thfitz

A little bit of back ground, When my truck was running good I could push 40 lbs of boost and be right around 1200* or less in 6 gear pulling anything, my egts began getting higher and it was hazy under boost, I did a boost test and figured out my intercooler was leaking so I got a new intercooler and also deleted the heater grid because it was also leaking boost out of the plugs under the wires. So now I have no visible boost leaks but when I do a boost test I have air coming out of the blow by tube. It never blows an excessive amount of oil out of the tube or anything when I'm towing but boost is going some where because now I can't push but like maybe 33-35 lbs of boost and I will be over 1200*. Also it is hazy at 20 or more lbs of boost, not really bad but enough for me to know something not right. One thought I had was maybe the valve stem seals (in the head, not the tires haha) are leaking? Could they let boost into the crank case on the intake side? Because it acts like it burns a little oil if I idle a long time or go down a long grade with no boost, so I could see a little oil running down the valve stems causing that but could they leak air into the crank case when under boost? any ideas? sorry my post is so long, Thanks Thomas

AlpineRAM

Well, to me this actually sounds like something from the injection side. (Assuming that your air filter is clean)

I would check the injectors and your pump timing before doing more research on the boost side.
Especially the rise of EGT for a certain amount of boost says that you have some retarded burn, either from poor atomization or from slipped pump timing.

HTH

thfitz

I just set my timing to 19-20* so I'm pretty sure that is still correct, and before I figured out my intercooler was leaking I swapped injectors with a guy, could they maybe be the wrong spray angle or something? Also what about the air coming out of the blow-by tube when I do my boost test? how much, if any are any of you guy experiencing?

madhat

The only thing I could think of is piston rings.

If you apply compressed air to the motor and it's coming out of the crank case breather tube (Blow by tube), then you have air getting past the pistons. Valves don't have anything to do with crank case pressure.

When you introduce compressed air into the system, the valves are either opened or closed depending on the position of the camshaft. Only half of the cylinders are getting air at once (roughly). If the intake valves are open, compressed air is being forced into the cylinder with nowhere to go- that cylinder's exhaust valves are shut. If it's making it into the crank case, then it's gotta be the rings or a hole in the piston.

I guess it could possibly be a head gasket letting pressure into the crank case... I'm sitting here trying to think about the mating surfaces IRT the intake, intake valves, pistons and exhaust valves and the head/block surface and I can't think of how it would do it, but I'm not looking at a diagram, and I haven't touched a 12v like this in years and years...

How much air pressure are you using? I might verify the position of the engine using TDC and the valve position on the first cylinder and see if anything changes when you rotate the engine to the opposite open/closed valve pattern. (There is a certain way to do this, TDC does not specifically mean the valves are open or closed on a given cylinder.)

The real way to do it would be to do a compression check. That'll take a minute to do...

I'm not a certified mechanic, I want to throw that disclaimer in there now. I've turned a wrench or two, but I don't know everything. I could easily be missing something simple- if so, I apologize.

thfitz

That was one of my theories also, either bad rings or a small hole in a piston, because like you said there aren't but so many ways to get air from the intake into the crank case. I was going up to about 40 lbs on the intake pressure when I was doing my test. I guess I was seeing if anybody had any other ideas besides that before I bought the tools for a compression test. And I hope it neither one but I don't know, Thanks

madhat

Man, it's a 97... with your mods, I'm sure it's seen more than stock power levels for a while. One of those play to pay.

On the up side... now you have an excuse to get some high dollar pistons...

You won't really know what's going on until you do the compression test. You could try running a little heavier oil and seeing if that puts a small band-aid on it, but that's just in theory... You're in Virginia, and it's starting to get cold, so a heavier oil (not sure what weights are available in a diesel compatible oil) might do more harm than good.

