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Question for the mappers, mapped for decats running cats


Arran

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Yeah I used a different gauge this time just incase. I followed this

 

Measurement of Compression Pressure

1. Warm up engine.

2. Turn ignition switch off.

3. Release fuel pressure (See How to Change Fuel Filter)

4. Remove all spark plugs.

5. Disconnect distributor center cable.

6. Attach a compression tester to No. 1 cylinder.

7. Depress accelerator pedal fully to keep throttle valve wide open.

8. Crank engine (let it turn over 7 times) and record highest gauge indication.

9. Repeat the measurement on each cylinder as shown above.

Note: Always use a fully charged battery to obtain specific engine revolution.

Compression Pressure kPa (kg/cm2, psi) / RPM

Standard = 1,236 (12.6, 179) / 300

Minimum = 1,040 (10.6, 151) / 300

Difference limit between cylinders = 98 (1.0, 14) / 300

10. If cylinder compression in one or more cylinders is low, pour a small amount of engine oil into the cylinders through the spark plug hole and re-test compression.

* If adding oil helps compression, piston rings may be worn or damaged. If so, replace piston rings after checking piston.

* If pressure stays low, a valve may be sticking or seating improperly. Inspect and repair valve and valve seat.

* If compression in any two adjacent cylinders is low and if oil does not help compression, there is a leak past the gasket surface. If so, replace cylinder head gasket.

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And another update! So done my compression test with all plugs out and wot. 125psi on all cylinders. Bad news applied some oil and it shot up to 300psi! So I'm guessing that'll be the rings shot then?

 

Something not right there, adding oil should not suddenly increase compression from 125psi to 300psi. that way over std.

How much oil did you add?

Edited by Tricky-Ricky
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something doesnt seem right here. like ricky says, 125 to 300 is quite a difference. is that guide for a vq engine?

it just seems weird that all cylinders are so low, what kind of mileage has it got on it?

by rebuilding the engine would you want to forge it or standard parts? where are you located?

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It came from the nicoclub forum iirc. I did put quite a lot of oil down the top so it's probably over pressurised it. It's done 98500 miles. I'm in falkirk scotland. I'd like to forge the engine but the best price would need to suffice 😞

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  • 3 months later...

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