Silly question about compression tests...

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jonahnaylor
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Silly question about compression tests...

Post by jonahnaylor » Tue Oct 08, 2013 5:13 pm

Hi this may seem like a ridiculous question, but my MGB has an immobiliser fitted which I've not seen on anyone else's cars and has no model no, or brand etc.

Do to this being wired to the coil and the wiring loom wired to the immobiliser I just wanted to check if I need to disconnect any of this when doing a compression check? Or can I simply immobilise the car, hook up the gauge in the place of a spark plug and turnover the car?

Thanks for any help.
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jonahnaylor
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Re: Silly question about compression tests...

Post by jonahnaylor » Fri Oct 11, 2013 8:09 pm

Today I used my MBG's immobiliser to do my compression tests and can confirm this works great - no need to disconnect any wires or connections.

These results are with a warmed up engine and closed throttle.

Here are photos of my 4 cylinders' results...
20131011_190107.jpg
Number 4
20131011_190107.jpg (141.64 KiB) Viewed 5504 times
20131011_185826.jpg
Number 3
20131011_185826.jpg (137.58 KiB) Viewed 5504 times
20131011_185445.jpg
Number 2
20131011_185445.jpg (132.66 KiB) Viewed 5504 times
20131011_185218.jpg
Number 1
20131011_185218.jpg (130.62 KiB) Viewed 5504 times
Does anyone know if these readings are good/bad/normal? Thanks
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oily-hands
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Re: Silly question about compression tests...

Post by oily-hands » Sat Oct 12, 2013 8:05 am

Generally speaking, if the lowest is within 10% of the highest, it's good to go.

How does the car run?
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jonahnaylor
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Re: Silly question about compression tests...

Post by jonahnaylor » Sat Oct 12, 2013 9:00 am

Generally it runs very well but I've recently noticed the ocassional misfire in 3rd and 4th gears. But it's very intermittent and some runs out are smooth, and the problem disappears again. I've not seen any smoke from the exhaust so I'm inclined to think it's more to do with mixture settings. I wanted to check compression though as I've never done it before and also occasionally spark plug 3 can be a little wet.
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jonahnaylor
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Re: Silly question about compression tests...

Post by jonahnaylor » Sun Oct 13, 2013 12:05 pm

Just to posting further results. I went back out and took the compression tests this time with the accelerator fully depressed which boosted the readings quite a bit.
mgb_compression_test_cylinder1.jpg
MGB Compression Check Cylinder 1
mgb_compression_test_cylinder1.jpg (59.07 KiB) Viewed 5497 times
mgb_compression_test_cylinder2.jpg
MGB Compression Check Cylinder 2
mgb_compression_test_cylinder2.jpg (54.29 KiB) Viewed 5497 times
mgb_compression_test_cylinder3.jpg
MGB Compression Check Cylinder 3
mgb_compression_test_cylinder3.jpg (46.7 KiB) Viewed 5497 times
mgb_compression_test_cylinder4.jpg
MGB Compression Check Cylinder 4
mgb_compression_test_cylinder4.jpg (48.12 KiB) Viewed 5497 times
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