Blowby and Injector Questions

Steelreaper80

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Indianapolis IN
Probably stupid questions. When my M925A2 is at temperature, I see blowby coming out of the blowby tube. It is a light grey color. It is not puffing like a steam engine but it is puffing more than I would like to see. I can put my thumb on the tube and hold it and it does pressurize and when I release my thumb it releases the built up pressure. Lately, it is coming out so much from the blowby tube that it drifts up into the engine compartment and I can see it with the hood open and standing at the front driver's side tire. I pulled the oil fill cap and it had blowby coming out of it. I put the cap back on with it not tightened down but just resting on the threads and the blowby did not blow the cap off. Other than having the blowby measured by a repair shop with a computer, how would I know if I have too much blowby? I don't really see blowby from the tube or oil fill when the engine is started and cold. Going down the road even loaded the truck runs cold at about 175 degrees. It only shows up when the temperature is around 200 degrees. Do I have a larger issue of stuck or cracked rings or worn liners or is it normal? Could it just be evaporating moisture from the crankcase when it is close to 212 degrees? It seems to come and go......There is not oil blowing out of the oil fill area. I looked down at the top of the head and everything looked normal other than looking at light grey blowby puffing out of the valve cover.
As far as I can tell the truck is not eating oil. I do have a very slight oil leak somewhere at the front of the engine but I don't think the motor is eating oil.

Second question. When do injectors need to be replaced? The truck has a light grey smoke at idle and heavy smoke after throttling up after idling for more than 10 mins. The exhaust smells strongly of diesel. I don't think that I am getting a good spray pattern and that the injectors are leaking in the cylinder. I could be wrong, which is why I am asking the experts. If I do need to replace injectors.......stock or bigger? I NEED more power. (Damned tamper-proof screw!)

The truck starts very easily and runs great. I just want to get in front of an issue at the shop rather than behind it hundreds of miles from home.

These trucks are older so would running something like Hotshots Stiction Eliminator help?

The truck is ran a LOT and gets regular oil changes at about every 7500-10K miles. I run fuel additives with each tank. Thanks guys, and I tried the search button but it seems less than helpful lately. I get every topic EXCEPT what I am looking for.
 

Mullaney

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Charlotte NC
Probably stupid questions. When my M925A2 is at temperature, I see blowby coming out of the blowby tube. It is a light grey color. It is not puffing like a steam engine but it is puffing more than I would like to see. I can put my thumb on the tube and hold it and it does pressurize and when I release my thumb it releases the built up pressure. Lately, it is coming out so much from the blowby tube that it drifts up into the engine compartment and I can see it with the hood open and standing at the front driver's side tire. I pulled the oil fill cap and it had blowby coming out of it. I put the cap back on with it not tightened down but just resting on the threads and the blowby did not blow the cap off. Other than having the blowby measured by a repair shop with a computer, how would I know if I have too much blowby? I don't really see blowby from the tube or oil fill when the engine is started and cold. Going down the road even loaded the truck runs cold at about 175 degrees. It only shows up when the temperature is around 200 degrees. Do I have a larger issue of stuck or cracked rings or worn liners or is it normal? Could it just be evaporating moisture from the crankcase when it is close to 212 degrees? It seems to come and go......There is not oil blowing out of the oil fill area. I looked down at the top of the head and everything looked normal other than looking at light grey blowby puffing out of the valve cover.
As far as I can tell the truck is not eating oil. I do have a very slight oil leak somewhere at the front of the engine but I don't think the motor is eating oil.

Second question. When do injectors need to be replaced? The truck has a light grey smoke at idle and heavy smoke after throttling up after idling for more than 10 mins. The exhaust smells strongly of diesel. I don't think that I am getting a good spray pattern and that the injectors are leaking in the cylinder. I could be wrong, which is why I am asking the experts. If I do need to replace injectors.......stock or bigger? I NEED more power. (Damned tamper-proof screw!)

The truck starts very easily and runs great. I just want to get in front of an issue at the shop rather than behind it hundreds of miles from home.

These trucks are older so would running something like Hotshots Stiction Eliminator help?

The truck is ran a LOT and gets regular oil changes at about every 7500-10K miles. I run fuel additives with each tank. Thanks guys, and I tried the search button but it seems less than helpful lately. I get every topic EXCEPT what I am looking for.
.
Something quick and easy to look at on the blowby tube... What shape is your intake filter in? Restricted intake can cause more "puffing" on the blowby tube.

Cummins has a blowby measuring tool. P/N 3822476
It has a special 5.613 mm [0.221 inch] orifice that you use to quantify what you are seeing. Got a turbo? You could be leaking boost into the crankcase. With the measuring tool, the measurement is liters of water per minute. 18 is pretty good (okay) and 22 or higher generally shows wear in the liners or rings. A compression test would tell you a lot about that.

Only thing that is a little confusing is that you say it cranks up and runs great. That and lots of blowby out of the tube just don't seem to "jive".
 

Lukes_deuce

Active member
424
109
43
Location
Long Island, NY
I had a similar situation on one of my trucks. No blow by at all when cold but it slowly showed more as the engine warmed up. It was constant when the truck at 180-190. Truck ran great, started well and did not burn oil. My guess it was a cracked ring or aging liner. When it was cold, Im guessing the issue was compressed and when warm the slight crack expanded and allowed crank case pressure to show.

As for injectors, 8.3 are know to have the injectors gum up over time to cause issues with the spray pattern. Thats why they haze and smell like diesel at idle. Mine did haze but didnt smell like diesel fuel, just diesel exhaust, so I let them be. They are not hard to remove. If your questioning them, any diesel injection shop can inspect and let you know what can be done. Also be careful if you do have them open up the injector for more fuel, as stock injectors with a turned up pump will be too much fuel for a stock motor. There are marine injectors available too but they start at something like 380hp.
 
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