To Trust or Not to Trust...the Scanner. That is the question.

[joetrainer31]

After receiving my new to me 95 GT. I've been addressing some TLC issues that the car needs. One of the things I've been doing is scanning the car for codes, fixing the problems, then scanning further. The last code that I did was a KOEO scan to test cylinder contribution to engine performance.

I'm happy to say that the report came back 90 = all 8 cylinders are contributing equally to the engine. I wanted to make sure that the test outcome could be repeated so I performed it again. The same results came back; 90.

My question(s) is this; Can I trust the scanners results enough to where I do not need to do a compression check? Is this scan something one would do in addition to a compression check or in leu of one? Any brainiacs out there have feed back?

 

[Noobz347]

After receiving my new to me 95 GT. I've been addressing some TLC issues that the car needs. One of the things I've been doing is scanning the car for codes, fixing the problems, then scanning further. The last code that I did was a KOEO scan to test cylinder contribution to engine performance.

I'm happy to say that the report came back 90 = all 8 cylinders are contributing equally to the engine. I wanted to make sure that the test outcome could be repeated so I performed it again. The same results came back; 90.

My question(s) is this; Can I trust the scanners results enough to where I do not need to do a compression check? Is this scan something one would do in addition to a compression check or in leu of one? Any brainiacs out there have feed back?

I would trust it to tell me that cylinder balance test tells you that none of the cylinders have failed. I would NOT accept a pass as an indication of perfect health. A compression and leak down test will tell you what condition the motor, rotating assembly, valves, seals, and springs are in.

 

[joetrainer31]

I would trust it to tell me that cylinder balance test tells you that none of the cylinders have failed. I would NOT accept a pass as an indication of perfect health. A compression and leak down test will tell you what condition the motor, rotating assembly, valves, seals, and springs are in.

Noobz, you are a wealth of information. Thank you for the feedback man. So then, I'll do the typical compression test one cylinder at a time and record the results.
1. If I understand correctly they should all be between 150-160 to indicate good health. Is that right? Am I talking about the same test as you are (i.e. gauge goes in 1 spark plug hole at a time & you crank the car with the coil wire disconnected)?

2. How does one discern between the health of the rings, seals, etc?

 

[Noobz347]

Noobz, you are a wealth of information. Thank you for the feedback man. So then, I'll do the typical compression test one cylinder at a time and record the results.
1. If I understand correctly they should all be between 150-160 to indicate good health. Is that right? Am I talking about the same test as you are (i.e. gauge goes in 1 spark plug hole at a time & you crank the car with the coil wire disconnected)?

2. How does one discern between the health of the rings, seals, etc?

The test you're talking about (standard compression test) will give a pretty good indication that the cylinders and heads are in decent condition.

A leak down test, concentrates more on exactly the condition of the rings, valves, valve seats, and valve seals. In other words... if those components aren't perfect, it tells you what their current condition is.

If you looking to buy a used car, I would do a standard compression test. If I were thinking about supercharging a car or troubleshooting blow-by, I would do a leak down test.

Your favorite search engine can give you procedures and more details. I'm sure that someone has listed a set of procedures on this site as well.

 

[joetrainer31]

The test you're talking about (standard compression test) will give a pretty good indication that the cylinders and heads are in decent condition.

A leak down test, concentrates more on exactly the condition of the rings, valves, valve seats, and valve seals. In other words... if those components aren't perfect, it tells you what their current condition is.

If you looking to buy a used car, I would do a standard compression test. If I were thinking about supercharging a car or troubleshooting blow-by, I would do a leak down test.

Your favorite search engine can give you procedures and more details. I'm sure that someone has listed a set of procedures on this site as well.

Awesome. Thank you. I already got the car. It basically cost us nothing & it only has 64k on the odometer. I'm just going through it and fixing issues as I notice them. I'll do both tests as soon as I finish this semester. I need to R&R the lifters, but I'll do a compression test first. If it fails the test then I might need to look at a short block. We will see. Thanks again Noobz.

 

[Noobz347]

With 65k, I would think that it should be in pretty good shape unless the previous owner just beat the crap out of it.

 

[joetrainer31]

With 65k, I would think that it should be in pretty good shape unless the previous owner just beat the crap out of it.

Well, it IS a 95 so, even with low miles there is time to consider. I mean, I hope all is right, but I don't like not knowing for sure. Plus, things like a rock solid dirty air filter, rusty water in the cooling system, and other issue give me pause. I've corrected all those issues, but it makes me wonder. I cannot watch the exhaust for clues because it got 4 cats.

 

[Noobz347]

Compression and leak-down will also identify if you've got a head gasket problem or if the last owner just did dumb things like fill the cooling system with tap water.

 

[joetrainer31]

Compression and leak-down will also identify if you've got a head gasket problem or if the last owner just did dumb things like fill the cooling system with tap water.

I'm going to go ahead and guess he did dumb, or careless things. I flushed the entire cooling system and the good news is that the rad looks brand new inside. Hopefully that is synonimus with the innerds of the block. Also, he seems to have put a 160 stat in the car. It runs way too cool even with under drives. I'll get a balanced 180 to put in it.

 

[Noobz347]

Your oil and engine will thank you.