Blue Smoke with 7.3IDI

smithman

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Hello all
I have a '92 7.3 that doesn't smoke at all except for some blue smoke in certain conditions. Mileage 153K. Original IP and injectors as far as I can tell (purchased truck at 150K). The blue smoke is only during shifting, coasting in gear at 50+mph in 5th, or when maintaining speed at higher RPM (2k+) . When maintaining speed at higher RPM, it's almost like the engine is sputtering a little...noticeable vibration in the cab. Vibration goes away at speed when mashing throttle, coasting, or when putting in the clutch.

My guess is that it's probably the IP or injectors, but can some of you please confirm my thinking. Anything else that I should look at? I replaced the CDR with a new one at 151K. Blue smoke usually indicates burning oil but it should be nearly constant if it's a bad seal or something...
 

franklin2

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If this were a gas engine, it would be worn valve guides. Don't know if a diesel is susceptible to this also on deceleration. These engines are known to have valve guide problems though. Do you get a huffing/spitting noise at the tailpipe at idle?
 

smithman

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Actually, yes it seems to have a slight spitting sound at idle every once in a while. I noticed it when I idled the truck to pulled it out the garage after rebuilding the entire suspension.
 

franklin2

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Well, make sure you do not have a exhaust leak, but a lot of the times the huffing noise is from a exhaust valve that intermittently does not seat and seal off. The noise is the compression getting past the valve. The guides can get so bad that the valves rock around in the head and don't seal off the cylinder correctly. I believe there are some pictures on a thread in here where the compression also goes up by the guide and gets under the valve cover causing a mess. See what comes up if you do a search for the word "huffing".

I believe also there is a thread in here where a guy's engine had it so bad the head of the valve broke off and fell into the engine causing major damage.
 

riotwarrior

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Do a search on exhaust chuff lots of info...blue smoke likely raw fuel not burned..due to possible poor valve seal so lack of compression/ignition

Just a thought..
 

smithman

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If it is a valve guide issue then I guess it's time for a head rebuild. I can confirm that the idle exhaust sound has a "chuff" to it. Now, would removing valve covers add any value to locate the problem, or should I go right to a compression test?
 

riotwarrior

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If it is a valve guide issue then I guess it's time for a head rebuild. I can confirm that the idle exhaust sound has a "chuff" to it. Now, would removing valve covers add any value to locate the problem, or should I go right to a compression test?

If you find my thread on CHUFF post mortem...and I won't link it..learn search function here!!! you will see I could indeed see a massive build up of soot inside valve spring...that was my case, and each one is different.

Here is the problem as I see it for doing a compression test VS running and engine and hearing chuff.

1. you are only turning it over maybe 750 RPM max and the valves don't move much and get any flutter in the guide at that RPM and the time the valve is closed allows it to actually seal reasonably ok.

2. Compare the above to running and you'll see that the valves actually don't have much time to close and stay closed/seated and thus wobble in guide more.

This is just my observation based on some experience over the years.

Both in my opinion are the best way to see and maybe you can CAREFULLY attempt to wiggle exhaust valves side to side with valve cover off....hard to say what would happen.

Keep us posted.
 

smithman

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I'll put it back in the garage this weekend and start to tear into it. Thanks for the tips, riot.
I was planning to pull the engine this winter anyways for a new oil pan plus a whole lot of other work. I was hoping the heads would last until 250K before needing some work but whatever.
Even though pulling the heads sucks, it's better than some other things. Thank God that International built the bottom end of these things like a tank. Just slap on new heads and keep on rollin'!
 

Agnem

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With 150K on original pump and injectors, I wouldn't be doing anything to the engine until that fuel system was replaced.
 

smithman

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Either way it's going back in the garage. I won't pull the heads unless it's clearly needed...
 

smithman

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Valve covers came off, and there was no noticeable soot or other contamination inside either valve covers to indicate a leaky exhaust valve. I couldn't inspect each valve spring in detail, but it appeared they were all OK. The engine is still in the truck, but will be out in a couple of weeks as I have time. Further inspection may show an issue but we'll see.
Potentially still a valve seal issue, or a fuel system in need of a rebuild. New IP and injectors were already on the to do list.
 

smithman

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Resurrecting this older thread. I am working on replacing valve seals now and inspecting valve guides. I have only done cylinder 2. Intake valve guide fine, good fit to the valve.

Exhaust valve guide has between 0.012" and 0.015" play between valve stem and guide based on my feeler gauge. Valve stem looks good. Is there an opinion about how much is acceptable here?
 

smithman

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Updating.
Cylinder 2 is the only victim at 0.012"+ gap. There is a small amount of soot around the upper edge of the valve guide.

OEM ford manual says valve stem to guide clearance is 0.0055". Mine is more than double that number. Looks like the early stages of a valve guide failure.

Suggestions before I tear into it any further....pull both heads, or just the one?
 

icanfixall

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Well if you repair only the bad head just how long will it be before your in it again for the other head. In for a penny... In for a pound.. Personally I would do both heads because you may have to buy another valley pan gasket. Thats 40 to 60 bucks most places. Your going to be purchasing a complete valve job gasket set anyway. Thats both heads gaskets. All the valve seals for both heads and both valve cover gaskets. As Mel posted.. your fuel system is worn out at the miles you have on it so injectors and injection pump are a must do also.
 

stealth13777

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Labor wise, it isn't much more to do both heads. Materials and machine shop costs (if needed; idk what you have access to) will go up, but imo not enough to justify doing all the work twice. Not even close. Plus as mentioned above you'd probably end up buying the same parts more than once.

Worst part of these is once you get going, you just keep finding things to fix. Ask me how I know haha. But doing the work can be enjoyable and it's nice to know you fixed everything and won't have to redo the same work a month down the road.


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