Please let us know what you find out.

thfitz

Okay, when I get time to work on it I will let you know what I figure out. I have done all the work to the truck myself over the past years with help from online forums and this is my first time I have registered and posted something because I wasn't sure what to try next, Thanks

AlpineRAM

How did you do your boost test?

thfitz

I made a big plug that I clamp onto the inlet on the smaller turbo and I have a regulator to control how much pressure is going in.

AlpineRAM

OK, now you should remove the oil drain and the oil feed of your small turbo.

With the engine not running it is possible that your pressurized air leaks through the turbo because it does not get supplied with fresh oil, and it does not turn at sufficient speeds to seal.
(Or it could also be damaged, but you will find whether your air leakage is in the turbo or in the engine. )
Another thing to consider is that with a test like that you only have a very short time that you get realistic results, because you blow the oil from the piston rings and get no resupply.

Another path for the air would be the inlet valve shafts. (Just remove rocker arm cover and squirt some oil on the valve guide, look for bubbles)

HTH

madhat

That's a brilliant point.

I was thinking of the air being supplied post intercooler...

thfitz

Okay yeah I will check the turbo, that was the other possibility I was thinking of. AlpineRAM that's what I was getting at in the original post, the inlet valve shafts, I just didn't know how to explain it I guess. Because since the valves go down through the head those seals have to be the only thing that keeps boost in the intake and out of the crank case, I was trying to see if anybody else has had this happen? Being me its probably the first time haha. I kinda hope that is what it is, because that wouldn't be too hard to fix.

AlpineRAM

@thfitz- well it is quite easy. The Cummins has no valve seals, and a bit of air getting into the crankcase is not only OK, but it is designed that way.
The reason is that as soon as you have boost no oil leaks into the intake, and the wet valveshafts have still enough oil to slide freely.
My take on your "problem" is that as long as you don't have oil vapour or oil drops coming out of the crankcase breather the engine works as designed.

Look at
Measuring Blow by, The Real Test For Internal Engine Condition - Seaboard Marine

and test accordingly. (This is for marine engines, blowby measured under full load)

With the truck you can measure nicely with a heavy trailer and a steep hill. (But don't go over 21 psi of boost, this is the stock tuning and if you boost 40-50 psi you will naturally fave much more blowby than at stock boost levels, so the numbers won't compare)

Your raise in EGT and smoke/haze from the exhaust after swapping injectors steers me towards injectors as the cause. Did you pop and leak test them? Check the spray pattern? (they might simply be defective or worn out) or they might be the wrong geometry (like 370 marine injectors, they have a different spray angle due to the different pistons installed in the 370 marine engine)

If you can get hold of your former injectors this would be a quick swap..

thfitz

Okay that makes sense about that air by the valve stems, more pressure on the intake = more air that would enter the crank case under boost. I will try that test and see what i figure out.
As far at the injectors is there a way to check the spray pattern and pop test them my self? (if I could be pointed in the right direction) or would I need to take them somewhere and have them tested?
Also, say they are just no good and I buy a new set are 5x14 a good size for my set up in y'alls opinion? I obviously want pretty good power but I daily drive this truck so I want to maximize my mpg (as much as reasonably possible). or would 5x12 make much of a difference as far as mpg or would 5x16 be too much? (I know there are tons of threads on injectors already so may it be annoying to answer haha)

AlpineRAM

I don't think that you can test the injectors yourself, you need a pop-tester. (Basically a manual injection pump with a manometer)

My take on injectors is that there is much more to them than number of holes x diameter of holes.
The spray angle must match the piston bowl, and the timing. (just consider where the piston is if you change timing- and still need to "hit the bowl")
Then it is the pattern of atomization- how big are the droplets, and how fast are they? This needs to match your engine build.
My experience with that stuff is- try to get hold of DonM! He is a guru on that stuff.

The overall size (as 5x12) will determine the flow- so at part load (daily driver) a bigger injector will inject the same amount of fuel in much shorter time, therefore effectively increasing timing. This can lead to negative effects like haze when below a certain RPM, and kills fuel mileage.