[Archived]

Bill,

Thank you for the reply. Yes the engine is power debating due to intake manifold temp. But I believe it is returning to normal power once the event is over, ie it powers down at the time but seems at least to me while driving that the power returns to normal until it happens again. That said the powering down does not seem to be very noticeable. I lost cooling fan tensioner roller bearing once and that power down was extreme..

If you are able to reply directly please do so directly to my email address which is as follows.

jonp@trederr.us.

Thank you Bill, standing by to hear what you find.

Jon

[Gary]

Bill,

Sorry did not proof my reply. My email is jonp@treder.us Just one r at the end.

[Archived]

I don’t have a clue where to begin looking, but I do know the EGR system is very complex because it involves a multi-speed turbo, and exhaust cooler and all sorts of programming related to emissions and controlling NOX.

The reason exhaust gas is routed back through the engine is to reduce the heat of combustion which reduces the creation of oxides of nitrogen which the EPA wants less of. When the EGR causes the exhaust to re-enter the cylinders the turbo boost goes up as high as 50PSI which is not reflected on the gauge. To allow the engine to continue to produce power when the cylinders are being flooded with engine exhaust the fuel flow is increased.

All of this magic happens because of the hardware and the DDEC programming. The downside is of course the substantial complexity of making this happen, some loss of mileage, and possible long term engine damage.

What the Ugly Fix does is lie to the engine senors and software. The engines are supposed to be set up so the EGR is disabled above 11,000 feet altitude because the EGR can rob the coach of performance so Detroit provided that capability because turbo boost drops off in the thinner air. The Ugly Fix replaces the altitude sensor and tells the DDEC the coach is always above 11,000 feet. However not every coach has a DDEC set up that way. On some the Ugly Fix is ineffective because the default setting on the DDEC is to have the EGR function at all times regardless of altitude. So my uneducated guess as to where to begin is to determine if the Ugly Fix is in fact working.

A Detroit dealer should be able to determine if the programming in DDEC is for the EGR to function regardless of altitude, or if it will not work over 11,000 feet altitude. If the EGR is disabled I would guess codes that relate to the EGR system will not appear, and boost will be limited to about 30 PSI.

My EGR system is not functioning and I have gone so far as to plug the tube going from the EGR intercooler to the intake manifold. I have never had a check engine light except when the charge air cooler was leaking so bad the turbo boost was inadequate and that did cause the DDEC to derate the engine.

Mark Monson had serious issues relating to the EGR as a result of issues relating to the V-pod which controls the turbo output. I hope he can take the time to offer his advice.

[Bernie]

There is one of 3 things that usually cause these codes. One is the Turbo itself binding and not letting the blades change angle. Second are the VPOD which is an air operated device that operates the rurbo and EGR controls. Third is the Turbo speed sensor may be intermittent. This one is tricky to determine. The best way I have found to determine what the issue is, is to drive the coach with the computer connected when the engine faults take a snapshot of the data, the graph mode works best. Then you can look at all the data and see what is not right. This is the easiest way to catch a turbo speed sensor.

[Archived]

The VPOD is the likely suspect. I had a failure of the original, and then the reman also failed. The third time was the charm. Easy to change out and not very expensive if I recall. Try that if nothing else seems to work.

They also put in a turbo speed sensor, but that did nothing to fix the issue.

[Doug]

Jon

Sent you an email… but posting here as well

Sorry it took a while to get back with you.

I had my Vpod and turbo boost sensors changed and that
didn’t solve the problem.

On the last visit the log indicated code 44 and 39 which are
air intake temp fault and VNT vanes not responding.

They changed the air intake sensor and have not had the
issue since and drop all the way to Moab Utah and Colorado to ski.

Hope this helps.

Bill

[Archived]

Thank you all, Jon, Bill, Bernie, Mark and Miknee for your input and suggestions.

Once we performed a test drive with the Detroit software connected and monitoring the codes as they occurred we were receiving multiple fault codes of 44 and 49, Air Inlet temperature high and engine power derate due to intake manifold temp respectively. But the engine was not actually derating just registering a fault. Both Prevost and Valley Power were stumped. It was thought that the Ugly Fix would solve the problem but it did not so we removed it and went back to Valley Power. After the suggestions offered by all of you I started focusing on the sensors and questioning whether any of them had been changed or replaced. I was working directly with John at Valley Power late in the 4th day of trouble shooting. End of story is we changed the air inlet temp sensor on the intake manifold and the sensor on the air intake from the air filter. Test drove for the 6th. time and the fault did not appear. I retuned up to the central coast ascending the two grades as a final test with no faults so for now my problem is resolve.



I really appreciate all attention and help I received through the Prevost Community forum.



Thank you all so much.

