compression numbers?? for a 7.3 IDI
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Laughing Gas
Joined: Nov 2003
Posts: 898
Likes: 1
From: southeren Oh
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??
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??
Fleet Owner
Joined: Jul 2006
Posts: 20,345
Likes: 802
From: Mi'kma'ki
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.
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.
Methanoholic
Joined: Mar 2009
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From: Maine (NorCal Native)
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Post Fiend
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From: Ottawa, Ontario
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Laughing Gas
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From: southeren Oh
Right after I started this thread I read about the CDR. I'll defintly check into that.
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Cargo Master
Joined: Nov 2005
Posts: 2,694
Likes: 45
From: La Ribera, Baja, Mexico
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?
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?
Senior User
Joined: Oct 2012
Posts: 333
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From: Co
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?
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?
Frankly on yours Im thinking its more along the lines of timing/injectors/injection pump in need of adjustment/replacment
Cargo Master
Joined: Nov 2005
Posts: 2,694
Likes: 45
From: La Ribera, Baja, Mexico
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
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
Mountain Pass
Joined: Aug 2012
Posts: 114
Likes: 0
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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