A question, concerning jake brakes and boost............

[mr. cob]

Howdy All,

As I am known to take the back roads I had an interesting drive going to Chelan Washington, I came down a road, can't recall the number right off hand that had us coming down a 12% grade to an intersection with Hwy 97, on the east side of the Columbia River just before crossing the bridge to get to the west side of the river.  Coming down this grade I was in 6-7 gear, 1,500-2,000 rpm jake brake on full, using the service brake only to slow a bit more for the 20mph switch-backs.  While doing this I noticed for the first time, I am assuming its always been this way that while using the jake brake I was registering pressure on my boost gage.  At 2,000 rpm I was getting a reading of 12 psi on the boost gage, is this normal or am I losing braking power and some how building boost in the engine when I have my foot completely off the throttle?

If this is normal, I guess I just never noticed it before, if its a sign of a problem, what could it be?  Thanks for any information you can share.

Dave

[Darryl&Rita]

Sounds like Jake was on Max? If so, normal.

[beyerjf]

The boost was occurring because you were at relatively high RPM, causing the turbine in the exhaust manifold to spin fast. . The air flow through the exhaust manifold was also increased because the Compression brakes work by opening up the exhaust valves early, dumping more air into the exhaust manifold. The turbocharger has 2 turbines on the same shaft, one in the exhaust manifold which in this scenario was spinning fast and in turn spinning (driving)the turbine on the intake side fast creating some (12 psi) boost. The difference being if you were feeding maximum fuel into the combustion chambers the turbine on the exhaust side would have been spinning even faster with expanding exhaust gases giving you the maximum boost psi(30 psi) in the intake manifold.  

Completely normal. Put one on one of your Ural's and see how she goes....

[mr. cob]

Howdy Darryl and Jeff,

OK, I understand how the jake works and know about the turbo-charger, just didn't think of the exhaust side of the turbo still being driven even when your foots not in it.  Makes sense now that I think about it.

As to turbo-ing the Ural, let me relate to you my tale of woe, in 1982 I bought my first brand new Harley a FXWG 80 incher the Harley hot rod of its day.  In early 1983 I spent a ton of money and installed a custom turbo-charger on the bike.  Darn thing went like a bat out of hell in a straight line but at 15 pounds of boost I couldn't keep a head gasket in it.  Tore it down and "O" ringed the heads, the head gasket lasted now the rod bearings went after 2,500 miles.  Dropped the boost down to 12 pounds the head gasket held, the rod bearings were doing good, started to drop the rear cylinder exhaust valve.

Long story short, in the next 10 years I spend enough money keeping that hot rod Hog running that would have enabled me to buy a couple of Japanese crotch rockets that were way faster no matter how much money and labor I put into the Hog.  In 1994 I sold the turbo charger to some other fool went out and bought a brand new Kawasaki ZX-11D, at that time the fastest stock production motorcycle on the planet.  Rode that beast for years, scared the heck out of myself every time I rode it that's why it was never crashed and I am still alive to tell the tale.  Sold the ZX-11D when I started to ride with a couple of guys who really knew how to ride such bikes, the ZX-11D was FAST but it wasn't built to handle, went through a series of different sport bikes, in 1998 I bought one of the  very first Yamaha R1's to come off the boat, this thing was not only FAST but it could turn on a dime and give you change and had brakes that would pop your eye balls out if you had the guts to really use them.  I still have the R1 after all these years, to gimped up to ride it for more then a few miles every now and then but when ever I need an Adrenalin rush I fire that bad boy up  and proceed to play with the time-space continuum.

Dave

[Shifted]

There might be another aspect to the turbo pressure while the jake brake is engaged.  As I understand it, the turbo control valve is also actuated by the jake brake controller specifically to increase the back pressure.  At least, that's my understanding.  And it seems to be supported by the fact that I will lose some air pressure when my jake brake engages at level 3 (highest setting), which has led me to suspect a leaking turbo control valve.

 

[Darryl&Rita]

Turbo Control Valve?

[beyerjf]

Is a turbo control valve also known as a waste gate? My turbo charger has a waste gate set to open at 30 psi to moderate the boost and in turn extending the longevity of the engine. Some guys defeat them and get an increase in power and a decrease in service life and reliability. I don't think the jake engagement affects the waste gate operation , at least on a Detroit Diesel series 60.

[Ronbo]

Over the past couple days running from West Yellowstone to Fort Collins, Co I also noticed that as I was rolling down the hills with no throttle applied, jake on max, that there was some level of boost showing on the gauge. Glad it is normal. 