[Mike]

Further update: I now have about 3,000 miles on the bus with the power module in place. Have been through several different areas with different hill conditions. The DDEC has stayed at 6.4 versus the 5.7-5.8 it did before the module installation. I use the DDEC number not as an absolute but for an apples to apples comparison. I have not yet had the time to do a timed trial with and without the module in place. My perception is still a significant power gain, no smoking, temp or other issues so far.

Chris

[John]

Thanks for the update. I am still thinking about it. Keep us up to date if anything changes.

[Archived]

My last post last year indicated that the problem was likely solved but it was not. Check engine light continued to come on pulling grades in high outdoor temp conditions. Back to Prevost Mira Loma for the 4th time last March 2018. Prevost this time determined the fan clutch was not operating at low speed thus allowing the engine temp and the CAC to reach the high fan speed temp before the fan would run and cool. Thus I suspect that with the high outside temp, it was difficult to cool quickly enough to maintain proper running temp and thus alarm. After Prevost replaced the Fan Clutch with Pervost’s new style during a test drive the Prevost Mechanic with a Computer connected to the ECM visually checked the fan clutch operation to verify that the fan was actually running on low and high speed. Low speed was still not coming on when the ECM indicated that it should be. Come to find out and now what I believe is the final solution was the low speed fan relay in the engine control cabinet above the engine. I traveled from the California Central Coast through Las Vegas with very high outdoor temps and pulling grades no Check Engine Light. I now believe that my problem is finally resolved and wanted to post this for those who had helped me and for those who may have the same problem in the future.

In addition I had Prevost install a switch on my dash to manually control/activate the high speed fan so I have additional control over its operation.

[Archived]

Thanks for the update Jon, you would have thought that a relay check would have been one of the first and easy things to do.

[Dan]

I agree with Tom and am blown away that such a check was not the first thing on the list.

Having said that however I would not dump all the responsibility for pushing you into a new fan clutch when the other one was likely OK. Fan clutch replacement has been often reported on this forum and I have replaced 2 so I am aware as is Prevost that the quality of their purchased components sometimes sucks. All of us know about lousy mirrors, lousy charge air coolers and lousy fan clutches so with the fan clutch having such a lousy service history it almost forgive the Prevost technician for not making such a basic check of the relay.

[Tim]

I presume after finding the relay was bad you can have a conversation with Prevost regarding re-installation of your old clutch or a seriously discounted price for the new one.

[Archived]

This trip I am on now in Southern Utah was the big test for whether the Check Engine problem was solved or not. It appears now to in fact been solved with my travels across the desert successful with no faults.

I must say that regardless of this issue these coaches should have the manual fan clutch switch like I had installed so when pulling difficult grades we can manually control the cooling. Pervost told me that the current busses all have them. My trucker buddy is who suggested I make that improvement as all the big semi trucks have them.

As for the cost of all these repairs over the last year Jon, I am now going to have that serious conversation with Prevost about all the money they threw at this bus $10-$11K worth, all of which I have not paid until I was convinced they fixed it. Obviously the relays should have been a first check. Thanks to Burney’s comments a year and a half ago led me to question Prevost as to what controlled the input temp to the turbo, where I learned from Burney was the CAC. When I confronted Prevost with that question they immediately indicated that they would check the Fan Clutch. Why they didn’t check the Relays first I do not know. To the credit of Oscar the Mira Loma mechanic who did not take the ECM as a true indication that the fan clutch was running instead he visually confirmed that the fan was actually running when it was suppose to be is what led him to check the high and low speed fan relays and replace them.

My intention is to only pay Prevost for the relay repairs, not the new EGR installed, nor the EGR cooler, nor the fan clutch, nor the Valley Detroit Diesel trouble shooting, nor the sensors replaced, nor the attempted fix installing the Ugly Fix. Should be an interesting conversation with the Branch manager and the Service Manager. They have indicated that my satisfaction is foremost so we will see come next week.

Thank you all again,

Jon P.

[Archived]

I hope you prevail in your discussion with Prevost because it sounds like they kept throwing parts (and your money) at the problem and did not exhibit the skills we expect from Prevost.

However I have to disagree with a manual switch. Like you I have had a failure of the clutch to respond to calls for its operation so my solution was easy. Lock the clutch and then when convenient assess and fix the problem which in my case was in fact a bad clutch.

Our DDEC is set to control the clutch and the manner in which it does that not only conserves power, but it is more fuel efficient. Having read thousands of posts on this and other sites I am convinced a manual clutch switch will be abused, meaning some folks will leave it on all the time in the mistaken impression it is needed, some folks will use it instead of fixing their coach (pity the poor next owner who finds out an expensive clutch repair is needed) and it has the potential to not only mask a problem, but to make the complex coach even more complex.

A driver who monitors his gauges can see his high speed clutch cycling on and off as needed and if that cycling of the clutch is not seen in high ambient conditions under high power (either locked on and climbing temps) or not on and climbing temps it is a problem that is seen and then repairs can be made.

But that is just my opinion and if folks want to be able to lock their coach fan on with a driver actuated switch it has no impact on me.