2.5 TDI - No power after head replacement / Starting issues

Hello,

Shortly after purchasing it, I discovered that the oil consumption in my T5's 2.5 TDI AXD engine (130 hp) had increased significantly, and starting the engine without prolonged cranking became impossible. As a result, I had no choice but to have the injectors resealed and install the well-known shims.

During the dismantling process, I discovered a crack originating from a hole drilled for a pressure drop element (PDE) in the head.
I decided to install a new cylinder head from AMC, including the camshaft, lifters, and valves. The entire assembly was installed and sold by GMC (Gütersloher Motorencenter) because their prices were very reasonable, and they also made a good professional impression.

I sent the injector pump elements for processing to have PD shims installed preventatively. Afterwards, I took them to a workshop for ultrasonic cleaning. However, when I picked them up again, they looked as if they hadn't been in the ultrasonic bath, but had instead been cleaned with a wire brush . At least visually, the holes of the bores seemed okay...
The injectors were not dry when inspected, and diesel fuel was also leaking from the nozzle tip during installation (which rules out internal corrosion as the cause).

The seals for the components and those for the rest of the fuel system on the cylinder head were, of course, replaced. Just like all the other seals and expansion bolts.


Now, let's get to the problem:

The engine can be started even after a long period without being connected to the organ, but then it runs very unevenly for a few seconds (sometimes more, sometimes less) and below idle speed. Even after it stabilizes somewhat, there is still a rather rough idle. When I increase the RPM to around 1100, it seems like only 4 cylinders are running. The whole situation improves as the engine runs longer.After some time, the engine will then run normally.
However, the full performance is not available during test drives. I do, however, have the feeling that the performance gets a little better with each drive.

During the initial test drive, I noticed that one valve was making a ticking sound. After a short period of driving, the constant ticking changed to an irregular ticking, as if the camshaft was only engaging intermittently.
Out of fear that I might have left a piece of cloth in an intake air duct, I removed the intake manifold and checked to see if any fragments had become lodged in the valves, preventing them from closing completely. However, this was not the case!
Shortly after I checked the intake channels for any fabric remnants, the knocking sound completely disappeared.
My guess is that perhaps a valve wasn't properly lubricated with oil before installation.


I have attached the log file from a measurement run (I hope the data is accurate enough for you ). Otherwise, I am happy to be corrected and will do my best to provide useful results .

Regarding the fuel injection deviations, I must say that they were significantly better yesterday and fell within a range of +/- 0.10 mg/H. Also, all other relevant values were completely within acceptable limits.

My assumption is that the drilling process performed by PDE might have caused some damage to the components. This could potentially explain both the perceived increase in performance and the fluctuating deviations observed in the idle speed control.

I would like to add that the engine was disconnected using original tools and manually rotated by hand after assembly. The bevel gear drive was installed and adjusted according to the repair manual. Torque specifications were, of course, observed! The rocker arm shaft was also adjusted using a dial indicator and according to the specified values.

I have to admit that pump-nozzle technology is still quite new territory for me. Until now, I've only had experience with my 1.9 TDI engine with a vacuum pump .

At the beginning, immediately after starting (at 0:14 seconds), NO gas was given! The dull sound comes from the microphone .

The quality isn't amazing, but you can at least see what I mean. Maybe later I'll be able to make a better video with my partner's less prehistoric phone .

Hi Andreas,

If you align the email addresses of the shop and the forum, you will automatically be recognized as a customer.
Please always upload videos and similar content within the topic itself, and do not link to external hosting services.

I'll take a look at everything later.

Best regards, Rainer.

Hello,

The measured deviations look much better than the engine running would suggest.
Could it be that air or foam is only being drawn into the fuel system while the engine is running? The engine sounds like it's misfiring.

Quote:

My assumption is that the PDE's drill holes may have been damaged due to rough handling. This could potentially explain both the (perceived) increase in performance and the fluctuating deviations of the idle speed control.

Or, you might have set the PID parameters too aggressively... How did you configure the PID parameters (okay, probably all the same values, but what were they)?

What is the fuel injection amount (measurement block 1 in the engine control unit) when the engine is cold and idling?

Best regards, Rainer.

Hello, thank you for the advice; I will keep that in mind in the future .

Apparently, I just logged in with the wrong username. I had some problems changing my password or being recognized as a customer some time ago, so I created another account.

Yes, you're right, the engine has occasional misfires when it's cold, especially at slightly higher RPMs around 1100 RPM.

I adjusted the elements using a dial indicator. Specifically: rotate the camshaft until the corresponding cam on the rocker arm shaft is at its highest point (measured with the dial indicator directly on the rocker arm roller). Then, screw in the adjustment screw of the PD element all the way. Afterwards, loosen it by 180 degrees, hold the screw in position, and tighten it to 30 Nm using a torque wrench. Both the adjustment screw and its counterpart on the PD element are new.
I noticed that the counterpart (which was included in the Bosch set) did not have a hole in the center. The older inserts used to have this hole.

