When it comes to purchasing a used car, especially one with known issues, it's important to do your due diligence to avoid any costly surprises down the road. That's exactly what one Audizine forum user did when they bought a 1999 Audi A4 Quattro with a suspected timing belt issue.

The previous owner had attempted to fix the problem by replacing the timing belt, rollers, and tensioner, but the car still wouldn't start. As a result, the new owner suspected that the valves had been bent and decided to check the compression levels in each cylinder.

However, they encountered an unexpected problem. Despite using a compression tester from a popular auto parts store, they were unable to get any reading from any of the cylinders. This indicated that there was likely a problem with the compression tester itself.

To get a more accurate reading, the new owner decided to try a different method - a leak down test. This involves pressurizing each cylinder and measuring the amount of air that leaks out. Using a leak down tester, they found that there was indeed a problem with compression, as air was leaking out of the engine.

But, despite this, the valves appeared to be okay. So what could be causing the compression issue? The forum user suspected that it could be a problem with the piston rings or cylinder walls.

While it's never ideal to encounter problems with a used car, it's always smart to thoroughly check the vehicle and diagnose any issues before making a purchase. In this case, the compression tester used may have been faulty, but fortunately, the new owner was able to use a leak down tester to identify the issue and start working towards a solution.

So what can we learn from this? When checking the compression levels in a car engine, it's important to use reliable equipment that will give accurate readings. If you suspect there may be an issue with the compression, a leak down test can be a helpful alternative. And, ultimately, always do your research before purchasing a used vehicle to avoid any costly surprises.