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Registered User
Join Date: Jan 2007
Location: Virginia
Posts: 56
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I am new to this forum and have an '89 930 I'm working on. I want to do a compression / leak down test on it. Can this be done without dropping the motor? If so, what needs to be removed to get to the plugs? Also, How do I check the turbo unit to make sure the it is working properly and in good shape?
Thanks, Todd |
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Registered User
Join Date: Jul 2004
Location: Burlington, ON
Posts: 605
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I've never performed a compression test/leakdown on my 930 personally, but I have changed the plugs. It can definitely be done with the engine in the car. The intercooler and air filter assembly have to come out.
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- '00 Dodge Viper GTS - Steel Grey - Yep...a domestic. - '87 930 - Guards Red - Sold - '82 911SC - Grand Prix White - Gone - '78 928 - Silver - Long gone - '04 Subaru WRX wagon - Sold |
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Registered User
Join Date: Jul 2005
Location: Columbus, OH
Posts: 650
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General consensus is that leakdown is the test to conduct. My understanding is that you get to opertating temp (important), shut down, pick a cylinder, pull the plug, rotate crank so that valves are closed on cylinder to be tested, insert tester and pressure up.
Turbo, you can check shaft play (axial and radial) from the exhaust, visually check for FOD and look for oil in the compressor housing.
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Maxx 86 Ruf'd and rebuilt (sold) |
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Registered User
Join Date: Mar 2002
Posts: 3,563
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If you suspect any internal engine wear, you should do a compression test first to identify any suspect cylinder which has a large difference in compression to the other cylinders. If there is one, then you do a leakdown test on that cylinder to ascertain whether it's leaking out the rings or valve(s).
My understanding is that if air is leaking back out through the intake, it's intake valve, if it's leaking out the exhaust, it's exhaust valve and if it's leaking back out through oil filler, then it's piston rings. Maybe some of the more experienced would chime in to verify this ![]()
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Merv '89 911 Turbo Cab Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition ![]() |
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Registered User
Join Date: Feb 2005
Location: Atlanta Metro
Posts: 219
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Quote:
You need to be sure that the cylinder you're testing is at TDC to get good data, and that the car is in gear and the wheels are well blocked - 100psi will move the piston down, and it will roll the car over your toes. Also, with a Porsche, they have a bad habit of dislodging carbon whenever you pull a plug, which then usually finds its way into the exhaust port. So, if you get a good exhaust hiss, it's wise to either go drive it a few miles and check it again, or if the motor is out of the car, hit the exhaust valve with a rubber mallet while it's pressurized to see if you can dislodge the carbon. Good Luck |
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