6.9L Fix or replace
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Freshman User
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6.9L Fix or replace
Hello, Newbie here not having much luck with the search system so I would like to ask. I have a 85' f250 diesel 6.9L engine. The engine will not start without a tiny shot of either,Once running it has a dead cylinder. It also has a large amount of blowby coming from the oil filler cap and also blue/white smoke from the exhaust. From the best I can tell this truck engine has about 350k miles. Engine has great oil pressure and clean oil,no signs of coolant leaks into oil. Coolant is also clean no signs of compression leaks. I am new to Ford diesels and just purchased this truck and don't know its history. I have owned VW diesels so I do understand diesels and have mechanical skills but need to get up to speed on 6.9-7.3 diesels. What should I check first? Where do I start!! Is it worth saving?
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
danield,
First welcome to FTE and the IDI diesel forum.
My first place to start would be a compression test.
Starting may be some burnt out glow plugs.
The dead cylinder may be a bad injector.
Since the compression ratio is 22.5 to 1, you will normally see what looks like a lot of blow by.
The blue smoke may be a CDR that needs cleaned out.
CDR would be called a PVC valve on a gasser.
First welcome to FTE and the IDI diesel forum.
My first place to start would be a compression test.
Starting may be some burnt out glow plugs.
The dead cylinder may be a bad injector.
Since the compression ratio is 22.5 to 1, you will normally see what looks like a lot of blow by.
The blue smoke may be a CDR that needs cleaned out.
CDR would be called a PVC valve on a gasser.
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Freshman User
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Thanks for the Welcome!!! What is the normal place to take a compression test on this engne? The glowplug hole or injector hole? I bought a compression tester for diesels and had planned on doing a compression test. The tester comes with about a dozen adapters with it to fit almost any sized hole. What is normal compression? I also took a RAYTEC lazer temperature gun from work to check wich cylinder is dead.
Post Fiend
Joined: Nov 2004
Posts: 5,638
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From: Manitoba
Glow plug hole on a warm engine......... do at least 5 revolutions per cylinder noting what stroke the highest compression was attained. The lowest cylinder must be at least 75% of the highest.
Now removing GPs can be somewhat dangerous so visit ...Don's site and read all about GP removal and timing/cylinder position so you can remove the GPs safely.
http://www.members.shaw.ca/k2pilot/
Now removing GPs can be somewhat dangerous so visit ...Don's site and read all about GP removal and timing/cylinder position so you can remove the GPs safely.
http://www.members.shaw.ca/k2pilot/
Posting Guru
Joined: Mar 2005
Posts: 1,701
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From: KY
Is the blowby in rythym with the engine. Puffing? IT could be the dead cylinder. IF you don't have a compression tester remove the glowplugs and get a rubber tipped air blow nozzle and put shop air in the glowplug hole. Take the truck out of gear so the motor can spin. It will go to BTC on that hole and if you have a bad cylinder the air will come out of the oil fill tube. KEEP your hands clear of the fan and belts. Shop air can get you qiuck.
It is a easy and quick way of finding a bad cyl. You need the piston to go down so you don't have a valve wide open.
You can also let it run and crack each injection line open. The cylinder with no or very little change is the culprit. Then check for a bad nozzle or other damages.
A motor in great shape will have 500PSI or right at it on compression.
It is a easy and quick way of finding a bad cyl. You need the piston to go down so you don't have a valve wide open.
You can also let it run and crack each injection line open. The cylinder with no or very little change is the culprit. Then check for a bad nozzle or other damages.
A motor in great shape will have 500PSI or right at it on compression.
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I dont think I could hurt this engine anymore than whats been done to it. Prevous owner has started it on ether for at least 2 years. It has a can of ether that is mounted to the inner fender well. It screws onto a regulator and a hose from this to the air cleaner. Then it has an electric push button on the dash. Push the button twice hit the starter and it's running. Probaly not good for the motor but it has not hurt it yet!!
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Lead Driver
Joined: Nov 2003
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From: Campbell River, B.C.
Originally Posted by danield
I dont think I could hurt this engine anymore than whats been done to it. Prevous owner has started it on ether for at least 2 years. It has a can of ether that is mounted to the inner fender well. It screws onto a regulator and a hose from this to the air cleaner. Then it has an electric push button on the dash. Push the button twice hit the starter and it's running. Probaly not good for the motor but it has not hurt it yet!!
I have heard of other cases like this on HD diesels as well.
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Freshman User
Joined: Sep 2006
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Crack!!
Usually cracked rings are devistating to the cylinder walls. I can't imagine this engine would be running for the last 2 years on cracked rings. Massive cylinder scoring usually results.
Last edited by danield; Sep 15, 2007 at 11:43 PM. Reason: spelling
Senior User
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Originally Posted by danield
Results from compression test. 7 cylinders good with 400lbs compression. Problem is in passenger rear cylinder it has 0 pounds of compression. No compression at all on cylinder #7
A word or two about ether. A starting agent, ether dries oil left on the cylinder walls resulting in cylinder scoring when used excessively. Its functions are twofold: it's non-compressible thus raising compression when used, and it's flammable. Long-term use almost always causes problems. Large bore diesels suffer the same issues, but are somewhat less prone to damage as their compression ratios are lower than those used in automotive diesels.
Having said all that, you must now determine if you like the truck enough to put another $4000.00 into it.
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Bad Rings?
I have not dismantled the engine so I am not sure what is going on for sure but I have never heard of bad rings causing 0 lbs of compression. There is a slight pulse you can feel with your finger over the hole when the GP is removed but it is not enough to even move the compression tester guage. It don't have low compression in this cylinder it has none at all. My guess is it has a hole in the piston from a dropped valve? I bought the truck with it being down a cylinder and don't know what events lead to the dead cylinder.
Lead Driver
Joined: Nov 2003
Posts: 6,900
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From: Campbell River, B.C.
I would think even with NO piston rings, there should still be something to bump the tester.
A hole in the piston would also explain the blowby. Did you ever find any debries in the oil while changing it?
A hole in the piston would also explain the blowby. Did you ever find any debries in the oil while changing it?