Soot on back of Jetta

[Rat407]

I was just wondering how normal it is to have a build up of black soot on the back of my 91 Jetta TD.  It takes about a tank of fuel for it to really build up on the back of the car.  While driving down the road it smokes a good bit when it is still cold but when it warms up it doesn't seem to smoke to much. I can see some in the rear view but nothing major, unless I run up the gears and have it floored.  

I guess I can start tinkering with the LDA to see if it helps some. I'm under the impression that the "smoke screw" isn't something to mess with untill the last resort.
Thanks

[MacGyver]

I used to get this on my 87 TD, and still do on my 97 TDI, to some extent.
Also noticeable since I typically wash my car bi-annually :oops:

I found what made the biggest difference regardless of smoke quantity, is having a turn down on the end of the exhaust as opposed to it sticking straight out as most custom shops leave it.
Just doesn't seem to swirl up onto the car as much.
Plus when you let 'er rip, you can leave three black marks on the road instead of two

[wyldman]

Not much you can do about the soot on the back of the car.Some tuning may help make it better,but you still will get some.

The exhaust turndown is a good solution,it will cut down on a lot of it.

I wonder if adding a small lip or spoiler to the back of the car would help.I know it makes a big difference in keeping the back window free of road dirt,maybe it would help with the soot as well.

[TDForNow]

I wonder if adding a small lip or spoiler to the back of the car would help.I know it makes a big difference in keeping the back window free of road dirt,maybe it would help with the soot as well.

Actually, while helping downforce at the rear, the lip would aggravate this more. The increased low pressure area created behind the lip would draw more air up from the bumper area bringing up more soot with it.
 
You didn't say how old the injectors are, if they're any kind of tired, you'll be making more smoke from the same amount of fuel due to deteriorating spray pattern. I usually get about 50-60k miles out of a set of rebuilts before they start getting "loud n' smokey" (as they are now :oops: )

[Rat407]

The injector are good, they were new 12K miles ago when I put the engine together. I had them flow checked before I put them in even thought I just bought them new.  Just because you hope to buy things in good order, my luck has it that never happens so I had them checked. The IP is also new, as in completely rebuilt and bench flow checked.  I guess it is just a matter of adjustment at this point to get everything in line. My timing is right on according to the Bentley.  I was just wondering if any others had the soot effect. Most of my drive time is highway miles.  Thanks for the help.

[hillfolk'r]

I found what made the biggest difference regardless of smoke quantity, is having a turn down on the end of the exhaust as opposed to it sticking straight out as most custom shops leave it.
Just doesn't seem to swirl up onto the car as much.
Plus when you let 'er rip, you can leave three black marks on the road instead of two

 yea lets hear it for a blackspot in the driveway,,from your parking space, nice buildup,,even melts snow and makes it black!!!!,i got a turndown!!!!

[TDForNow]

 yea lets hear it for a blackspot in the driveway,,from your parking space, nice buildup,,even melts snow and makes it black!!!!,i got a turndown!!!!

Yeah, no-one complains much when I "mark" my territory this way!! :lol:

[hillfolk'r]

now its gettin broken in a little,ive had a few tailgaters etc,,sometimes ill give them a lil puff,,jus floor it for half a second ,when cruisin,,,,either they backoff,or back off,then go flyin by holdin their nose,,,only thing is now if i try and puff it,,itll torque up :twisted: