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Old 09-22-2005, 11:56 PM   #1
anthonyrb98
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Default can compression test be done with accessport and antitheft mode?

i was just wondering if you can do a compression test with an accessport and antitheft mode (where the car won't start if you load the antitheft map)
to crank the engine without having to disconnect any fuses and such to disable spark and fuel.
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Old 09-23-2005, 11:33 AM   #2
Rick Schu
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The car has to crank in order to do the compression test. I've never used the anti-theft map, but I would imagine the starter won't even work at all.

You don't need to pull fuses - there is a green connector under the glovebox behind the ride side passenger kick panel. Disconnect this and then start the engine until it dies. Then crank for 5 more seconds.

You have to pull out ALL the spark plugs anyway for a compression test, even before testing the first cylinder. So, that means you have to pull out the coils anyway. That takes care of the ignition side.
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Old 09-23-2005, 12:02 PM   #3
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actually yes it should. i forget which on one of the two maps is better ...

i would pull the fuel pump fuse and let the car idel for a sec before hand but yes this is a fair idea

and yes the starter will work just fine
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Old 09-23-2005, 12:21 PM   #4
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I cannot reccomend using this map for a compresion test.

The best way to do this for a WRX is to disconnect the ECU, the fuel, Floor the throttle to let air in, and turn the car over.
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Old 09-23-2005, 01:02 PM   #5
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According to the Cobb website, the anti theft mode allows the car to idle. Once it goes over 1000 RPMs, the engine cuts out.
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Old 09-23-2005, 04:18 PM   #6
Rick Schu
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Quote:
Originally Posted by Corkfish
According to the Cobb website, the anti theft mode allows the car to idle. Once it goes over 1000 RPMs, the engine cuts out.
Well, if it lets it idle, then you still have fuel pressure. I think he wanted to use the anti-theft map instead of disconnecting the fuel pump relay. So, this doesn't help you at all.

Just disconnect the fuel pump relay and start it still it stalls and then crank for 5 more seconds - takes like a minute to do. You have to pull all the plugs anyways to get an accurate reading, even before you test the first cylinder - this means your coils will have to come out, so that takes care of your ignition. Hook up your gauge. Put the accelerator to the floor. Then crank for like 3 seconds. Repeat for the other cylinders.

Last edited by Rick Schu; 09-23-2005 at 04:24 PM.
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Old 09-23-2005, 04:41 PM   #7
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that's anti-theft map B

map A keeps the car from starting, period. I'm not sure if it simply closes the injectors/turns off the pump/sets the rev limit to 0.
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Old 09-23-2005, 08:00 PM   #8
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yeah, one of the antitheft maps will not allow the car to start, so i thought that would be sufficient as far as cranking the car without having to disconnect anything
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Old 09-24-2005, 12:32 PM   #9
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Quote:
Originally Posted by parker/slc/gc8fan
I cannot reccomend using this map for a compresion test.

The best way to do this for a WRX is to disconnect the ECU, the fuel, Floor the throttle to let air in, and turn the car over.

um since parker is a cobb employee
his post shold have ended this thread ...
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Old 09-24-2005, 01:30 PM   #10
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The other anti-theft map still uses a rev limiter - just set really low, so the car can't idle. That means some fuel pressure.
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Old 09-24-2005, 01:38 PM   #11
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The best way to do a compression test is to pull the "IGN" fuse from the underdash fuse box. This completely disables the ECU in one easy step so there will be no spark or fuel. Pulling the fuel pump relay plug is fine for depressurizing the fuel system, but the ECU will still be active when the engine is cranked and the coil packs will have power (although they won't be grounded if removed to pull the plugs). Also even with the fuel pump disconnected the injectors will still operate and there will be residual fuel injected into the cylinders which could affect the compression readings.
Pull the fuse, do test, replace fuse, done.
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Old 09-25-2005, 03:16 PM   #12
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Quote:
Originally Posted by Mulder
The best way to do a compression test is to pull the "IGN" fuse from the underdash fuse box. This completely disables the ECU in one easy step so there will be no spark or fuel. Pulling the fuel pump relay plug is fine for depressurizing the fuel system, but the ECU will still be active when the engine is cranked and the coil packs will have power (although they won't be grounded if removed to pull the plugs). Also even with the fuel pump disconnected the injectors will still operate and there will be residual fuel injected into the cylinders which could affect the compression readings.
Pull the fuse, do test, replace fuse, done.
How much residual fuel can there be if he cranks the engine until it stalls and then cranks for 5 more seconds? Not enough to affect a compression reading. Pulling the fuse would probably be a tad easier though.
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Old 09-25-2005, 04:05 PM   #13
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Probably not much fuel, but pulling the fuse will completely shut down the ECU so the injectors and coil packs will not be active at all.
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