2.5 TDI: No Power After Head Replacement / Starting Issues

Hello,

Shortly after purchasing it, it turned out that the oil consumption in my 2.5 TDI AXD engine (130 hp) in my T5 was significantly increased, and it was no longer possible to start the engine without prolonged cranking. 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've 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), as they offered a competitive price and made a good professional impression.

I sent the injector pump elements for processing to have PD shims installed as a precautionary measure. 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 been cleaned with a wire brush . At least visually, the holes in the bores seemed okay...

The injectors were not dry when installed, and diesel was also leaking from the nozzle tip during installation (which rules out internal corrosion as the cause).

The seals for the components and 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 has stabilized somewhat, there is still a rather uneven idle. When I increase the speed to about 1100 rpm, it seems like it is only running on 4 cylinders. The whole situation improves the longer the engine runs.
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 improves slightly 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 forgotten a piece of cloth in an intake air duct, I removed the intake manifold and checked to see if a piece of it was lodged in the valves, preventing them from closing completely. However, that wasn't 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 volume deviations, I must say that they were significantly better yesterday and were within the range of +/- 0.10 mg/H. Also, all the other relevant values were completely within the acceptable range.

My assumption is that the PDE's drilling process may have caused some damage to the components. This could potentially explain the (perceived) increase in performance and the fluctuating deviations in the idle speed control.

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

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

At the beginning, immediately after starting (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'm talking about. Maybe I'll get a better video later using my significant other'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 and do not link to external hosting services.

I'll take a look at everything later.

Best regards, Rainer.

Hello,

The variations in the measurements look much better than the engine running would suggest.
Could it be that air/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 the (perceived) increase in performance and the fluctuating deviations in the idle speed control.

Or, you might have set the PD elements too aggressively... How did you set the PD elements (okay, probably all the same, but how)?

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 in advance 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 a different 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's roller). Then, screw the adjustment screw of the PD element in all the way. Afterwards, loosen it by 180 degrees, hold the screw in position, and tighten it with a torque of 30 Nm. Both the adjustment screw and the corresponding part on the PD element are new.

I noticed that the counterpart (which was included in the Bosch set) didn't have a hole in the center. The older inserts did have this hole.

The cylinder leakage was significantly higher before the engine swap, and the engine ran better. However, after the cylinder head replacement, I also achieved values of less than 0.10 mg per cycle with a warm engine for an extended period. This afternoon, however, I briefly saw values close to 3 mg per cycle, so it's very inconsistent.

"Tomorrow, I'm going to try attaching a piece of transparent tubing to both the inlet and outlet of the pump, just to see what happens. I'll check the injection amount right away."


Just a thought: When I first started the engine, 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's also possible that I was simply more attentive to noises during that first start.

Hello,

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

Best regards, Rainer.

The nozzles are almost certainly mine.

Due to insufficient fuel injection: Could this indicate a faulty pressure sensor? Or possibly a problem with the wiring harness for the pressure sensor...?

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 kind of effect if I disconnect the camshaft hall sensor?

Hi.

Andreas_M wrote:

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

"It's unlikely, because the values for the idle speed control are too good. It would be quite a coincidence if all the injectors were worn equally. Regarding the misfires: It could be, but to me it sounds more like a control 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, 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 6 to 7 mg/hour, but it still fluctuates 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... However, it shouldn't have such significant consequences yet.

Unfortunately, I haven't been able to check yet if there's air in the diesel supply 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 is within a reasonable range compared to the readings from 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 km, 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 air in the fuel lines. I installed different lines for testing, but 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° is still acceptable (the feed angle is something different). Does the tensioner 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 spur 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 VW. 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 pinion gear to 50 Nm. Therefore, a certain amount of play was acceptable to 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, which is connected to the timing gear drive via a Gates coupling, has a slightly larger amount of play, which is why I considered the play in the drive located in the cylinder head 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 1.5° to 1° when switching from a cold to a warm engine. But not always.

It should be absolutely straightforward...

Best regards, Rainer.