Odd Intake Noise

[dunc12]

Hi all, I recently picked up a swapped 1.6TD Jetta coupe. It runs great, fuel turned up a bit and running 12psi with an intercooler. Gets great mileage too (compared to what I'm used to with my 16V GTI).

However, a recent issue has started to concern me. The engine has a cone filter intake on it, just hanging out in the engine bay. I'm starting to get an intermittent "thunk thunk thunk" sound from the filter, sounding like it's occurring once every engine cycle. The noise will come and go, seemingly without any specific condition.

The car doesn't noticeably lose any power while this is happening, but I worry that I have a dying component in the engine. I have yet to perform a compression test.

Is this a common occurrence with these engines? Or is it something I really need to worry about. I can try to capture a video, if it makes diagnosing through the interwebs easier.

Thanks in advance 

[CODE4LS1]

I recently had this problem with my '91 Jetta.  Try checking the timing belt for proper tension.  I managed to not tighten the adj. nut properly and it worked it's way loose, causing a "ticking/tapping" noise at about the same rhythm as the crank.  I think maybe a valve was kissing the top of a piston because it was so loose.

[air-cooled or diesel]

make sure everything is tight around 'everything intake'. is noise at any speed?could it be suspension or brakes? if engine id be careful of running it until you find cause of noise. check intake 1st for anything loose. esp check timing belt, turn engine over 2x by hand, and also check belt visually, turn over a few more time and take a look.

[dunc12]

make sure everything is tight around 'everything intake'. is noise at any speed?could it be suspension or brakes? if engine id be careful of running it until you find cause of noise. check intake 1st for anything loose. esp check timing belt, turn engine over 2x by hand, and also check belt visually, turn over a few more time and take a look.

Thanks for the replies. I recently had my entire intake apart for some cleaning and inspection. Nothing remarkable besides a fair bit of oil in my intercooler piping. Minimal turbo shaft play. The timing belt is good and tight as well. I'll give it some turns by hand tomorrow morning and report what I find.

The noise is seemingly completely random. If it follows a pattern, I have yet to figure it out. It usually appears at startup, regardless of engine temperature. From there it will persist at any engine speed until sometimes randomly disappearing,

It drives me nuts and has me a bit worried, but the fact that the engine runs great otherwise has me puzzled...

[theman53]

Are you sure it is intake? Also, with the cone you can hear things you cannot with the stock box. Is it at a certain RPM like right between 1,000 and 2,000 rpm?

[dunc12]

Quite sure it was intake, yes.

It's been an odd week for my car. It's my daily, so I have to drive it every day. About a week ago, the odd intake noise I was hearing stopped occurring, right about when it started getting cold here. Not sure if they're related.

This would be great, except that this was also accompanied by a fairly significant loss of power. Car still started fine, didn't smoke, gets roughly the same mileage. Just a quieter exhaust note and noticeably less pickup when putting the foot down.

Today when I tried to start the car, I had to crank it much longer than usual to get it to start, and it suddenly had it's power back. Not a clue why. Had a hint of the previous intake noise as well.

Now, tonight, it seems that it's back to its low power state. This is driving me nuts. Can I assume it's a fueling issue?

Thanks in advance.

[TylerDurden]

I'd get down & dirty with the basics: Clear lines in and out of the IP. New fuel filter. Timing, compression, pop-pressures on the injectors.

Timing & compression tools are not expensive.
Pop tool is not hard to make (some simple brazing).
Bentley manual is worth the price.

[dunc12]

Yes, in suppose you're right. This will be a learning experience, as it is my first diesel. I'll let the Bentley guide me  (along with you experts, in times of need).

I'll report back with what I find, thanks for your help.