Alrighty guys so I am looking at a truck its a 1994 f250 ext cab 4x4 7.3 IDI turbo (stock). The owner says it has a misfire but runs and drives fine. "Since I have had it, it has smoked when started and ran, I started investigating by doing a compression check. I so far checked cylinders number 5, 7 & 8 with 5 being 250 PSI 7 is 340 PSI and 8 is 220 PSI. being out of fords spec of being within 25% of highest and lowest (and recommended of at least 350 PSI)." is what the owner said. does that seem about right? Any ideas on what may need to be done? This is what the truck looks like http://images.craigslist.org/00k0k_5...vk_600x450.jpg

https://gm1.ggpht.com/sy9rKX91q3zyur...96-h841-l75-ft

Also he wanted 2700 but i talked him down to 2300 does is sound like a good deal? Can I drive the truck safely?

 

If your highest Cyl is 340 psi and you need to be in a 25% range of the highest Cyl then you need to have the lowest Cyl at around 260psi anything below that is too low. you don't say how many miles are on it either, it may just be wore out.

I had a 94 CC 2wd with the 7.3IDI Turbo. I bought it used and it only had 160k on it. Everything checked good, but after about 15k all the problems started happening. The PO changed all the fluids before I bought it and it all looked good, but when freeze plugs started blowing, water pump failure, Trans problems, Finally head gaskets, I knew it had been beat to death. I hhad to pull the trans for the rear freeze plug twice and that's when I discovered all the corrosion in the block from not doing regular maintenance. All I can say is buyer beware. Take the truck to a good diesel shop and have them check it over, it'll be worth the $100+ dollars for your sanity.

 

Was the engine warmed up before compression was checked?

Check blowby (pull oil cap). If blowby is not excessive, it could be valves and/or seats worn out leaking compression into the intake/exhaust.