Engine Misfire 1.0L - Troubleshooting Tips

Hi.

I've already experienced the uneven running and hammering sound on one cylinder in my 1Z engine. It's especially noticeable under load, and the strange thing is that the louder it gets, the colder the engine block is. I'm worried that in winter, when it's -10 degrees Celsius, it might explode, but when it reaches operating temperature, it almost disappears (you really have to listen closely to hear it).
I've already replaced all 4 injectors with new ones, and recently I also replaced all 4 pressure relief valves on the pump with new ones, but nothing has changed; it still hammers. The idle fuel quantity is 6mg, which I assume means the pump isn't worn out, and it also starts up immediately without any problems. The idle speed control sometimes shows slightly different values, but on the next measurement, they are normal again.
I'm slowly running out of ideas. It probably can't be the hydropneumatic suspension, because in case of a defect, they should just make a clicking sound, and that shouldn't be load-dependent, or am I mistaken?
What the hell else could possibly be going on?

Greetings.
Jan.

Volkswagen Golf 3, 1Z engine, 165,000 km, 1994.

Hi,
The knocking sound could actually be coming from a faulty hydraulic lifter. Try using a stethoscope (a long screwdriver) and listen near the valve cover to pinpoint the exact source of the knocking. In my car, the lifter for the vacuum pump (which is driven by the camshaft in the 5-cylinder engine) makes similar noises, and it's difficult to distinguish it from a faulty lifter; however, the noise temporarily disappears if you pump the brakes a few times. Does the noise still occur if you turn off the engine for 20 minutes while it's still warm and then restart it, or is it actually directly dependent on the temperature?

Best regards from Berlin.
Olli.

Hello.

After 20 minutes, it starts up again slightly, but by then the engine isn't completely warm yet.

It's probably not the vacuum pump. Pressing the brake pedal doesn't seem to make any difference.

Furthermore, I have a problem: I failed the emissions test (Rust test) at the SYN (which is the equivalent of the TÜV in Denmark). When the engine is idling, there's a lot of smoke coming out of the exhaust. Is this normal, or should I be concerned?
I suspect that one of the valves isn't sealing properly, and that the hydraulic lifters compensate for it to some extent when the engine is warm.

Regards,
Jan.

Jan03 wrote:

It's probably not the vacuum pump. Pressing the brake pedal doesn't seem to make any difference.

The 1Z also has a rotary vane pump that is driven by the auxiliary shaft .

Jan03 wrote:

I suspect that one of the valves is not closing properly, and that the hydraulic lifters compensate for this to some extent when the engine is warm.

Have you ever measured the compression, or at least performed the "Hoppeltest" (-> used car buying tips)?

ulf wrote:

Have you ever measured the compression, or at least done the "Hoppeltest" (-> used car tips)?

I haven't done that yet, but it's next on my list. Unfortunately, there isn't a hill or mountain nearby for the hopping test.
I'll give Bosch a call tomorrow. They should hopefully have a compression tester.

/Jan

Hi,
If a valve is indeed not closing properly, you might be able to detect it (if it's an exhaust valve) by holding your hand near the exhaust pipe while the engine is running. You should be able to feel a noticeable increase in the exhaust flow speed, pulsating in time with the "hammering" sound.

But also an intake valve that no longer opens properly (due to a faulty hydraulic lifter).
can lead to a lack of air supply to a cylinder, which in turn can cause soot formation.

Best regards from Berlin.
Olli.