BMW 525 tds Starting Problems - Troubleshooting

Hello.

My problem is starting the engine after a long period of inactivity, for example, after being parked for a day.
Car: BMW e34, 525 tds, manufactured in 1995, 85,000 km.
It reluctantly starts after a long period of inactivity and a puff of dark smoke from the exhaust. However, it starts well if it has been idle for a shorter time (hours).
I have checked:
Spark plugs (cold resistance approximately 0.6 ohms).
Voltage is present at the glow plugs during the preheating process.
No air bubbles visible in the fuel hose.
Pre-charge pump is running.
el. Absteller o.k. (or) el. Absteller: OK.
Battery OK (1 year).
Diesel filter: OK.
My question: What could be broken, and what's the most effective way to troubleshoot it? (I'm not completely unfamiliar with technical matters).

Thank you very much in advance!

Sincerely,
Willi Linsmeier.

(PM from Rainer reinkopiert)

Hello Willi,

Quote:

Hello, My problem is starting the engine after a long period of inactivity, for example, one day. Car: BMW e34, 525 tds, manufactured in 1995, 85,000 km. It reluctantly starts after a long period of cranking and a puff of dark smoke from the exhaust. It starts well if it has been idle for a shorter time (hours). I have checked: Spark plugs (cold resistance approximately 0.6 ohms). Voltage is present at the glow plugs during the preheating process. No air bubbles visible in the fuel hose. Pre-charge pump is running. el. Absteller o.k. (or) el. Absteller: OK. Battery OK (1 year). Diesel filter: OK. My question: What could be broken, and what is the most effective way to troubleshoot it? (I'm not completely unfamiliar with technical matters)

Unfortunately, I don't know anything about your engine.
Normally, after starting the engine for a few seconds without the glow plug system, white diesel fumes will emerge from the exhaust.
Therefore, it's important to know if this is the case for you, meaning whether you're experiencing a slight white smoke initially, and then a sudden burst of black smoke from the exhaust when starting the engine.
or nothing at all from the exhaust, and black smoke when starting.

In the first case, the problem is most likely not related to the fuel supply (fuel injection pump, fuel shut-off valve, etc.), but in the second case, it probably is.

A low compression reading in your engine could be due to several factors. In the past, there may have been damage to the engine that could have allowed foreign objects to damage the cylinder walls, such as a broken turbine shaft in the turbocharger.

You have already checked your preheating system.
Were the glow plugs replaced in the past, and if so, could the wrong type have been installed (e.g., too short)? Or are these the original glow plugs?

Does your engine have a type of "throttle valve" in the intake manifold, which is used, for example, to gently shut down the engine or to regulate the exhaust gas recirculation rate?
If so, such a valve could simply get stuck and prevent enough air from being drawn in to achieve a sufficient temperature when the air is compressed in the cylinders.

Best regards, Rainer.

PS: All BMW mechanics, please come forward .

Hi,

"I'm not a BMW mechanic myself, but I know someone who is..."

"Quote from an anonymous BMW mechanic:"

"I had the same problem with my 525 TDS, model year 1994 (with 80,000 km on the odometer)."
The cause was a faulty fuel injector that couldn't maintain the pressure in the fuel injection system. The pressure drop lasted for a while; I could start the car without any problems after 2-3 hours, but after 24 hours, it took longer (about a minute of cranking), and if the car sat for a week or two (during a vacation), it wouldn't start at all. After replacing the fuel injector, using a fuel injector cleaner (from a specialized workshop) helped a lot; the engine runs smoother and responds better to the accelerator.
Since the repair, a year and 35,000 km have passed, and it still starts well after the preheating ).

Furthermore, I had a leak in the intake manifold (oil residue on the intake manifold flange), and a cracked downpipe (soot on the metal mesh). However, these defects are not related to the starting problem, but only to the poor acceleration and rough running at low RPMs.

"Oh yes, and Chip is no longer original either, now with 40,000 km, it uses 1-1.5 liters less diesel, the pump-nozzles are no longer a problem, and it just keeps running and running and running ))))".

I hope this helps.

Bertil wrote:

... The cause was a faulty injector nozzle, which failed to maintain the pressure in the fuel injection system.

"Hello, I thought the 525TDS also had a radial fuel injector? Then it shouldn't matter if you even remove the entire fuel line from the injector, let alone if one of the four injectors is leaking?"

Best regards, Rainer.

Shhh, the 525tds has a six-cylinder engine --- but don't tell anyone!!!

Bertil wrote:

Psst, the 525tds has a six-cylinder engine --- but don't tell anyone!!!

Okay *g*, I fell for it. But 1 out of 6 nozzles is defective, and then it doesn't start?

Best regards, Rainer.

Hi,

While I don't have a solution to the problem, I can post a link to the BMW engine forum. Perhaps the 'BMW experts' there can offer more helpful advice. They also have a search function.

Regards,
Arne.

Look here!

Rainer K. wrote:

... But if 1 out of 6 nozzles is defective, and then it doesn't start?

If the nozzle doesn't seal properly, air can enter the pressure line. Then, the system needs to be bled again, which can lead to "starter motor overruns."

Hello.

Have you ever measured the glow plugs?
If you need help, please email me!
[email protected]


Best regards, Micha.

Okay, as an experienced BMW mechanic and a passionate VW enthusiast, I would say:

Static base setting for distributor injection pump, as new, original.

The fuel injection pumps are correctly calibrated at the factory. Any adjustment to the basic setting over the engine's lifespan is achieved only through the elongation of the timing chain.

Since there is a causal relationship between the start of injection and the pump setting, an error code is only stored in the fault memory if the actual value of the start of injection deviates significantly from the target value (greater than +/- 2.5 degrees KW from the target value).


Have you already adjusted the pump?
What is the internal pressure of the pump?
What does the error memory say?