Help with compression test #’s and spark plug reading

[earlbrown]

I pulled the valve out of the compression tester and set my regulator to like 15psi just to see if I noticed anything.

Set it at full pressure and you'll probably find the weak link. It'll either hiss out of the intake, exhaust pipe or valve cover breather.

 

[1984 t-type]

For the videos i could find on the harbor freight one seems like most of them only got to about 15psi on the supply gauge so thats why i chose 15, what would be full pressure ? My compressor can supply 150psi.

Hey and thanks to everyone for the help ! I did expect much holiday support lol

 

[earlbrown]

That's for a leakdown test. You shoot 100psi into the gauge block then read the second gauge. If the cylinder is holding 95%, for example, that means you have 5% leakdown.

The noise will tell you what part of the engine is leaking.

Since you don't have the gauges, you can still fill the cylinder and tell if one hole leaks more and where it's going.

 

[1984 t-type]

I planned on going to harbor freight to get their kit wasn't sure if i could rent one at the auto parts stores. Is the harbor freight one ok ?

 

[ScottHeidinger]

Harbor Freight Is fine.


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[ScottHeidinger]

Like Earl said set it for 100 psi with what you have and you should be able to hear the leak.


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[ScottHeidinger]

You might have a bad check valve in the booster or a bad booster. Have you tried caping the vacuum line to the booster to see if you’re losing vacuum thru the brake system?


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[1984 t-type]

You might have a bad check valve in the booster or a bad booster. Have you tried caping the vacuum line to the booster to see if you’re losing vacuum thru the brake system?


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No i actually have not tried this, it will be on my list of test for tomorrow.

 

[No disintegrations]

The supply hose to the vacuum block is what Cruz provides with the kit, i cant go larger without changing out the fittings. The line to the booster is 3/8'' cant go any larger there either, 3/8 should be what all the vacuum brake conversion cars use.

Right but it looks like a small line is feeding the block which may cause lag in the time it takes to recover vacuum at the booster.

 

[earlbrown]

A bad booster won't cause the engine itself to have low vacuum and a weak cylinder. It'd have an even harder time messing with manifold vacuum with the undersized feed line to the block.

 

[1984 t-type]

Ok this harbor freight gauge is very inaccurate but when I can manage to get it to reproduce the readings I am getting about the same number 25% which I still believe is incorrect may be higher or lower who knows. Every time I touch this gauge it gives me a different reading. I do hear a faint sound of air and it seems to be in the crankcase.

 

[No disintegrations]

Ok this harbor freight gauge is very inaccurate but when I can manage to get it to reproduce the readings I am getting about the same number 25% which I still believe is incorrect may be higher or lower who knows. Every time I touch this gauge it gives me a different reading. I do hear a faint sound of air and it seems to be in the crankcase.

Squirt oil in and do the compression test again. If the reading is higher than no oil rings or cylinder issue suspected.

 

[Mr.Spool]

So here’s the scoop, my vacuum numbers have been low ( around 9” ) since I got this car a few years back and I have just kinda dealt with it. But I’m thinking it is the reason for my not so good brakes and now I want to track this issue down. In that time I have blown the drivers side head gasket and replaced both gaskets, have chased a High BLM issue which went away when I switched over to the Cruz vacuum manifold and intake spacer kit and now my BLM’s are in check. So today I decided to do a compression test and here are my numbers, took some pics of the plugs also if anyone can tell me what they are saying. I recently installed a new coil pack because 1 of the banks went out and have new plugs ready to go back in. Car runs on E85 at about 20lbs of boost, I will turn the boost up in the spring to around 25lbs or so when I take it in to have it tuned. View attachment 332968View attachment 332969View attachment 332970

follow this,do the compression test cold,get new numbers.then warm the car up,then do the compression test hot,you will find out everything you need to know with that.now plugs put a fresh set of plugs in the car do a pull then shut the car right off pull the plugs,thats the only way to get a true reading.

 

[1984 t-type]

follow this,do the compression test cold,get new numbers.then warm the car up,then do the compression test hot,you will find out everything you need to know with that.now plugs put a fresh set of plugs in the car do a pull then shut the car right off pull the plugs,thats the only way to get a true reading.

What does doing the test cold then hot show me ? Not questioning your method just asking, im here to learn.
/

 

[Mr.Spool]

What does doing the test cold then hot show me ? Not questioning your method just asking, im here to learn.
/

it show alot if you do it i will go further.

 

[1984 t-type]

Working on it now, have to put the rockers and valve covers back on

 

[1984 t-type]

Ok. Cold engine, wide open throttle, fully charged battery, no oil poured down spark plug holes, and using a different compression gauge than from the other day here’s what I got. Will have to test with the engine warm later when my daughter wakes up. Not sure what was the issue but I’m liking the new results so far. When I took the rockers off I tapped on the top of the springs to make sure the seals were seated wonder if this did it.

1- 145#
2- 145#
3- 145#
4- 155#
5- 150#
6- 155#

 

[earlbrown]

Those numbers look at little better.

Still need to work on your low manifold vacuum.

 

[1984 t-type]

Ok engine brought up to temp, wide open throttle, same gauge as previous cold compression test, temp gauge reading about 145 at time of testing.

1- 150#
2- 155#
3- 155#
4- 150#
5- 155#
6- 150#

 

[1984 t-type]

Oh forgot vacuum in park anywhere from high 9 to low 11's, in gear high 7 to low 9's. I isolated the vac line and pulled vac on my mighty vac, numbers on mighty vac and vac gauge were very close and it held the vacuum so the gauge and line are good.