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MIGClub Member
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Compression Test

For this test you will need a compression gauge (available form Halfords for about £12)
A spark plug removal tool
Some engine oil

Firstly remove the fuse from the injection system. This is usually situated in the fuse box and is marked on the diagram on the back of the fuse box cover as "FI". Now start the engine, which will only run for a few seconds. Now remove the HT leads keeping note, of which are which. Next remove the spark plugs using the appropriate tool, making sure that no dirt is dropped into the bores.

Fit the compression tester to each bore one at a time. Each time, turn the engine over for at least 10 seconds, making a note of the pressure on the gauge. Typically you do not want a spread of more than one bar pressure (15psi), or a difference of 10% between the lowest and the highest bore pressure. If you have two adjacent bores with low pressure, this may be down to a damaged head gasket between them. If you suspect that one bore is reading low, add a teaspoon full of engine oil into the bore. This will help temporarily seal the bore and should yield a greater compression pressure. If this is the case, the engine may need new piston rings, honing or even a re-bore.

After checking, making sure everything is put back together correctly and that HT leads are connected in the correct order.
 
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