Running Rough

On the old wastegated TDIs, the N75 just bleeds boost pressure back into the air cleaner. Essentially it is an old fashioned self regulated wastegated turbo (like the old IDI diesel turbo engines used) but the ECU gets to have a say in the boost control.

Since they use boost pressure, and not vacuum, the hoses (red, blue, and black, from the factory) tend to get icky over time, because the normal operation of the crankcase breather will have some oil in the charge air. So the N75s can start to stick and malfunction after a while. Usually they can be cleaned out with some brake cleaner periodically and be fine again.

On those, the charge air control is completely its own thing, totally independent of anything else. The EGR is controlled by vacuum, which is sourced from the vacuum pump.

Replaced N75 hoses. No difference. Changed BK ECU to a GQ. I have boost now.

However, it still runs rough as though it’s running on three cylinders.

Also rechecked the compression. 480, 500, 500, and 480.

I’ll check the idle balance tomorrow. Block 11, I hear.

It’s block 13. Originally read 1.81 mg/str, 2.99 mg/str, 1.29 mg/str, blank.

Ran a couple cans of LiquiMoly Diesel Purge directly from the cans into the IP.

Now I’m at 0.77 mg/str, 1.24 mg/str, 0.14 mg/str, blank.

Seems to run a little better, though not much. And of course now I have a huge four inch long bubble in the clear fuel inlet line from when air got in it from changing from the filter nipple to the LiquiMoly and back again. Also, the engine continued to idle like crap when running straight from diesel purge to pump and back with no air bubbles in the feed or return lines to and from the can.

mustangmarty said:

It’s block 13. Originally read 1.81 mg/str, 2.99 mg/str, 1.29 mg/str, blank.

Ran a couple cans of LiquiMoly Diesel Purge directly from the cans into the IP.

Now I’m at 0.77 mg/str, 1.24 mg/str, 0.14 mg/str, blank.

Seems to run a little better, though not much. And of course now I have a huge four inch long bubble in the clear fuel inlet line from when air got in it from changing from the filter nipple to the LiquiMoly and back again. Also, the engine continued to idle like crap when running straight from diesel purge to pump and back with no air bubbles in the feed or return lines to and from the can.

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If you have a perpetual bubble in your fuel line then you have an air leak somewhere in the fuel supply.

A properly functioning IP will be able to eliminate some minor amount of air getting into the fuel line because the lift pump can draw more quickly than the air enters, however, if the leak is big then the lift pump cant deal with it and you have gaps in fueling.

If you still have the thermo T installed at your filter you need to check and see whether that's the cause of your problem. After that I would go to the rear of the car and check the fuel line from the tank all the way to the IP.

Steve