Looking at a good deal on a truck - engine doesn't seem right

[IDIDieselJohn]

Looking at this 1986 F350 2wheel drive 6.9 diesel, everything is good about it, runs great drives great, but When you start the engine cold, fire off instently but has a little shake, nothing bad though (that's on high idle) onces the high idle kicks off, it starts shaking even more. Sounds perfect, smooth idle sound, but visually shaking, if you rev it past 1000RPM it stops. Went for drive, abit of stop and go, then hit the highway, everything is A1. When we got back, was idling the same but very smooth, not shaking at all. Guy said it has new injectors, IP pump, lift pump and updated glow plug system on it all from within the last 3 years. He said it's been shaking like that for over a year, but after you take it for a drive it stops doing it. I don't get it what the hell could it be, runs and sounds perfect!

Edit: Engine shakes on low idle after cold start up, after a drive idles perfectlly smooth. Sound doesn't change. No smoke of any colour, only black smoke when you put your foot in it.

Truck specs: 1986 F350 stock 6.9 Diesel 2 wheel drive, C6 transmission, 140,000 miles (3.55 gears not sure though) been used to haul a 30ft. fifth wheel for over 12 years.

Any thaughs appriciated

 

[jtate]

sounds like one of those new injectors is leaking just a bit. even though they are new doesnt mean they were installed with the upmost cleanliness that it needs.

 

[ameristar1]

Ok, let's try again. Unless receipts are produced, don't believe about the work that has been done. But at the same time, it's not a deal breaker. If you like the truck, go get it and go through it just on principle. Get the pump timed properly, and as jtate said, check the injectors. 140k is nothing. Pull the fuel filter, put a fresh one on and fill it with ATF, and then dope the fuel up with some Howes Lubricator ( throw some big bottles in ) for a couple of tanks.

You better buy it before someone else does.

 

[IDIDieselJohn]

Has receipts for everything. I'm in no hurry to buy a truck, i'm still going around seing what I can find, really i'm only looking for a Cab to restore mine. But I just had to ask this question cause I found that to be pretty weird, my 87 6.9 does the same thing so that's why I wanna know what can it be.

 

[sassyrel]

run a compression check--almost sounds like a lung or two is a bit low--and when warm, compression is up--and fires right--ive got one the same way--i know what it is--and dont care--just a beater!!!!!

 

[IDIDieselJohn]

A lung? What's that?

 

[IH_444]

A lung? What's that?

A cylinder

I second the problem being possibly an injector.