Just bought an 85 6.9 idi with a 4spd and 4wd been sitting for ten years we got it running had to prime the system to get it to run oddly there wasn't any leaks under the truck when we pulled it out of the weeds and now it starts everytime after you push the glowplug button for 20-30 seconds however.....it is pouring an off white smoke that reiks of raw unburned fuel doesn't idle rough once up to temp but still continues to pour smoke I've drive it 50 miles in the two days I've had it burns no oil leaks no oil at least onto the ground where does a guy start with the police evasion device I've seemed to acquire
Welcome and nice find. In terms of a list of things I'd look at... I'm not the best wrench... just some of my recommends after having done something similar.
Return Lines - these things cause so many vacuum leaks, if they are old I'd just replace them paying particular attention to the grommets. Manifests typically as cold starting problems due to drawing fuel so far.
Fuel / Water separator - another cold start vacuum problem, but typically much worse.
Fuel Switch - Make certain the fuel tank switch unit inside the drivers frame rail is passing fuel in both directions.
Vacuum Lines - There are not that many of them, so just pull them off individually and test them. Any doubt - replace one.
Water in Fuel - if the separator is good, but full of water... if the separator is bad - and the tanks have 10 years of vapor in them...
Old Fuel - As others have noted, treat the fuel, replace it - whatever you can to get rid of it.
Bad / clogged Fuel return line?
Compression problems - one or two cyls with bad rings, holes, etc. really Bad head gasket. If you're doing that - do the work of a leak down test.
Head gasket - this is more likely to cause white smoke, except for everything else...
Injector Pump - this is the one I think of with "grey smoke" - equivalent to running rich. The cheap test I know of - is to adjust the fuel delivery screw.
Instrument Voltage Regulator - this is a very small thumb size PITA which plugs onto the back of the instrument panel. On my '85, it was good for a delta of no change to reading F at full, and E at 1/3rd full.
Old Wiring. Will have nothing to do with grey smoke problems. But will have issues with starting and maintaining voltage from your fuel sending units.
Starter - nothing to do with smoke, but its really easy to get the wrong starter, which will not spin the motor fast enough, and really lacks power. You could inherit one of these...
Battery Cables - another infrequent but sometimes PITA intermittant / low starting power issue
Glow Plugs - get the right motorcraft plugs, and be aware there are fakes out there. You should *always* be on the hunt for a spare set... And be very, very careful when replacing them, the conterfit tips breakoff and mushroom.
Vacuum & fuel problems are the most vexing of the issues when these trucks get old. Remote issues will be electrical.
The list above is long, the reality is they decompose into a fairly straightforward decision tree based on your symptoms. Once the engine is running well - near indestructable and so simple, not much to go wrong. Last piece of advice:
Forum Search - this forum software isn't the easiest search to figure out, so spend some time learning what it does/does not do. There is so much information here - which will cover ALL the topics above in great detail thanks to the many really sharp and experienced wrenches here on this list.
The group loves photos. There are a couple of very long running posts, one is: "what did you do with your truck today" and another contemplating issues and other life affirming truck maintenance...
Members - did I miss anything major?