C9 Engine brake/Turbo issues?

[LEAH DRAPER]

I just read a short article by Brett Wolf in the latest FMCA magazine describing the engine brakes used in our coaches.  What alarmed me was the description of the variable geomerty(sp) compression brake the new C9 engines have, in that the turbines are supposed to "reverse direction" in this process.  Do you suppose that when the engine brake seems not to engage immediately, as mine does at times that this is an indication of impending turbo failure that some have had?

Will attach the article below if I can......

Diesel Engine Brakes
By Brett Wolfe, F252125 February 2012
Three different types of brake retarder systems are used on diesel engines: exhaust brakes, engine compression brakes, and variable-geometry turbo brakes. Here’s a brief description of how each works.

An exhaust brake uses a "flap" that closes off exhaust flow just downstream of the turbocharger in the exhaust system. This causes back pressure (55 psi on my motorhome), which generates braking power. On motorhomes equipped with an Allison transmission, the exhaust brake usually is tied in with downshifting of the transmission to a preselected gear (usually second gear or fourth gear). Think of this type of system as a potato stuffed in the tailpipe.

An engine compression brake, including the popular Jacobs Engine Brake, or Jake Brake, involves manipulating the normal stroke cycle in the cylinder. The exhaust valves are opened as the pistons reach “top dead center” on the compression stroke after the engine has done the work of compressing approximately 18 volumes of intake air to 1 volume. If the exhaust were not allowed to escape when the compression brake opened the exhaust valves (such as when coasting with the compression brake off), the compressed air would force the piston back down. But with the compression brake on, the engine works to compress air in the cylinder, but then the air is let out. This generates quite a bit more braking force than an exhaust brake. The smallest engines to offer an engine compression brake are the Caterpillar C9 and Cummins ISL.

A variable-geometry turbo brake involves putting the turbocharger’s vanes in reverse or closing the aperture (depends on the engine manufacturer) to create back pressure with much the same effect as an exhaust brake.

Gerald and Gil....what do you think.

[Gerald Farris]

Leah,
There are many reasons for a delay in activation of the exhaust brake on your coach. The exhaust brake is controlled by the engine control module (ECM), and it will delay activation of the exhaust brake until all of the parameters that are programmed into it are meet. So when you turn on the exhaust brake control, you are not turning on the exhaust brake, however you are telling the ECM to turn on the exhaust brake as soon as everything is within the preprogrammed parameters.

I would not worry about the turbocharger. I think that most of the turbo "failures" on the C9 engines are related to Monaco's intake sizing and Caterpillar's ECM programming being to restrictive to allow for it.

Gerald  

[Gil_Johnson]

Leah,

I'm with Gerald in that the exhaust brake triggering and turbo failure aren't linked.  If there are times when the brake doesn't come on or is delayed it's most likely because the engine and transmission control units are agreeing not to let it happen.  One common reason of delay is that you may be going to fast in the gear you're in for it to activate.  It's smart enough not to activate when doing so would increase the engine speed beyond its limits.  Engine braking with our engine is a two action effort.  The turbo restricts flow and the transmission down shifts.

Gerald,

I'm curious as to your theory.  I'm not sure how an undersized fresh air intake can result in turbo failure.  On my coach my air filter restriction guage hardly moves.  That should suggest that the turb is getting as much air as it's asking for.  My theory is that CAT's programming of the exhaust regeneration is wrong.  They are, in my theory, allowing the exhaust soot filter to get too restrictive before commanding a regen burn.  This delay is greating too much back pressure that is creating too much heat that's leading to early turbo failures.  My understanding is that the latest software did include changes to the exhaust regeneration system.  What I don't know and wish I did is what are those changes.

