Checking engine compression/leakdown

[Vspec]

See thread in sig for more background to the car.

Before attempting to pass inspection to put the car back on the road, couple of things needs to be addressed, several of which would be easier done with the engine and trans out of the way (steering rack replacement, shifter bushing+short throw, rust that needs to be taken care of, finish ABS removal and general tidy up). I'd rather leave the engine in but with the age and mileage, it might not be bad idea. Also

Before I take the plunge and take engine out and discover more suprises, I'd like to check the vital signs of the engine.

The consensus seems to be that a compression test only tells part of the picture, I am also considering a leak down test.


Regarding the compression test, my plan was to take fuel pump fuse out and plugs but about spark?

The engine has been not started in weeks, should I do a dry then wet then hot?

Also the battery is dead and needs to be boosted to start the engine, can I just hook up cable to the boosting and turn the starter to get the readings?


Regarding the leakdown test, with all the engine ancillaries attached, how can I turn the crank by hand to reach TDC on each cylinder?


Yes, I have spent countless hours using the search function

[jlevie]

A good way to run compression tests is to leave the ignition off and use a remote starter switch connected across the starter main and solenoid lugs. A fully charged good battery is necessary, the throttle must be locked open, and all plugs out. The most meaningful results will be with the engine hot. After getting dry numbers, repeat the after adding a hlf teaspoon of oil to each cylinder. A rise in numbers between the dry and wet results area sign of worn rings or cylinder bores.

For the leak down numbers, get the front of the car up in the air and use a 22mm wrench on the crank bolt to turn the engine. You really need two people to do a leak down test. One to turn & hold the crank and one to get the numbers.

[Vspec]

After getting dry numbers, repeat the after adding a hlf teaspoon of oil to each cylinder. A rise in numbers between the dry and wet results area sign of worn rings or cylinder bores.

So I should warm up the engine first before the dry and warm? How long should I wait after warming up?

For the leak down numbers, get the front of the car up in the air and use a 22mm wrench on the crank bolt to turn the engine. You really need two people to do a leak down test. One to turn & hold the crank and one to get the numbers.

So that crank bolt is accessible with clutch fan/waterpump attached to the engine? I will have my partner in crime with me.

Dumb question does the engine rotates cw or ccw?

[jlevie]

So I should warm up the engine first before the dry and warm? How long should I wait after warming up?

Get the engine up to temperature and immediately run the tests.

So that crank bolt is accessible with clutch fan/waterpump attached to the engine? I will have my partner in crime with me.

Dumb question does the engine rotates cw or ccw?

The crank bolt is easily reached from under the car. Viewed from the front of the engine the crank rotates CW.

[Vspec]

Is taking the fuel pump fuse enough for compression testing?

[jlevie]

Is taking the fuel pump fuse enough for compression testing?

Yes, but only if you release the stored pressure in the fuel rail.

[Vspec]

Yes, but only if you release the stored pressure in the fuel rail.

How can I release it? Otherwise wont I potentially flood the cylinders?

[jlevie]

To release the stored pressure you have to remove the hose that feeds the fuel rail or the hose at the filter. If the fuel pump and FPR are good there will be a significant amount of fuel released, which will make a mess.

Since I just realized that this is an 88, another option is to disconnect C191.

[Vspec]

01/88 to be specific.

Just to confirm, is this C191?



From this pics it is connected to the fuel rail:



Documenting for posterity sake and whoever else walks down this path.

[jlevie]

The bottom picture shows the injector side of C191.

[Vspec]

Follow up question to the leak down testing procedure, how can I tell when each piston is at TDC?

[jlevie]

Look at the cam shaft lobes. When both are pointing down the cylinder is at TDC.

[Vspec]

I'd rather not take the vc off but I fail to see any other way :(

Can the vc be removed with the intake still attached?

Done with engine warm or cold?

[jlevie]

Hot compression and leak down numbers are what matters.

No problem taking the valve cover off, the intake doesn't interfere. Do have a new gasket and the four rubber bungs on hand. While the cover is off and the plugs are out you have a perfect opportunity to adjust the valves.

[Vspec]

While the cover is off and the plugs are out you have a perfect opportunity to adjust the valves.

That will depend on the numbers that come out of the compression and leak testing :neutral: If they are no good, the whole thing is coming out anyway.

All plugs should be out for each test?