This compression tester by Gunson, is an extremely useful tool which can assist the diagnosis of an engine which isn't working as it should. Computer diagnostic tests don't seem to pinpoint some faults as the 'Check Engine Light' (CEL) doesn't always turn on, or generate a fault code.
In my case, the engine has lost power, is very thirsty on fuel and has a irregular idle - but no CEL or fault codes. Using this compression tester has revealed one of the cylinders has a much lower pressure test reading than the others (two of which are also lower than they should be). The cylinder head will need to be removed to investigate this problem as I'm pretty confident now the valves are not sealing correctly or may be damaged.
Before you commence the compression test on your engine, the following suggestions may be helpful:
- Locate and remove the fuel pump fuse then start the engine and run it until it stalls - this is to ensure no fuel is injected during the tests.
- Remove the spark plug leads and use cable ties to identify each lead (one cable tie on plug one, two on plug two etc) unless they are already marked.
- BEFORE removing the spark plugs it is essential to clean around each spark plug to prevent dirt or any objects from dropping into a cylinder. Use a cardboard tube taped to a vacuum cleaner hose and push this over each plug and down to the cylinder head.
- Ensure any small objects, which could pass through an open spark plug hole, such as screws or washers etc. are moved well away. It would be very difficult to retrieve these items from a cylinder without removing the cylinder head. If an item accidentally dropped into a cylinder un-noticed and the engine was cranked over or run, then serious damage to valves, the piston/rings, and cylinder walls would probably occur.
- Disconnect the low tension side of the ignition coil to prevent it operating when the engine is cranked over. Failure to do this could result in damage to the coil pack (insulation failure) and/or the ECU, due to the spark plug leads being open-circuit !
- Screw in the compression tester and open the throttle wide before turning the engine over.
- Record each cylinder pressure.
- Perform the 'wet' test if required, but afterwards run the engine for 15 minutes to burn off the added oil and so help to reduce damage to the catalytic converter.
If you are intending to use this compression tester on a Ford Zetec engine (with black top plastic valve cover) or any other engine which uses 14mm spark plugs with taper seats - e.g. NGK type PTR5A-10 etc. then be aware the 14mm connector supplied with this kit will not fit ! The length of the threaded part isn't long enough to reach into the cylinder head and screw in - it will reach the spark plug hole by turning the rubber tube, but the threaded section in the cylinder head is recessed further into the head preventing the threads from engaging. In my case I have a modified adaptor which overcame this problem. I believe Gunson do manufacture an extension adapter for use with Zetec engines.
To sum up, this is a very good quality and accurate compression tester - highly recommended.
| Manufacturer | Tool Connection (EU) |
|---|---|
| Brand | GUNSON |
| Model | G4101 |
| Product Dimensions | 3 x 15 x 29.5 cm; 460 g |
| Item model number | G4101 |
| Manufacturer part number | LASG4101 |
| Item Weight | 460 g |
