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Gtr Compression Question

GTR.Lady
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GTR.Lady Rising Star

GTR.Lady

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Hi,

I just have a question regarding my R32 GTR (RB26dett).

I did a compression test on it today and these are the figures I got:

1 - 160 2 - 155 3 - 165 4 - 160 5 - 150 6 - 55 (YES 55 psi)

Now, car is running perfect, never misses, Idles great, gets up to speeds great.

Sparks plugs are perfect colour, NO oil on spark plugs, not leaning out or running rich.

I pured 500ml (a lot, I know) of oil on top of the piston, it held the oil but the compression test showed it was 260psi (with the oil in there), I then started the car and let the oil burn off, once that was done I did the compression and it was 150, I was like wtfff, so I re-done it and again 150 ... The only thing I did different was I connected jumper cables from another running car as the battery died while doing the compression test on cylinder 5, after jump starting it, I continued on number 6 and got the reading 55 but when I did it the second time, I had the cables still connected and got 150 ...

Another test I did was I disconnected number 6 while the car was running to see if it would sound different on Idle, it dropped a cylinder which proved cylinder 6 was firing etc. The car revs fine and doesn't missfire all the way to redline ...

A few theories went through my head -

Sticky valve - but if it was stuck open, there shouldn't of been any compression in the cylinder.

Low voltage as the battery died while doing the other cyliders, so I jump started it and did number 6.

OR it could be something more serious ... ALL opinions welcome PLEASE !

What do you think?

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GTR.Lady Rising Star

GTR.Lady

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Posted (edited)
If the battery died doing #5, how did you test #6 initially?

Sounds like you did it with a flat/near flat battery, which would explain the result.

Woops, I worded that wrong, sorry ...

How I did number 6 was I connected the jumper cables and did it ... which the result was 55 ...

BUT then I re-did the test after I actually started the car, let it run to burn off the oil and then re-did the test, it was 150 ...

A few people told me the battery wouldn't effect the compression? ...

Edited by GTR.Lady

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