Sirion compression test DAIHATSU SIRION (M3_)

Having such uneven compression pressure (170, 175, 125 psi) can cause a number of problems for your rice purity test engine. Low pressure at cylinder 3 can lead to poor performance, vibration and increased fuel consumption. It can also cause a fault in the engine control system, resulting in an error message on the dashboard. A thorough check should be done to determine the cause and correct it promptly.

Uneven compression after replacing a burnt exhaust valve on your Daihatsu Sirion M3_ (with readings like 170, 175, and 125 psi) can definitely cause some trouble, though it’s not necessarily a deal-breaker yet. The cylinder showing 125 psi is lower than the others, and that imbalance can lead to rough running, misfires, and reduced engine efficiency.

Since you couldn't test cylinder 3 before, and now it’s been repaired but still shows a lower reading, the uneven compression may be due to issues like a valve not seating perfectly, a slightly bent valve, imperfect valve grind, or even a less-than-perfect valve seat surface. It might also point to piston ring wear or a slightly damaged cylinder wall in that cylinder.

Will it throw a fault code? Possibly. If the uneven compression causes misfires or the engine runs rough enough to trigger the car’s engine control unit (ECU) to detect a misfire or efficiency problem, you’ll likely see diagnostic trouble codes (DTCs) related to misfires (like P0303 for cylinder 3 misfire). However, compression issues alone aren’t directly measured by the ECU; it only flags problems it can sense via sensors.

In practical terms: this compression gap could cause running issues, misfires on that cylinder, and potentially increased emissions. If it’s not causing running problems or misfires yet, it may allow continued use for a while, but it’s a good idea to monitor the car for rough idling, poor fuel economy, or warning lights.

So, the verdict: Uneven compression isn't ideal and can cause mechanical and operational problems. It will likely cause fault codes if it leads to misfires. You might want to consider valve adjustment, checking the valve seating again, or further inspection of the piston/ring condition if problems arise. Just think of your engine as a barbershop quartet—with one member slightly off-key, the harmony isn't quite right anymore!

Keep an eye on it and consider a leak-down test if in doubt for a deeper diagnosis.