Hi,
I've got a 1991 Jetta with a 1986 Golf engine in it, that has about 320,000 miles on it (80k on the engine, if I can believe the PO). I've had it for a couple of years, but I still have more questions than answers. This is my first diesel and I've been lurking here and at vwvortex for a while. Poking around has given me a lot of good information, but figured I ought to just sign up and ask you guys straight out.
It's got a greasecar kit installed in it, which makes the hoses under the hood look like a plumber's nightmare. I ran on wvo for a little while, but other non-veg parts started failing so often I lost touch with my wvo sources. For now, I just want to get it reliable enough to be a good diesel daily driver.
I should say that the problems I have had are not really enough to keep it off of the road, it's just that I don't get a lot of time to tinker, so a bad rear wheel bearing had the thing sitting in the driveway for a month instead of an afternoon.
1. Right now, the downpipe has rotted and broken in two. I've rigged a really awful temporary patch, but in my dreams I'd like to do something like what clbanman did here:
http://www.vwdiesel.net/forum/index.php?topic=20427.0Trouble is, I've never welded anything before. I've thought about buying something like a 2.25" system for a 91 gasser from germanautoparts.com - which looks like it would probably fit, but I'd still be stuck for a downpipe. Does anyone know where I could get a "storebought" 2.25" downpipe? Or is the whole thing a bad idea?
2. I'd like to run a diesel purge through the system. Like I said, the hoses are a nightmare so I've been afraid of touching them and starting a leak because they're also old-looking and may be about to fail. I've bought some new hose and some clear hose from mcmaster-carr and I'm working up the courage to tear into it.
The reason for the purge is that the car runs fine, but misses at high rev. I tried doing the next best thing to a diesel purge by filling a new fuel filter with seafoam and running that through the engine. Like I said, at low-to-medium rev (no tach - just guessing by sound) everything runs smoothly. When you step on it, you hear a miss followed by some black smoke belching out of the tailpipe. Does that sound like a purge would help, or do I need a new Giles pump?

3. Black smoke also happens on hills and on-ramps - probably because I'm standing on the accelerator begging it to go faster. Someone suggested using Mann filters, which seemed to pep it up a little bit. The PO has a shop vac hose sucking air from the inner fender, so I was wondering if there was a better way than that to get more air - and if that would help. Should I ditch the Mann for a K&N? I haven't measured the I.D. of the shop vac hose, but it fits nicely into the air filter housing. I've been pondering cutting a bigger hole in the housing and piecing together a Spectre system.
4. I'd like to replace the injectors, but they look so rusty that I'm afraid I'll break them off. Someone told me that impact wrenches actually snap fewer bolts because they give a little extra vibration that helps break things loose. It seems crazy to take an impact gun to something like an injector though.
I saw a post where someone had gingerly tightened and loosened their injectors by hand while marinating them in some kind of penetrating oil, eventually getting them out. That seems more reasonable, but I do have a history of snapping bolts so what do I know?
Any help would be greatly appreciated.
Thanks,
-Bill