jseremba

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

VikingTrad3r

What are the other psi values?

ive always managed to get it into 8. frustrating excercise i know.

jseremba

I have done the others. I wanted to go hardest to easiest. Number 7 180 psi.
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.

VikingTrad3r

i get the same frustration level with it. patience.

jseremba

thank you

GREGGPENN

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.

Joe C

number 8 and interference with the AC (compressor) - ??? do you mean number 2 cylinder? either way, I've run compression test on L98's without the use of any adapters. if you can get a spark plug in there, the hose adapter shouldn't be an issue. one tip, try removing the center section of the RH inner fender - will give you a straight shot into number 2 (if we're talking the actual number 2 cylinder, that is...).

good luck -

RichS

I just did one on a 89. It takes patience and a lot of cursing to do the pass side! I just used the hose.

jseremba

This is really great information. The injectors are new, like 2000 miles on them. I do have an exhaust leak at the manifold. So I will tighten that up. My problem is I am almost positive the compression on all cylinders is good. All of the plugs look a little rich.
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

GREGGPENN

I assume the backfiring did not start with the installation of new injectors?

Describe the backfiring.

ctmccloskey

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!

Hot Rod Roy

The question is #8 cylinder and interference with the a/c heater box. A spark plug is a challenge, but I haven't found a compression gauge with a super-flexible hose to get into that spot! It's got to be a straight shot to get that fitting in the hole. Joe, what brand compression gauge do you have?

CTMc, is your Leak Down tester any easier to get into that #8 cylinder? Where would I get one of these?

ctmccloskey

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

jseremba

Sorry it took so long to get back to you.
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