Compression test procedure?
02-17-2006, 07:28 AM
#11
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Pulling the fuse for the fuel pump only stops the fuel pump . The injectors will still fire , and with pressure still in the line will put fuel into the cylinders or your eye because you have the plugs out . 
The easiest way is to just unplug the cam sensors this will not let the injectors fire .
You will have to reset the ecu when you are done , To get rid of possible codes you have triggered from unpluging the coils and sensors .
The easiest way is to just unplug the cam sensors this will not let the injectors fire .
You will have to reset the ecu when you are done , To get rid of possible codes you have triggered from unpluging the coils and sensors .
02-17-2006, 08:13 AM
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I have heard that it is not a good idea to leave the secondary side of the ignition coil(s) open circuited (left dangling in midair) while the primary side is getting excited by the CDI. An electrical engineer I went to school with (he's now a regional field engineer with Solar turbines) told me that open-circuiting the secondary side of a transformer (ignition coil) is the essentially the same as short-circuiting the primary side (infinite load). I'm a mechanical engineer with a lot of electrical experience. THis sounds reasonable, but . . .
But I have done just this myself many times w/o any apparent problems. I quit ignoring the warning until I noticed one detail that made me think. One of my jet skis has dummy terminals permanently attached to the engine block. When you need to run the starter w/o firing the engine, you remove the plug wires from the spark plugs and connect them to these grounding dummy terminals. Yamaha wants you to ground the coil while cranking only. So now on most engines I remove the plugs, set them back into their plug wires, and set the spark plugs ground electrode to rest on the engine block away from fuel. You can watch the plugs fire and verify spark, just don't touch the damn things or they will light you up like a Christmas tree. 50,000 volts!
Does anyone know for sure if you need to ground out the spark plug leads to the engine block or disable the ignition by pulling a fuse? Or does pulling the cam sensor leads disable the ignition as well as the injectors?
But I have done just this myself many times w/o any apparent problems. I quit ignoring the warning until I noticed one detail that made me think. One of my jet skis has dummy terminals permanently attached to the engine block. When you need to run the starter w/o firing the engine, you remove the plug wires from the spark plugs and connect them to these grounding dummy terminals. Yamaha wants you to ground the coil while cranking only. So now on most engines I remove the plugs, set them back into their plug wires, and set the spark plugs ground electrode to rest on the engine block away from fuel. You can watch the plugs fire and verify spark, just don't touch the damn things or they will light you up like a Christmas tree. 50,000 volts!
Does anyone know for sure if you need to ground out the spark plug leads to the engine block or disable the ignition by pulling a fuse? Or does pulling the cam sensor leads disable the ignition as well as the injectors?
02-21-2006, 11:57 AM
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You don't want the engine 'hot', just warm. Letting it idle until the car designates some progress on the coolant temp is usually sufficient.
Always use a screw in type compression tester. You shouldn't run your battery out testing 4 measely cylinders. It should only take 3-5 cranks to read maximum compression. I've done as many as 12 cylinders without killing the battery, though 11 and 12 we redid since the numbers were sliding off due to the strain on the battery [MB S600].
On my own cars, I never mess with the fuel unless I want 100% correct numbers, as the extra fuel can distort them a few percent. On other people's/customer's cars, I'll ask them and they usually say they don't care.
You shouldn't have to ground anything either.
Always use a screw in type compression tester. You shouldn't run your battery out testing 4 measely cylinders. It should only take 3-5 cranks to read maximum compression. I've done as many as 12 cylinders without killing the battery, though 11 and 12 we redid since the numbers were sliding off due to the strain on the battery [MB S600].
On my own cars, I never mess with the fuel unless I want 100% correct numbers, as the extra fuel can distort them a few percent. On other people's/customer's cars, I'll ask them and they usually say they don't care.
You shouldn't have to ground anything either.
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