[mr. cob]

2 hours ago, Darryl&Rita said:

Turbo Control Valve?

Howdy Darryl,

I assume, your talking about the "waste gate", as Jeff said this bleeds off excess drive pressure to control the speed-boost the turbo puts out, mine is set at 28 pounds or at least that is the maximum I have ever seen my boost gauge register. 

On my Dodge Ram 3500 the stock maximum boost level was set at 22 pounds, I was running an "Edge" programmer box that allowed that number to go up to 40 pounds, needless to say I drove that truck with one eye glued to the EGT ( exhaust temperature gauge ) and the other on the road ahead of me. 

With the Dodge if I could hit a 7% grade at 70mph and didn't have to slow down for any reason I could pull my old trailer all the way up the grade at 70mph, if I had to slow down for any reason I could never regain speed as the EGT's went right through the roof in a heartbeat.  Proof that the old saying, "There's no replacement for displacement." is so true.  I love my HDT.

Dave

[Shifted]

I have an ISX and Cummins calls it a turbo control valve.  It controls the wastegate.  Air actuated.  And according to the documentation I've read, the engine brake on a Cummins ISX does adjust the trim on the wastegate using the turbo control valve to modulate the back pressure and effective engine braking.

But, I'm not 100% certain of the details, so if someone who is more familiar with how the ISX, jake brake and turbo all interact with each other, I would welcome the education.  Especially if you can provide a link to some technical manuals or diagrams specific to the ISX.

[Darryl&Rita]

Interesting. Dang ol technology keeps changing. Never seen a waste gate controlled by anything but manifold pressure.

[Shifted]

On gm 6.5's, the wastegate is controlled by a vacuum actuator, controlled by a vacuum solenoid, controlled by the ECU.  Most turbos that I am familiar with have some ECU managed control mechanism.

[MrSeas]

The Cummins ISX (CM870 and newer models) use a "VGT" (Variable Geometry Turbo) type of turbo made by Holshot. This type of turbo  does not use a "waste gate" and regulates the boost levels by changing the angle of the blades  (vanes) in the turbo to increase or decrease  boost pressures based on ECM inputs. The "turbo control valve" controls the air actuator on the turbo that controls the angle of the turbo blades (vanes) and gives you boost. The ISX is a double overhead cam engine that uses one cam bank to operate the intake and exhaust of the motor and allows it to run. The other cam bank is used as the "Engine Brake" and will utilize 2,4,6 cylinders as braking force depending on engine brake selection position 1,2, or 3. The turbo will also be commanded to increase back pressure in the exhaust system to aid in engine braking. The ISX engine brake is ideally used at higher RPM's but can be very effective at lower RPM's as well. 

As a side note the "turbo control valve" mentioned earlier in this thread is a part that needs to be maintained if you value the use of your turbo. They need to be replaced if they start to leak. 

[jollyrogr]

LGTs all use a VVT nowadays. Don't HDT's use them?

[Shifted]

Thank you for the clarification.

[rickeieio]

6 hours ago, jollyrogr said:

LGTs all use a VVT nowadays. Don't HDT's use them?

I think you hinted at the answer with "nowadays".  Did LGTs use VVT back in '01 when my ISX was built? I suspect a few may have.

[jollyrogr]

51 minutes ago, rickeieio said:

I think you hinted at the answer with "nowadays".  Did LGTs use VVT back in '01 when my ISX was built? I suspect a few may have.

Dunno about Ford or Dodge.  I'm a Chevy guy, so I know for a fact GM switched from wastegated turbos to VVT with the 2nd gen duramax in 2004.

[noteven]

mr. cob - waaay back in '81 my boss in Alberta had a Z1000 that had that Garrett turbo/Weber side draft carb/ single 3" open tailpipe conversion done by a shop in California. Quick pull in 1st to 10000 rpm/50mph, turbo was nicely spooled to initiate a Big Wheelie in 2nd ... nothing but throttle required... weeee! All on 8psi...pressed crankshaft gave troubles if I recall. 

 

[MrSeas]

On 7/29/2017 at 1:25 PM, Shifted said:

Thank you for the clarification.

I hope it gave you a slight insite to the ISX... (CM870 and newer models) I learn something every day about the motor. I'm by no means the "expert"  when it comes to the ISX but am happy to share any "pearls"  of wisdom I have " harvested " along the way.

