Low Engine Compression And Injectors Related?

[Darren83]

Hey guys , recently i dynoed my car and after the dyno, i did a engine compression test and the numbers were pretty bad compared to 2 years ago ~ which was around 130 across all 5 cyclinders except for the 2nd cyclinder which is 100. But after adding some oil on the 2nd cyclinder, the compression on the 2nd cyclinder immediately jumped back up to 125 psi. So they concluded that the injector in the 2nd cyclinder is faulty. But after asking few other workshops, they are saying injectors and low compression rates are unrelated..

any ideas guys ?

Thanks

[r33_racer]

injectors are before the valves. The oil let the loose rings in cyl2 seal better which bumped up the compression, temporarily. If they added oil to the other cylinders they more then likely would have jumped up much the same, so across the board would have been something like 155.

[Abo Bob]

Surely all the oil is doing is sealing the rings better which means that's what's no good in that cylinder. If the test with oil didn't go up then you would be looking at valves. That's my theory anyway.

[Darren83]

  Abo Bob said:

Surely all the oil is doing is sealing the rings better which means that's what's no good in that cylinder. If the test with oil didn't go up then you would be looking at valves. That's my theory anyway.

thanks for the replies guys, so is it safe to say its unrelated and irregardless if the injector is faulty or not adding oil will bump the compression readings up ?

[wrxhoon]

  Darren83 said:

thanks for the replies guys, so is it safe to say its unrelated and irregardless if the injector is faulty or not adding oil will bump the compression readings up ?

Unrelated with injectors mate .

You are correct abo .

If a little amount of oil increases comp it means rings and or bore worn but don't forget a substantial amount will increase comp because the combustion chamber is smaller because of the oil . In a low comp cyl if puting oil in to it doesn't increase comp it means the valves are leaking.

Do a leakdown test as well.

[mattymagoo22]

leakdown test is the best test to do.

Remove the sparkplugs, remove the intake and oil cap do your test. if its intake valves and there is reasonable leakage you'll hear/feel it coming out the intake, same for exhaust if its piston/rings you'll hear/feel it coming out the oil cap. just make sure that each cylinder is firing TDC (top dead centre).

Its a good idea to turn the motor over a few times once spark plugs are removed just incase theres any foreign matter between the valve and the seat which will give a false reading.

[Darren83]

  mattymagoo22 said:

leakdown test is the best test to do.

Remove the sparkplugs, remove the intake and oil cap do your test. if its intake valves and there is reasonable leakage you'll hear/feel it coming out the intake, same for exhaust if its piston/rings you'll hear/feel it coming out the oil cap. just make sure that each cylinder is firing TDC (top dead centre).

Its a good idea to turn the motor over a few times once spark plugs are removed just incase theres any foreign matter between the valve and the seat which will give a false reading.

Thanks guys for the replies, im sending my car in for the leakdown test tommorow. Will see how it goes and check out what is the problem

Cheers

[Darren83]

  Darren83 said:

Thanks guys for the replies, im sending my car in for the leakdown test tommorow. Will see how it goes and check out what is the problem

Cheers

HEy guys, got my leak down test and compression test done today. results were

Compression test Leak down test

cyc 1 : 155 10%

cyc 2: 155 20%

cyc3 : 155 5%

cyc4: 153 5%

cyc 5 : 150 5%

cyc 6 : 151 5%

looks like all went well and will be proceeding to the next mods

Thanks for the feedbacks

[wrxhoon]

  Darren83 said:

HEy guys, got my leak down test and compression test done today. results were

Compression test Leak down test

cyc 1 : 155 10%

cyc 2: 155 20%

cyc3 : 155 5%

cyc4: 153 5%

cyc 5 : 150 5%

cyc 6 : 151 5%

looks like all went well and will be proceeding to the next mods

Thanks for the feedbacks

That indicates bore and or ring wear on number 2. and to a lesser extend in number 1 as well .