Rebuilt Engine Misfire: Causes & Fixes

Hi there!

I've spent the last 6 weeks completely refurbishing my Touran (2009, BMM).

"Engine bored and honed, new oversized pistons, crankshaft polished, engine block and cylinder head machined, new valve seats, new valve guides, new valves, PD elements refurbished, new camshaft, all gaskets replaced, new turbocharger, and a bunch of other small parts. Additionally, I installed a supplementary heater to function as a parking heater. All work was done according to workshop specifications."

So far, so good. I've driven about 800 km. The engine doesn't misfire, starts well, has good acceleration, and runs smoothly.

However, the engine is extremely noisy under load. The valve timing is correct, and my OBD scanner (unfortunately not VCDS) doesn't show any error codes. My friend (a certified mechanic) and I are at a loss. Does anyone have any ideas?

To determine how much material needs to be removed from the head, it needs to be measured first. Normally, machining the head is not allowed on a diesel engine. If too much material has been removed, I can imagine that it might cause knocking.
Did you check the piston alignment?

After planning, we measured the piston protrusion and installed a thicker gasket accordingly. I'm not sure about the "Deachsierung" part. The engine rebuilder took care of the pistons.

chli1976 wrote:

To determine how much material needs to be removed from the head, and then measure to determine which gasket you need. Normally, machining the head is not allowed on a diesel engine; if too much material has been removed, I can imagine that it might cause knocking. Did you check the piston alignment?

Isn't the head already flat? I just checked on Google.

The valves cannot protrude, otherwise, the cylinder head design would not be feasible.

Therefore, the design of such a ZK (presumably referring to a specific component or system) has no significant impact on the compression ratio.

The correct head gasket thickness should still be used because the piston protrusion varies.

Are the connecting rod bearings and piston pin okay and not loose, so that the pistons are hitting the top of the cylinder?

Best regards, Rainer.

Only a few hundredths of a millimeter were removed from the head and block. The valve seats were also set inwards to adjust the dimensions. No, the engine runs absolutely freely. The piston pins are brand new, just like the pistons. Of course, we also measured the axial play and radial play of the crankshaft. Everything was within the tolerance range. That's why we're so puzzled.

dieselschrauber wrote:

The valves cannot protrude, otherwise, the cylinder head design would not be feasible.

Yes, there are some, although not many. They must be removed before the tarpaulins are installed. (Exception: older ZK swirl chamber diesel engines).

I don't understand what people are always complaining about regarding thicker diesel fuel after it's been blended according to the specifications.

Just imagine a board being planed – it's flat before, and it's flat after. There's no combustion chamber in the ZK!

And, what was the cause?
I experienced this after replacing the camshaft and lifters on a BPW engine. I had been careless and didn't adjust everything correctly.

Best regards.

Okay, please provide the German text you would like me to translate.

Okay, now...

Okay, so: The cylinder head and engine block were modified because the surface just looked awful. And modifying the cylinder head and engine block makes a significant difference in terms of compression. The cylinder head and engine block were modified because we were already tearing everything out and rebuilding it anyway. This makes everything run more smoothly and with less play. We've now installed the thickest head gasket that VW offers. Due to the increased compression, it was running much stronger than before. It's calmed down a bit now.
"The cylinder pressure is 32 bar, and on the test bench, it produces a healthy 155 horsepower with the new turbocharger (Stage 1). Last week, it received a completely new suspension system (all bearings) including shock absorbers and brakes. Now, I just hope the transmission holds up. That's the only thing we haven't replaced yet..."

Hello,

Then, I would first check if the engine is knocking even without any tuning. If it is, then the cause is clear.

Attention: Were the same PD (pump-injector) units installed in your new engine as were in the old engine?
The engine control unit and the power distribution units must be compatible.

Best regards, Rainer.

The "tuning" consists only of a Stage 1 turbocharger, which has an improved impeller and better bearings. It's not really tuning. The knocking noise has also improved significantly; it was extremely loud initially. The PD injectors were already installed in the Touran. They were only rebuilt by a specialist. However, I reinstalled them in their original locations just to be safe.