[mr. cob]

4 hours ago, noteven said:

mr. cob - waaay back in '81 my boss in Alberta had a Z1000 that had that Garrett turbo/Weber side draft carb/ single 3" open tailpipe conversion done by a shop in California. Quick pull in 1st to 10000 rpm/50mph, turbo was nicely spooled to initiate a Big Wheelie in 2nd ... nothing but throttle required... weeee! All on 8psi...pressed crankshaft gave troubles if I recall. 

 

Howdy noteven,

I never could solve the rear cylinder head problem, just couldn't get the heat out of the head fast enough.  For a drag bike that only runs for a few seconds its no big deal for a bike that was run HARD on the street it was an engine killer.  The exhaust valve would seize in the guide, the head would snap off the valve, I tried every valve and valve guide combination available at the time, but just spent tones of money and put in an awful lot of work trying to keep that bike alive.

First gear was just to get the bike moving, nothing but tire smoke it you hammered hard in first, second would twist the swing-arm to the point where you were steering like a flat tracker coming out of a corner to keep it going in a somewhat straight line, third, forth and fifth were arm stretchers that had to be experienced to be believed.  God I loved that bike but it kept me broken hearted in spirit and busted when it came to cash.  But I am glad to have had the experience, some memories are priceless.

Dave

[Shifted]

After further reading in the Cummins ISX manual, it turns out that my original understanding was correct.  I have a non-EGR ISX, which is also called an Automotive CM570.  The EGR version, called an Automotive CM870, has the VGT (variable geometry turbo) with an electrically controlled actuator that uses the truck's compressed air to adjust the turbo geometry.

 

The CM570, however, uses a traditional wastegate and actuator that is controlled with air pressure.  In the below diagram, you can see the wastegate actuator tucked behind the turbo.  I've circled it in red to make it easier to spot.  It is directly behind the turbo input.  The line coming off of it and going into the block is the air control line for the actuator:

 

 

Here is another view with the turbo dismounted from the exhaust manifold.  You can see just a small part of the actuator behind the turbo, circled in red:

 

 

And here is a full view of the wastegate actuator and the control arm of the wastegate itself.  Note, in this diagram the output horn for the turbo is oriented in a downward position, rotate about 180 degrees from the other diagrams.

 

 

And here is the wastegate control coil on top of the intake on the driver's side of the motor (opposite side from the turbo):

 

 

My ISX does not have a wastegate actuator, an externally adjustable wastegate or a wastegate control coil.  So the wastegate and actuator shown in the above diagrams are not installed on my truck, nor is the wastegate control coil.  I doubt if the truck originally came this way, but pre-EGR ISX motors can be configured with non-wastegate turbos.  It looks like the part # is 4089754.

Which puts me back at square one of....why is my system air pressure dropping when the engine brake is active?  From what I can ascertain, the pressure supplied to the wastegate actuator comes from the intake, not the truck's air system.

 

 

 

[Scrap]

Great Quickserve digging!  What air dryer do you have?  AD-SP or SS1200?  Maybe they are regenerating at the time you are watching?

[Shifted]

I'll check which one I have and see if it has the heater connector and is connected.  I can replicate the problem just by turning the engine brake switch on and off.  Let off the throttle with the engine brake off, no air loss.  Flip the switch on, air pressure slowly drops.  Turn the switch off, pressure holds steady.  Turn it back on, pressure slowly drops.  As soon as I apply throttle and the engine brake shuts off, the air loss stops.  It does seem like it stabilizes at some point and stops losing air after the engine brake has been active for a bit.  But I may need to play with it some more to see if that's really the case or if my attention is being redirected to driving and I'm missing a continuous loss.

At this point it is more of a slightly annoying curiosity, but I am worried that it might be a symptom of a bigger problem developing.

 

[Scrap]

That's a tough one.  Only thing I can brainstorm is the truck has a bad case of the rear squats under braking and an older instant response leveling valve that is using up all your air to try and make up for it.  Or it is programmed for fan on with engine brake and that has a leak? Like you said, there was no airline going to an ISX until 2003.

The two dryers I mentioned were real common in the 90's and early 2000's and use system air to regenerate.  They'll purge and then use up 10-15 psi of front service air within 2 mins of the purge.

[Shifted]

The fan can be ruled out.  It was leaking badly at the hub so I disabled it for the test drives.  The behavior with the engine brake remained unchanged with the fan disabled.  I currently have the fan clutch out of the truck waiting on the replacement to arrive.

The leveling valve sounds like a distinct possibility.  It's been on the truck since I bought it and it has needed adjustment a couple of times.  I'll go ahead and replace it and see if there is any change.  Thanks for the help in troubleshooting this.