I don't usually make my way to this forum, but I thought maybe I could get some answers about a potential buy answered over here.
I may have found a good truck to replace my <acronym title="Indirect Injection">IDI</acronym> but I need some technical advice. I'm looking at a 2001 F250 7.3L powerstroke <acronym title="Four Wheel Drive">4x4</acronym> with an automatic. It has just over 300k on it but the body, interior and frame are in excellent shape. That of course is where the good part ends.

Now for the bad. The guy that owns it mentioned that it had a bit of a intermittent, slight knock when he first got it 50,000 miles ago. Typical from what I have read. But, upon investigation the #8 piston had been hammered pretty hard so he went ahead and replaced it. He claims it ran great for the past 50k up until now when the intermittent knock wouldn't go away and in fact got worse.

He mentioned that he replaced the under valve cover harness but no dice there either. He then tried swapping injectors between one of the other cylinders but no change.
Unfortunately he wasn't able to tell me if any oil was flowing out of the injectors when he started it without the valve covers on. He did note alot of thick slime on the valve covers though...

When I drove over and looked at it today, it started up nice but as soon as it started to warm up the knock became VERY audible. Of course I climbed around in the engine bay like a monkey trying to find the source. Again, expecting a split/dead injector. While doing so, I noticed a few things.

For one, it had a good amount of blowby when I had the oil fill cap off. Also when I had the cap off, I noticed a white/green foam around the edges of it with a smell of antifreeze. A bit alarmed, I pulled the stick expecting to see chocolate milk. Oddly, the oil was black with no tint of mix. Hmm...

Secondly, I also found that the knocking sound was resonating the loudest from underneath the truck...not necessarily toward the back.

Thirdly, while running in this condition, there is a good amount of blue colored smoke rolling out of the tailpipe. Not enough to smoke out the neighborhood but noticeable. The owner also noted that the coolant level was dropping a little right before the knock came back.

Lastly and the most obvious, the truck would shake constantly and stumble the worst when you would put on the brakes. Even just cycling through the gears while sitting in place it would shake violently. Oddest thing to me, no service lights were on even with its poor running condition.
The owner mentioned it had flickered on and off intermittently as well but changing the fuel filter or just romping on it a bit would kick it off.

Sorry for the long read, but does anyone have an idea of what I am up against here? I know a few things about powerstrokes but if this truck requires a full rebuild, I just couldn't afford that right now. The guy is asking $3000 although it books for $10k-$12k.

Any advice is appreciated!

EDIT: The truck doesn't appear to have ever had a chip in it. The owner doesn't believe in them either from what I gathered.

 

Hard to say from here, but sounds like it may be time for a rebuild. When you say bad blowby, you're referring to pressure, not just smoke, right? Smoke is ok, but pressure behind the smoke is bad.

Take the truck for a test drive and get it up to 50 mph or more so the torque converter is locked. Preferably find some slight downhill grade and take your foot off the go pedal. With the torque converter locked, the injectors will stop firing when you let off the accelerator. If the knock is still there, it's mechanical and not the injectors. If the knocking stops, but picks back up again when you touch the pedal or when the torque converter unlocks, then it's likely injector related.

My guess would be that more than just changing number 8 should have been done 50k ago and now it's time for an overhaul or shortblock.

 

Thanks for the quick reply!

The blowby definitely had some pressure behind it. Enough pressure that it was blowing out from around the line for the crankcase vent into the intake with the cap off.

I will give the truck a test run as you described when I'm back in town on Tuesday. I agree that it should have had a rebuild by now, but that I guess is the current owner's loss and my project to take on if I choose to do so.

I'll update with what happens this coming week, thanks for the help.

-Dave