Opel turbodiesel engine (Isuzu) starts poorly when cold

'I already replaced the piston rings and cylinder head two years ago. After driving at full throttle, the engine runs worse the next day, around 4000 RPM. Without measuring, I suspect a loss of compression due to valves sinking into their seats. Now, adjusting it is a real pain because shims are used on the tappets. Does anyone have experience with Opel diesel engines? Are there perhaps valve seat inserts that can prevent this sinking?'

Hello fellow car enthusiasts!

Welcome to the forum.

Unfortunately, I'm not familiar with the Isuzu diesel engine. Perhaps you could describe the engine in more detail to shed some light on the situation and to make troubleshooting easier.
If you answer the following questions, we can certainly provide you with better advice and assistance.

1) Is it a pre-chamber diesel engine or a direct injection engine?
2) What type of fuel injection system is installed in the engine (distributor injection pump, common rail, in-line injection pump, etc.)?
3) Is it a turbocharged engine or a naturally aspirated engine?
4) Does the engine have an electronic control system or a purely mechanical pump control system?
5) Basic engine specifications: displacement, number of cylinders, power output, engine type, etc.
6) Who is the manufacturer of the fuel injection system, and if possible, please provide details?
7) Year of manufacture and mileage of the vehicle.

Spontaneously, if I were to encounter a cold start problem, I would suspect the glow plug system (especially in engines with a pre-chamber) or incorrect fuel pump timing.

Regards,
Alex.

hi, donalexo!

It's a pre-chamber diesel engine with a VE injection pump, mechanical control, turbocharger, and an intercooler. It has a displacement of 1686cc, produces 60kW, has 4 cylinders, 2 valves per cylinder, and uses tappets with shims.
I believe it's a Lucas fuel pump installed, set to a stroke of 0.85mm.
Year of manufacture: 1993, Mileage: 267,563 km.
Heating system checked, all okay. Pump settings also okay.

Hello fellow car enthusiasts!

Okay, so, if the heating system and the pump settings are okay, then I would next perform a compression test.
Furthermore, a weak battery (insufficient starter current), a sluggish starter motor, or a corroded cable/ground strap on the starter (high resistance) could also be responsible for the poor starting performance. A starting speed that is too low will not generate sufficient compression, which can make it difficult to start the engine.

You suggested that the valves might be leaking. What makes you think that? Didn't you already install a new cylinder head? Have you checked the valve clearance in the meantime? There may be deviations here that fall outside the tolerance range.

Does the engine make any unusual noises? What is the oil consumption?

Regards,
Alex.

Hello donalexo,

I think you're right about the compression test; I should probably do it sometime (but I don't have the time).
Okay, the battery is brand new, just replaced. The starter has been rebuilt after it ran once and was almost destroyed. Before the compression test, I'll check the valve clearances (which is standard procedure anyway). The noise is okay. Oil consumption between oil changes (every 10,000 km) is about 0.75 liters.
As I mentioned, I had the engine open two years ago and replaced the piston rings. However, they were in really good condition with minimal wear. The engine also didn't have good compression at that time. The aluminum head doesn't have valve seats installed; I think the aluminum itself yields due to material compression, which reduces the valve clearance. This changes the valve timing and working volume. I suspect that this may have caused the compression to decrease again. I did the repair at 198,000 km, and now it's at 267,563 km. That's not a huge difference.


Best regards, André

Hello!

Sure, I know a story about Isuzu diesel engines.

My father once had an engine failure in his Passat because the drive sprocket for the timing belt twisted, which altered the valve timing. Although the sprocket is secured with a pin, this pin was apparently not strong enough. According to a mechanic specializing in engine repairs, this type of failure is apparently more common in VWs and is often misdiagnosed at VW workshops, leading to the installation of a replacement engine. Then, the customer is told about things like broken timing belts or similar issues.
Anyway, it started with the diesel engine having trouble starting and producing a lot of smoke.
To get to the point, a friend of mine with an Isuzu SUV experienced similar symptoms. A Bosch service center then tinkered with the fuel injection system, but without any improvement. He then went back to the Bosch service center, mentioning the possibility of misaligned timing. They had never heard of such a problem and laughed at him. However, after some discussion, they removed the timing belt, unscrewed the lower pulley, and... the locking key was broken. A new shim was used to secure the sprocket, and the motor started running normally again.
Good luck!

Regards,

Christian

Thank you for your report. Unfortunately, I still haven't found the time to work on the car. I'm just not able to get to it (even though I repair cars every day), but I'll remember to do something about it when I do have time. Thanks again.
Andrè