Missing Compression: New Toy/Building Set?

hello

"I've bought another piece of junk," my wife says. Well, it's a Volvo TDI with a 5-cylinder engine (I've only ever owned TDI cars). But for the price, I had to get it.
I'm not picking up the car until the weekend; I've been following the discussions about these issues on the Volvo forum for a while.

The car is extremely difficult to start. However, if it does start (which can take a few minutes), it runs perfectly fine – as long as it doesn't cool down for more than 10 hours.

The previous owner had the car at a workshop, and they made several diagnoses. Ultimately, they told him that the problem was likely due to a lack of compression, which would require disassembling the engine. He considered the cost of that repair too high, and he wasn't willing to invest in it (just hearing that was enough for me to leave the workshop immediately...).

It might be true, or it might not be - it's basically irrelevant.

I just wanted to ask something - if the problem really is related to the compression, then the car wouldn't run properly after the initial start-up phase, right?

and what are the causes of a lack of compression?

Another funny task and an exciting challenge - it could also be a really small problem (maybe something to do with air...).

Let's see.

Thank you for the answers.
best regards, uwe

I honestly don't believe it's a compression issue... the five-cylinder engines are too robust for that. Besides, if it were a compression problem, it would run unevenly when cold, and possibly smoke blue.

It must have over 500,000 kilometers on it.

However, the five-cylinder engines seem reluctant to start if the injection pump is set too far advanced, either at the limit or outside of the tolerance. We've seen this before with the nearly identical five-cylinder engines in the LT vans. In those cases, the engine will take forever to start, even with the glow plugs on, but once it starts, it runs without any problems.

How about the nozzles?
Is the battery okay? If the starting speed isn't right, then those five-cylinder engines really won't perform well.

hello and thank you.

Okay, so far I only have the information he posted on the forum.

and it needs to run perfectly - I made sure of that, as I have to drive 300 km in the car on Sunday.

The battery seems new, and the starter motor is working well. I'll check everything else later.

I have software here, and I'll start by checking everything using the live data. I had a colleague who had a faulty control unit that reported a temperature of -90°C, so quite a few things are possible.
"However, a belt replacement was performed on the vehicle, and apparently the pump adjustment wasn't done properly - which would be a simple task."

Okay, now that I've already dismantled two identical cars/engines and have almost everything in the basement, troubleshooting any mechanical issues will be quite fun – and inexpensive. I have all the necessary components like the engine control unit/injectors, etc. And I could even replace the ESP system...

So, therefore, I'm looking forward to the challenge and to the knowledge and expertise that I can gain from it.


"And the thing about compression would be a problem, of course. I do have a short block here, but I doubt I'd be able to do a complete engine overhaul. I mean, if it fails completely, it wouldn't matter anyway. But when doing an overhaul, you should be fairly certain about having to revise or invest in a few things."

Let's see.

"Thank you."

Sure, here is the translation of the text from German to English:

"Hello"

...or is the initial amount incorrect due to a faulty temperature reading? Could you perhaps swap the sensor in the coolant? I'm not familiar with these things, but I assume they have something like that.

Okay, as I said, I think I have a few things I can test. And I hope I can find the error. Of course, a temperature sensor could also be the issue, but I can check everything through the software.

My question here was more about the underlying principle of compression. Specifically, I'm wondering if a car with insufficient compression, which makes it difficult to start, could suddenly run normally when warm, or if we can rule out a compression issue altogether.

or rather,

What problems did you experience when the engine, or a particular cylinder, had insufficient compression?

THANK YOU
Sure, here is the translation of the text from German to English:

"Hello"

Sure, it's possible that the compression isn't providing what's needed to start the engine. I'm thinking of things like wear in the valve seals in the top dead center area. But that's something that can be measured.

But: Your engine is so robust that this is rather unlikely.

Does it smoke when it starts?

hello uwe

I strongly suspect it's going to produce smoke. That's what happens when you really push the engine. My everyday TDI also had starting problems due to a faulty glow plug system, and it would also produce some smoke then.

Actually, I can only say for sure when I have the car here, when it's warmer, and when I feel like tinkering.

I assume the Bosch service measures the compression? Through which opening?

Okay, I just saw, apparently it's the glow plugs; that makes sense. Now I need some values for the engine that indicate whether something is good or bad. Then I'll get something like that and test it.

It's questionable what happens if the compression isn't right. If that's the case, I'll have to start taking it apart... but without tools to measure, that would be quite difficult. Then I guess I can dust off the short block from the basement and rebuild it.

THANK YOU

best regards, uwe

Quote:

Now, I need some values for the engine that are good or bad.

Okay, for a 1997 (Audi) AEL:

new: 25-31 bar

Wear limit: 24 bar.

Maximum 5 bar pressure difference between the cylinders.

Quote:

The question then is, what if the compression is not correct?

In that case, I would have to start disassembling things... but without tools to measure, that would be quite difficult...

Quote:

Experience has consistently shown that if the compression is so poor that the engine won't start even when cold, then a valve adjustment is unnecessary. Normally, that's how it appears. Either the tread is worn, rings are stuck together and hardened, or the wear on the reversal point of the top ring is already alarmingly advanced.

I do have a short block here - but I doubt I would be able to undertake a complete engine overhaul:wink:.

Did you not have a moped when you were young? It's basically the same thing, just bigger }.

perfect - thank you!!

vwSchrauber wrote:

Did you not have a moped in your youth? It's basically the same thing, just bigger

.

Hehe, yes, indeed. Based on my experiences with several DT50s, I was fortunately also able to own a few 400cc and 620cc KTMs, and I've gained my own experiences with those as well.
The problem I'm having in this regard is the size! I was able to remove the engine from my motorcycle in 30 minutes, then I went down to the warm basement and disassembled it on the workbench, all in the warmth.
Since my garage is too small and also exposed to all kinds of environmental conditions, I see this as a problem.
Just thinking about how I used my winch (which I had screwed into the concrete ceiling with concrete anchors) to pull out the first engine and transmission gives me goosebumps . The garage was built 40 years ago, and no one knows how much weight it can hold in the middle.

"But - and this is something I've been thinking about - since the car is essentially a collection of parts and I don't currently have any use for them, and I don't really have a time constraint right now, this could be the starting point. And even if it remains just an experiment, that's fine too. Then I'll just have a lot of parts that will definitely find a use somewhere."

"Thank you."
Sure, here is the translation of the text from German to English:

"Hello"