compression values

[ulmapache]

Anyplace I can look up compression values and blowby for my '84 f250 6.9idi...odometer has rolled over an unknown number of times...Whats a good number to work with? Want to determine if truck is worth putting anymore time and effort into...new IP, injectors, and GPs...looks to be around another couple of grand.. When she runs, she runs good...no blue smoke to speak of, will roll a bit of coal at low rpms and full throttle... But showing signs of IP and injector issues (hesitation and surging under full throttle..starting to do that under normal driving conditions..)...already replaced GPs about 3 months ago and they are bad already...

 

[DaveBen]

Post the numbers you get. Asking us to give you the values on an unknown engine is impossible. Your compression numbers should be within 15% of each other for a good engine.

 

[ulmapache]

Actually, I was asking what are 'normal" numbers for an engine in good shape...should be a range of values out there...*** pounds when new....*** pounds when getting ready to die at 500,000 miles...that will give me a good idea of what kind of shape that engine is in... Numbers like 150 pounds +- 10 or so pounds on all cylinders would indicate a "good" engine...but in reality, the engine would be trash...

Post the numbers you get. Asking us to give you the values on an unknown engine is impossible. Your compression numbers should be within 15% of each other for a good engine.

 

[DaveBen]

https://www.quora.com/What-is-the-compression-pressure-in-diesel-engine?share=1

After doing some checking it looks like 400 psi is pretty good for a 7.3.

 

[ulmapache]

https://www.quora.com/What-is-the-compression-pressure-in-diesel-engine?share=1

After doing some checking it looks like 400 psi is pretty good for a 7.3.

I'm guessing the same would hold for a 6.9?

 

[DaveBen]

They are pretty much the same engines. The 6.9 has thicker cylinder walls and a few other things.

 

[ulmapache]

Cool beans...so if 400 is good, what would be the minimum for decent compression? Is there a lower value that one should not go below when deciding whether to spend more $$ on an engine unless a rebuild is next on the list?

 

[DaveBen]

The lower the compression psi, the more likely you will start to have starting problems. I have not been able to get a number for you. Google is your friend.

 

[ulmapache]

Have not been able to get any values on the googlemachine...starts good when the GPs are working...another clue...replaced them about 6 months ago...back to hard starting...found a fuel leak around the FSV...I think that is half my problem...just had the entire fuel system replaced from the front tank forward...new tank, sending unit, lines, lift pump...no FSV...checked function, it works...clunk when switching from tank to tank...fuel gauge working on both tanks...rear gauge not reading correctly anymore...and did not touch the rear except to change out the fill tube when bed was off...

 

[Kevin 007]

I often see high mileage engine still holding 400 psi. And some low mileage engines at 300 and lower. all depends on how it was driven and maintained. If you find yourself with 400 or so, you're doing great but really anything over 350 and fairly even across the table, you are still doing good. Run it and be happy