be something else like a vacuum leak (as I can't get it to the 18 to 20 inHG range), plug gap etc
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TJ
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Sun Sep 11, 2005 6:23 pm Post subject: |
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Sounds about right, but you might have a combination of a couple of things,
Weak spark, if your spark plugs haven't been gapped properly or are nearing the end of their lives, this can account for around 1Hg I've found and helps steady out the "lumpyness"
slight timing or valve tappet adjustment needed
Wearing of the valve seats/valves
My main problem used to be around the throttle body, only cause I used to take it off and not use gasket sealer when replacing.
Also have you checked the battery charge from the alternator, as this can have an effect on vaccum/engine performance, should be 14.0Volts at idle or your belt might need tightening/replacing.
If you have a bad vaccum leak then when at WOT you will only somewhere around 2Hg-1Hg, a good sealing system will get almost to 0Hg which it seems you have.
Leadfoot
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Sun Sep 11, 2005 7:32 pm Post subject: |
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| leadfoot wrote: | | Weak spark, if your spark plugs haven't been gapped properly or are nearing the end of their lives, this can account for around 1Hg I've found and helps steady out the "lumpyness" |
Plugs are about 1 year old. I never checked the gap when I got the plugs & just assumed they'd be correct. Correct gap is 0.7 mm, is that correct?
| leadfoot wrote: | | Also have you checked the battery charge from the alternator, as this can have an effect on vaccum/engine performance, should be 14.0Volts at idle or your belt might need tightening/replacing |
Battery is new & the charge at idle with no load is very close to 14v
| leadfoot wrote: | slight timing or valve tappet adjustment needed
Wearing of the valve seats/valves |
If I move the distributor around I can get to about 17.5 inHg max. I backed the timing off 1 inHg from this so now I have about 16.5 inHg. Not sure if there is enough movement in the readings to indicate valve problems or not. Guess I probably should tackle the tappet adjustment at some stage.
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TJ
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sun Sep 11, 2005 10:53 pm Post subject: |
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| Your valves are fine, a leaking valve or broken spring will cause a violent flickering of the needle. |
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leadfoot
Joined: 11 Dec 2002
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Location: gOLD cOAST Australia
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| Posted: Mon Sep 12, 2005 9:12 pm Post subject: |
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Spark gap is correct 0.7mm, for bosch UK models
just pull the number four cylinder spark plug and check for wear as it cops it the most... if you haven't done many Km's then I think this is where you can draw a baseline for further testing.
If you've set timing correctly with a tming light and RPM analyser then the only other big difference to vaccum will be made in the fuel mixture settings.
Looks like you've got a healthy engine.
Leadfoot
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carbon fiber GT mish mash
LS1 conversion in progress... |
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Mon Sep 12, 2005 10:04 pm Post subject: |
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| leadfoot wrote: | Spark gap is correct 0.7mm, for bosch UK models
just pull the number four cylinder spark plug and check for wear as it cops it the most... if you haven't done many Km's then I think this is where you can draw a baseline for further testing |
Done about 4000km since I got the car a little over 12 months ago. 3000 of that has been done in about last 4 to 6 months. 126000km total on the (working) odometer.
| leadfoot wrote: | | Looks like you've got a healthy engine |
Except for the difficult hot & cold start (which I think is the WUR) & the "jerky" ride when cruising, particularly at around 60kph in 3rd.
After my initial observations posted here I reconnected the decel valve & found I lost 2 inHg vacuum. Faulty decel valve or is that normal? I have now left the decel valve disconnected & all the lines plugged (old sparkplugs can come in very handy) & zip-tied down. Still hard to start hot or cold, but I think much less jerkiness while crusing (the car that is, I'm still just as jerky - hey, I'm driving a Porsche  ). I'll leave it for a few days to make sure, but my current thinking is definitely faulty decel valve.
Oh, the other thing I did do was get a 3' ground cable & ran it from the engine block to where the battery ground cable goes. I took off the old ground cable that ran from the block to the coil mounting bolt.
Now wondering if I should look at taking out the vacuum valve & AAV as well. Would simplify the vacuum setup a lot, but not sure how the fuel tank would vent. Maybe take out the charcoal canister as well & let it vent to the air? That would just leave the crankcase breather, brake booster & distributor (which is actually capped & has NO vacuum advance on the stock Aus setup - don't know why - I just connected a line to it a month or so ago, so that one could probably come off as well).
Would it be worth "playing" with the mixture after I check the plugs, or should I check the fuel pressure & injector spray patterns before I touch that?
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TJ
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leadfoot
Joined: 11 Dec 2002
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Location: gOLD cOAST Australia
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| Posted: Wed Sep 14, 2005 5:29 pm Post subject: |
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4000KM is a fair distance to travel, I normally do my engine oil changes and at 5000kms... I at least inspect the plugs and see if wear and tear is enough to warrant a change.
Not sure about the operation of the decel valve cause I've never had one....
I'd leave the AAV in cause it will upset the air/fuel mixtures at start up if you remove it.... It would make your mixture way too rich at start up and probably end up fouling the plugs. Check yours for a black powdery coating if this is the case... Otherwise if they look whiteish then suspect running lean.... if they look grey then things should be fine and your spray pattern is probably fine too. If you get the energy and want to pull the injectors to confirm this after it might ease your mind.
As for adjusting the mixtures, there are ways that you can do it without testing equipment, but I'd just rock on down to the mechanics and let them do it, it will be far more accurate, but by all means do aquantitive system test and a pressure test if you've got the tools.
The jerkiness can be attributed to mixtures settings amongst other things but tackle the mixture settings first and see if it goes away.
Not sure why your distributor doesn't have vaccum advance, I would suspect it should and I'd leave it on and I'd leave the charcoal cannister connected to.
In respect to hot start, do you have the supplementary solenoid thats attached to the underside of the fuel distributor?? This is what adjusts control pressure for warm starts.
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Thu Sep 15, 2005 8:35 am Post subject: |
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| leadfoot wrote: | | Not sure why your distributor doesn't have vaccum advance, I would suspect it should and I'd leave it on... |
It appears that Aus delivered cars (82 at least, haven't checked other years) had no vacuum advance on the distributor as the vacuum advance port was actually capped. The cap is shown in PET as an Aus-only part.
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TJ
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Thu Sep 15, 2005 12:01 pm Post subject: |
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Do you have DITC ignition or something else?? I wonder if the dissy was maybe recurved or the flyweights are different as well?? Did you notice any extra power belo 3000RPM when you hooked up the vaccum advance??
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Thu Sep 15, 2005 6:33 pm Post subject: |
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| leadfoot wrote: | | Do you have DITC ignition or something else |
Definitely not DITC
| leadfoot wrote: | | Did you notice any extra power belo 3000RPM when you hooked up the vaccum advance |
Nothing noticable
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TJ
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