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D2AUE

Compression test

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Help please, I have a 1988 Esprit Turbo, engine running smooth, not missing, not irratic on idle, good power, plugs dry with mixture spot on, I decided to do a compression test, warmed engine up, removed all plugs, three where at 75 and 1 at 90, baffled! Any thoughts? 

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You could try a wet test where you put some oil down the bores.

A rise in compression would indicate worn rings, no rise bad valve seating. :thumbup:

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Cheers,

John W

http://jonwatkins.co.uk

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When you performed the compression test, did you stuck the trottle open to allow for good airflow while cranking? This is often forgotten.

I  prefer to do a cylinder leakdown test. You need a compressor for that. It gives a better evaluation of your engine and it allows for good detection of where a problem occurs. Is it inlet valves/outletvalves/cylinder rings/headgasketproblem ... You can evaluate the loss in % and by listenng to the hissing, you can detect where the loss happens. If you never did one , google cylinder leakdown test, and you will find some good youtube videos.

 

furthermore : 3 down , 1 high seems odd ??? Not sure if the measuring is accurate here.

1 cilinder down ( can be valve seating or piston rings or bores

2 ajacent cylinders down, can be head gasket problem or tear in the head between the two cylinders

all cylinders down is a worn out engine., or stuck pistonrings 

But 3 cylinders down or one cylinder high ????? no clue and not logic

EDIT:

There is one theory that could explain one cylinder high. :

If that cylinder has excessive carbon build up on the top, compression will be higher. The reason for carbon build up in one cylinder can be to much oil in that cylinder due to f.e. leaking valve seals or other?

There is a way of cleaning carbon build up in your cylinders. I have used it on all of my cars in the past, but I will not recommend it, it's at your own risk . For me it works fantastic. Take a bottle of tapwater in a spraycan. Let the engine run at about 1500rpm. Open the filterbox and spray a continued mist of water in the inlet trumpets. The water gets soaked in and on a warm engine , it will form steam in the cylinders. Steam does an excellent job in decarbonizing the inside of your engine ( valves, cylinder top....) . Be carefull , It also highers your compression, so empty the bottle , but do it with care, dont just pull the water in and let the engine stall. You will see white smoke at the back, that is normal.

If you look at an open engine that had a leaking headgasket, where cooling water has been sucked in, you will almost always see that the cylinder that got the coolant is brand clean without carbon, while the other cylinders are dirty and black.

Also, engines with waterinjection stay clean inside, because of the same principle.

Geert

 

 

Edited by gvy

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1 hour ago, gvy said:

When you performed the compression test, did you stuck the trottle open to allow for good airflow while cranking? This is often forgotten.

I  prefer to do a cylinder leakdown test. You need a compressor for that. It gives a better evaluation of your engine and it allows for good detection of where a problem occurs. Is it inlet valves/outletvalves/cylinder rings/headgasketproblem ... You can evaluate the loss in % and by listenng to the hissing, you can detect where the loss happens. If you never did one , google cylinder leakdown test, and you will find some good youtube videos.

 

furthermore : 3 down , 1 high seems odd ??? Not sure if the measuring is accurate here.

1 cilinder down ( can be valve seating or piston rings or bores

2 ajacent cylinders down, can be head gasket problem or tear in the head between the two cylinders

all cylinders down is a worn out engine., or stuck pistonrings 

But 3 cylinders down or one cylinder high ????? no clue and not logic

EDIT:

There is one theory that could explain one cylinder high. :

If that cylinder has excessive carbon build up on the top, compression will be higher. The reason for carbon build up in one cylinder can be to much oil in that cylinder due to f.e. leaking valve seals or other?

There is a way of cleaning carbon build up in your cylinders. I have used it on all of my cars in the past, but I will not recommend it, it's at your own risk . For me it works fantastic. Take a bottle of tapwater in a spraycan. Let the engine run at about 1500rpm. Open the filterbox and spray a continued mist of water in the inlet trumpets. The water gets soaked in and on a warm engine , it will form steam in the cylinders. Steam does an excellent job in decarbonizing the inside of your engine ( valves, cylinder top....) . Be carefull , It also highers your compression, so empty the bottle , but do it with care, dont just pull the water in and let the engine stall. You will see white smoke at the back, that is normal.

If you look at an open engine that had a leaking headgasket, where cooling water has been sucked in, you will almost always see that the cylinder that got the coolant is brand clean without carbon, while the other cylinders are dirty and black.

Also, engines with waterinjection stay clean inside, because of the same principle.

Geert

 

 

EDIT : I didn't mention that I find the measured values low. I have no information on the Turbo Engine and it is logic that turbo engines have a lower compression ratio than the NA, but still...

You are sure that you had the trottle WIDE OPEN, while doing the test,because if not, that would explain low and wrong readings.

Edited by gvy

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Thanks, Yes throttle fully open, if worn rings would I not have oily plugs? They are dry and perfect condition, if they are half what they should be, I would expect running problems? Why would the engine perform and run well? 

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Could it be something to do with the air intake to the twin carbs being sealed to the turbo not generating enough air for compression test? 

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14 hours ago, D2AUE said:

Could it be something to do with the air intake to the twin carbs being sealed to the turbo not generating enough air for compression test? 

No, wouldn't have thought so.

As long as your'e sure the throttles were fully open there should have been plenty of air flow.

Was the battery fully charged & in good condition so spinning the motor strongly throuout the testing?

Which cylinder gave the high reading, wasn't the first you tested was it? If it was then the slower spinning motor may explain the other 3 low readings. :thumbup:


Cheers,

John W

http://jonwatkins.co.uk

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Hi again thanks for your replies, was the third cylinder I tested, when you say throttle fully open, I have opened fully the throttles on the twin carbs, am I missing something obvious here? 

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54 minutes ago, D2AUE said:

I have opened fully the throttles on the twin carbs, am I missing something obvious here? 

No, don't think so.

Do you know what Lotus state the compression should be on a healthy turbo motor?

Have you tried a wet test as I suggested in my first post?


Cheers,

John W

http://jonwatkins.co.uk

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No not yet will give that a go tomorrow maybe, but I have read on hear quotes of 130, which would make mind half what it should be, would expect running problem also recently passed emissions with flying colours. Very strange 

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