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1985 2.3L Compression check


swingjunkie

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The sticky thread at the beginning of this forum does not provide the nominal compression for this engine.
Just tested mine with the following results
Dry Test
Cyl = PSI
1=165
2=160
3=158
4=175

Wet Test
Cyl = PSI
1=260
2=270
3=265
4=250

I need some specs to tell me if these are in range.

Thanks
Carl
 


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tomw

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There is a general rule of thumb about compression test results that says the lowest should be with 10-15% of the highest.
With the numbers you have, I think you are ok no matter the +/- range given.

However, the results don't make sense in that #4 went up 75psi ... and it had pretty good compression from the start, so rings should have been sealed already... better seal, if rings, than all the other cylinders... IOW, the best compressing cylinder increased the most, which should NOT happen. The worst will get the largest boost from the temp seal provided by a Tbsp of oil.
Maybe run again, warmed up, ignition disabled, throttle plate blocked wide open. A good 'three strokes' for each cylinder, listening or watching the gauge to see the pump-up and then plateau.
tom
 

RonD

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1985 2.3l Ranger engine could be a diesel engine, with 21:1 compression ratio

I will assume you have a gasoline 2.3l with 9:1 compression ratio
General rule of thumb is to multiply compression ratio(9:1) by 18.5 if testing near sea level(15psi air pressure) to get approximate PSI expected on compression test.
9 x 18.5 = 166.5psi

Normal test is cold engine, all spark plugs removed, battery charged, and throttle open

The dry test numbers look fine
Wet test isn't correct, numbers are bad

Wet test is only done to see if rings are bad and if so how bad
Leak down test is done dry and then wet to see if it is valves or rings that are leaking on a low compression cylinder.


As tom said what this type of test is for is to see if one cylinder has much lower compression than the others.
And yours show similar numbers on all 4, so test passed.

Although................because the wet test numbers are so far away from normal gasoline engine numbers I would suspect a bad gauge, I might retest dry with another gauge if possible.
Because if all 4 tested at 80-100psi I would think timing belt had slipped a notch.
 
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swingjunkie

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RonD,

Thanks for your reply. I noticed the discrepancy on cylinder#4, as you did.
My wet test was after putting in 2 Tablespoons of oil into the cylinder, and I had to use a tube extension to get oil into cylinder#4. I noticed after the test that a good bit of the oil was stuck in the clear plastic tube after the test. So I think #4 did not improve as much as the other cylinders because it did not get as much oil into it prior to the test.

In testing these I cranked the engine until the gauge pressure did not increase.

TomW
Thanks for your reply. This is a gasoline 2.3l EFI.
My DRY test was as you describe, cold engine, plugs out, throttle full open, fuel system disabled.

Sounds like the concensus is that the compression on this engine is OK. I will test this gauge against a reference to make sure it is OK.

Can you explain the leak down test. You said" Leak down test is done dry and then wet to see if it is valves or rings that are leaking on a low compression cylinder." Sounds like you are presurizing the cylinder (to what PSI?) in both a wet and dry condition. I'd assume if the leak rate did not improve wet the seals/valves are the culprit.I'd be interested in exactly what the procedure is for this.

At this point my plan is to replace the valve seals. I think oil blowing by these 29 year old seals is the most serious problem this engine has. Ran like a top for 20 miles with new plugs then started stuttering. Plugs were fowled.
 

RonD

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Yes, leak down test is using air pressure at a preset psi

Easiest to explain is using 100psi as the set pressure from compressor/tank
You connect a gauge to the air line and connect air line to spark plug hole.
Piston in that cylinder should be at power stroke TDC so both valves are closed.
If gauge shows 95psi you have 5% leakage, which would pretty much be a new engine.

The 10-15% leakage is where problems start.

If you had 20% leakage and add some oil to cylinder, turn crank 2 revolutions to spread oil and then retested and got 10% leakage then the rings are the problem.
If it is still 20% then valve seats are the problem.
This won't test valve guide seals

Only way to test valve guide seals is with a running engine.
Let it idle for a minute then give it gas, if you get a puff of smoke out the tail pipe time for new seals.
 

tomw

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Most leakdown testers have two pressure gauges, one for supply air pressure, and one for 'test' air pressure. That way you don't depend on compressor or regulator pressure to stay at the desired psi, and can see directly the pressure differential.
As was noted, feed the air at a given psi, and see what the test cylinder will contain. You can listen at the intake and the exhaust pipe for valve leakage hiss, and at the oil fill for ring leakage. Use a rubber hose or tubing for the oil fill...
tom
 


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