My '87 6.9 project that I started back in January was just about done. I've been noticing some smoke under hard acceleration. So I picked up a compression tester; which I probably should have done in Jan. At the time the driver side head was weeping coolant from one corner. I pulled the cover and found a broken head bolt. So I put in a a new one, torqued both sides and no more leak. Well after I was finally able to get it titled and registered I was able to drive it more than 5 minutes. So I did a compression test, and the same cylinder that was weeping is the lowest in pressure. It went like this--
7-475 8-475
5-470 6-480
3-475 4-500
1-480 2-420

It's a HF compression tester, so I'm thinking 500 should be 400, etc. Unless the pressure gets that high-- I don't know. There was no leakdown, I held the cylinders for a minute.
A mobile mechanic I know thinks I'm pulling in oil from a return galley. I'm not losing any coolant, or blowing bubbles. So does this sound about right? I'd appreciate the input. So I'm going to pull the head, or heads.

????

broken head bolt
I'm kicking myself in the *** because I told myself I should test it, but took the gamble.
Could it be valve a guide? It doesn't smoke at idle, only when I accelerate kinda hard.

 

it ain't a valve guide... the broken head bolt is your clue.

Valve guides never really figure into compression numbers

Replace the head bolt and retorque you might be fine.

 

500 psi is normal for a good 6.9. PSI is a universal imperial measurement, where you bought it from doesnt change that. Would say the HG diagnosis was confirmed well before the compression test, but i would say the fire rings are in good shape.

 

I agree..... and if you do replace head gaskets then have the heads checked for true

 

Lonewolf, the broken bolt is what I found back in Jan. I replaced the bolt , and re torqued both heads. That was #2 cylinder, and the give away was a drop of coolant at the corner of the head. #2 is also the cylinder with the lowest compression-420. That's why I'm thinking head gasket. Could the piston be pulling oil in on the downstroke from up top. Is there an oil return galley close by that could be leaking? It doesn't smoke at idle, only on hard acceleration. Also it seems to load up, even though that's a fuel issue. When I go for coffee the truck sits at idle for 10 min, and when I get on it afterwards it leaves a good cloud.

 

Ahhh ok I guess I misread your OP

I wouldn't think you would be pulling oil in, as there is no pressurized oil in the Heads
Now that number being low could be a Valve seating issue.
one thing you could do is put that cylinder to TDC compression stroke then do a Leak down test on it.

 

Had a friend stop by who has worked on heavy equipment over the years,and I asked him to take a whiff of the exhaust when I jammed on it as I drove by. He said it smells like a mix of fuel and oil to him. I think it's pretty much the same- I haven't felt like it was just oil cause It would smoke all the time.

 

Lonewolf, when I did the compression test, I held them all for a minute. They all held with no leakdown.

 

the gauge holds pressure until you press the Release Button but the Cylinder doesn't.

https://www.mobil.com/en/lubricants/...-leakdown-test

 

But the release is below the gauge. Not by much. I know what your saying, but when I hit the release alot of air came out of those holes.Not just a pop. That gauge isn't holding all that air.

 

If it was guides, can only really be exhaust, and you would see it in the exhaust. They will burn oil just fine and you would never know it.

 

So I took the truck out today, to give it a first run down the interstate. I held it at 2800- 3000 rpm for about 45 minutes. Before I even got on the highway I noticed there was nothing- no smoke. So the whole time it was clean. Pulled off to turn around and stopped at a light , nothing. Ran it back through the hills where it usually would smoke and got nothing. Did not smoke the whole time. Went out an hour later to the store and it smoked somewhat as I got up to speed. WTF. Fuel, oil, I don't know what to think anymore. Had a **** eating grin on when I pulled in the driveway then wanted to ****ing scream when I went out later.

 

It could be your injectors or injection pump.

My old motor had a few leakers, you could go run it nice and hard and it would clean it out. Then after a little easy driving it would come right back.

When diesel is left over from a leaky injector it makes a terrible smell that's hard to diagnose if it's just a little leaking by. It'll usually result in white smoke at idle, and gray under acceleration. It'll burn your eyes and nose too if it's bad enough.

Just food for thought.

 

Pump and injectors are newly remaned. Injectors are from a place in Michigan. I always thought it was fuel, but it had a blue tint when I really got on it. That made me think oil. Took it out this morning and just seen a little bit of smoke a few times. Checked the oil and it's still steady on the dipstick. I'm going to run it like it is till the spring and if it's burning oil I'll pull the head.

 

As stated there's no pressurized oil in the head, if it was somehow getting to suck in oil from the head gasket, it would show up as a big puff when you take the oil cap off when that cylinder fires, since it passed compression I would say it's probably fine unless you have a stuck oiler ring or something of that sort.

When you did your compression test I'm assuming you pulled your glow plugs? Did they all look the same or was one a bit more crusty looking? That would help you isolate it to a specific cylinder.