Help: Compression test

Post by **AshNazg** » Wed Jul 14, 2004 6:34 pm

Here's my problem:

I've got a 93 240sx, stock engine. It's been smoking. I did a compression test with a screw in compression meter and it came up around 160 psi... not bad. Took it in for a diagnostic on why it's smoking and they said their compression test came up around 80 psi.

Why are our numbers so different? Any special procedures I need to follow to check the compression on the car? I let the thing turn over like 7 times, they said they only did like 4 times. Are they just retarded?

Post by **pacman88** » Wed Jul 14, 2004 6:34 pm

You have to get the fuel pressure out b removing the fuse and let it run until it dies and hold the throttle @ WOT

Post by **AshNazg** » Wed Jul 14, 2004 6:34 pm

pacman88 wrote:You have to get the fuel pressure out b removing the fuse and let it run until it dies and hold the throttle @ WOT

wtf...?

never did a compression check like that in my life... u mean the fuse to the fuel pump? what's WOT? why would the throttle be involved if u'r just turning over the engine? sorry man i must be 100% lame

Post by **Hijacker** » Wed Jul 14, 2004 6:34 pm

pacman88 wrote:You have to get the fuel pressure out b removing the fuse and let it run until it dies and hold the throttle @ WOT

i've never done a comp test like that either. all i've ever done is disconnect the ignition and begin cranking.

what compression did all of your cylinders show?

Post by **DAEDALUS** » Wed Jul 14, 2004 6:34 pm

If you don't disconnect the pump and/or injectors, the fuel being squirted into the cylinders will wash away the oil from the oil ring and your compression drops. WOT = wide open throttle. The butterfly valve has to be open to let as much air in as possible. Also, all plugs have to be removed.

Post by **onosqv** » Wed Jul 14, 2004 6:34 pm

DAEDALUS wrote:If you don't disconnect the pump and/or injectors, the fuel being squirted into the cylinders will wash away the oil from the oil ring and your compression drops. WOT = wide open throttle. The butterfly valve has to be open to let as much air in as possible. Also, all plugs have to be removed.

Oops. I did mine w/ the throttle closed. I just let in crank 4 times. Got compression of 150psi each cylinder.

That's decent rite?

. Yes, i'm a thread jacker.

Post by **Nismo_Freak** » Wed Jul 14, 2004 6:34 pm

brokeAs240sx wrote:Oops. I did mine w/ the throttle closed. I just let in crank 4 times. Got compression of 150psi each cylinder.

That's decent rite? . Yes, i'm a thread jacker.

You might have good static compression, but you could have bad leakdown through the rings. If your car is smoking it's more than likely either the rings (if it smokes when you get on it), or it's the valve seals (if it smokes in puffs).

Post by **MidnightS14** » Wed Jul 14, 2004 6:34 pm

You do not have to pull the fuel pump fuse and let the car die......you could simply pull the plugs off the injectors. Doesn't matter if the system is pressurized...as long as the injectors don't fire sending fuel into the combustion chamber, you'll be fine....

I guess I'm lucky.....did my compression not two weeks ago and got 182 across the board...on a 120,000+ mile motor...

-Bill

Help: Compression test

Help: Compression test

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