Have a stock '98 6.5L Turbo C3500 Crewcab. Use it to pull 18k trailer (short distances). The last two days, I haven't had power and when putting the hammer down, black smoke poured out. I was reading in previous posts about the wastegate solenoid. Could this be the culprit? I have vaccuum pressure. What else could it be? Have to pull again tommorrow and don't want to wreck anything.

Where did you check for vacuum? At the wastegate solenoid, or at the wastegate on your turbo? If you have vacuum pre-solenoid but not at the turbo it is the solenoid. Can you move your wastegate linkage while the truck is running?

I checked the vaccuum at the wastegate. Everything seemed fine there. Funny thing though, today the turbo worked fine ( I think). I could here the whine again and seemed to have power. Could the solenoid be an intermittent problem? I unplugged it this morning to make sure contact was being made. It seemed fine. Maybe a broken wire. Tested tonight with test light. OK. Should the solenoid be changed regardless? Also fuel economy is in the toilet lately, could this be the lack of turbo?

Its cheap, and often intermittent, just change it.
All that smoke your seeing is not really black, its green, all your money blowing out the tailpipe ;)

If you want to try and make it work, squirt WD-40 or the like into the vacuum connection at the turbo with the truck idling. This often frees up the mechanism in the solenoid and makes them work a while longer.

Actually it's not black coming from the tailpipe. It's red and brown or should I say fifties and hundreds.

the wastegate solinoid fails and causes those symptoms, i've changed two on my 95,they are about $50

If you get a Turbo Master you can scrap the whole vacum system, and not have to worry about any more maintaince on the darn system, I took off my pump one less item to fail sieze and burn up a belt out in the middle of nowhere chasing dogs looking for birds.

I have a 95 GMC 2500 LIGHT 3/4 6.5 TD with the same problem . My wastegate solenoid and the wiring to the computer are good. I have been told that I have to replace the computer. I have the wastegate wired closed and the egr plugged. Now I pull a fifth wheel and I am scared that I will start taking out pistons if I dontfix it . I will replace the computer if I have to but I want a better prom for it. I am looking for a pic programmer for my removable prom ,and some advice . Thanks

Lance Welcome to the site Please drop by welcome notes and FAQs,

Unwire the WG ASAP you are headed for possible problems, that will leave you walking home. Best bet is buy a reflash chip from reputable vendor(read member sig lines to know good vendors) but other things to do 1st before adding fuel & boost that will help without putting your engine at risk, like a wired shut wastegate does, pay me now pay me later condition you have set yourself up for

had the same problem a while back. compuuter was shot... do you have access to a scanner when i hooked one up it showed sensors like 150% when they should have been25 50%. replaced with used computer now no problems..

IMO, get a turbo-master and throw that electronic/vacuum setup in the trashola.