Well gang...

Mopar1973Man is down... I had a air system failure yesterday about Council, ID climbing the grade and passing a RV and heard. BOOM! Psssst.... As I let off the throttle the noise stopped. Get back into the throttle and boost might climb to 5-8 PSI, pyro going like a rocket, lots of black smoke and the noise returns... I stopped in New Meadows, ID for a moment to look and can't see the leak... so I stopped at the hardware store to pickup the stuff to build a boost tester. So I'll be fixing 2 leaks now A/C and boost...

Well gang...

Mopar1973Man is down... I had a air system failure yesterday about Council, ID climbing the grade and passing a RV and heard. BOOM! Psssst.... As I let off the throttle the noise stopped. Get back into the throttle and boost might climb to 5-8 PSI, pyro going like a rocket, lots of black smoke and the noise returns... I stopped in New Meadows, ID for a moment to look and can't see the leak... so I stopped at the hardware store to pickup the stuff to build a boost tester. So I'll be fixing 2 leaks now A/C and boost...

That sucks - was gonna ask if it could be your pyro-probe itself come loose from the threads in the manifold - but not sure this would cause low boost or not since pre turbo. Plus you say egt's still move way up there.

Curious on how you build a boost tester - so 'subscribed'.

Well John...

The boost tester is basically a 4" rubber sewer boot a small piece of 4" black ABS sewer pipe and a 1 4" plastic sewer cap. You glue the cap on the pipe. Trim the pipe to fit the boot without being overly long. Drill and tap the cap to fit a male air chuck. Now assemble and clamp onto your turbo. Pressurize the system with about 20 PSI and now look for the hissing air or soap the system and look for bubbles.

Mine will look simular too...

http://www.dieseltruckresource.com/pics/data/500/medium/Boost_Tester.JPG

Sounds like one of the boots blew off of the intercooler or other piping boots. Hopefully that is all it is.

Sounds like one of the boots blew off of the intercooler or other piping boots. Hopefully that is all it is.

Boots are all in place... I was a assuming its a fender rip from contact because I can still build about 5-8 PSI...

---------- Post added at 11:26 AM ---------- Previous post was at 08:04 AM ----------

Nevermind...

Problem figured out... 1 of the manifold bolt blew out hit the hood and fell back into the injection lines and laid there... So I found my boost leak and will still build my boost test to verify I find and other air system faults now... So time to break out a 10mm socket and tighten a few things...

Yeah I know Dodge makes and Cummins shakes it... Well the old girl is shaking out here fastners...

cheaper the better.... how much psi did it take to blow the bolt up to the hood?

Well it must of rattled loose and pop out just as I ramped up to 35 PSI (Bang!)... Passing a RV on a grade... But the funny part is I just got done wrenching the bolt back in tight and found out the bolt never hit the hood because of my crankcase vent was in the way... So looking at it closely it hit the pipe and tumble back against injector line #4 and laid there... Talk about lucky... Closest hardware store with metric bolts is 20 miles away now...

Told ya it was the manifold bolt - just the wrong one (pyro) !! - do I get 1/5th of a point ? thanks for the link on the boost tester

Hey JohnFak... I just bought the supplies for building a boost leak tester... I'll assemble mine tomorrow and get pics of it for ya...

Hey JohnFak... I just bought the supplies for building a boost leak tester... I'll assemble mine tomorrow and get pics of it for ya...

Cool .... for the dumb q's - how do you build 20 lbs boost ? Essentially your capping off the turbo which prevents air intake to the turbo and then onto the cooler, elbow and finally engine ? And doesn't any existing air pressure just pass through to the exhaust bypass and out ? Unless you keep engine off I guess ?

Engine remains turned off... Place the cap over the mouth of the turbo and now you use compressed air and regulate it to 20 PSI. Which this now simulates turbo boosting 20 PSI. You should be able to see wastegate function on a stock setup. If not you'll have to increase the air pressure to your wastegate setting... Don't exceed ~35 PSI I don't want to hear about blown head gaskets from boost testing. As for the air if you got a regulated air supply you now can spray down the system with soapy water looking for bubbles. Check IAT & MAP sensor, manifold cover gasket, boots, intercooler, etc... If the air is bleeding through the engine shut off the air supply and rotate the engine a bit and try again. I don't want to hear about people getting tangled up in the fan as the air pressure twisted the crank around on them.

