Compression Test VW/Audi 3.0 V6 TDI

Hello everyone!

I have a 3-liter V6 TDI engine that is not running on all cylinders. The (VAG) workshop supposedly checked the compression and found that cylinders 1 and 5 have no compression. My question is, how can the compression be checked on this relatively new engine without removing the glow plugs or the piezo injectors? There are no visible signs or marks on the fittings of either of these components?

Best regards!

Frank.

Hi, you can try the "hopping test." It's quite basic, but it might give you some indication.
You position the car on a slight incline, put it in a high gear so that it slowly rolls down (with the engine off!). Then you observe whether it bounces evenly and is in good condition, or whether it bounces unevenly, indicating that something is not right.
If you're looking for "Hoppeltest," you should also find a better description.

See you later.

P.S. How many kilometers has he run?

It is probably correct that a "hopping test" can be performed. While the achieved accuracy may be sufficient to detect significant compression loss, this loss would likely already be noticeable through other symptoms.

I think what Frank was trying to say was more about whether the workshop actually measured the compression. In my opinion, it's not possible to do that without removing the glow plug/injector.

Is there a compression protocol in place?

ok, I understand.

Sorry for the misunderstanding.

Possibly, a compression test was performed using guided troubleshooting.

I'm not sure if that's possible with your car.

Hello everyone!

Yesterday evening, I spoke with a friend who's a VW mechanic. Apparently, there's actually a way to determine if individual cylinders have low compression by using the diagnostic interface in conjunction with a measurement of the starter motor current draw (quite a mouthful!).

I don't have a diagram/measurement log; the first thing was to figure out what's wrong with the engine. And definitely, there's a lack of compression in 2 cylinders...

Best regards, Frank.

Alternatively, you can keep an eye on the LLRR values as a rough indicator. However, if you suspect something like this, I would use the method developed by VW as a "basic diagnosis" and then verify it using established methods.
I'm completely unfamiliar with the 3-liter engine class. How complex is the installation? Is it possible to perform a GSK (Grundüberholung, or complete overhaul) without having to learn the entire engine compartment?

He probably already has ceramic glow plugs installed, and I wouldn't remove them unless it's absolutely necessary.

Well, if there are any real abnormalities associated with such a diagnosis, and if there's no other way forward, what's the alternative?

Well, if there are any real anomalies associated with such a diagnosis, and if there's no other way forward, what's the alternative?

Hello!

Okay, the alternative is to remove the injectors and use an endoscope to look into the combustion chamber. If there's a hole in the piston, you've found the problem. Otherwise, screw in the 'normal' compression tester and try that. Then you'll definitely get reliable readings. If there's no valve stuck in the piston, and the valve itself looks good, then it's most likely a leaking valve. The most probable solution is to remove the cylinder heads and take a look. That way, you'll be certain about what's going on.

Best regards, Frank.

Hi,
In every compression test, there are actually measured values and they are recorded in a protocol. What position was calculated for you?
Alternatively, what does the LLR (Idle Speed Control, see Matthias above) indicate? This allows you to quickly and easily see if there's a problem with a particular cylinder without having to adjust anything. Next, you should check the injector or the mechanical components.
Sure, here is the translation of the text from German to English:

"vg"

This is a common abbreviation for "very good" in German. It is often used in online forums and chat rooms.
Herbert.

Hello everyone!

I spoke with the workshop manager. He told me that the compression can be determined using a tester. Apparently, there's a method to derive the compression from the starter motor's RPM and current draw. No one has actually measured it yet. Nothing has been calculated; it was just a free assessment. The workshop's suspicion is that the injectors weren't working correctly. The injection time was too long, causing the pistons to be hit -> resulting in melted pistons.

Okay, here's what I'm going to do: I'll pick up the car with the trailer, remove the injectors, and use an endoscope to take a look inside. If the diagnosis of melted pistons and faulty injectors is confirmed, then that's it for the machine.

Best regards!

Frank.

Frank F. wrote:

I'm going to do the following now: I'll pick up the car with the trailer, remove the injectors, and look inside with the endoscope. If the diagnosis of melted pistons and defective injectors is confirmed, then that's it for the machine.

"That's nonsense in my opinion! Take out the spark plugs and do a classic compression test. You don't just tear the whole engine apart if you're not sure what's wrong. How does the engine sound when starting? If there's no compression in two cylinders, you'll hear the starter motor revving up briefly."

Hello!

Removing the glow plugs at 173,000 km is something I'm a bit apprehensive about. Nobody willingly messes with those ceramic things; they're supposed to be so fragile. What's the problem with removing the injectors? I haven't touched those piezo elements yet; thankfully, there hasn't been a need so far.

My suspected procedure is to disconnect the high-pressure line, disconnect the return line, and remove the injector. I will look inside, and if I don't see anything, I will perform a compression test through the injector bore. The unknown in this equation is that I don't have a precise idea of how easy or difficult it will be to remove the injectors.

Best regards!

Frank.

Frank F. wrote:

What's so difficult about unscrewing the injectors?

Since you might not have any experience. What if you've taken everything apart and can't see anything, what then? It's all for nothing. Let the candles settle properly over 1-2 days, then it should work. You can also break a lot of things when removing the injectors. So, be careful...

The candles will have to be removed eventually anyway. Either they'll be taken out at the designated time, or not. If not, you can always still see something.