Engine Misfire: Causes and Solutions

Hello, I have a Golf TDI from 1994 with 180,000 km. For about 50,000 km, it has had this sporadic jerking, which you could also describe as engine misfires, sometimes accompanied by heavy black smoke. Now, I installed and activated a GRA (Gas Recirculation valve) – it's really easy to do and great for driving . However, I noticed that whenever I drive with the GRA active and my Golf starts jerking again, the GRA deactivates. This is obviously very frustrating }. Could it be that the engine control unit (ECU) switches into a kind of emergency mode at that moment, which then deactivates the GRA? The main problem I'm having is the jerking, but unfortunately, you can never read any error codes from the ECU. Is there perhaps somewhere an indication that the ECU went into emergency mode, and if so, why?
Thank you for any help you can provide.

Regards,
Maik.

Hi Maik,

... I would guess it's relay 109.
Since the GRA (presumably a safety system) can only be deactivated by domes, brakes, or regular shutdown procedures, something of similar importance must be happening in your situation.
And for that, I can only imagine power outages, which are usually caused by relay 109.
The strong jolts also seem to be related, although there's often some garbage in the error memory as well.

I had the same problems with my first car once.

After replacing the needle stroke sensor, they were gone.

Best regards, D.

Hello,
I finally got around to doing the tap test on my needle injector. Here's the result: about 10 taps resulted in a misfire. Does this indicate that the injector is defective, or is it within the acceptable tolerance?
No error codes were found in the memory.

Sure, here's the translation:

'Thank you.'
Maik.

Maik wrote:

. . .to perform the tap test on my needle injector. Here's the result: approximately 10 taps result in a miss. Can it be concluded from this that the injector is defective, or is this within the tolerance range? No entry can be found in the error memory.

Hi Maik,

Starting from the assumption that the NHG should not react to tapping at all , he probably already has some kind of problem.

An empty error memory is not unusual in this case.

Hello Ulf,
Thank you for the reply. I will go ahead and replace it then.

Regards,
Maik.

Choose the option that costs the least: Relay 109.
I had the same problem, and after that, the stuttering was reduced by at least 90%.
Regarding the alleged error codes in the vehicle's memory: in my case, it even indicated a defective control unit.
After that, everything was back to normal.
It could also be a brake light switch that is incorrectly adjusted (the one for the control unit). Check it in the 'Measurement data block, display group 06'.
The two rightmost zeros must simultaneously change to a value of 1.

Hello,
I finally got around to replacing the fuel injectors (at 181,000 km). I found them cheaply on eBay (new for €200). And sure enough, my car is now running over 700 km without a single misfire. I'm absolutely thrilled. Thank you very much for the good tips here.
Regards,
Maik.