The cylinder leakage was significantly more pronounced before the engine swap, with better engine performance. However, after replacing the cylinder head, I had already achieved values of less than 0.10 mg per stroke with a warm engine for an extended period. This afternoon, however, I also briefly saw readings close to 3 mg per stroke, so it's very inconsistent.

"Tomorrow, I'm going to try putting a piece of clear tubing into both the inlet and outlet lines of the pump. I'll also check the injection amount right away."


Just remembered something: During the first start, I noticed a kind of sucking or popping sound coming from the area of the air filter box. Now I can't hear it anymore. Of course, it could also be that I was simply paying too much attention to noises during that first start.

Hello,

The amount of fuel being injected seems too low to me, but the PD adjustment method is okay. Did you also receive the correct PD elements back?

Best regards, Rainer.

The nozzles are almost certainly mine.

Due to insufficient fuel injection: Could this indicate a faulty pressure sensor (PDE)? Or possibly also a problem with the wiring harness for the PD system...?

Das Prüfen der Elemente habe ich leider sein lassen, nachdem der Bosch-Dienst pro Düse 80 Euro zzgl. Swanted to be expensive...

Edit: Shouldn't there be some consequences if I disconnect the camshaft hall sensor?

Hi.

Andreas_M wrote:

Due to insufficient injection quantity: Would that then be another indication of a faulty PDE? Or possibly also a problem with the PD wiring harness...?

"It's unlikely; the values from the idle speed control are too good for that. It would be quite a coincidence if all the injectors were equally worn. Regarding the misfires: It could be, but to me it sounds more like a regulation problem due to unexpectedly high actual injection amounts."

Andreas_M wrote:

Edit: Shouldn't there be some consequences if I disconnect the camshaft hall sensor?

Yes, during engine start-up, and furthermore, the synchronization angle should no longer be measurable at that point. What is the actual value of that angle anyway?

Best regards, Rainer.

The amount of fuel injected immediately after startup fluctuates between 11 and 13 mg/hour. After some time (while misfires are still present), it settles down to around 6 to 7 mg/hour, but it also varies significantly.

The warmer the engine, the fewer fluctuations. For example, at a coolant temperature of 38°C, I already achieved a clearly readable value of 5.5 - 5.8 mg/h, and the engine also ran noticeably smoother.

The twist angle is .5°. So, it could be better... But it shouldn't have such significant consequences yet.

Unfortunately, I haven't been able to check yet if there is any air in the diesel fuel line.

Is the coolant temperature that the engine control unit sees in the corresponding measurement block plausible?

Best regards, Rainer.

With a cold engine, the temperature reading from the sensor is plausible (it's within a reasonable range compared to other sensors and the actual outside temperature). The temperature also increases gradually, and today, while measuring, it remained at 83°C.
However, today I only managed to drive about 8 kilometers, and the heater was running the whole time.

If the engine is cold tomorrow, I'll try starting it with the temperature sensor disconnected.

While taking measurements, I noticed that the rotation angle is now set to 1 degree.

I also stopped by a friend's workshop today. He mentioned that the engine running issue might be related to the fuel injection start and that the twist angle of 1.5 degrees could also be the culprit? However, he also admitted that he doesn't really know the engine and doesn't really want to deal with it .

Today, I also checked if there was any air in the fuel lines. Although I installed different lines for testing, I couldn't see any bubbles or foam. Maybe tomorrow I can somehow connect the transparent hose to the original lines to rule out any issues with the hose couplings.

Hi,

A rotation angle of 1.5 degrees is still acceptable (the belt tensioning angle is something different). Does the tensioner pulley also tighten the timing belt, or is it too loose? Does the motor even have a timing belt, or does it use spur gears?

Best regards, Rainer.

The motor has a planetary gear drive.

Andreas_M wrote:

The motor has a planetary gear drive

.
Could something have gone wrong during assembly that's causing this play between the camshaft and crankshaft? Is the synchronization angle displayed in VCDS stable, or does it fluctuate significantly? Small fluctuations are normal...

Best regards, Rainer.

During installation, I adjusted the eccentric shaft as described by Volkswagen. There was a slight play in the camshaft or eccentric wheel.

VW also states that you should use the special tool and a torque wrench to remove any play from the pinion gear assembly, and then, while maintaining the torque, tighten the screw of the crankshaft pulley to 50 Nm. Therefore, a certain amount of play was acceptable for me.

The value of the twist angle doesn't fluctuate constantly and only changes from 1.5° to 1° when transitioning from a cold to a warm engine. But not always.

"Edit: The alternator is also connected to the front sprocket drive via a Gates coupling and has slightly more play, which is why I considered the amount of play in the drive system within the cylinder head housing to be normal."

I've decided to take everything apart again, have the injector nozzles checked, and adjust the injection timing more precisely. Hopefully, we can find the problem this way.

I don't think there could be any negative consequences, so I will do it at the next opportunity.

Quote:

The value of the twist angle does not fluctuate constantly and only changes from a cold to a warm engine from 1.5° to 1°. But not always.

It should be absolutely straightforward...

Best regards, Rainer.