Compression Test
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,460
Likes: 48
Compression Test
Hi
I own a 1989 Z51 6 spd. I am doing a compression test on the motor. I have some backfire issues and feel I should check the compression. Having said that.
Is there an adapter for getting the compression gauge screwed into the number eight cylinder. The hose is proving to be a challenge. The A/C is in the way.
What I am thinking is there an elbow that I can screw into the head and then thread the compression gauge into the elbow.
Thank you
I own a 1989 Z51 6 spd. I am doing a compression test on the motor. I have some backfire issues and feel I should check the compression. Having said that.
Is there an adapter for getting the compression gauge screwed into the number eight cylinder. The hose is proving to be a challenge. The A/C is in the way.
What I am thinking is there an elbow that I can screw into the head and then thread the compression gauge into the elbow.
Thank you
Last edited by jseremba; Dec 18, 2016 at 06:53 PM. Reason: more clarity
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,460
Likes: 48
As I was struggling with the hose. I know I did the test on my 1984. Same arrangement. Probably a little more patient back then. Thank you for the help.
Oil Producer
Joined: Apr 2014
Posts: 9,365
Likes: 2,734
i get the same frustration level with it. patience.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
After you finish (if you find little to worry about) ohm the injectors (hot and cold). My started banging on decel when they went bad. I had two on the driver's side that were shorting out.
When the side with the O2 sensor says "add more fuel" to the ECM (because the injectors are dying), the passenger bank gets TOO much fuel. Really ALL the good injectors go "rich". I'm not sure whether it is that OR that the malfunctioning injectors "squirt" at the wrong time. In either case, too much fuel ends up in the manifolds and can get reignited.
Hence "backfiring" (that's not true backfiring). Of course, valves/springs might be it too....so carry on.
When the side with the O2 sensor says "add more fuel" to the ECM (because the injectors are dying), the passenger bank gets TOO much fuel. Really ALL the good injectors go "rich". I'm not sure whether it is that OR that the malfunctioning injectors "squirt" at the wrong time. In either case, too much fuel ends up in the manifolds and can get reignited.
Hence "backfiring" (that's not true backfiring). Of course, valves/springs might be it too....so carry on.
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 763
Hi
I own a 1989 Z51 6 spd. I am doing a compression test on the motor. I have some backfire issues and feel I should check the compression. Having said that.
Is there an adapter for getting the compression gauge screwed into the number eight cylinder. The hose is proving to be a challenge. The A/C is in the way.
What I am thinking is there an elbow that I can screw into the head and then thread the compression gauge into the elbow.
Thank you
I own a 1989 Z51 6 spd. I am doing a compression test on the motor. I have some backfire issues and feel I should check the compression. Having said that.
Is there an adapter for getting the compression gauge screwed into the number eight cylinder. The hose is proving to be a challenge. The A/C is in the way.
What I am thinking is there an elbow that I can screw into the head and then thread the compression gauge into the elbow.
Thank you
good luck -
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Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,460
Likes: 48
After you finish (if you find little to worry about) ohm the injectors (hot and cold). My started banging on decel when they went bad. I had two on the driver's side that were shorting out.
When the side with the O2 sensor says "add more fuel" to the ECM (because the injectors are dying), the passenger bank gets TOO much fuel. Really ALL the good injectors go "rich". I'm not sure whether it is that OR that the malfunctioning injectors "squirt" at the wrong time. In either case, too much fuel ends up in the manifolds and can get reignited.
Hence "backfiring" (that's not true backfiring). Of course, valves/springs might be it too....so carry on.
When the side with the O2 sensor says "add more fuel" to the ECM (because the injectors are dying), the passenger bank gets TOO much fuel. Really ALL the good injectors go "rich". I'm not sure whether it is that OR that the malfunctioning injectors "squirt" at the wrong time. In either case, too much fuel ends up in the manifolds and can get reignited.
Hence "backfiring" (that's not true backfiring). Of course, valves/springs might be it too....so carry on.
I bought a PROM from Scott Hansen. Once I have verified that all the cylinders are operating correctly. I am going to use his Tunepro software and see if that can help.
I am also going to pull the valve covers and look at the springs.
Thank you all
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I assume the backfiring did not start with the installation of new injectors?
Describe the backfiring.
Describe the backfiring.
Safety Car
Joined: May 2001
Posts: 4,747
Likes: 1,642
From: Fairfax Virginia
How do injectors cause backfiring?
I am not used to hearing people trying to stop popping or backfiring by checking their injectors on a fuel injected engine.
My 1988 L-98 was popping upon deceleration and I found the cause to be a dried up cracked vacuum line going to my cruise control system.
When having trouble getting the hose threaded into the spark plug hole enlist somebody with small hands. My 17 year old daughter changed my plugs in August all by herself.
If you really want to know the condition of an engine I do what I used to do on my Cessna. A "Leak down test" is one of the best tests I have ever learned to use. You can identify specific problems more readily using the Leak Down test, especially on the top of a motor. Oil samples tell vast amounts regarding engine wear but the leak down shows the wear over time if you keep records.
If you pay somebody to do a "Leak Down" make sure that you either trust them or stay and watch. I have seen a lot of car mechanics who don't know how to do it properly. I saw one do a compression test and then he tried to tell me "that is how you do it".
Good Luck out there and I wish you all a Very Merry Christmas and success with your Corvette endevours!
My 1988 L-98 was popping upon deceleration and I found the cause to be a dried up cracked vacuum line going to my cruise control system.
When having trouble getting the hose threaded into the spark plug hole enlist somebody with small hands. My 17 year old daughter changed my plugs in August all by herself.
If you really want to know the condition of an engine I do what I used to do on my Cessna. A "Leak down test" is one of the best tests I have ever learned to use. You can identify specific problems more readily using the Leak Down test, especially on the top of a motor. Oil samples tell vast amounts regarding engine wear but the leak down shows the wear over time if you keep records.
If you pay somebody to do a "Leak Down" make sure that you either trust them or stay and watch. I have seen a lot of car mechanics who don't know how to do it properly. I saw one do a compression test and then he tried to tell me "that is how you do it".
Good Luck out there and I wish you all a Very Merry Christmas and success with your Corvette endevours!
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Safety Car
Joined: May 2001
Posts: 4,747
Likes: 1,642
From: Fairfax Virginia
"How to do a Leak Down Test" Instructions
CTMc, is your Leak Down tester any easier to get into that #8 cylinder? Where would I get one of these?
Yes it is possible to do the test of #8 as the tester I have has a long hose with a quick disconnect to make it easier. Get a decent tool and you will be happier. I use a digital compression gauge from "MityVac" and it works great. My leak down tool is designed for aircraft mechanics but will work on either. Below is a decent link to show you what I am talking about.
https://mobiloil.com/en/article/car-...-leakdown-test
Yes it is possible to do the test of #8 as the tester I have has a long hose with a quick disconnect to make it easier. Get a decent tool and you will be happier. I use a digital compression gauge from "MityVac" and it works great. My leak down tool is designed for aircraft mechanics but will work on either. Below is a decent link to show you what I am talking about.
https://mobiloil.com/en/article/car-...-leakdown-test
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,460
Likes: 48
No actually the injectors were purchased because I was told that the injectors made in that year were NFG.
I still did not get back to the car. It will have to wait till Christmas weekend.
Like I said based on the appearance of the plugs I think that the compression is good. But, started this so I will finish it. Thank you
And everyone have a Merry Christmas