Rebuild Time

[NVW]

Last Tuesday I was going to the auction mart and noticed a miss when I pulled up. Nothing noticeable on the highway.

At home I ran GMTDScanTech and got codes 94 & 95 which is a miss fire in cylinder 4 & 5, the odd thing with my ScanTech is it states code 94 is a miss fire in # 5 and 95 is # 4. I had added some Power Service and 2 stroke oil which may have dislodged some crap. It will run smooth at times.

I checked cyl. balance

I then did a comp. test: #1-360; #3-360; #5-380; #7-360
#2-420; #4-400; #6-25; #8-400

Why would shutting off #6 injector have the effect it did with only 25 lbs compression?

The puff is from #6 cyl.

 

[NVW]

I wet down cyl. 6 and there was no change. Could anything other than bad compression rings cause the low comp. along with the blowby?

 

[ak diesel driver]

burned valve, valves not opening

 

[ak diesel driver]

those wouldn't explain the blowby tho.. maybe a hole in the piston?

 

[ak diesel driver]

got a borescope?

 

[bison]

Ieo, Why wouId it detect a misfire on Iow compression if injector is good?
Test injectors first i say.
The engine obviousIy has some wear , bIowby is to be expected but no reason for a rebuiId yet.
If adding oiI to the jug did not raise compression...suspect a vaIve

 

[NVW]

The bad blow by just started.
The miss fires are on #'s 4 & 5
I am in the process of building a POP tester but wanted to be sure I was going in the right direction.
Could a rocker retainer mimic a bad valve?

 

[Will L.]

Yes it could. Rocker not moving means valve not moving. 25 lbs is psycho low. Rings have to be completely gone for that low, and oil wont recover a broken ring. REALLY need to get a borescope in there. Call your local pepboys, napa, etc about the tool loaner program.

Hole in piston or valves jammed is only real option. blowby suggests piston...

 

[3500GMC]

Doubt a bore scope will pass the prechamber, or low lift valves these engines have.

 

[ak diesel driver]

I was thinking if you pulled the inj that you might be able to see thru the precup hole. If it is a hole in the piston it should be right there.

 

[NVW]

Those scopes were on sale at Canadian Tire a while back. I'll have to check one out.

 

[Will L.]

It won't fit past the cup, but putting it into the prechamber through the injector hole (needs to be lighted borescope) will let you see the piston through the prechamber port no problem. It is faster than pulling the valve cover to see if it is massive cylinder or piston damage.

Seeing the valves is not an option unless you could get your hands on one of the medical scopes that you can "drive" with the fiber optic lead- HAHA. probably 3/4 of a million bucks for one of those.

Valves require tear down. Valve covers to see operation would be worth it here because the low of pressure hopefully its a pushrod off a arm. Otherwise it really doesn't matter what it is-either run it as a 7 cylinder or tear it down if it cant be fixed under the valve cover. I just prefer to yank an injector and see if the engine is getting pulled before the time of a valve cover in the truck. If it weren't for the injection lines it would be quick.

 

[Burning oil]

With both valves closed apply alittle air pressure to cylinder. Then listen for air coming out oil filler neck, exhaust pipe, intake or bubbles in coolant.

 

[3bals]

This doesn't answer your questions, but here was my rocker issue.

 

[WarWagon]

You have a hole in a cracked piston. Nothing else will give you that kind of blowby "puff" and low compression. Valves being bad would not puff out the oil fill tube. The cylinder is likely scored badly so do not expect to be able to re-use the block. (Cracks + scored cyl usually doom it...)

Hole in piston here, best I can tell it was from getting hot and then shock cooling when the bad cap finally let loose:
http://www.thetruckstop.us/forum/threads/pics-of-the-carnage-what-was-the-cause.21491/

 

[emdmechanic]

If you think its a hole in the piston , just fill it with oil and see how fast it drains if you cant physically look at it. Use a heavy oil , if you can see the level dropping its a hole more than likely. Oil really wont pass rings in a good cylinder , nothing you wont grow hair watching anyway.

 

[schiker]

I had an exhaust rocker break on a gasser and it would pop back through the carburetor when the intake would open. I am curious will Diesel do similar? Not sure what a non opening intake would do. ??? I guess just be dead from lack of oxygen. Or will cylinder vacuum open the intake and or exhaust valve(s) just enough to get a little air into cylinder?

I wouldn't think a bad valve would blowby that bad through the filler neck it would either bark through the turbo or be dead ???????????

I would think that low of compression would have to be a hole in piston .?. A crack in block would have to run entire length of cylinder to have no compression I would think ???

Good luck do let us know.

 

[NVW]

I'm not going to have much time to deal with it in the next week or so.

I'm thinking it has to come apart, I don't want a 7 cyl diesel, and the only way I can see a valve cause the blowby is if the exh. valve wasn't opening, but then compression wouldn't be an issue? It should also make a hell of a knock.

Going to be out the rest of the night.

 

[btfarm]

I'm voting holed piston in this poll... NOT good news.

 

[Burning oil]

I know where you can get a brand new AMG P400.