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10 Hg Vacuum, Running Rich?
Topic Started: Sep 13 2012, 07:51 PM (851 Views)
cnshealy
New Member
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I have a 98 chevy metro 3 cy 5 sp. I did a compression test and everything was good. I don't see any vacuum line leaks. Power is down and mileage has dropped to 38 mpg. Are there any other things that can cause a loss of vacuum on this motor? Any suggestions will be appreciated. Thanks.
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evmetro


Blocked cat.
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evmetro


If it is your cat, you can get down on the ground and kick or slap it to see if it rattles, if you are not already hearing rattling sounds when you take off. Sounds kinda like a loose heat shield when it rattles.
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cnshealy
New Member
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It is not a blocked cat. It came apart about 10,000 miles ago and was gutted.
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Memphis metro


Check your timing belt and marks. What do you call good compression numbers>?
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evmetro


I like to to spray starting fluid around the manifold and vaccum lines to check for leaks, but i suppose with the fire hazzard that this presents, I will not suggest this...
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evmetro


If your cat was gutted, was it because it was coming apart? If so, some of that crap could have blown downstream and plugged the resonator or the muffler.
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cnshealy
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Compression numbers were all around 180. Cat did break apart. I can see through the resonator but I can't varify the muffler is good.
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Memphis metro


With compression numbers that high the vaccum numbers should normal as well. Not only will an exhaust restriction cause issues but a intake restriction can as well.
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iamgeo
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Big League

My '98 just started to throw a P0400 code the other day. Yesterday it was idling like crap and the vacuum gauge was at about 10hg and the needle was bouncing around, it was at just over 800 rpm. Give it a little gas and it smoothed right up. Looked under the hood and the EGR valve was fully pushed back. After I made a few deliveries it "fixed" itself. Although it still keeps throwing the code after I clear it.
I have a vacuum gauge and a scangauge ll. That's how I know the CEL code and am able to clear it.
Is yours doing anything I just described?
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fritzgeo
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This could be your problem, check your fuel filter out see if she is gunked up, she could not be getting enough fuel into her, another thing to check for is your IAC(Idle Air control Valve) Or your Fast Idle Air Control valve. Look down your throttle body and see if its dirty! Whens the Last time you replaced your PCV Valve or spark plugs and wires? BTW if it turns out to be your fuel filter! your going to need to goto Oriley Auto to get it and its part number 33824 for a Wix filter if its the small skinny size.

BTW if it was the Cat and if it was block the engine would of cut off. The best way to test the CAT is to remove the two bolts from the exhaust manifold and drop it and see if she runs better RPM or drop those bolts off and shake it and listen for rattles. Rarely its your CaT.

But check all that and check your spark gap for .40 or 1.0mm
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evmetro


Maybe a rat was sleeping in you intake duct when you started it up.
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cnshealy
New Member
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I have a scanguage II and it gets a P0400 code occasionally. The egr valve opens and closes as it is supposed to. I have cleaned the egr valve and passage ways recently. I don't think my metro has a fuel filter. I think chevrolet removed the filter when it took over in 1998. I am gonna replace all vacuum lines this weekend just to be sure that is not my problem.
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Shinrin
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you can drop the exhaust from the manifold, two bolts, and see if the vacuum improves any. It'll run loud as crap, but you should be able to tell a difference if the problem is without the exhaust system.
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mwebb
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FOG

flutter in the intake vacuum at idle always equals
valve train problem

restricted exhaust should not cause flutter

10" of vacuum at idle with flutter
with correct cam and base ign timing and
compression of 180 psi on all cylinders is not plausible .

place a dollar bill over the tail pipe when idling
if the dollar bill is always puffed away , you are not misfiring
if the dollar bill gets sucked into the tail pipe
regularly
there is misfire and i would bet one valve never opens or compression values above are
not correct

compression is useless anyway
post cylinder leak down values
Edited by mwebb, Sep 15 2012, 09:40 PM.
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