91ZLS6

iTrader: (2)

May seem like the dumbest question ever heard,

Here's my deal,

My motor's been running like crap the last day, found a bunch of fowled plugs, figured id do a test to see what outcome i got.

So i hooked my compression gauge up, hit the ignition, counted 4 turns, and read my gauge, read 150psi. I figured it might be hurting, but not that bad.

I tried just holding the key to it to see how high it got, and it eventually reached up to 180psi.

Question here, is if im holding it open longer, am i just allowing it to keep piling up compression and giving myself an inaccurate reading?

it hits 175-180 and it doesnt go past there after i hold it over for 10-15 seconds.

Just looking for some clarification here to know whether my motor's fubar'd, or just lower compression

All help appreciated.

91ZLS6

iTrader: (2)

Here are my readings i got.

Kept the key over for 10 seconds:

1 - 170
2 - 175
3 - 175
4 - 180
5 - 180
6 - 178
7 - 170
8 - 170

So, im thinking the motor is hurting. I dont have a leakdown tester unfortunately.

WYD-01

iTrader: (2)

your readings look great. What you don't want to have is more than 20 % difference between any of the cylinders. You are within 20% with the readings you posted.
If you had 1 cylinder that read about 144 psi, then I would be worried. That would be about 20% below your highest reading.

A leakdown test is a completely different test. It will tell you where you arer losing your compression.

91ZLS6

iTrader: (2)

Exactly what i was looking to hear! Appreciate the help!

twitchtwice

iTrader: (12)

yeah what he said ^^

as long as they are all close to each other then there is nothing to worry about.

Gen414

iTrader: (38)

Next time you do one, don't do it for that long. Gonna burn starter up. All you need is a few turns of the motor. In the 3-4 sec range is all.

Also, make sure battery is strong. As a weak battery will turn motor over slow, and give you false readings

I also do test with all plugs out (to help starter out)

And as said, as long as all numbers are within range of one another, you are good to go (unless of course, they are ALL low ) Our motors (depending on compression, and cam, etc...) will make @ 160-190 cranking PSI

Kix

iTrader: (3)

Agreed... we always hook up a battery charger or boost pack to make sure we are cranking consistent speed during all cylinders.... and taking the plugs out is a great tip!

Old Geezer

iTrader: (3)

All plugs out, throttle blade blocked open, inj's unplugged, 4 "hits", read the gauge.

DaddySS

bczee

iTrader: (12)

Yes.. a fully charged battery is key, remove all of the plugs. Pull the fuse out for the Fuel pump and keep the throttle at WOT should give you the best readings. But 3-4 cranks should do it.