[LEAH DRAPER]

Gerald and Gil
Thanks for your thoughts on this, puts my worrier more at ease.
Leah

[Gerald Farris]

Gil,
From the limited research that I have done on the problem of repeated turbo failures on the C9 engines, it appears that numerous Cat dealers are replacing the turbo because of lower than expected boost pressure at the intake manifold. If the intake side of the turbo is not restricted, this can be caused by two things, an underperforming turbo or a restrictive air flow system between the turbo and the intake manifold (undersized intercooler). Since it is much easier and quicker for a commissioned mechanic to condemn a turbo than it is to reengineer the intercooler (charge air cooler or CCA), I think that many turbochargers are being replaced for poor performance when the Cat engine control module (ECM) programming is expecting something that can not be delivered on a consistent basis due to the restrictive intercooler (CCA).  

Gerald  

[Gil_Johnson]

Gerald,

You might have some bad info from all the research and involvement I've had on this subject.

I'm pretty sure the turbo failures are real in that they have zero boost after failure.  The low intake pressure issue may have never really been an issue, but that's something no one will own up to.  My coach was used for testing of the low intake pressure issue.  My CAT regional service rep stated that my coaches air restriction through the CAC was at's CAT's thresholds.  That should mean that the CAC meets CAT's requirements.

CAT would not release to me their CAC requirements, which is strange as they release to any company buying their engines and have to given CAT doesn't supply the CAC.  The new Monaco could not find their documention from CAT certifying their engineering and installation.  Modine, the CAC manufacturer, will only talk to Monaco given they were contracted by Monaco to design and supply the CAC.  FWIW, my CAC has zero restriction up to 20 psi and then gradually developes restriction up to a maximum of 2 psi at WOT.  There's no way CAC restriction can lead to turbo failures.  The turbo will, especially these electronically variable vane turbos, will produce a give boost and whether that boost is restricted at the engine intake or at the CAC, the turbo won't care.  An overly restrictive CAC can affected performance, but that's another topic.

CAT has changed their software such that the trigger point for low intake boost pressure works with the CAC orginally supplied.  To me this suggests that CAT realizes their alarm threshold was to sensitive.  CAT also worked with the Monaco and Modine to develop the engineering specs for a replacement less restrictive CAC.  CAT did test this in one coach; not mine even though they said that was the plan given my was the test coach.  There is a replacement CAC available from Monaco that's about $1,700 and is not a bolt in replacement.  Given CAT has corrected their software and the only benefit to a less restrictive CAC is possibly some performamnce improvement at high RPMs, I'm not changing mine.

As for the turbo failures, one CAT service center said they did receive a bad batch from their supplier.  I have no idea if that's true.  I stand by my theory that they failed due to high heat produced when the exhaust regeneration system nears it's point of regeneration.  This is the point of maximum backpressure.

Gerald, does this make sense?

[Gerald Farris]

Gil,
Since you own one of these coaches, you have been much more involved in the turbo problems than I have, however I have a little trouble in agreeing with the idea that late exhaust regeneration is causing turbo failure. The most heat and RPMs that a turbo will be subjected to is at wide open throttle (WOT). If a turbo is designed to function under sustained WOT conditions like climbing a long high mountain pass road, the increase in back pressure from late regeneration should not create a failure point.

I agree that the original Cat software was flawed in that the threshold to set a diagnostic trouble code (DTC) for low boost pressure was to narrow. These narrow parameters are set because the EPA regulations are so strict and punitive for engine manufacturers that they have to be very conservative in their programming. That is the flaw that I was referring to when I stated that turbochargers were being replaced that had not failed. I know of two C9 equipped coaches that had turbochargers replaced because of repeated check engine lights (DTC) for low boost pressure even though the turbo was operating when checked.

A restrictive CAC (charge air cooler) could be causing the DTCs if the 2 lbs of pressure drop that you are getting is outside the software parameters, however that does not matter if Cat has rewritten the software to take into consideration the CAC caused drop in boost pressure. If they also lowered the exhaust backpressure that is allowed before regeneration, you should see better performance at least, and better turbo life if I am wrong about that.    

The turbochargers that provided zero boost were definitely turbo failures, and it is a good possibility that there were some design flaws in the early variable geometry turbochargers that were corrected in later units, however they probably will never tell us.  

