Compression numbers/help...

Godslayer · 05-12-2002, 06:56 PM

I did a compression test on my car today and everything looks ok but I'd like opinions.

First some background: 86 GT with 172k on the body. Supposedly prior owner swapped in this 20k motor.

1 147
2 150
3 147
4 150
5 147
6 147
7 147
8 143

These are the dry numbers. I wanted to do a wet test but couldn't find the damn oil can

I tried to use a turkey baster to get some oil in there but that was futile

I was happy with the consistency. What are the numbers for a fresh motor?

Also this may seem a bit odd, but I have to ask. When I did the test, all the cylinders on the left side bled down after I stopped cranking. On the right side they all remained at their peak values until I manually released the pressure. Any ideas? Thanks.

Bob

Unit 5302 · 05-12-2002, 07:18 PM

I think your gauge is leaking. It shouldn't matter if you pull the thing out before you hit the release. Pressure should hold steady internally. I think those numbers look good to me. Everything seems to be very consistant.

USMC302 · 05-13-2002, 12:25 PM

Sounds like bad rings..It leaked before you manually let it? Then that is the compression reading, all of mine help good compression until released. it could also be a bad or start of a bad head gasket. Good luck

Godslayer · 05-13-2002, 02:18 PM

USMC: I didn't post this but it's worth noting. When i first did the left side I forgot to block the throttle open. With the throttle plate closed the compression did not bleed off. Only when I did the test with the throttle plate fully open dd the compression bleed off.... ???

USMC302 · 05-13-2002, 02:25 PM

When I did mine I had the trottle plate wide open and it didn't bleed off on either side. Is your car running good or no? Maybe that was my problem with the GT i tested, it wasn't running well, but had outstanding compression throughout the cylinders and did not bleed out. The GT isn't running worth a crap though....

Godslayer · 05-13-2002, 04:56 PM

USMC: It runs great and the plugs looked good. With the plate open it bled on every cylinder on the left side bot not at all on the right. Odd... When I get my oil can I'll do a wet test and run a dry again and see what happens.

LX XLR8R · 05-14-2002, 12:43 PM

i saw in your site you are putting in a ZEX kit..did you get one yet..im in NY and im selling one still new in the box..

swandog311@hotmail.com

exgmguy · 05-14-2002, 06:13 PM

If it is bleeding down after cranking it is your gauge, and nothing else. Compression gauges have a small schrader valve in the hose that lets air in, and hold it there until you press the release button.

Your numbers look decent. Was the engine warm? Usually a warm engine will show 5 or so more psi. Also you want the peak number to be hit in the first 2 or 3 pulses. If the number slowly rises you have a major compression issue.

PKRWUD · 05-14-2002, 10:56 PM

Quote:

Originally posted by exgmguy
If it is bleeding down after cranking it is your gauge, and nothing else. Compression gauges have a small schrader valve in the hose that lets air in, and hold it there until you press the release button.

Bingo.

You beat me to it.

Engine condition has absolutely no effect on the gauge bleeding down. It is controlled by the valve in either the hose or the gauge, depending on the type. Think about it... When you stop cranking the engine over for the compression test, what are the odds that it will stop at exactly TDC on the compression stroke?

Replace the valve.

Take care,
-Chris

05-12-2002, 06:56 PM	#1
Godslayer Registered Member Join Date: Mar 1999 Location: Largo, FL USA Posts: 274	Compression numbers/help... I did a compression test on my car today and everything looks ok but I'd like opinions. First some background: 86 GT with 172k on the body. Supposedly prior owner swapped in this 20k motor. 1 147 2 150 3 147 4 150 5 147 6 147 7 147 8 143 These are the dry numbers. I wanted to do a wet test but couldn't find the damn oil can I tried to use a turkey baster to get some oil in there but that was futile I was happy with the consistency. What are the numbers for a fresh motor? Also this may seem a bit odd, but I have to ask. When I did the test, all the cylinders on the left side bled down after I stopped cranking. On the right side they all remained at their peak values until I manually released the pressure. Any ideas? Thanks. Bob __________________ Negative Mustang @ present time.

05-13-2002, 12:25 PM	#3
USMC302 Registered Member Join Date: Apr 2001 Location: Gallatin, Tn Posts: 1,326	Sounds like bad rings..It leaked before you manually let it? Then that is the compression reading, all of mine help good compression until released. it could also be a bad or start of a bad head gasket. Good luck __________________

05-13-2002, 02:18 PM	#4
Godslayer Registered Member Join Date: Mar 1999 Location: Largo, FL USA Posts: 274	.... USMC: I didn't post this but it's worth noting. When i first did the left side I forgot to block the throttle open. With the throttle plate closed the compression did not bleed off. Only when I did the test with the throttle plate fully open dd the compression bleed off.... ??? __________________ Negative Mustang @ present time.

05-13-2002, 02:25 PM	#5
USMC302 Registered Member Join Date: Apr 2001 Location: Gallatin, Tn Posts: 1,326	When I did mine I had the trottle plate wide open and it didn't bleed off on either side. Is your car running good or no? Maybe that was my problem with the GT i tested, it wasn't running well, but had outstanding compression throughout the cylinders and did not bleed out. The GT isn't running worth a crap though.... __________________

05-13-2002, 04:56 PM	#6
Godslayer Registered Member Join Date: Mar 1999 Location: Largo, FL USA Posts: 274	... USMC: It runs great and the plugs looked good. With the plate open it bled on every cylinder on the left side bot not at all on the right. Odd... When I get my oil can I'll do a wet test and run a dry again and see what happens. __________________ Negative Mustang @ present time.

05-12-2002, 07:18 PM	#2
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	I think your gauge is leaking. It shouldn't matter if you pull the thing out before you hit the release. Pressure should hold steady internally. I think those numbers look good to me. Everything seems to be very consistant.

05-14-2002, 12:43 PM	#7
LX XLR8R Dirk Diggler Join Date: Feb 1999 Location: SLOATSBURG, NY Posts: 1,931	i saw in your site you are putting in a ZEX kit..did you get one yet..im in NY and im selling one still new in the box.. swandog311@hotmail.com __________________ 95 undecided cubes, AFR 185s,undecided cam, undecided intake, and a 150 hit 89 "turbonotch" 2.3T You might want to hold on..i saw this on a cartoon once

05-14-2002, 06:13 PM	#8
exgmguy Registered Member Join Date: Feb 1999 Location: Utica, Michigan Posts: 2,631	If it is bleeding down after cranking it is your gauge, and nothing else. Compression gauges have a small schrader valve in the hose that lets air in, and hold it there until you press the release button. Your numbers look decent. Was the engine warm? Usually a warm engine will show 5 or so more psi. Also you want the peak number to be hit in the first 2 or 3 pulses. If the number slowly rises you have a major compression issue.

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