1.) Air filter. Look and see if the air filter box is intact i.e. no broken tabs / cracked housing / loose or cracked intake boots / pieces. Make sure it hasn't been bypassing dirt into the engine. You can also look at the fins on the turbine in the turbo. If it is eaten up bad (more than just a little) it has been making some serious contact with dirt and could indicate "dusting".
See any alerts here, demand a Cylinder Pressure / Compression Test before purchase.
2.) What about service records. It's nice to KNOW whether the services have been done or not. Not necessary but good to have. The more miles on the truck the more imortant the service records become.
3.) Melted stickers under the hood. You can look at the stickers under the hood to check for melting / distortion. This could indicate excess heat in the engine compartment and would require further investigation were it me. Also look for tears in the underhood insulation from broken belts or other things that could have gone awry.
4.) Towing equipment. Set up to tow? 5th Wheel / Gooseneck / Reese Hitch? See how much wear those components have. Try to find out what it used to tow, you don't want a tired old hotshot rig if you're looking for a daily driver to power up.
4.) The Tranny / Drivetrain. How does it drive down the road? How does it shift? At full throttle or light traffic driving. There's not much more you can do but feel it while you drive.
5.) Chips, Programmers, Mods? If it is modded, you have no idea how they treated the truck unless you know them or can trust them. Besides, it's more fun to start fresh and do the mods YOU want, if any.
6.) Water damage. Of course
7.) Fluids. A used oil analysis (IE: from blackstone labs) would be nice. It would let you know if wear levels are within spec and give a good indication of how well the previous owner maintained oil changes. The tranny fluid should be a rich red/pink color SHOULD NOT smell burned or look black. Brake fluid should be full / clean. See if the pinion seal on the rear differential is leaking, fairly common. If it is leaking, take the cost to fix off the price. You could also make sure the rear wheel seals aren't leaking.
8.) Brakes, Balljoints, and Wheel Bearings. Does it go down the road and stop smooth? Any play in the front hub assy? Brakes may "vibrate" while coming to a stop since these are heavy trucks and the OEM rotors like to warp. In order to check for ball joints and wheelbearings jack one side of the front up. Have someone strong or capable hold the tire at 12 and 6 o clock. Have then forcefully move the tire back and forth. While this is happening you need to get in behind the tire and see if there is any movement. Check the hub assembly and ball joints for movement, if there is any then you need to replace them. here is a link to Powerstrokeshop.com - PSD and Ford Superduty Parts that sells kits for ball joints, wheel bearings, and other things.
9.) CPS Failures, some of these trucks are notorious for eating CPS's. They can leave you stranded anywhere anytime intermittedly. Finding out if it has been replaced (maybe more then once) might be a good idea. You never know when they'll go out, so it is best to carry a spare. These can often be had for under 60 bucks shipped on ebay, and can easily run in excess of 200 dollars at the dealership!!! It is a simple fix that is described in the "tech files" for the 7.3 forum.
Things To Look For When Buying A Used PSD
You might take the air tube off the back of the air filter and look inside of it. If there is dirt build up, that is a very bad sign, so are the turbo fins looking sand blasted or bent. A little oily film is normal since the valve cover breather exits inside the tube.
Check the two bolts holding down the airbox lid. If they are plastic with a square recess, it is a recalled part. The recall is expired, but without the updated lid the risk of dirt infiltration is greater, the lid was updated with more supports and the updated bolts are metal with a straight slot.
If you buy a truck with an auto tranny, finding out if it's been maintained is essential, as the E4OD is an expensive transmission. Also, (if auto) seeing if the truck has an auxiliary transmission cooler would be worthwhile. For sticks, listen for clunking when shutting off or small vibration while operating. It could be an indication of a dual mass flywheel going out. Many have replaced them with single mass units.
Rear Gear Ratio:
4:10 will pull better, get slightly lower mpg’s and run a higher RPM compared to 3:55.
Ask the previous owner about the coolant - have they been adding FW16 or DCA4 to keep a proper SCA level? It is very important for stopping cavitation. You can get test strips to check the SCA level from NAPA, International, or Ford. I would test the current condition while looking over the truck, the SCA level should be between 1.5 and 3.0. Also, see if it has a block heater (it was an option on 97's).
Check the front end for wear, or have an alignment shop check out the ball joints and steering linkage (tie rod ends). If they are shot, it is spendy (all four tie rods are around $400 just for parts, ball joint labor is also very spendy)
The questions to ask are how often the oil was changed (at least every 5,000) and what kind of oil they used (diesel rated)? An oil analysis could tell you if there might be an engine problem or not.
Seeing if the truck has got an aftermarket downpipe would be nice, a chip, or gauges (pyrometer, trans temp, etc.). Ask about any added items and who installed them.
Find out if the glow plugs are in good working condition as well as the relay. Ask if either has been changed and when. You can check the glow plug resistance through the valve cover connector if needed and the relay should have power to both large terminals on top when the key is turned on, and one of the terminals should go out before ~2 minutes.
Some of these trucks are notorious for eating CPS's. They can leave you stranded anywhere anytime intermittedly. Finding out if it has been replaced (maybe more then once) might be a good idea. You never know when they'll go out, so it is best to carry a spare. These can often be had for under 60 bucks shipped on ebay, and can easily run in excess of 200 dollars at the dealership!!! It is a simple fix that is described in the "tech files" for the 7.3 forum.
The injector O-rings have been known to be a problem. The new o-ring sets have a pink middle seal. If the truck has an o-ring problem, one of the signs can be a discoloration of the fuel in the filter bowl. There is a drain on the passenger side front of the filter bowl for draining water (the filter is also the water separator) and you can catch some of the drained fuel in a jar – it should be dingy yellow and not blue or dark.
Leaks and Drips:
You can check the valley between the heads of the V8 for moisture and/or fluid. It should be dry not wet. Most leaks will run through this valley and down the back of the motor dripping off by the tranny/engine coupling.
If you take the VIN to any dealer, they can tell you when it was built, when it went into service, and some of the work that might have been done on it. You can also run prospective VIN's through Carfax.com to see the title history.
Compiled from various links around the net.