Gerald

[Gil_Johnson]

Gerald,

Consider this: WOT, long ascend, AND restrictive exhaust due to late regeneration.  This increased back pressure might just be the straw that broke the camels back or in this case led to turbo failures.

I may well have the last surviving original turbo charger and we're headed from FL to AK this summer.  I hope I can return claiming I still have the last original turbos.

[Gerald Farris]

Gil,
I understand your viewpoint, but these coaches are very rarely run at WOT (wide open throttle) for any significant time, as opposed to a heavily loaded truck that often sees WOT on grades. The turbo was designed to last under the load of the trucking industry, so I do not think the our coaches are stressing the turbo to the point that failures should happen, unless there is a design or production flaw or misdiagnosis of the problem, with or without late regeneration.

I acknowledge that late regeneration may add extra stress on the turbo at WOT, however, with the few times that the coach is at WOT, the chances of high backpressure from late regeneration and extended WOT happening at the same time is extremely low.
But anything is possible.

Gerald

[william thorup]

Gil...reading your posts, I am interested to hear about your journey from Fl to Ak.  We made that trip without incident and with only fond memories in our last coach with nearly 100,000 miles.  Would love to do it again but have yet to have the confidence in the C-9 after so many problems. It could be a long tow to the nearest Cat dealer should there be a problem. Don't want to ruin those good memories.  If your trip is half what ours was, it will be tremendous. Lets hope it is.......

Bill Thorup
2008 Contessa Westport 42

[marty christensen]

Bill, a lot will depend on which C-9 engine you have.  If you have the 06 400 HP C9 as I do and many early 08 Contessa models do you are you not going to experience a lot of the problems that Gil has.  I had what I consider more normal engine problems that have all been repaired and in the last 4,500 miles no problems.  I live in Colorado and tow a 5200LBS Tahoe with a 42 Rome model.  The coach is no fireball but, does manage to climb the grades.  Downhill the exhaust brake is a little lite for the 50,000 lbs it is trying to hold back.  I have learned to use the exhaust brake earlier than normal in anticipation of what is to come.  For a lot of mountain travel a better combination would be a C13 and a 2 stage engine brake.  But I have learned to work with this.  At sea level or the flatlands where there is AIR my coach has plenty of power.

On the other hand if your C9 is the 07 425HP you are most likely looking at the same problems Gil is experiencing.




Marty
08 Contessa 400HP

[Gil_Johnson]

All I can say is that I'm hopeful that Cat's last software release corrected the problems.  I know the load did make adjustments to the exhaust regeneration system.  Only time will tell.  It is really running quite well right now.  I did have the ARD module fail last week.  It's the diesel injection and ignition module for the exhaust regeneration system.  Apparently these have failed with enough regularity that they've been through a few redesigns.

Fingers crossed,

Gil

[Wayne Baumann]

Gil,
We have been on a 3500 mile trip south to Florida this winter and everything has been running great, until we got to Oklahoma and the check engine light came on and it has stayed on for the last 400 miles.  The regen system also did its systems regen.  I have boost oil pressure, and the water temp and engine temp are all normal, and it runs just fine.  Every time I have left the lower elevation and start for home to higher elevation, something all ways happens to the engine.  Have had all the programs done, but I still say the elevation is a factor for the C9 engine.  I have been to Alaska with two other motorhomes, but not with this CAT engine.  I really would be afraid to do this with this unit.  There are a lot of steep mountains.  Has anybody else had the check engine light stay on, and still run good?

Thanks Wayne

[Gil_Johnson]

Wayne,

With my recent ARD module failure the check engine light stayed on and it ran fine.  I drove it 150 miles that way.  Occasionally the Regen light also came on.  Your display unit should tell you the code being raised.

BTW, do you have a CAT owners manual for our engine?  I wonder if there is one, because my manual is for the pre 2007 engine.

[Wayne Baumann]

Gil.  
My cat engine book is also pre 2007.   The code that I have is 0.4   We have been parked for 2 days and I just started the engine to see if the engine light would go off, and it just stayed on.  
Wayne