BMW 525 tds Touring: Starting Problems & Glow Plug Issues

Hello fellow DIY enthusiasts,

I'm posting here on behalf of my brother and would appreciate your advice.

Although this forum is primarily focused on VAG TDI vehicles, I would like to address the BMW specialists here as well.

Here's the translation:

'This is about the starting problems/glowing plug issues with a BMW 525 tds Touring.'
Year of manufacture: Feb./1999; 6-cylinder, 2.5-liter turbo diesel engine; 143 horsepower; automatic transmission; 330,000 km mileage.

Before I describe the problem, I want to mention that I've really tried using the search function, not just in this forum. Since I'm a TDI enthusiast, I don't want to register in other BMW forums just for this issue.

The problem is that the glow plug system isn't working correctly. It doesn't always activate, whether the engine is cold or slightly warm, which means you have to crank it for a long time.
The indicator light shows whether the glow plugs are activated, and if they are, the engine starts perfectly. However, occasionally (not regularly, but increasingly often!), the light doesn't come on, and the glow plugs don't activate. If you have to crank the engine for a long time, you first see white smoke (unburned diesel fumes = diesel injection is occurring!), and then black smoke when it finally starts.

Unfortunately, I'm not familiar with this machine. In my opinion, the control system (relay or temperature sensor) is not working correctly. The question is, where are these components located in this car?

For TD and TDI engines, you can check the glow plug system by disconnecting the temperature sensor connector. This will cause the glow plugs to activate continuously, regardless of whether the engine is cold or warm. Does this same method apply to a 525 tds?

What else can one do?

I am grateful for any advice.

Best regards, Georg.

I'm not entirely sure, but I believe the E39 has a separate control unit for the glow plug system.
In addition, there are 1-2 large fuse elements located in the engine compartment for the spark plugs.
If it's broken, it might sometimes make contact and sometimes not.
It happens occasionally.

Okay, go ahead and remove the 2 microfilter boxes in the engine compartment and take the cover off from underneath. You'll probably be able to tell which ones they are right away.

Hello Steffarn,

Thank you for the first tip.
I will forward this suggestion to my brother.

The issue with the fuses might actually fit the picture, as it seems like there's a loose connection somewhere causing problems. Because if the glow plug system is working, the engine starts perfectly. This suggests to me that all the glow plugs and the fuel injection system are okay.
If it doesn't pre-heat, then nothing helps. Repeatedly turning the ignition on and off won't improve the situation either. So, you're in for a long cranking session.

Since I'll be visiting my brother in a few weeks, I'll be studying this topic myself. Therefore, I'd like to learn as much as possible from you before then.

I would also like to check the temperature sensor for the glow plug system. To do that, I need to know where the temperature sensor is located. Does anyone have any idea?
Is it a separate temperature sensor?

I'm waiting for more tips from you...

Thank you.

Georg.

Georg-TDI wrote:

I am waiting for more tips from you...

Hi Georg,

I also initially asked a colleague who owns an E34, and he got the information from the E34 forum.

Quote:

... only temporarily helps to unplug the temperature sensor connector for the glow relay (the second one from the front, at the back), then it will glow. (There are three of them, so it's the middle one.) Otherwise, measure the voltage. However, in 99.99% of cases, the glow plugs are defective. Please replace all of them at once and get them from BMW. Bosch glow plugs are not supposed to last more than 10,000 km... What you can find in the e34 forum… http://forum.e34.de/

Sure, I'd be happy to translate the text for you. Please provide the text you would like me to translate.

There are three temperature sensors located at the top, under the intake manifold. The one in the middle is the one being referred to.

Thank you, Bertil,

That's exactly the information I was missing!

Now I know where the temperature sensors are located, so I can check the system.

I know that spark plugs are usually the culprit, but in this case, it's probably something else.

First, all the glow plugs were replaced at approximately 240,000 kilometers and should still be in good condition. Second, the engine starts perfectly with the glow plugs activated, which supports the functionality of the glow plugs.

I will keep you updated. However, your suggestions are always welcome.

Thank you.

Georg.

Hello everyone,

There are new developments in this case.

Before I describe the solution to the problem, I would like to briefly address the issue itself.
After a long observation period, the following was determined. (slightly deviates from my original problem description!!!)

The engine pre-glows every morning and then starts perfectly. However, during the day (whether it's cold or warm), it no longer pre-glows, which means it takes a long time to start.


Now, my brother's car was at a free repair shop because of the starting problem. The guys there were able to read the error memory, but since there was no error message: ==> helplessness...

After that, my brother took the car to a reputable BMW workshop, and they identified and fixed several issues (taking a total of 3.5 hours).

The preheating system is functioning correctly, and the preheating cycles are appropriate for the weather conditions.

2. The camshaft was incorrectly adjusted after the cylinder head gasket and timing chain replacement (which was performed by an independent workshop).
Almost a tooth towards the back.

3. The start of fuel injection was set to a very late timing.


After correcting these 'defects,' the engine now starts within approximately 2 seconds, even when warm.
So, hopefully the problem is solved for good.

At this point, I would like to thank everyone involved for their support.

Best regards, Georg.