Is this normal?

[dpuckett]

I tested out my air intake system tonight, and found that I have a goodly leak out the blow-by/ vent tube . WHat is going on here? It sounds like I need rings, apparently, but when I turn the engine to another point, it isnt as bad. Sometimes the leak gets worse, just depends on where it stops. Could i need valve work? I just slapped the head back on after it got milled for the head gasket (after cleaning up the mating surfaces, and getting all the little pieces of gunk out it) Any ideas of where to look next are appreciated.



Daniel

 

[MMiller]

If you had a exhaust valve problem the hissing would be out the exhaust.

Does it use alot oil?

Does it run like is always has?

Does it blue smoke excessively?

Have you ever listened to the engine when turning it over by hand when doing the valves? You get a hiss out of the breather because the air rushes through the ring gaps, because you can't turn the engine fast enough to compress the air, and it gets out where it can. If the rings did not leak a little you would not be able to turn the engine over by hand. I'd not worry about it unless something else has changed.



Man, no wonder Mr Murphy visits you so much, you worry too much!



Michael

 

[cerberusiam]

You have an intake valve open at some point all the time. It will always leak some with a valve open. Not sure about the 12V's but I think the pistons are gas ported so the compression will help seal when it comes up. At a rest you will have enough leakage by the rings to cause this.



Not sure what pressures and specs a leak down test calls for. Anybody got that info handy? Seems to me it would take a fair amount of pressure to seal the rings well enough to get a valid test but not sure what pressure is supposed to be used.

 

[DValentine]

I agree with Michael, air escapes through the ring gap. Could your intake valves be set too tight?

 

[rlyons]

You can't leak test the intake with it connected. You will always get an air leak back through a valve.

 

[DValentine]

Ha Ha silly me, I remember now, making the same mistake. Rlyons you nailed it.

 

[Greenleaf]

Yes, you leak test the intake system with the system intact. And you will have air escape out the exhaust and the crank case. The air has to go someplace... ... ... ... ...



Soap down all the air intake connectiuons. Even the gasketed joints/flange , everything. This is the manner in which you check the system. If you disconnect a portion, you can test only that portion.



You will need about 15/20 psi regulated. (you gotta feed the air into the system the while you are testing. ) Your not pressurizing and removing the air.



I hope this is clear.

 

[rlyons]

Well yes you can test it but I guess his question was why he had air escaping out of the engine. What I meant was if you don't want the lose of air then you need to disconnect the intake pipe and plug it.

 

[JLEONARD]

Soap down all the air intake connectiuons.

Sounds pretty kinky to me Scott. :-laf

 

[dpuckett]

Hey, thanks, guys. I needed the reassurance. I am long overdue for a visit from Murphy, Michael.



I had forgotten about the ring gap, and the pressure took almost a minute to drop from 5psi, so that makes perfect sense. I soaped the entire intake system and had no bubbles, save a small one from my AFC hose set up, which was cured with some teflon tape.



WHich leads me to my high EGTs again. They were better with the new pump, but still arent as low as Mom's (same truck, only I have a flatbed and a manual) at cruise. I wouldnt think 1200# would add 200-250 to EGT? Timing has minimal effect. It does seem to be smoking quite a bit lately, along with idling rougher. Time to get the DDP injectors pop tested and see what the spray looks like. I have a set of stockers lined up for testing purposes. ACtually, to run and test smoke, EGT, MPG, ETC.



DP

 

[RWWinslow]

Daniel - the following caught my eye in your last post. . . .



"It does seem to be smoking quite a bit lately, along with idling rougher. "



My EGT had also creeped up. I had been dealing with these issues through last summer and had corrected the problem by performing the following work and replacing these parts:



* Injector Pump: Died at 375,000 miles - probably due to the effects of aging and a long hard life - coincidentally with the intro of ULSD

* Injectors: 4 of the 6 spray patterns were very poor to almost non-existant. Pop off pressure varied by 30%.

* Fuel Tank level assembly: Replaced. The suction and return fittings were found to be cracked.

* Suction and return fuel hoses: Replaced



In January of this year, the symptoms returned. Working on a fuel system at -10F was not my idea of fun so did not get a chance to put a wrench on the system until this past weekend when it finally warmed up a bit. I found the suction line hose clamp broken - looked good but would not tighten - This allowed enough air to leak into the suction line and really cause problems with injection timing, spray pattern, fuel volume delivery, etc. which caused rough idle, smoking, and changing EGT's. I was able to replace this fuel line hose clamp and the symptoms have disappeared.



I have noticed that the new fuel hose that is certified for diesel fuel / fuel injection applications is a heavier material and is therefore more difficult to clamp off and seal on a vacuum side application with rubber hosing and steel fuel lines. This heavier hose material will also result in the clamp relaxing more after it has been in service a-while. I may be considering a change to fittings / disconnects.



Bottom line - you might want to check all of your hose clamps and hose connections before proceeding any further.

 

[dpuckett]

Good idea. Fuel lines have been on my "need to do" list, but I havent gotten around to it. Injector pump is fairly new (2500mi, tops), injectors are a year old (~12K mi), and if new springs were installed, could be part of the problem if they have settled like some guys claim they do. Or it could be the ultra high quality fuel we have here (10K on a fuel filter is doing quite well). I figure injectors arent that hard to pull and get tested, and it's free, so why not? I wil check the fuel lines today or tomorrow. I'm almost positive they are original. Now to find diesel rated hose... ...



DP

 

[bmoeller]

You will always get an air leak back through a valve.

Can't forget about valve over lap either. Helps with scavenging to have them both open briefly on the exhaust stroke.

 

[dpuckett]

RWWinslow, you were on the right track. Though it has nothing to do with my apparently normal air leak, changing the hose and clamps did help my EGTs. I started a new thread with more details, as someone may benefit more from the thread than a reply at the end of an unrelated topic.



DP