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Engine removed - when to put spark plugs?


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7 replies to this topic

#1 bearbalu

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Posted 22 December 2004 - 12:25 AM

My legacy 98 outback engine is out. Haynes manual says:

a) Install engine
B) "With the spark plugs out of the engine and the coil electrical connector (low voltage unplugged), crank the engine over until oil pressure registers on guage"

c) Install spark plugs, hook up plug wires, reconnect coil and fuel pump

I have a few questions:

1. Why spark plugs have to be out in B) above ? - they are pain to install with the engine in the car. If intent is to avoid a spark, can't I just unplug the spark plug wires or the coil connector to prevent sparking?

2. What does "low voltage" in B) above mean?

3. Oil pressure in B) would register on which gauge? I don't have an oil pressure gauge on dashboard...

#2 shimonmor

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Posted 22 December 2004 - 12:47 AM

Well, I think they are getting at priming the oil system. Spark plugs out so engine doesn't start AND to reduce compression so it turns over easier. They are probably assuming you have a mechanical oil pressure temporarily attached to the engine so you can confirm oil pressure. The low voltage thing is the wiring going into the coil so that it doesn't produce an output spark to the spark plugs.

You can also crank until the oil pressure light goes out and you could leave the plugs in as long as fuel or spark doesn't get into the cylinders.

#3 Setright

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Posted 22 December 2004 - 11:00 AM

Yeah, just keep the plug wires off. The starter can handle the compression.

#4 Phillip

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Posted 22 December 2004 - 01:08 PM

If you decide to crank the engine with the plug wires off, be sure to ground them. In addition to the danger of fire, high voltage arcing can damage electronic components. Personally, On a fresh engine, I'd fill the oil filter and engine with oil, and start it. I'm not saying immediate oil pressure is not a good thing, but assuming everything was lubricated properly during the assembly process, critical load components (crank shaft bearing, valve train, etc) have sufficient protection to run until long after oil pressure builds (a few seconds).

#5 Setright

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Posted 23 December 2004 - 01:47 AM

Oh yeah, that's a good point!

Disconnect the crank sensor and the engine won't fire. Leave the plug wires on the plugs.

#6 bearbalu

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Posted 23 December 2004 - 03:32 AM

I was thinking of leaving the connector that goes to the coil unconnected, but keep the wires plugged. Would that work?

That way I don't have to worry about high voltage coil.

Is crank shaft sensor another option? You are saying keep coil connected, but just disconnect crank shaft sensor?

I just redid the head gasket, lubricated camshaft bearings with assembly lube - that's the only point that was exposed...

#7 Setright

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Posted 27 December 2004 - 04:11 AM

If the ECU doesn't register the crank signal it won't activate the ignition system.

If your crankshaft hasn't been out, then there is probably little reason to worry.

#8 bearbalu

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Posted 02 January 2005 - 02:52 AM

Thanks.

I just unplugged the connector on ignition coil and put the plugs in before putting the engine back in. Worked fine.




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