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  #1  
Old 05-26-2010, 11:19 AM
80broncoman 80broncoman is offline
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compression numbers?? for a 7.3 IDI

I have a 89 7.3 IDI that has QUITE a few miles on it in a F-superduty rollback tow truck.
It is smoking slighty and I'm wondering just how close it is to needing a refreshening.
I know I have to buy the tester for a diesel, but what kind of compression numbers should I see on a 7.3??
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  #2  
Old 05-26-2010, 10:43 PM
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260-440 psi

the hynes diesel book states that if more than 20% variance is seen,and if there is a slight rough idle,the exhaust cam lobe could be the cause.
the compression should build quickly on a healthy engine.slow at first and slowly building pressure indicates worn rings.if it doesn't build up at all after the first stoke,this indicates bad valves/bad head gasket/cracked head,or carbon buildup on the valves.
you need to crank at least 6 compression strokes (listen for at least 6 "puffs") record your highest reading.

if compression varies greatly between cylinders,then you can have a shop pressure test the crankcase to pinpoint the problem.
if you see a couple low ones side by side,it can indicate a blown head casket between them.
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  #3  
Old 05-27-2010, 06:36 AM
PLC7.3 PLC7.3 is offline
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I have had up to 500psi........ 440 is very good, lowest must be 75% of the highest

Never use oil in the cylinders..... or it will hydrolock and bend a rod.
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Old 05-27-2010, 01:16 PM
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Quote:
Originally Posted by PLC7.3 View Post
I have had up to 500psi........ 440 is very good, lowest must be 75% of the highest

Never use oil in the cylinders..... or it will hydrolock and bend a rod.
You're not supposed to dump a cup in it, just a couple table spoons, it will not hydro lock on that!

-Enjoy
fh : )_~
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Old 05-27-2010, 02:14 PM
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Yea just a lil bit of oil to see if the rings are bad
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Old 05-27-2010, 03:48 PM
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if its got real good compression it might just fire up and run on that oil lol
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Old 05-27-2010, 05:13 PM
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Ever thaught about cleaning the CDR? Could be your smoke problem.
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Old 05-27-2010, 08:44 PM
80broncoman 80broncoman is offline
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Quote:
Originally Posted by IDIDieselJohn View Post
Ever thaught about cleaning the CDR? Could be your smoke problem.
Right after I started this thread I read about the CDR. I'll defintly check into that.
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Old 02-26-2013, 01:38 AM
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7.3 Diesel compression numbers?

OK, I have read all the forum entries on 7.3 non turbo, compression, and not one entry gives any numbers?? How many pounds of compression is good? ok? needs rebuild?

My '93 F250 4x4 does not smoke, other than a small amount when starting, and runs fine. It does, and never has, gotten very good mileage. Like, 12 mpg on the average. I am running it now in Ca. which is suppose to have a cetain rating of 50 or so.. It has 220,000 miles, and seems to not have the power it once had... well duh, its getting older. I was wondering if I do a compression test, just how many pounds of compression should it have?
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Old 02-26-2013, 02:12 AM
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Quote:
Originally Posted by bajafishnut View Post
OK, I have read all the forum entries on 7.3 non turbo, compression, and not one entry gives any numbers?? How many pounds of compression is good? ok? needs rebuild?

My '93 F250 4x4 does not smoke, other than a small amount when starting, and runs fine. It does, and never has, gotten very good mileage. Like, 12 mpg on the average. I am running it now in Ca. which is suppose to have a cetain rating of 50 or so.. It has 220,000 miles, and seems to not have the power it once had... well duh, its getting older. I was wondering if I do a compression test, just how many pounds of compression should it have?
http://www.ford-trucks.com/forums/12...sion-test.html

Frankly on yours Im thinking its more along the lines of timing/injectors/injection pump in need of adjustment/replacment
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Old 02-26-2013, 05:32 AM
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Injectors, timing, pump & more..

You are probably right, and I had thought of buying a new/rebuilt pump, but have decided to have the pump's pressure checked. I purchased the truck in 99 with only 37,500 miles on it, but noticed right away, that it would not keep up with my older '88 that had 220,000.

I had a rebuilt pump, (from the pump man in Redding Ca.), put on when I had 110,000 miles, but no new pump since then. I have however, put in new injectors, like, maybe... 3 times.. and used the Delphi brand, new from the box.

I use the truck as my Baja runner, and it makes 4 trips up and back annually. which is about 1000 miles each way. Its usually all pavement, other than washouts during the hurricane season. I have a K&N air cleaner, which I noticed someone made derogatory comments about ?? Is it not what I should be running? What then?

Perhaps its time for a pump, new injectors, and pump timing.. I will have it checked out. If you know a reputable diesel mechanic in the San Diego area, I would appreciate the turn oun..

thanks amigo,

Baja
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Old 02-26-2013, 12:30 PM
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Quote:
Originally Posted by Festus Hagen View Post
You're not supposed to dump a cup in it, just a couple table spoons, it will not hydro lock on that!

-Enjoy
fh : )_~
It can start on that though, never do a wet test on a diesel. Leakdown is the best way to find out where your problem is.
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Old 02-26-2013, 12:30 PM
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