Engine remains turned off... Place the cap over the mouth of the turbo and now you use compressed air and regulate it to 20 PSI. Which this now simulates turbo boosting 20 PSI. You should be able to see wastegate function on a stock setup. If not you'll have to increase the air pressure to your wastegate setting... Don't exceed ~35 PSI I don't want to hear about blown head gaskets from boost testing. As for the air if you got a regulated air supply you now can spray down the system with soapy water looking for bubbles. Check IAT & MAP sensor, manifold cover gasket, boots, intercooler, etc... If the air is bleeding through the engine shut off the air supply and rotate the engine a bit and try again. I don't want to hear about people getting tangled up in the fan as the air pressure twisted the crank around on them.

Correct me if I'm wrong but I don't believe that 35 psi is real critical to a stock head gasket with the motor shut off, isn't a stock cummins gonna make well over 100 psi compression? I think a tired 350 chev will do that. I believe that over 35 psi of boost will translate into maybe a couple hundered with compression stroke?...... I think:shrug:

Correct me if I'm wrong but I don't believe that 35 psi is real critical to a stock head gasket with the motor shut off, isn't a stock cummins gonna make well over 100 psi compression? I think a tired 350 chev will do that. I believe that over 35 psi of boost will translate into maybe a couple hundered with compression stroke?...... I think:shrug:

Ummm... Someone did the math for me awhile back and it about 960 PSI at 35 PSI... (Trying to remember)

With a 17.2 compression ratio the cylinder pressure at 35psi of boost is 602psi, when you ignite that air the cylinder pressure can be upwards of 2000 psi.

By chance do you have the math for that figures??? I would love to add it to my collection of weird things...

Hope I am doing it correctly :-)17.2 (compression ratio) x 35 psi boost.

Hope I am doing it correctly :-) 17.2 (compression ratio) x 35 psi boost.

Actually no... There is much more to it... Because no boost was still like 300 PSI compression... There was displacment, compression ratio, and boost pressure... I do remember that ^ was used in the math... _________________ Added to the post... Found this...

The actual position of the piston can be determined by trigonometry, using the stroke length and the connecting rod length (measured between centers). The absolute cylinder pressure is the result of an exponent of the dynamic compression ratio. This exponent is a polytropic value for the ratio of variable heats for air and similar gases at the temperatures present. This compensates for the temperature rise caused by compression, as well as heat lost to the cylinder. Under ideal (adiabatic) conditions, the exponent would be 1.4, but a lower value, generally between 1.2 and 1.3 is used, since the amount of heat lost will vary among engines based on design, size and materials used, but provides useful results for purposes of comparison. For example, if the static compression ratio is 10:1, and the dynamic compression ratio is 7.5:1, a useful value for cylinder pressure would be (7.5)^1.3 × atmospheric pressure, or 13.7 bar. (× 14.7 psi at sea level = 201.8 psi. The pressure shown on a gauge would be the absolute pressure less atmospheric pressure, or 187.1 psi.)

So in the Atmosphere pressure just add you boost pressure to the 14.7 PSIA figure... (35+14.7=49.7 PSIA) I'm pretty sure Cummins is 16.3 or 17.0 Ratio... (SO and HO) (17.0) ^ 1.3 x 49.7 = 1,976.7 PSI compression pressure... (35 PSI boost) (17.0) ^ 1.3 x 14.7 = 584.7 PSI compression pressure... (0 boost) I know if someone want to verify the formula and the math...

Whats the 1.3 for? You doing something for altitude? As far as I can tell, you just take 14.7 and multiply by compression ratio and thats your no boost cylinder psi. Add boost to 14.7 and multiply by ratio for your boosted cylinder psi. :shrug:Hmm, or is 1.3 the constant for air compression.

Oh yeah.. didn't think about atmosphere pressure...x2 on the 1.3..My service manual shows my compression ratio at 17.2:1, with a minimum cylinder pressure of 350psi.

Alright I did some physics searching. Mike is 100% right. So you take your compression ratio to the 1.3th power, then multiply that by the total amount of pressure (boost + 14.7).Whats interesting is monatomic gases have a constant of around 1.6, like helium. So if you somehow had a helium engine with the same 17 compression ratio and 0 boost it would be at 1367.8psi, or 1030 if you make it 1.5 for heat reasons.

Did you ever snap any pics of the tester you built Mike? Im fixin to go to home depot and get some parts.